Routine Preparation for Surgery
A careful assessment of the child must be made at the time of the preoperative visit. Although many children are healthy, some have diseases with significant implications for the anesthesiologist. A thorough history is obtained from the child’s chart and the parents. Review the systems and search for special problems that may complicate anesthesia ( Table 4-1 ). When a significant history is obtained, it is important to establish the current status of the disease; this may require consultation with the pediatrician, the surgeon or radiologist, and other physicians. Although most children take no medications, some may be taking medications that have implications for management during the perioperative period. Document all medications, neutraceuticals, and drug allergies. Common medications for children and their significance to anesthetic management are detailed in Table 4-2 ; ( N.B. Some herbal preparations may have anesthetic implications [ Table 4-3 ]). Throughout the preoperative interview, strive to gain the confidence of the child and the parents; always invite questions from both the parents and the child so as to help establish rapport and confidence.
|Systems||History||Concerns for the Anesthesiologist|
|Central nervous system||Seizures||Adequacy of seizure medication, recent control of convulsions. Phenytoin increases nondepolarizing relaxant and fentanyl requirements, produces gingival hyperplasia and bleeding, and may cause hepatic dysfunction. Ketamine, enflurane, and methohexital are relatively contraindicated.|
|Hydrocephalus||Possible raised intracranial pressure. Repeated anesthesias. Possible need for prophylactic antibiotics to prevent shunt infection.|
|Head injury||Possible raised intracranial pressure. Current status. Possible danger of hyperkalemia with succinylcholine.|
|Cerebral tumor||Possible raised intracranial pressure, vomiting, change in electrolyte status. Chemotherapeutic agents and possible drug interactions.|
|Cerebral palsy||Nutritional status, presence of chronic infections. Possible history of chronic aspiration and difficulties with positioning. Intelligence may be normal—careful psychological preparation needed.|
|Down syndrome||Optimal cooperation at induction may be a problem. (Possibly get help from parent.) Airway (large tongue, subglottic stenosis). Heart disease. Evidence of joint hypermobility and indications of atlantoaxial instability.|
|Neuromuscular disease||Difficulty positioning. Repeated surgery—careful psychological preparation needed.|
|Associated hydrocephalus. History suggesting latex allergy. Renal infections. Impaired renal function.||Meningomyelocele|
|Cardiovascular system||Heart murmur|
|Cyanosis||Evidence of congestive cardiac failure. History of digoxin and/or diuretic therapy. Digoxin level.|
|Dyspnea, tachypnea||Previous heart surgery|
|Sweating||Need for prophylactic antibiotics. Cardiac conduction defects. Pacemaker. History of arrhythmias.|
|Hypertension||Renal disease, coarctation of the aorta, endocrine disease.|
|Respiratory system||Prematurity||Risk of perioperative apnea.|
|Respiratory distress syndrome||Present postconceptual age, gestational age at birth. Anemia. History of apnea, residual chronic respiratory disease, impaired gas exchange. History of prolonged ventilation, residual subglottic stenosis.|
|Recent upper respiratory tract infection||Evidence of acute infection. Pyrexia. Lower respiratory tract infection. Reactive airways prone to secondary infection. Increased risk of laryngospasm, bronchospasm and oxygen desaturation.|
|Bronchiolitis||Reactive airways, evidence of bronchospasm.|
|Croup||Possible subglottic stenosis. Avoid intubation, use LMA.|
|Asthma||Reactive airways. Current status. Theophylline therapy (blood level). β-Agonist drug therapy, history of corticosteroid therapy (prescription supplements). Develop a plan to ensure optimal status preoperatively.|
|Cystic fibrosis||Present pulmonary function. Any acute infection? Can condition be improved? Can regional analgesia be used? Present drug therapy. Nutritional status. Emotional status.|
|Gastrointestinal system||Gastroesophageal reflux||Evidence of aspiration pneumonia. Reactive airways and bronchospasm. Recent food intake, risk of regurgitation, and need for antacid and H 2 -blockers. Evidence predicting difficult intubation.|
|Vomiting||Nutritional and hydration status. Electrolyte values. Urine output. Immediate full stomach danger.|
|Diarrhea||Nutritional, fluid, and electrolyte status. Risk of hypoglycemia and hypovolemia.|
|Liver disease||Drug metabolism. Increased requirements for nondepolarizing relaxants|
|Genitourinary system||Renal failure||Anemia and coagulopathy, electrolyte abnormality, volume status. Acid-base status. Hypertension, pericardial effusion and incipient congestive cardiac failure. Date of last dialysis. History of infection? Impaired immunity? Psychological status.|
|Bladder surgery||Is history suggestive of latex allergy?|
|Bladder Extrophy||Is history suggestive of latex allergy?|
|Endocrine system||Diabetes mellitus||Current status and therapy. Plans for perioperative management. Need for planning with surgeon and endocrinologist.|
|Thyroid disease||Current status and medication? Euthyroid? Enlarged thyroid effect on the airway.|
|Pituitary disease||Intracranial pressure? Adrenal insufficiency? Thyroid function? Diabetes insipidus?|
|Adrenal disease||Need for corticosteroid therapy? Volume and electrolyte status|
|Hematopoietic system||Anemia||What is cause? Possible medical therapy. Urgency of surgery. Will anemia affect the course of anesthesia? Is transfusion indicated?|
|Bruising or bleeding||Is coagulopathy present? Are further tests required? Preoperative therapy? Order products.|
|Sickle cell disease||Trait or disease? Are other abnormal hemoglobins present (Hb electrophoresis results)? Is preoperative preparation required?|
|Muscular system||Muscular dystrophy||Risk of hyperkalemia with succinylcholine. Avoid nondepolarizing relaxants if possible. Ventilatory reserve? Cardiac function? Will postoperative ICU admission be necessary?|
|Immune system and allergy||Latex allergy|
|Drug||Implications for Anesthesia|
|Analgesic, antiinflammatory Acetylsalicylic acid (ASA, aspirin)||Prolonged bleeding time due to platelet inactivation; check bleeding time if ASA given within 10 days.|
|Nonsteroidal antiinflammatory drugs (NSAIDs; e.g., ibuprofen, ketorolac)||Affect platelet aggregation and prolong bleeding time. Effect of antihypertensive agents may be decreased. Ketorolac decreases diuretic effect of furosemide|
|Antibiotics||Many of the “mycins” may potentiate neuromuscular blockade. Monitor neuromuscular block, check reversal carefully.|
|Aminoglycosides||May potentiate succinylcholine and nondepolarizing relaxant drugs. Renal toxicity.|
|Clindamycin||Cardiac depression when given rapidly. May potentiate nondepolarizing relaxant drugs.|
|Erythromycin||May prolong the effect of alfentanil and midazolam. Decreases theophylline clearance rates. Potentiates anticoagulant effect of warfarin.|
|Gentamicin||May prolong the effect of succinylcholine. Potentiates nondepolarizing relaxant drugs.|
|Vancomycin||Potentiates nondepolarizing relaxant drugs. Rapid administration (<1 hr) may cause “red man syndrome” with severe cardiovascular collapse.|
|Anticancer agents||All may cause blood dyscrasia, coagulopathy, anorexia, nausea, stomatitis, and reduced resistance to infection.|
|Doxorubicin (Adriamycin)||Cardiotoxic, may cause arrhythmias.|
|Daunorubicin (Cerubidine)||Severe cardiac depression with halothane, especially likely when cumulative dose exceeds 250 mg/m 2 (or 150 mg/m 2 plus radiation).|
|Bleomycin||Pulmonary fibrosis—may be exacerbated by excess oxygen. Limit carefully.|
|Busulfan||Inhibits plasma cholinesterases. May prolong the effect of succinylcholine.|
|Cyclophosphamide||Inhibit plasma cholinesterases; prolonged effect of succinylcholine or mivacurium.|
|AnticonvulsantsPhenytoin||May cause blood dyscrasia, hypotension, bradycardia, arrhythmia.|
|Mephenytoin||May increase requirements for nondepolarizing relaxants and may cause peripheral neuropathy.|
|Valproic acid||May cause hypotonia. Hepatotoxic.|
|Antihypertensive drugs||Severe hypotension may occur with potent anesthetics, especially if dehydrated.|
|Captopril||Hyperkalemia with potassium- sparing diuretics (spironolactone). Indomethacin reduces antihypertensive effect.|
|Clonidine||Must not be abruptly withdrawn—severe hypertension may result. Interaction with β-blockers—bradycardia, hypotension.|
|Hydralazine (Apresoline)||May cause systemic lupus erythematosus (SLE)-type syndrome. Decreases tachycardia with atropine.|
|Labetalol||Cimetidine may potentiate labetalol action.|
|Prazosin (Minipress)||May potentiate effects of ketamine. Diuretics potentiate antihypertensive effect|
|Antiviral agentAcyclovir||Nephrotoxic, bone marrow depression.|
|β-Agonist agents (e.g., albuterol, Alupent)||May cause tachycardia, hypertension, arrhythmia. Albuterol has increased effect with tricyclic antidepressants or monoamine oxidase inhibitors. Blocked by β-blocking drugs.|
|β-Blocking drugs||May cause bronchospasm, block effects of albuterol. Potentiate cardiac depression caused by halothane. May cause bradycardia with anticholinesterase drugs (e.g., neostigmine) and hypoglycemia.|
|Calcium channel blockers||Potentiate nondepolarizing relaxant drugs. Severe bradycardia or heart block with β-blocking drugs.|
|Verapamil, nifedipine||May interact with β-blockers to cause severe cardiac depression.|
|Corticosteroid preparations||Chronic therapy may lead to depression of the hypothalamic pituitary axis; severe collapse may occur perioperatively. Supplemental steroid therapy should be ordered preoperatively.|
|Digoxin||May potentiate bupivacaine toxicity. Hypokalemia, if induced (e.g., by hyperventilation), predisposes to arrhythmias.|
|Diuretics||All may result in electrolyte disturbances.|
|Acetazolamide (Diamox)||Produces hyperchloremic metabolic acidosis.|
|Furosemide||Hypokalemia, if present, may prolong action and delay reversal of relaxant drugs.|
|Ophthalmic topical drugsEchothiophate (anticholinesterase)||Inhibits plasma cholinesterases.Prolonged apnea with succinylcholine.|
|Phenylephrine||May cause tachycardia and hypertension.|
|Timolol (β-blocker)||May exacerbate asthma.|
|Theophylline||Severe arrhythmias may occur with halothane; check blood level|
|Herbal Preparation||Reason for Use||Anesthesia Implication|
|St John’s wort||Anxiety, depression, sleep problems, etc.|
|Gingko||Improves memory and concentration|
|Aloe||Skin problems||Allergic skin reactions. GI constipation bleeding, renal damage with oral use.|
Preoperative Feeding Orders
Infants and children should not be subjected to prolonged preoperative fasting. Excessive fluid restriction rapidly leads to dehydration and hypovolemia because of their high metabolic rate; hypotension in infants during induction of anesthesia has been shown to be directly related to the duration of fasting. In addition, excessive fasting may precipitate hypoglycemia and/or metabolic acidosis, particularly in young infants. Studies have shown that healthy children may safely be given unlimited clear fluids up to 2 hours before induction of general anesthesia. The volume and acidity of the gastric contents are not increased when this regimen is used. Indeed, clear fluids 2 hours before anesthesia may reduce gastric contents at induction, possibly by stimulating gastric emptying. Furthermore, this practice reduces hunger and thirst and makes for a happier child! Fasting guidelines are presented in the Table 4-4 .
