•  Infant chest wall deforms easily → because of cartilaginous structure

• Accessory muscles provide limited support (poor anatomic rib configuration)

• Infantile diaphragm contains 20–25% of fatigue-resistant type I muscle fibers → paradoxical chest wall movement when there is ↑ inspiratory effort

• ↑ work of breathing → deterioration into resp failure, esp in premature infant

•  FRC similar in both infants & adults per kg

• Owing to limited elastic recoil, infant closing capacity may near/exceed FRC:

Leads to air trapping → when small airways close at end-expiration

Cause of age-related changes in PaO₂

•  ↑ tracheal compliance in infants; can lead to dynamic tracheal collapse

•  Changes in PaO₂, PaCO_2, & pH control ventilation → act on chemoreceptors

• Degree of response directly related to gestational & postnatal age

• Hypoxia stimulates newborn resp effort; high conc of O₂ may depress it

• Nonspecific factors (blood glucose, Hct, temp) also affect infant breathing

Cardiovascular

•  Infant/neonatal myocardium contains less contractile tissue than adult heart

• Neonatal ventricle less compliant during diastole & generates less tension

• Infant ventricle cannot adequately ↑ stroke volume when metabolic needs ↑

• Cardiac output proportional to changes in heart rate

• Bradycardia → ↓ cardiac output; factors contributing to bradycardia (hypoxia, hypercarbia, surgical manipulation) should be corrected

•  Consider empiric anticholinergic admin (atropine) to offset laryngoscopy-induced bradycardia

Renal

•  Kidneys very active in utero & produce copious amounts of urine (contribute to maintenance of amniotic fluid volume)

•  At birth GFR = 15–20% of adult levels; reaches 50% within 2 wks & 100% by 1 yr (low GFR means infants cannot excrete excessive fluid loads/renal cleared drugs)

•  Ability to excrete organic acids poorly developed in neonates (causes observed “physiologic acidemia” of newborn)

•  Concentrating ability poor & newborns can conc urine only to 600–800 mOsm/kg

Hepatic

•  Gluconeogenesis & protein synthesis begin at 12 wks’ gestation (liver structure near term similar to adults; functional development lags)

•  Preterm & small for gestational age infants usually have diminished glycogen stores

→ Prone to hypoglycemic episodes after delivery

→ Treat hypoglycemia promptly (D10 at 4 mL/kg/hr)

•  Albumin levels in preterm infants are often low and affect drug binding & availability

•  Physiologic jaundice: Due to RBC breakdown & ↑ enterohepatic circ of bilirubin

→ As opposed to pathologic jaundice (encephalopathy from kernicterus)

Gastrointestinal

•  Esophageal tone ↓ in many newborns; reaches adult level ≈6 wks

→ Projectile vomiting after feeding = classic sign of pyloric stenosis

•  Meconium (water, pancreatic secretions + intestinal epithelial cells)

• Usually passed a few hours following delivery

• Premature infants often have delayed evacuation

• May also indicate GI dz (meconium ileus/intestinal atresia)

Hematopoietic

•  Neonatal estimated blood volume = 85–90 mL/kg at term, gradually ↓ with age

•  HbF: Most prevalent after birth, greater O₂ affinity than HbA (adult)

• “Physiologic anemia of infancy” due to HbF (replaced with HbA by 3 mos)

• Hg levels rise to 12–13 g/dL by age 2; in adults, they reach 14 for females & 15.5 for males

•  Vit K–dependent coag factors ≈40% adult levels (2° to immature liver synthesis)

• Prolonged PT normally seen in both preterm & full-term infants

Neurologic

•  Brain growth phases: (1) Neuronal cell division (15–20 wks’ gestation) & (2) glial cell division (25 wks–2 yrs); myelination continues into 3rd yr

•  Malnutrition, disruption of blood–brain barrier, & trauma may affect development

•  Developmental milestones represent average rate of neurologic maturation

• Deviations from norm do not necessarily indicate significant problems

• Premature infant’s developmental delay may be considered normal (depending on degree of prematurity)

Temperature Regulation

•  Infants lose heat rapidly 2° to: ↑ surface area:wt ratio, lack of adipose/SQ tissues

• Infants rely on nonshivering thermogenesis

• Cathecholamine-mediated increase in brown fat metabolic activity

→ Catecholamines also cause: Pulm & peripheral vasoconstriction, ↑ O₂ use, hypoxia, acidemia

•  Effective methods for limiting heat loss include

• ↑ ambient room temp, cover infant with thermal insulator, use of heat lamp

PHARMACOLOGY

Body Fluid Composition

•  TBW in infants ≈85%, ≈60% by 1 yr of age; extracellular water (ECW) dec faster than intracellular water (ICW)

•  Fat, muscle, organ wt are age dependent, affect pharmacodynamics/kinetics

•  Infants have greater ECW than adults → volume of distribution for drugs is expanded

• Drugs with limited tissue uptake may require higher wt-based dosing

Organ System Maturity

•  Enzyme systems involved in biotransformation relatively immature

• Drugs may have prolonged elimination half-lives

Protein Binding

•  Often only unbound drug is clinically active (many drugs are protein bound)