|Clear fluids||2 hr||Water, ginger-ale, apple juice; any particle-free fluids|
|Breast milk||4 hr|
|Formula/cow’s milk||6 hr||Also dry toast, black tea|
Children who are scheduled for afternoon surgery may have a light breakfast (dry toast and black tea) early in the morning. These rules must, of course, be modified in special cases (e.g., for diabetics). Children who require emergency surgery, those with gastrointestinal disease, and any others at increased risk for vomiting during induction should receive intravenous fluids and a rapid sequence induction. When evaluating injured children, the interval between last food or fluid and the injury is the best predictor of the likely stomach contents. Children for whom any period of fluid deprivation might pose a risk (e.g., those with cyanotic heart disease) should have an intravenous infusion established at the commencement of any prolonged period of restricted oral intake.
Prophylaxis Against Hemorrhage for Infants
Ensure that the neonate undergoing surgery has been given vitamin K 1 to prevent Vitamin K deficiency bleeding (VKDB). Aqueous vitamin K 1 (1 mg IM or IV) corrects the deficiency within a few hours and therefore should be given as early as possible. Late onset VKDB may occur in breast-fed infants who were never given vitamin K; check the history.
Basic Laboratory Tests
Preoperative laboratory tests are considered unnecessary for most children; however, in some regions, these tests are legislated requirements. Preoperative urinalysis has not been found useful in detecting significant diseases or in routine screening of children. However, because a history is unreliable, urine (or blood) for pregnancy testing has become mandatory in many centers for all females who have reached menses. Hemoglobin (Hb) determination is likewise of little value in otherwise healthy children. Mild degrees of anemia have not been shown to increase the risk of anesthesia and do not alter the anesthesia technique selected. Most authorities now recommend that these tests may be omitted in healthy children undergoing minor surgery. All small infants, especially those who were born preterm, should have a preoperative Hb determination to exclude anemia, which is more common in such infants and may increase the risk of complications. Older children with systemic diseases, those with a history of anemia, and those who may lose significant amounts of blood intraoperatively should also have a preoperative Hb determination. A sickle cell test is now performed routinely in neonates immediately after birth in many regions. Older infants and children whose sickle status is unknown should be tested with a Sickledex and if that is positive, a hemoglobin electrophoresis should be performed.
Drugs may be given preoperatively to block unwanted autonomic reflex (vagal) responses, produce preoperative sedation and tranquility, facilitate separation from parents if necessary, and smooth the induction of anesthesia.
Topical Local Anesthetics
For topical local anesthetics, see Appendix 3, page 634 .
Vagal Blocking Drugs
Vagal blocking drugs (atropine, hyoscine, glycopyrrolate) are no longer routinely given to children preoperatively; however, they may be useful to decrease secretions for specific procedures such as bronchoscopy, to smooth induction in the child with a suspected difficult airway or to reduce secretions in neurologically impaired children.
Brisk vagal responses may occur during anesthesia in infants and children. Atropine should immediately be available for injection (preferably IV) should it become necessary. Serious bradycardia may occur in young children and may lead to significant hypotension or more dangerous arrhythmias. This can result from instrumentation of the airway, manipulation of the eye, traction of the peritoneum, or administration of cholinergic drugs (i.e., halothane, succinylcholine). If bradycardia occurs, it must be treated promptly; ventilate with 100% oxygen, withdraw the precipitating stimulus, and give intravenous atropine.
Atropine is the preferred anticholinergic in children. It is more effective in blocking the cardiac vagus nerve and causes less drying of secretions than hyoscine or glycopyrrolate. Respiratory tract secretions, in fact, are not a serious problem with current inhalational anesthetics.
Children require larger doses of atropine than adults to achieve the same effect on the heart rate. If indicated, atropine (0.02 mg/kg; maximum, 0.6 mg) may be given IV at induction. This is the preferred route of administration since it ensures effective drug action and spares the child a painful intramuscular injection and a preoperative dry mouth. If successful venipuncture is in doubt, the same dose of atropine may be given orally 90 minutes or IM 30 minutes preoperatively to ensure a peak effect at the time of induction. Atropine may also be given per rectum if a rectal barbiturate is used for induction of anesthesia. In an emergency, the usual dose of atropine diluted in 2 ml of saline is rapidly effective by the intratracheal route.
Infants with established bradycardia have a longer onset time for the chronotropic effect of intravenous atropine because of their reduced cardiac output. Therefore, if bradycardia is attributed to a vagal response, atropine should be given as early as possible. A very common cause for intraoperative bradycardia in infants or children is hypoxia, so the first treatment for any unexpected bradycardia is ventilation with 100% oxygen.
Contraindications to the use of atropine are few in the pediatric age group; infants and children tolerate tachycardia much better than bradycardia. Children with heart disease who might tolerate tachycardia poorly (e.g., aortic stenosis or cardiomyopathy) require special attention; if bradycardia develops; small incremental doses of atropine should be given until the desired heart rate is reached. Studies have failed to confirm a reputed increased sensitivity of children with Down syndrome to atropine and as such they should be given the usual doses if indicated.
True allergy to atropine is extremely rare (if it exists), but it is common for parents to state that their child is “allergic” to atropine. This claim has usually been prompted by the appearance of a rash after a previous atropine administration. This erythematous rash commonly involves the upper part of the body and is thought to be caused by histamine release.
Sedatives and Tranquilizers
There is a voluminous literature and many widely divergent opinions concerning the use of sedative premedications for children ( Table 4-5 ). Sedatives, opioids, or hypnotics may not ensure calm cooperation at the time of induction, but they may be associated with postoperative respiratory depression, slowed emergence, delirium, and vomiting.
|Midazolam (mg/kg)||Ketamine (mg/kg)||Clonidine (µg/kg)||Dexmedetomidine (µg/kg)|
The oral route has become most popular for administering premedication to healthy children. Midazolam is the most widely prescribed sedative premedication for children. Given orally, it is effective in calming the child, easing separation from parents, and smoothing induction of anesthesia. Recently, oral clonidine was reported to produce good preoperative tranquility, reduce anesthetic drug requirements and smooth emergence; however, it requires a 90 minute onset time and if larger doses are used, may cause postoperative sedation.
Midazolam is a water-soluble benzodiazepine with a shorter duration of action than diazepam. It may be given orally, nasally, rectally, or intravenously. For healthy infants and children up to 6 years of age, the oral route is preferred; a dose of 0.5 to 0.75 mg/kg produces sedation and tranquility in greater than 95% of children within 10 to 15 minutes, after which time its effects start to wane. Older children (>6 years) require smaller mg/kg doses (0.3 to 0.4 mg/kg, maximum dose of 20 mg) than children less than 6 years of age. In infants, midazolam may be applied sublingually with a medicine dropper; this technique ensures rapid oral transmucosal absorption. However, children with OSA may be at risk; 3% of children with OSA who received oral midazolam desaturated. Children with confirmed OSA should be premedicated with great caution and observed closely.
Oral midazolam produces sedation and tranquility with an approximate 50% incidence of antegrade amnesia, does not significantly affect the volume or acidity of gastric fluid, but does improve cooperation on separation from parents and during induction. Recovery is not delayed after surgeries lasting 1 hour, but after a brief procedure, early recovery may be delayed. Some children given midazolam are more restless during emergence after a brief procedure possibly because of paradoxical excitation.
There is some evidence that effective midazolam premedication reduces the incidence of emergence agitation after sevoflurane administration and also adverse behavioral outcomes after hospitalization; however, it is also suggested that some children have an increased incidence of bad dreams.
Intranasal midazolam (0.2 mg/kg) is effective particularly in the uncooperative child who will not swallow an oral premedication, although giving it by this route is unpleasant and usually makes the child cry. As a result, it is not recommended. Rectal midazolam (0.3 to 1 mg/kg) may be useful for small infants who cannot take the drug orally, but the onset of sedation is less predictable. Children with established intravenous access may be given midazolam 0.05 to 0.1 mg/kg IV immediately before arrival in the operating room for a rapid calming effect. It should be noted that the peak brain effect after IV administration is slower than that of diazepam occurring at approximately 5 minutes vs. approximately 1.5 minutes for diazepam.
Lorazepam is very useful for adolescents greater than 12 years of age. In an oral dose of 1 to 2 mg, it produces good anxiolysis with a significant degree of amnesia. There is insufficient data to recommend its use in children less than 12 years of age.
Ketamine may be given orally in doses of up to 6 mg/kg but must be accompanied by oral atropine if excessive secretions are to be avoided. The combination of oral midazolam (0.3 to 0.5 mg/kg) and oral ketamine (3 to 5 mg/kg) produces very effective sedation for the more disturbed child. If this combination is used, the child should be closely observed as the drugs become effective. The combination should not be used when heavy sedation might be dangerous (e.g., in the child with a difficult airway). Immediate postoperative emergence agitation has been reported in a 12-year-old given 6 mg/kg oral ketamine after surgery that lasted less than 1 hour.
Clonidine 4 μg/kg may be used as a premedication, but given orally requires a 90 minute onset time, much greater than oral midazolam (10 to 15 minutes). It reduces anesthesia requirements and smoothes emergence, prevents agitation after sevoflurane and enhances analgesia. In addition, clonidine diminishes cardiovascular responses to endotracheal intubation and facilitates planned induced hypotension. Clonidine may result in unwanted postoperative sedation and this may be a disadvantage in the outpatient.
Intranasal dexmedetomidine (1.0 µg/kg) has been reported to be effective as a premedicant in children when given 60 minutes before separation from parents. Neither pain nor discomfort was reported. Neurotoxicity studies of dexmedetomidine have not been forthcoming; because it is unclear whether dexmedetomidine may cause nerve damage, this unapproved route of administration should be viewed with caution.
Opioids are rarely used as premedications in children unless pain is present. Opioids have traditionally been given intramuscularly, which children find unpleasant. Dizziness, nausea, and vomiting are common after their use. Fentanyl in the form of an Oralet (lozenge) is available as a premedication in some countries. This formulation takes advantage of the rapid effect that may be obtained by oral transmucosal absorption of the drug. The fentanyl Oralet produces good sedation together with analgesia that complements the anesthesia regimen and may extend into the postoperative period. Provided the total dose administered is 15 µg/kg, significant respiratory depression is unlikely, but the child should be continuously monitored with pulse oximetry. As with all opioids, fentanyl may increase the incidence of nausea and/or vomiting.
Neurosurgical patients who may have increased ICP should not receive any sedative premedication.
Children with a suspected difficult airway or OSA should be sedated with caution because it could lead to respiratory depression or airway obstruction.
Atropine should not be given intramuscularly to children with a fever because it may exacerbate the fever by abolishing sweating. If needed, it may be given intravenously at the time of induction.
Some children undergoing correction of strabismus are assessed by the ophthalmologist immediately before the operation and should not be premedicated with atropine. They may receive atropine (0.02 mg/kg intravenously) at induction to block the oculocardiac reflex.
MANAGEMENT OF THE AIRWAY
During mask anesthesia, always have age and size appropriate equipment for endotracheal intubation immediately at hand:
A selection of suitably sized tracheal tubes with connectors in place ( Table 4-6 )
Age of Child (yr)
Internal Diameter (ID) (mm) †
Approximate depth of insertion (cm) to mid- trachea* from:
2.5 (for infants <1500 g) to 3.0 (for infants >1500 g)
† Formula: (age of child (≥2 yr) in years ÷ 4) + 4.0 = size of tube ID in millimeters. The tube diameters listed are given only as a guide. Always prepare a selection of tubes, and use the one with the best fit (see text).
Two properly functioning laryngoscope handles with several suitable blades
Labeled syringes containing atropine, succinylcholine, and induction agent (propofol, thiopental, ketamine, etomidate)
Select a mask that fits the contours of the child’s face and minimizes the dead space if possible. The Rendell Baker mask is ideal for infants and small children; however, the anesthesiologist may find it easier to achieve a good seal with a cushion-type mask.
The relatively large tongue in infants and adenoid or tonsillar hypertrophy in older children may cause airway obstruction. If obstruction occurs, insert an oropharyngeal or nasopharyngeal airway of suitable size. Alternatively, sublux the temporomandibular joint by applying digital pressure to the apex of the ascending rami (behind the pinna) directing the force towards the frontal hairline. This maneuver translocates the mandible anteriorly and rotates the joint, thereby lifting the tongue and intraoral tissues off the posterior pharyngeal wall and opens the airway and the mouth.
Infants have soft laryngeal cartilages and tracheal rings. Therefore the anesthesiologist should avoid applying pressure over the airway in the neck during mask anesthesia. Monitor breath sounds, EtCO 2 , and the movement of the reservoir bag continuously.
Laryngospasm occurs most commonly during induction of anesthesia, but also during emergence and occasionally during maintenance of anesthesia if the child is stimulated while lightly anesthetized. It occurs more commonly in infants (compared with older children), in preterm infants, children with recent URIs, children with reactive airways disease, after airway surgery and in those exposed to second-hand smoke. The clinical hallmarks of laryngospasm include high-pitched sounds with inspiratory stridor that may progress to silence as the glottic aperture closes. Suprasternal and supraclavicular retractions occur with paradoxical chest wall motion, increased diaphragmatic excursions and if the spasm persists, hemoglobin desaturation and bradycardia/asystole. As soon as laryngospasm is suspected, the precipitating event (such as secretions, blood, or other foreign material) should be cleared. Initial treatment should include the application of a facemask to deliver 100% oxygen with positive end-expiratory pressure (maximum pressure of 10 to 15 cm H 2 O) ( Figure 4-1 ). If laryngospasm continues, the mandible should be displaced by transiently applying pressure to the superior end of the ascending ramus of the mandible (i.e., the condyles) using a single digit behind each pinna (see previous discussion). Although subluxing the mandible, the thumbs should seal the facemask to the face. Oral airways must be used with great caution in these circumstances as short oral airways may push the tongue into the glottic opening and long airways may push the epiglottis into the opening, in both instances obstructing rather than helping the airway. An additional benefit from pressing on the ascending ramus of the mandible is that the stimulation incurred increases respiratory effort. However, if these measures fail and the oxygen saturation and heart rate continue to decrease, early treatment should include IV atropine (0.02 mg/kg) followed by IV propofol (1 to 2 mg/kg) and/or succinylcholine (1 to 2 mg/kg IV or 4 to 5 mg/kg IM) and intubation. If the child is in extremis (i.e., bradycardia and hypoxic) from laryngospasm, then intubate the trachea immediately, and ventilate the lungs with 100% oxygen.
Postobstructive Pulmonary Edema
Postobstructive pulmonary edema is a complication that may occur after relief of acute (laryngospasm) or chronic upper airway obstruction (tonsillectomy). The mechanism of this pulmonary edema appears to be the generation of extreme negative intrathoracic pressure against a closed glottis and its sudden release causing a dramatic increase in pulmonary blood flow resulting in low pressure, noncardiogenic pulmonary edema. This complication should be suspected when pink frothy sputum appears in the tracheal tube and oxygen desaturation continues unabated. Treatment is to continue positive pressure ventilation and IV lasix as needed.
Postintubation croup or subglottic edema is associated with traumatic intubation, tight-fitting endotracheal tubes, coughing on the tube, a change in the child’s position, prolonged intubation, surgery of the head and neck, and a history of croup. Treatment includes the inhalation of cool mist, steroids, and racemic epinephrine. Inhalation of racemic epinephrine (0.5 ml in 3 ml normal saline over 10 minutes) is usually effective although its effects are temporary and its use may be followed by rebound edema. Prolonged observation or overnight admission may be required.
Ensure that the head is correctly positioned and supported.
For infants and children younger than 6 years of age, the head should be on the level of the table and supported in a low head ring. At this age, the larynx is positioned high in the neck and there is no advantage to anterior displacement of the cervical spine because the relatively large head accomplishes this naturally. Extension of the neck at the atlanto-occipital joint aligns the oral, pharyngeal, and tracheal axis for optimal visualization. External pressure (so called optimal external laryngeal manipulation [OELM]) applied to the thyroid cartilage region of the anterior aspect of the neck (applied most effectively by the anesthesiologist using their second hand, in a posterior and cephalad direction) may further improve the view of the glottic aperture.
For older children and adolescents, place a folded sheet or blanket under the head as a pillow to cause anterior displacement of the cervical spine and improve the alignment of the airway and the view of the glottis as in adults.