• Albumin is the major binding protein for acidic drugs (benzos & barbiturates)

• Neonatal albumin quantitatively & qualitatively deficient → dec binding capacity

Receptors

•  Age-related variations in response to drugs may be 2° to receptor sensitivities

PREOPERATIVE EVALUATION

Psychological Assessment

•  Use clear, simple language to discuss potential risks (avoid disclosing info in a child’s presence that may ↑ anxiety)

•  Psychological goals of the preoperative interview

• Identify specific causes of anxiety & evaluate potential benefit of preop sedation

• Address potential risks pertinent to procedure

• Describe reasonable expectations for postop discomfort, side effects

• Reassure both parents & patient

•  Child-life specialists can facilitate pt education & relieve anxiety

• Comfort objects may accompany pt into OR

• Parental presence may be useful; perceived legal risks are largely exaggerated

OR EQUIPMENT AND SETUP

•  Oral ETT size ≈ (age/4) + 4; depth ≈ (ETT internal diameter × 3)

Intravenous Fluids

•  Fluid replacement: Based on NPO deficit, ongoing maintenance requirement, blood loss, & potential for surgically induced fluid shifts (3rd spacing)

•  Lactated Ringer’s often appropriate

•  Normal saline advised for pts with renal dysfx, mitochondrial myopathy, or neurosurgical procedures

•  Dextrose soln for neonates (limited glycogen stores) & diabetes who got hypoglycemic meds

•  “Buretrol” or other metered device often used for children <6 mos

• Allows careful control of fluid admin

• Older children may receive IV fluids through a 60 drop/mL gravity infusion set

• Remove all air bubbles (risk of PFO) from IV tubing & injection ports

Emergency Drugs

•  All emergency drugs should have 1.5 in. 22 gauge needle for emergency IM injection

ANESTHESIA TECHNIQUES

Induction

Maintenance

•  Volatile agents or TIVA-based techniques can be used

• Drug selection guided by coexistent dz & surgery duration

•  “4–2–1 rule” can guide fluid replacement

• Neonates & infants require additional care to avoid fluid overload (metered devices) & provide glucose supplementation (D5NS)

• EBV should always be calculated to guide fluid when surgery has high EBL

• While children tolerate lower Hcts, they also have ↑ metabolic rates & O₂ needs

CLINICAL CONDITIONS

Respiratory

Apnea of Prematurity

•  Newborns <34 wks’ gestational age → inc risk for perioperative resp complications

• Immature response to hypoxia & hypercarbia → central apnea

•  GA may exacerbate; regional may ↓ incidence of postop spells (does not eliminate); other contributing factors include hypoglycemia, hypothermia, anemia

•  Therapies: Positioning (avoid mechanical airway obstruction), resp stimulants (methylxanthine/caffeine 10 mg/kg) in high-risk pts, appropriate monitoring

•  Usually premature newborns <60 wks’ postconception → need continuous cardiorespiratory monitoring for 24 hrs postop (no outpatient procedures)

Prematurity—Perioperative Concerns

•  ↑ risk of hypothermia

•  Unable to regulate glucose control

•  ↑ risk of postop apnea (esp if <50 wks’ postconceptual age)

•  Retinopathy of prematurity (esp if. <44 wks’ postconceptual age)

•  Pulmonary dysfunction

Meconium Aspiration

•  Presence of thick, meconium-stained amniotic fluid during concerning aspiration → may result in profound resp distress & hypoxemia

•  Suction nares & oral cavity immediately after delivery

• Transfer newborn to a radiant warmer & intubate

• Apply suction & withdraw ETT; repeated until only trace meconium seen

•  PPV should not be used initially

• Can spread meconium distally into bronchial tree

• If bradycardia/cyanosis develop → gentle PPV with 100% O₂ pressure

Bronchopulmonary Dysplasia (BPD)

•  Lung dz of newborn; problematic to accurately define as presentation has varied

•  Initially described lung injury from aggressive mech ventilation & high FiO₂

• Develop smooth muscle hypertrophy, airway inflammation, pulm HTN

• Exogenous surfactant, steroids, & gentler vent modes → improved survival (overall dz incidence has not decreased)

•  Babies <30 wks’ gestational age →

• Present with immature lung parenchyma & dysfunctional alveoli

•  Pulm dysfx will be persistent to varying degrees (may affect later management)

• Airway hyperreactivity & resp infections common

• Supportive care in the OR → gentle ventilation, limit barotrauma, β2-agonists

• Consider need for postop ICU admission

Congenital Diaphragmatic Hernia (CDH)

•  Diaphragmatic defect → presents at birth with cyanosis, resp distress, scaphoid abd

• Get herniation of abd contents → result in lung & pulm vessel hypoplasia

• Not simply lung compression & atelectasis

•  Surgical correction → postponed several days to optimize pt cardiopulmonary status

• Severe defects often require more support (ECMO or nitric oxide)

•  Anesthetic management

• Intubation (awake, inhalation, or RSI) should minimize gastric distention

• Maintenance usually volatile + narcotic (avoid N₂O → risk of pneumothorax)