Beware of conditions that may be associated with an unstable cervical spine (e.g., Down syndrome, Marfan syndrome). In such cases, note the range of spontaneous motion of the neck when the child is awake and inquire about the presence of neurologic symptoms preoperatively (wide based gait, urinary or fecal/urinary incontinence). There is no evidence that cervical spine films are helpful in ruling out unstable cervical vertebra; however, we advise extreme care be taken to limit neck movement during intubation or surgical positioning.
Examine the teeth carefully; many young children have loose deciduous teeth. The teeth must be kept in view throughout laryngoscopy: retract the lip with your thumb and exert no pressure on the teeth during laryngoscopy. If loose teeth are present, it should be noted preoperatively and the parents should be informed that it may be safer to remove them once the child is anesthetized. If teeth are removed, they should be retained and given to the parents after the anesthetic. A plastic tooth guard may be applied to the maxillary teeth and is particularly useful for older children and adolescents when a Macintosh (curved) blade is used.
In infants and children, the anesthesiologist’s view of the glottis may be obscured by the epiglottis unless it is raised with the tip of the straight blade. (This is why we advocate the use of a straight blade in this age group.) In small infants, it is sometimes a problem to lift the epiglottis without it slipping off the laryngoscope blade. If this happens, advance the blade into the hypopharynx (with the entire tongue to the left of the blade) and slowly withdraw it until the glottis slips off the blade and the base of the epiglottis is firmly held. Alternatively, a straight blade may be used as would a curved blade and slowly advanced along the surface of the tongue. As the tip of the blade enters the vallecula, lift the base of the tongue to avoid trauma to other laryngeal structures.
Insufflation of oxygen into the pharynx during laryngoscopy (especially in infants or those with a difficult airway) improves oxygenation during attempts at intubation. Specially designed blades with an oxygen port are available (Oxyscope, Anesthesia Medical Specialties, Santa Fe Springs, Calif.), or an oxygen catheter may be taped to the side of any blade so as to deliver approximately 2 L/min of oxygen.
The optimal size of the tube is the largest one that passes easily through the glottis and subglottic regions without incurring resistance. The presence of a leak around an uncuffed tube at 20 cm H 2 O positive pressure depends on a number of factors (including head position and muscle relaxation). A leak should be tested and achieved between 20 and 30 cm H 2 O peak inflation pressure. If the leak is too large, the next half size larger tube may be inserted. If there is no leak at 30 cm H 2 O, then a smaller diameter tube should be considered. In deciding that the tube size is appropriate, many clinicians depend more on the absence of any resistance when the tube passes through the cricoid region than on the presence of an audible leak. There is increasing use of cuffed tracheal tubes in children in the operating room (OR) and PICU but these tubes should also have a leak when the cuff is deflated (see later discussion).
Clear, thin-walled polyvinyl chloride (PVC) tubes (Z79-approved) are preferred.
Cuffed tubes may be preferred for major surgery in children whose lungs may be difficult to ventilate and who may be at increased risk for regurgitation of gastric contents. Even in infants and young children, the use of an appropriately sized cuffed tracheal tube does not increase postoperative morbidity. The use of a cuffed tube reduces the need to change tubes, reduces OR pollution, and may reduce the risk of aspiration. It also obviates the need to have a close fit in the subglottic region to ensure effective ventilation. For this reason it may be preferable, in children with a known tendency to subglottic stenosis (e.g., Down syndrome), to use a tube of smaller diameter together with a cuff to seal the airway. Small-sized cuffed tubes are now available with a wall thickness similar to that of uncuffed tubes. In infants and small children when a cuffed tube is used, the cuff may not require inflation to achieve an adequate seal for ventilation. However, positioning the cuff below the cords places the tip of the tube much closer to the carina in small infants and may increase the risk of an endobronchial intubation. The new MicroCuff tubes have addressed these shortcomings by designing a high compliance, better shaped cuff that is more distally attached to the tube.
Endotracheal connectors must have a lumen at least equal to the internal diameter (ID) of the tube and must be firmly inserted. Tracheal tube connectors (particularly in small diameter tubes) should be removed, moistened with an alcohol swab, and reinserted into the tube up to the shoulder.
The correct positioning of the tracheal tube should be immediately confirmed by observation of the chest excursion, the presence of humidity within the lumen of the tube, the capnograph trace, and chest auscultation. Ventilation should be auscultated in both axillae. The length of the trachea of the infant and young child is short, only 5 cm in the neonate. The tip must be accurately placed at midtracheal level to minimize the risk of an endobronchial intubation or accidental extubation. Note carefully the length of tube that is passed through the cords, and check the tube length marking at the teeth. An easy method of determining the correct depth of insertion of the tracheal tube when it is even with the teeth or alveolar ridge is 10 cm in a neonate, 11 for a 1-year-old and 12 for a 2-year-old ( N.B. The second digit is the child’s age in years.); beyond 2 years, halve the child’s age and add 12 cm (see Table 4-6 ). Tubes must be firmly taped in place, preferably near the middle of the mouth, where they are less likely to kink. When cuffed tubes are used, the cuff should be positioned just past the vocal cords; check for bilateral ventilation and secure the tube carefully. As previously mentioned, the margin of safety before the tip passes into the bronchus is shorter with cuffed tubes.
Avoid pressure by anesthetic hoses and other equipment on the child’s face or head by the use of suitable padding. Facial nerve palsy has been reported after anesthesia because of pressure of anesthesia equipment.
The anesthesia circuit and tube must be carefully positioned and supported to prevent any traction on the tube that might cause it to kink or become dislodged. Endotracheal tubes used in children kink very easily, and this is a potential cause of disastrous accidents.
Remember that extension of the neck withdraws the tip of the tube proximally in the trachea and flexion advances the tube; 1 to 3 cm of movement may occur between full flexion and full extension in infants. Position the tube carefully and consider the effects of changing the head position. Always reassess bilateral ventilation after repositioning the child.
Be aware that some neonates and infants have a congenitally short trachea, which increases the danger of endobronchial intubation (e.g., DiGeorge syndrome).
If the nasal route is chosen, the child should be prepared as outlined earlier. When performing nasotracheal intubation it is not unusual to cause some bleeding from the nose. As a result, several strategies have been developed to reduce this risk. Although warming the tip of the tube softens it, this has not been shown to be effective in reducing nose bleeding. Two effective strategies are application of a vasoconstrictor (e.g., oxymetazoline) to the nares and/or telescoping the tip of the tube into the flange end of a smooth red rubber catheter. With the latter, the catheter tip should be lubricated and passed along the floor of the (preferably left) nostril followed by the tube. (The left nostril aligns the tip of the tube [bevel on the left] directly with the glottic opening and aligns the bevel of the tube on the turbinate side.) The catheter is then advanced into the oropharynx where it is visualized in the hypopharynx and pulled off the endotracheal tube with McGill forceps. The tube is then directed using McGill forceps into the trachea.
A Note on Awake Intubation in the Neonate. It was common practice to intubate the neonate awake; however, it is now usual to induce anesthesia first. Intubation is more likely to be successful and less desaturation to occur if the neonate is first anesthetized. Awake intubation might be considered in neonates who are hemodynamically unstable, have micrognathia or a difficult airway, or who are extremely premature. To perform an awake intubation, pretreat the neonate with oxygen and atropine, have a styletted tube available, and have an assistant position the neonate’s arms fully abducted against the head to stabilize the neonate’s head. With the laryngoscope in one hand and the tube in the second, remove the facemask and intubate the trachea rapidly. Awake intubation increases blood pressure and intracranial pressure to a similar extent as crying and coughing. There has been a concern raised regarding an increased risk of IVH in preterm infants whose tracheas were intubated awake; however, this risk has never been confirmed. If awake intubation is deemed to be necessary, a local anesthetic solution (diluted, with upper limits predetermined) may be applied to the oropharynx and palate to reduce the infant’s distress and struggling. Small doses of fentanyl (0.5-1 µg/kg) and midazolam (0.05-0.1 mg/kg) may also facilitate the process. The use of a laryngeal mask airway (LMA) to establish the airway before anesthesia may also be considered (see later discussion).
Rapid Sequence Induction (RSI)
RSI is an intravenous induction technique used to rapidly and safely secure the airway with a tracheal tube when there is a risk of vomiting or regurgitation and aspiration. Careful preparation for a RSI is essential and requires the following:
Equipment; anesthesia machine, age appropriate laryngoscopes and tracheal tubes, functioning suction.
Predetermined drugs in weight-appropriate doses.
Skilled anesthesiologist and skilled assistant.
The equipment must include all standard monitors and the necessary airway instruments and supplies. The airway equipment should include two functioning laryngoscope blades and handles, two sets of suction tubing, cuffed tracheal tubes of age appropriate size (plus a half-size larger and smaller diameters) and a stylet. Predetermined drugs include 100% oxygen to be given before the sequence begins, an intravenous induction agent (propofol 3 to 4 mg/kg, ketamine 1 to 2 mg/kg, or etomidate 0.2 to 0.3 mg/kg) in predetermined doses according to weight and physical status ( N.B. Severity of dehydration and sepsis, etc.), atropine (0.02 mg/kg), and a muscle relaxant (succinylcholine 2 mg/kg or rocuronium 1.2 mg/kg). The child’s head is optimally positioned during preoxygenation and as anesthesia is induced, cricoid pressure (see below) is applied by the assistant. (Before commencing, ensure that your assistant is instructed in the effective application of cricoid pressure.) Once paralyzed, the trachea is intubated without delay and the cuff inflated. In the modified RSI technique, the lungs may be ventilated manually with 100% oxygen while maintaining cricoid pressure (see later discussion).
Cricoid pressure (Sellick maneuver) should be applied to the cricoid ring with thumb and long finger as anesthesia is induced and should be maintained until tracheal position is confirmed. Cricoid pressure has been popularized as an adjunct to the RSI to prevent passive regurgitation of gastric contents during induction of anesthesia. The use of this technique is widely advocated. However, evidence has not been forthcoming to support the effectiveness of cricoid pressure to either occlude the lumen of the esophagus or prevent passive regurgitation of gastric contents. MRI evidence indicates that the lumen of the esophagus is lateral to the cricoid ring in 50% of patients and is laterally displaced with cricoid pressure in 90%. Moreover, studies of the force required to occlude the lumen in adults report that inadequate force is applied in the majority of patients. Surveys indicated that cricoid pressure is used in only half of those children in whom it is indicated. In adults, 30 to 40 Newton (3 to 4 kg of force) must be applied to the esophagus; there are no comparable data in children. Cricoid pressure is known to relax lower esophageal sphincter tone. If mask ventilation is ever necessary in a child with a full stomach, it is probably prudent to continue to apply cricoid pressure to prevent gastric inflation and maintain small peak inflation pressures. Contraindications to cricoid pressure should be recognized ( Table 4-7 ). Excessive cricoid pressure may increase the difficulty of laryngeal visualization; OELM combined with cricoid pressure may be needed.
|Active vomiting||Rupture of the esophagus|
|Education||Lack of knowledge, expertise, and/or ability to apply cricoid pressure|
The Laryngeal Mask Airway
The LMA is an oropharyngeal tube provided with an anatomically conforming elliptical inflated rim designed to encircle the laryngeal inlet. If correctly inserted, the mask tip lies against the upper esophageal sphincter, the sides against the pyriform fossa, and the upper border against the base of the tongue. It was primarily designed as a substitute for mask anesthesia in spontaneously ventilating adults, but more recently its use has been extended to some children whose lungs were ventilated. In children, controlled ventilation without distention of the stomach may be possible if peak airway pressures are maintained at approximately 15 cm H 2 O. The LMA does not protect the airway should vomiting or regurgitation occur. LMAs are sized according to the child’s weight ( Table 4-8 ).
|Mask Size||Child’s Weight||Maximum Cuff Volume (ml)||Largest ETT (ID, mm) Inside Classic LMA||Largest ETT (ID, mm) Inside Unique LMA *||Largest Endotracheal Tube (ID, mm) Proseal LMA *||Largest FOB Inside ETT (mm)|
|1.5||5–10 kg||7||4.0||4.0||4.0, some manufacturers||3.5|
|3||30–50 kg||20||6.0, cuffed||5.0, cuffed||4.5||5|
|4||50–70 kg||30||6.0, cuffed||5.5, cuffed||5.0|
|5||70–100 kg||40||7.0, cuffed||6.0, cuffed||5.0, cuffed|
* Note that these sizes differ from the manufacturers recommendations, but have been found by us to be the better alternatives to ensure easy passage of the endotracheal tube through the LMA. In some cases the tubes listed are smaller, in some cases a cuffed alternative is given as an option rather than an uncuffed tube.
Insertion of the LMA is performed after induction of adequate anesthesia by inhalation or by an intravenous injection of propofol (3 to 4 mg/kg for children). The cuff should be checked before it is inserted. After the cuff has been completely deflated and the mask well lubricated, it is inserted blindly along the curve of the palate into the pharynx, with the aperture positioned anteriorly, until resistance is felt. If the LMA becomes “hung up” on the posterior pharyngeal wall, a finger should be inserted into the mouth to lift the tip of the LMA and continue insertion. The LMA is then advanced using gentle pressure. When the cuff is inflated, the LMA should rise slightly out of the mouth. The adequacy of ventilation and fit are checked. Generally, a leak will become obvious at approximately 15 cm H 2 O peak inflation pressure. An alternative method of insertion in children has also been suggested: with the cuff partly inflated, the LMA is inserted with the mask facing posteriorly and then rotated 180° as it enters the pharynx. In either case, a black guideline on the proximal visible tube should lie against the central incisors when the LMA is in place and correctly oriented. Coughing and laryngospasm may occur if insertion is attempted at too light a level of anesthesia; such complications may be more common in infants and small children than in adults.
Studies have shown that, when the LMA is in position, the tip of the tube lies in the hypopharynx but the relationship of the cuff to the epiglottis and laryngeal aperture may vary somewhat despite an apparently good airway.
Some difficulty with insertion may be encountered in up to 25% of children; this is more likely in the smaller child having a size 1 or size 1.5 LMA inserted. In a very small percentage of children, it may be impossible to place the LMA correctly.
When correctly positioned, the LMA provides a good airway with less resistance than an endotracheal tube. It avoids instrumentation through the glottis and frees the anesthesiologist from holding a facemask. It is particularly useful during imaging procedures, radiotherapy, and for other short procedures where mask anesthesia with spontaneous ventilation might be used. Somewhat surprisingly, some have found the LMA to be useful during adenotonsillectomy, and it has been suggested that less aspiration of blood occurs with the LMA than with an uncuffed endotracheal tube. (We, and most ENT surgeons prefer to intubate the trachea). A special application of the LMA is to use it as a guide to assist management of the child with a difficult airway, where it may be used as a prelude to fiberoptic endoscopy and intubation. The LMA can be inserted in awake infants (e.g., with Pierre Robin syndrome) after inhalation of nebulized lidocaine, and used to provide an airway to induce and deepen anesthesia before fiberoptic intubation. The LMA is useful when difficulty with ventilation occurs in a child during attempts at intubation. The LMA may also be advantageous in infants with tracheal stenosis, in whom passage of an endotracheal tube would severely reduce an already compromised airway diameter. It must be remembered that the LMA does not guarantee the airway as does an endotracheal tube, and it does not protect against aspiration. The ProSeal LMA provides a better seal (average leak at ~25 cm H 2 O peak inflation pressure) and a means for venting the stomach; this device may be optimal for management of the difficult airway in a situation where the child has a full stomach.
At the end of the procedure, the LMA may be left in place until protective reflexes have returned, or it may be removed while the child is still deeply anesthetized. Removal while the child is anesthetized results in fewer airway complications and less desaturation, but a facemask should be applied until the child is able to maintain a safe airway. The incidence of postoperative sore throat is similar whether an LMA or an endotracheal tube is used. Other supraglottic devices are available and each practitioner should decide which is best in their hands.
“Difficult Tracheal Intubation”
It is most important that the anesthesiologist carefully assess the airway before administering anesthesia to determine the likelihood of obstruction during anesthesia and to judge the likely ease of endotracheal intubation.
Beware of any child who does not look quite normal or who has any syndrome or association of defects. Always anticipate the possibility of an abnormal airway. When there is any doubt, assume the airway will be difficult and be prepared. Review the history and examine the child carefully. Always review any previous anesthesia records—but do not be lulled into a false sense of security by a previous uneventful anesthetic. First, not all anesthetic difficulties are detailed in the record or child’s chart. But even if they were, the ease of intubation may change as the child grows. In some cases, intubation may become easier, as in the child with a cleft palate and Pierre Robin sequence. In others, it becomes more difficult, as in the child with Treacher Collins, Goldenhar, or Klippel-Feil syndrome.
The examination of the child may provide clues as to the likely ease of intubation:
Assess the extent of mouth opening.
Check the extent of neck flexion and extension.
Check the shape and size of the mandible and maxilla (profile view).
Examine the mouth, tongue, and palate.
External ear deformities are often associated with mandibular hypoplasia.
Assess the distance between the ramus of the mandible and the thyroid cartilage.
Limited mouth opening, restricted neck extension, a large tongue, or a short ramus of the mandible predicts difficulty with laryngoscopy and tracheal intubation in children. Inability to fully visualize the fauces and uvula suggests difficult intubation, although the Mallampati scoring system does not predict a difficult laryngoscopy in children. Successful laryngoscopy depends on the ability to displace the soft tissues of the oropharynx into the mandibular space. Any deformity that limits this space (short or shallow mandible) or increases oropharyngeal tissue (large tongue) can be expected to compromise efforts to see the glottis.
It is most important to be prepared for every option when facing a difficult airway in a child. Confirm that all the equipment you may require is readily available. It is essential to keep all the “difficult pediatric airway” supplies on a special cart that is located centrally and can be wheeled into any room where it is required. It is always advantageous to have expert assistance on hand. If there are other members of the department with special skills, do not hesitate to enlist their aid, even if their initial role is simply to stand by, provide moral support, and be ready to intervene.
Preoperative administration of an anticholinergic drug may be advantageous to decrease secretions in the mouth and pharynx and minimize the possibility of laryngeal spasm. No heavy sedation should be administered; small doses of anxiolytics might be administered when necessary, using suitable caution and appropriate monitoring. Children who cannot be fasted and require emergency surgery may be prepared with the use of histamine 2 -blocking drugs and intravenous metoclopramide.
A recommended sequence to follow is outlined in the Pediatric Difficult Airway Algorithm ( Figure 4-2 ).
The choice of anesthetized versus awake intubation is quite simple: children, unlike adults, almost always require general anesthesia. Children are very easily upset and will not cooperate during attempts at an awake intubation (even after local anesthesia is applied to the airway). Small infants may be severely stressed by attempts at awake intubation and are more easily and rapidly intubated when they are anesthetized. An exception is advised for certain small infants (i.e., those with Pierre Robin syndrome), in whom intubation may be very difficult and who may be more safely managed by topical anesthesia of the mouth and insertion of a well-lubricated LMA while the infant is awake. The LMA can then be used as a route to induce anesthesia and, if necessary, as a conduit for fiberoptic intubation (see Table 4-8 ).
The classic traditional approach to the management of the difficult pediatric airway is by inhalational induction, deep inhalational anesthesia, continued spontaneous ventilation, and direct laryngoscopy. This method is advantageous in that it does not require complex equipment and does immediately determine the status of the airway and the degree of difficulty of direct laryngoscopy. These details, along with the type of laryngoscope blade used and other data, can then be clearly recorded in the anesthesia record. Although this procedure is still recommended as a standard basic management plan, some children may be more effectively managed by early insertion of the LMA or other techniques ( see Alternative Methods ).
Induction of anesthesia should be performed by inhalation; intravenous relaxant drugs are generally contraindicated. Sevoflurane is preferred for a smooth, rapid induction. If halothane is available, its greater solubility facilitates a more prolonged laryngoscopy than is possible with sevoflurane. As anesthesia is induced, the muscles of the tongue and pharynx relax. At this time, obstruction may occur, and immediate measures may be required to re-establish a clear airway.
Adjust the position of the head with increased jaw thrust to lift the tongue off the posterior pharyngeal wall and open the upper airway. A two-handed method is preferred, with one digit behind the most cephalad tip of the ascending ramus on each side of the mandible. The finger is wedged in the triangle formed at the base of the skull between the ascending ramus of the mandible anteriorly and the mastoid process posteriorly, immediately behind the tragus. Pull the mandible towards the frontal hairline. This maneuver subluxes the mandible anteriorly and rotates the temporomandibular joint, thereby opening the mouth. At the same time, two thumbs hold the mask on the face. With this maneuver, an oropharyngeal airway is often unnecessary.
If necessary, insert an oropharyngeal airway (see previous discussion); but be aware that if the child is too lightly anesthetized this may result in coughing and laryngospasm. Make sure that the airway is appropriately sized for the child; measure it against the outside of the face (the tip should extend just to the angle of the mandible).
When an airway is established, anesthesia is deepened with 8% sevoflurane in oxygen. Before the first attempts at laryngoscopy and intubation, 1.5 mg/kg of intravenous lidocaine and/or 1 to 3 mg/kg propofol are administered slowly to reduce the likelihood of breath holding or coughing during instrumentation. During laryngoscopy, oxygen may be insufflated into the pharynx via a catheter or by the use of a special laryngoscope blade. If an adequate view of the glottis is obtained, intubation can be performed; if not, other manipulations are required:
With the laryngoscope in place, apply posterior and cephalad pressure on the cricoid region of the neck to bring the larynx into view (OELM). In children with severe retrognathia, consider pushing the larynx to the right to visualize the glottis.
In some cases, a “two-person approach” to intubation is preferable. One person who holds the laryngoscope with one hand also applies pressure (as described previous discussion) to align the axes of the larynx and oropharynx. Once the glottis is visualized, the laryngoscopist tilts his head to the left to enable the second person to pass the tube through the cords.
A retromolar or paraglossal approach may be indicated. Insert a straight blade at the extreme right side of the mouth behind the bicuspid or last molar tooth while rotating the head to the left and retracting the corner of the mouth with a small surgical retractor. The epiglottis is visualized and the tracheal tube advanced off a stylet.
An alternative approach after induction of anesthesia and after confirming the ability to ventilate the child with bag and mask is to administer succinylcholine. Laryngoscopy can then be attempted during apnea with complete muscular relaxation. This may facilitate laryngoscopy and tracheal intubation, but at the same time, it limits the time available for each intubation attempt. Infants and small children desaturate more rapidly during apnea than do older children or adults. ( N.B. Administration of a relaxant drug might result in a “can’t intubate/can’t ventilate” situation with an apneic child.)
If laryngoscopy proves impossible by direct vision, the mask should be reapplied, deep anesthesia continued, and other options considered (see Figure 4-2 ). It is wise not to persist with prolonged attempts at direct laryngoscopy because these may become traumatic and result in bleeding, thus compromising the chances of success with other methods or by other individuals.
Laryngeal Mask Airway
The introduction of the LMA has made possible many new approaches to management of the difficult airway, provided the mouth and pharynx are of adequate size. If intubation under direct vision is impossible, the LMA may be inserted without delay. Insertion of an LMA at any stage is usually successful in establishing a patent upper airway, but laryngeal spasm may occur if the child is inadequately anesthetized. Once in place, the LMA can be used as a route for ventilation and oxygenation, to continue anesthesia, and as a conduit for flexible bronchoscopes, endotracheal tubes, airway catheters, light wands, or other equipment needed to complete intubation (see Table 4-8 ).
In some children it is impossible to insert an LMA (i.e., very small or scarred mouth) and it may be necessary to perform flexible bronchoscopy via the mouth or nose. The use of fiberoptic laryngobronchoscopes in children has been facilitated by the development of small-diameter scopes that accommodate small endotracheal tubes. The smallest scopes do not have a suction channel (see Table 4-8 ). A suction channel on the scope is a very desirable feature because secretions frequently obscure the view and this channel may also be used to administer oxygen in children who are breathing spontaneously; external suction may then be required to clear secretions.
If the nasal route is chosen, anesthesia should be cautiously induced with sevoflurane and spontaneous ventilation as previously described. The flexible bronchoscope should be prepared in advance by sliding an appropriate size tracheal tube (without the connector) over the scope. When the child is adequately anesthetized, the flexible bronchoscope is passed through the left nostril, to the glottis and into the trachea. The tube should then be passed over the scope and into the trachea. If the tube does not pass the cords, the tube should be rotated 90° so that the tip of the tube is midline. Practicing flexible fiberoptic bronchoscopy in children with normal airways is essential if the anesthesiologist is to become adept at a similar intubation technique with a difficult airway. When a very small endoscope is not available, alternative methods for children have been suggested including visualizing the glottis with a larger scope to pass an airway exchange catheter into the trachea under direct vision, over which the endotracheal tube can subsequently be threaded.
The Bullard laryngoscope and other similar devices are designed to indirectly view the glottis and thereby make it possible to direct the tracheal tube. All of these devices require practice, especially in the manipulation of the tube once the glottis is visualized. Initial experience should be gained with children who have a normal airway. The success rate for the experienced operator is reported to be high.
(Verathon Inc., Bothell, WA, 98011) This device incorporates a small video camera to observe the glottis on a monitor screen. The “Glidescope small GVL” is recommended for children 1.5 to 20 kg.
Light Wand Intubation
The use of a malleable lighted stylet, passed blindly into the trachea, makes it possible, with practice, to rapidly secure the airway. The stylet should be curved to suit the predicted shape of the child’s airway, and a suitable endotracheal tube is mounted on it. Always check that the lamp is screwed firmly in place. As the light passes into the trachea, the anterior neck can be seen to transilluminate. This is more easily seen with the room lights dimmed. The endotracheal tube can then be advanced over the stylet into the trachea. The method requires practice but may be successful in many children with a difficult airway. It is limited by the size of tube that can be passed over the stylet (5.0 to 5.5 mm with the Flexi-Lum *
* Concept Corp., Clearwater, Fla.); the Trachlight †
† Laerdal Inc., Long Beach, Calif.has two sizes: child accommodating tubes 4 to 6 mm ID and infant accommodating tubes 2.5 to 4 mm). This technique can be used with general anesthesia, appropriate sedation, and regional or topical analgesia. The use of a light wand via the LMA has also been described. The Optical Stylet ‡
† Storz, Inc., Endoscopy-America Inc, Culver City, Calif.provides a further advance since this device will accommodate a 2.5 mm ID tracheal tube with a video camera and monitor to facilitate visualization of the laryngeal inlet. The Shikani optical stylet best accommodates a 3.0 tracheal tube.
Blind Nasotracheal Intubation
This is a technique that requires much practice. It is an art that few acquire in an era when advances in technology offer so many alternative methods. Blind nasotracheal intubation may still be necessary if all else fails, or when equipment fails, and the child’s glottis cannot be visualized (see N.B. after item 7 next). The following are some hints:
It is essential to understand the anatomy of the nose. The septum is always angled; if the nares is open anteriorly, it is narrowed posteriorly and vice versa. The turbinates, which arise from the lateral wall, may be damaged (resulting in bleeding) or dislodged as the tube passes through the nose. To minimize damage to the turbinates and nasopharyngeal mucosa during passage through the nostril, consider instillation of vasoconstrictors (i.e., oxymetazoline) into the nares and/or the tube should be telescoped into a red rubber catheter (as described previously). The success rate for blind nasotracheal intubation increases if the left nostril is used because the leading tip of standard tracheal tubes is on the right and this tip will advance along the midline into the glottis. (Special tubes are made with the bevel on the right for use in the right nostril.)
Prepare and lubricate suitable tubes (ID 0.5 mm smaller than for oral intubation).
Use an inhalation induction (i.e., O 2 , + sevoflurane or halothane); if available, 5% CO 2 may be added to increase the tidal volume before intubation attempts. Do not use intravenous induction agents or muscle relaxants.
When the child is deeply anesthetized, position the head slightly extended, as in the sniffing position.
Insert the tracheal tube through the nostril and advance it as described previously. There are five possible outcomes:
Right of larynx—withdraw the tracheal tube slightly; turn it to the left and turn the child’s head to the right.
Left of larynx—withdraw the tracheal tube slightly; turn it to the right and turn the child’s head to the left.
Esophagus—withdraw the tracheal tube slightly and extend the head maximally before advancing the tube again.
Anterior to epiglottis—withdraw the tracheal tube slightly and flex the head.
If unsuccessful, repeat, using the other nostril.
Other useful maneuvers include:
Connecting the capnogram for the largest signal or listening at the end of the tracheal tube for maximal gas exchange to reach the larynx.
Passage of a second tube through the other nostril to block the esophagus.
External pressure to the neck which may direct the glottis toward the tip of the tube.
An angled stylet passed through the tube to direct the tip toward the glottic aperture. Usually this requires a 90 ° bend right at the tip of the tracheal tube.
Use of a smaller-size tube for initial intubation; the tube can then be changed up in size by passing an airway exchange catheter and leaving it in place to guide the larger tube.
At the glottic aperture, the tip becomes lodged at the anterior commissure of the cords and fails to advance. To advance the tube, three possible maneuvers may be used:
Rotate the tube 90 ° clockwise (so the bevel points superior)
With McGill forceps, grab the tube 2 to 4 cm proximal to the end, withdraw the tube several centimeters and then bend it downwards as the tube is advanced, or
Flex the child’s neck (by raising the child’s head and resting it onto your chest) while you perform laryngoscopy and maneuver the tube with McGill forceps (most difficult maneuver)
N.B. The technique of blind intubation requires considerable skill, which can be acquired only by extensive practice. It is a method that cannot be learned in a lecture but must be mastered by repeated practice. If the anesthesiologist is not sufficiently experienced and has no skilled assistant at hand, some other technique may be preferable or further attempts at intubation are abandoned and the child awakened from anesthesia.
As a means to simpler blind intubation, an endotracheal tube or an airway exchange catheter passed blindly through an LMA frequently passes into the trachea. Monitor end-tidal CO 2 via the catheter or tube to confirm its position.
This technique depends on threading a wire proximally through the vocal cords into the pharynx via a needle passed percutaneously into the trachea. This is a very dangerous technique with a reduced success rate particularly in infants and small children because of their compliant tracheas and the very small tracheal dimensions that together increase the risk of tracheal and extratracheal tissue injury. If cannulated successfully, the wire is then retrieved in the mouth and used to guide a tube into the trachea. A modification of this technique passes the retrieved wire retrograde up the suction port of a bronchoscope. The scope is then guided into the trachea by the wire and can be used to position the tube.
If intubation options are failing, consider the following:
Should we awaken the child and reschedule?
Can this case be done safely with mask anesthesia?
Can this case be done safely with an LMA for airway support?
Do we need a surgical airway?
Extubation of the Trachea
Children are prone to laryngeal spasm during extubation, especially if extubated during a light plane of anesthesia. Therefore,
Before extubation, ensure that all airway equipment to ventilate with oxygen and to reintubate if necessary are available.
Extubate when the child is fully awake (or, if indicated, deeply anesthetized).
Some children should not cough or strain with the endotracheal tube in situ during emergence (e.g., those having neurosurgery or intraocular surgery). This may be achieved with a planned “deep” extubation, preceded by careful suctioning of the stomach and pharynx. Lidocaine, 1 to 2 mg/kg IV administered slowly before extubation, also decreases the risk of coughing and breath holding. After the tracheal tube is removed, a facemask should be applied, the airway maintained, and oxygen administered until the child is awake. Studies suggest that oxygen saturation (Sa o 2 ) levels are better maintained if extubation is performed while the child is still anesthetized and oxygen is then given by mask until the child is fully awake.
When judging whether the child is “awake” enough for awake extubation, wait until the eyes and mouth open spontaneously, all limbs are moving, and the child resumes regular spontaneous ventilation after coughing.
Do not disturb the child unnecessarily during the awaking stage, so as to minimize coughing and bucking on the tube before the child is fully awake. A “No touch” technique while waiting to extubate awake is very successful in many children.
All monitors should be left in place until successful extubation is complete.
Severe laryngospasm upon extubation may be followed by pulmonary edema as the laryngospasm is relieved. If this occurs, it should be treated by continued positive pressure ventilation, a diuretic (e.g., Lasix) and morphine.
The following children should be fully awake before extubation:
All those in whom tracheal intubation was difficult.
All those having emergency surgery; these children may vomit gastric contents during emergence from anesthesia.
Children who have had a mouth gag with tongue blade inserted by the surgeon (e.g., for cleft palate repair) are at risk for postoperative swelling of the tongue; always inspect the mouth before extubation.
Extubation of the Difficult Pediatric Airway
Extubation should be performed as a well-planned exercise, with the necessary equipment and personnel to reintubate the child readily available. In selected children a trial extubation, leaving an airway exchange catheter in situ, may be indicated.
All children with difficult airways should be extubated or have the LMA removed only after they have fully regained consciousness and when all danger of swelling in the region of the airway has passed. Corticosteroids (dexamethasone) have been used before extubation to decrease the likelihood of stridor, and all children should be given humidified oxygen after the tracheal tube is removed.
The golden rule: If there is any doubt about the airway, leave the trachea intubated.
Pediatric Anesthetic Circuits
The ideal anesthetic circuit for children should be lightweight; with low resistance and dead space; with low compliance; adaptable to spontaneous, assisted, or controlled ventilation; and readily humidified and scavenged. These conditions are most nearly met by the T-piece systems; however, modified circle systems are now extensively used for children.
The T-Piece and its Variants
The T-piece, originally described by Ayre in 1937, was modified by Jackson Rees to provide for artificial ventilation. The T-piece relies on continuous flow from the fresh gas limb to flush expired gases from the expiratory limb, thus its performance depends on the rate of fresh gas flow and the minute ventilation of the child. Setting the fresh gas flow to target a specific Pa co 2 has proven to be unreliable and superseded by capnography.
Small fresh gas flows that permit some rebreathing are well tolerated by children provided a capnograph is used to maintain the EtCO 2 tension within acceptable limits. Indeed, it has become environmentally, economically, and physiologically rational to decrease the fresh gas flow and permit rebreathing with these circuits. If capnography is not available, then minimum fresh gas formulas should be used to reduce the risk of rebreathing exhaled gases; for mask anesthesia greater than 8 L/min and for ETT greater than 6 L/min.
Because the T-piece has no valves, it cannot malfunction and has a very low resistance. However, kinking or obstruction of the expiratory limb can lead to high pressure within the circuit and might cause barotrauma. Because it is also lightweight and convenient and has minimal dead space, it is considered by many to be the ideal circuit for transporting infants and young children, especially during spontaneous ventilation to and from the ICU. The Bain coaxial system is a modification of the T-piece. It has essentially the same characteristics and requires the same fresh gas flows.
Circle Absorber Semi-Closed System
The adult circle absorber semi-closed system can be modified for use in children by incorporating a smaller-diameter breathing circuit. The circle system is more economical and provides limited humidification of inspired gases, but the greater circuit resistance and the possibility of valve malfunction lead some to prefer the T-piece system for infants and small children, especially during spontaneous ventilation. From a practical point of view today, this does not appear to be a substantive concern in clinical pediatric anesthesia. The circle system facilitates EtCO 2 monitoring because there is less mixing of expired and inspired gases than occurs in the open T-piece system. The integrity of the circle system and the presence and correct functioning of the valves must be carefully checked before each use.
Humidification of Anesthetic Gases
Humidification of inspired gases during anesthesia in the past was recommended to prevent damage to the respiratory tract by dry gases and to minimize heat loss via the respiratory tract and thereby assist in maintaining normothermia. Dry gases inhibit ciliary activity and lead to the accumulation of inspissated secretions, which may, in the extreme, progress to obstruct the endotracheal tube. Degenerative changes in cells exfoliated from the trachea after exposure to dry gas have been described, but an increased incidence of postoperative morbidity from pulmonary complications remains unproved. However, the use of circle systems, particularly with low flows has reduced the need for a humidifier. Gases should be humidified during very prolonged surgery and in the intensive care unit to reduce the risk of tube blockage from inspissated secretions.
Humidified anesthetic gases significantly reduce heat loss during surgery, particularly in neonates and infants. However, heated humidifiers are not as easily incorporated into circle circuits and accumulated water may plug capnogram tubing. Humidifiers are less frequently used in pediatric anesthesia since other effective means for maintaining body temperature are now available. An alternative means of humidification for older children is the use of a heat and moisture exchanger (HME) inserted at the connection of the endotracheal tube to the circuit. The HME conserves approximately 50% of the water normally lost via the respiratory tract and thus prevents a corresponding heat loss. The HME is most efficient with smaller tidal volumes and greater respiratory frequency, so it is quite useful in pediatric cases. These normally are very low resistance, but if blocked by secretions will significantly increase airway resistance; always monitor ventilation carefully when an HME is used.
Controlled Ventilation During Anesthesia
During anesthesia, ventilation may be controlled using manual or mechanical ventilation.
This is used at times, especially during induction and when there is doubt about the adequacy of ventilation. It has been claimed that manual ventilation enables the anesthesiologist to monitor compliance continuously and to compensate rapidly for changes. Although this may be true for the experienced pediatric anesthesiologist, there is some question about the ability of individual anesthesiologists to detect even complete airway obstruction just by the feel of the bag. However, if there is any doubt about the adequacy of ventilation or in the event of sudden deterioration in the child’s vital signs, it is wise to switch to manual ventilation. Then the adequacy of ventilation should be further confirmed by auscultation of the lungs, observation of chest movement, and the EtCO 2 monitor.
Rapid ventilation with small tidal volumes provides optimal results in the neonate because this pattern of ventilation tends to maintain the functional residual capacity and prevent airway closure. EtCO 2 levels should be monitored continuously because it is very easy to overventilate small infants. Hyperventilation (and consequent respiratory alkalosis) should be avoided.
Mechanical ventilators have the advantage of maintaining a relatively constant level of ventilation while freeing the anesthesiologist to perform other functions. Remember that in small children the compression volume of the anesthesia circuit may exceed the tidal volume that is delivered to the lungs. Therefore the volume readings on the ventilator may be meaningless. The adequacy of ventilation must be judged by auscultation of the chest and observation of chest movement, along with EtCO 2 or arterial carbon dioxide levels.
Controlled ventilation with the circle system permits the use of extremely small fresh gas flows while monitoring the adequacy of ventilation by capnography. Several strategies for mechanical ventilation have been introduced into clinical anesthesia.
Volume cycled ventilation. In this mode, the ventilator delivers the prescribed tidal volume (unless it reaches the pressure relief limit—usually 40 mm Hg). Therefore during surgeries in which the compliance of the chest/abdomen changes, the delivered tidal volume remains relatively constant. (Tidal volume may decrease slightly because of the large volume of gas compressed in the anesthesia circuit as compliance decreases).
Pressure cycled ventilation. In this mode, the ventilator delivers a volume until the preset pressure is reached (usually 20 to 40 mm Hg). In this mode, if the pressure is reached before a desired tidal volume is delivered, the ventilator switches into expiration. During surgeries in which the compliance of the chest/abdomen changes, the delivered tidal volume varies from breath to breath as compliance changes. Hence, without an accurate capnogram, tidal volume delivered cannot be estimated. We find this mode only acceptable during minor peripheral surgery.
Pressure assisted ventilation—new ventilators incorporate the potential for various modes of ventilation. The place of these in pediatric anesthesia is undetermined at the present time.
Monitoring During Anesthesia
Routine Monitoring Methods
Monitoring during anesthesia must always include the following:
Pulse oximeter: apply before induction and leave in place during transport and during the recovery room stay. The light source and sensor must be positioned to transilluminate a part of the body (earlobe, finger, toe, palm of hand, or sole of foot, depending on the size of the child). Placement on the earlobe or buccal angle rather than the finger or foot may result in a slightly faster initial response time during acute desaturation. Placement at a preductal site (head or right hand) is desirable in infants with any potential for patency of the ductus arteriosus. A second postductal oximeter probe is useful to detect shunting. The sensor(s) should be protected to prevent outside light or pressure from interfering with the reading. Pulse oximetry has proved most effective in providing an early warning of developing hypoxemia. Failure of the pulse oximeter to detect and record a pulsatile flow may provide useful warning information about the child’s circulatory status. However, if the pulse oximeter fails, check the child first (color of mucus membranes or nailbeds, heart rate, breath sounds, blood pressure); then, if necessary, troubleshoot the equipment.
Pulse oximetry is relatively accurate throughout a wide variation in hematocrit. In children with cyanotic congenital heart disease the oximeter tends to overestimate saturation at lower readings (below Sp o 2 70%). Similarly, the faster the rate of desaturation, the more the oximeter underestimates the true hemoglobin saturation.
Fetal hemoglobin (HbF), hemoglobin SS, and hyperbilirubinemia do not affect the pulse oximeter measurement.
Nail polish or disease of the nails may affect the performance of the monitor (blue or green nail polish); the accuracy is unaffected by pigmented skin. Methemoglobin (MetHb) and carboxyhemoglobin (CoHb) affect the accuracy of readings: the former has a nonlinear effect, either underestimating or overestimating saturation and the latter overestimates saturation.
An arterial saturation of 80% to 95% reflects a Pa o 2 of 40 to 80 mm Hg—a safe range for the preterm infant. But because of the slope of the Hb/O 2 association curve, pulse oximetry is less precise in the assessment of hyperoxia than it is in hypoxia. If considered necessary, an arterial sample can be obtained to confirm which level of saturation is appropriate in terms of Pa o 2 for each child. This level of saturation can then be maintained by varying the fraction of inspired oxygen (F io 2 ).
The complications of pulse oximetry are few, but severe burns have occurred when an incorrect sensor from a different manufacturer has been substituted. Burns may also occur when pulse oximetry is incorrectly used in the magnetic resonance imaging suite (see Chapter 18 ).
Stethoscope, precordial or esophageal: there must be provision to monitor heart and breath sounds throughout anesthesia. Recently, there has been a trend away from the use of a stethoscope; however, should there be an equipment failure, this is an essential aid. If the monitors stop working, check the child first.
Blood pressure (BP) cuff of suitable width: the cuff should occupy two thirds of the upper arm. If the cuff is too narrow, the BP readings are falsely high; if it is too wide, they are falsely low. A width of 4 cm is recommended for full-term neonates. A noninvasive blood pressure device (i.e., Dinamap) may be used, but ensure that it is set to provide readings at a maximum of 5 minute intervals.
Electrocardiogram: It is standard to monitor the EKG; however, the EKG is of limited value in pediatric cases. Any arrhythmias that occur are usually benign and bradycardia on the EKG is a very late sign that the child is in trouble.
Thermistor probe (axillary, esophageal, or rectal) (see Management of Body Temperature).
End-tidal carbon dioxide: This device noninvasively reflects the adequacy of ventilation and pulmonary perfusion. It also provides the most reliable indicator of successful endotracheal intubation and should be used whenever intubation is performed. Two types of monitors are available: measuring carbon dioxide “in-line” at the connector or by sidestream sampling from the circuit. The latter method is more commonly used. However, it is not as easy to apply in infants and small children owing to the small size of the ventilatory volumes. When a partial rebreathing circuit is used (i.e., a T-piece plus ventilator), end-tidal sampling must be obtained from within the lumen of the endotracheal tube for all small children (i.e., those weighing less than 12 kg) if useful numbers are to be obtained. When a circle circuit is used, proximal sampling at the endotracheal connector gives valid results even for small infants. The presence of a leak around the endotracheal tube may also affect end-tidal sampling, especially when positive end-expiratory pressure is applied; with a very large leak, the EtCO 2 waveform may disappear completely.
EtCO 2 measurements correlate poorly with the Pa co 2 in children who have congenital heart disease with a right-to-left shunt or mixing lesion; the lower the saturation, the greater the Pa co 2 -EtCO 2 gradient. In those with left-to-right shunting, the accuracy of EtCO 2 readings is unaffected.
A decrease in the EtCO 2 provides a very early indication of a reduction in pulmonary blood flow. This may be useful in the early diagnosis of cyanotic spells in the child with tetralogy of Fallot. A decrease may also be diagnostic of pulmonary embolism, air embolism, or a low cardiac output state.
Peripheral nerve stimulator: should be used whenever nondepolarizing muscle relaxants are administered.
Arterial catheter: should be inserted for direct measurement of BP and to provide for intermittent blood gas analysis when required. The radial or femoral artery is usually cannulated (see later discussion); rarely, the axillary artery may be used. We recommend checking for collateral flow from the ulnar artery when cannulating the radial artery. Do not use the brachial artery, which has poor collateral vessels. (See Precautions with Arterial Lines.) Cannulation of the superficial temporal artery has been described but this introduces the possibility of retrograde intracranial embolization. Children with Down syndrome may have a single (median) artery in the wrist, in which case cannulation should be avoided. (Always check the wrist vessels before attempting cannulation.)
Urine output: record this at regular intervals for all children undergoing major surgery and all who have hypovolemic shock or whose renal function may be impaired.
Central venous pressure (CVP): record from a catheter inserted centrally via the internal or external jugular vein (see later discussion). The external jugular is a less reliable route for CVP monitoring but is often useful for fluid replacement and drug infusions. The CVP should always be monitored in children in whom major blood loss and/or impaired cardiac performance is anticipated.
Radial Artery Cannulation
The left radial artery is often preferred for arterial puncture (in right-handed children).
Locate the artery by palpation; if this is difficult, use the Doppler flow meter or ultrasound, or in small infants, transilluminate the wrist with a bright cold light.
Use careful aseptic technique and prepare the skin with povidone-iodine (Betadine).
Make a small skin incision over the artery with an 18-gauge needle. This prevents damage to the tip of the cannula during skin puncture.
Perform arterial puncture; as soon as blood issues into the hub of the needle, turn the needle so that the bevel faces down.
Advance the cannula gently into the artery ( Figure 4-3 ).