• A-line + CVP for blood sampling/fluid resuscitation; temp maintenance important

• Maintain low pulm vascular resistance → avoid hypoxia & hypercarbia

•  Contralateral pneumothorax → sudden cardiovascular collapse & ↓ lung compliance

•  Postop: Transfer to NICU intubated & paralyzed

Asthma

•  Triad of airway inflammation, reversible flow defects, airway hyperreactivity

•  Signs & symptoms: Wheezing, dyspnea, chest tightness, coughing

•  Preop interview: Freq of episodes, current meds, hospital admissions, steroid use

•  Severe bronchospasm → can restrict airflow so much that wheezing disappears

•  Anesthetic management: Supplemental O₂, bronchodilators, anticholinergics

• Epinephrine may be required to treat severe episodes of bronchospasm

•  Avoid ETT use (may precipitate bronchospasm) for noninvasive procedures

Upper Respiratory Tract Infections (URIs)

•  Children have ≈6–8 URIs/yr; most caused by rhinovirus

• Croup, influenza, strep pharyngitis & allergic rhinitis → may mimic URIs

•  URIs ↑ airway reactivity for 4–6 wks following onset of symptoms

• Potential complications from GA → laryngospasm, bronchospasm, & desat

•  Risk factors for resp events: Hx of prematurity, coexistent reactive airway dz, 2nd-hand smoke exposure, ETT, nasal congestion/secretions, airway surgery

•  Not practical to cancel all children with recent URI; reschedule elective surgery if:

• Purulent nasal discharge, productive cough, fever >100°F

• No change in functional status (appetite, activity), likely to tolerate brief proc

•  LMA acceptable technique to avoid unnecessary airway manipulation

• Consider deep extubations (spontaneously breathing under ≥2 MAC of sevo) to minimize airway irritation during emergence

Secondary Smoke Exposure

•  2nd-hand smoke leads to inc risk of adverse resp events under GA → laryngo-/bronchospasm, breath holding, airway obstruction, ↑ oral secretions

Cardiac

Patent Foramen Ovale (PFO)

•  Intracardiac shunt → permits fetal circulation in utero (interatrial communication)

• Usually closes during delivery, soon after infant’s 1st breath

• Pulm vascular resistance falls & L atrial pressures exceed R → closes flap

•  Conditions which ↑ R-sided atrial pressures may reopen this conduit → hypoxia

•  Paradoxical air embolism: Can occur in pts with PFO → if precautions are not taken

Atrial & Ventricular Septal Defects (ASD/VSD)

•  ASD & VSD → result left-to-right shunts, do not present with systemic hypoxemia unless defects large & volume overload severe

•  Small defects usually asymptomatic & hemodynamically stable

• Over time, shunt flow may → lead to R-heart volume overload & CHF

• Corrective procedures usually timed according to disease severity

•  Anesthetic management

• Avoid hypoxia & hypercarbia (increased pulm vascular resistance)

• Conditions which ↑ R-sided heart pressure above L-side may provoke shunt reversal & critical hypoxemia

Neurologic

Duchenne Muscular Dystrophy

Associated with malignant hyperthermia, trigger-free anesthetic techniques should be employed

Metabolic

Mitochondrial Disease (MD)

•  Diverse group of enzyme complex defects that adversely affect energy metabolism

• Incidence 1:5,000 with variable age of onset & presentation

•  Abnl ATP production affects brain, heart, & muscle; can lead to:

Seizures, spasticity & developmental delay, hypotonia, cardiomyopathy, arrhythmias, chronic GI dysmotility, delayed growth

•  No proven assoc between MD & malignant hyperthermia

• Pts may be sensitive to propofol, but no clear guidelines regarding its use

• Be aware of potential for metabolic acidosis

•  Normal saline generally recommended for maintenance fluids

• Lactate admin may cause worsening of symptoms

• Fluid requirements may be elevated

• Children may also require glucose supplementation & serial monitoring

Gastrointestinal

Pyloric Stenosis

•  Obstruction of pyloric lumen usually age 5 wks → persistent, bile-free projectile vomiting

•  Condition = medical (not surgical) emergency

• Infant may be severely dehydrated & have concurrent electrolyte abnl

• Emesis is H⁺ ion rich, causes hypokalemic, hypochloremic metabolic alkalosis

• Must correct before surgical repair

•  ↑ risk for aspiration

• Need gastric decompression (NG) immediately before induction

• Rapid-sequence IV induction with succinylcholine or

• Awake, oral ETT intubation may require help to physically restrain infant

• Procedure = usually brief, long-acting muscle relaxation unnecessary

Tracheoesophageal Fistula (TEF)

•  Most common presentation (85%) = Type C (proximal esoph atresia w/distal fistula)

•  Symptoms: Coughing, excessive drooling, & cyanotic episodes

• Failure to pass soft-tipped suction catheter into stomach = diagnostic

• Presence of blind esophageal pouch confirmed by x-ray

•  Preop assessment: Focused on resp support, aspiration precautions, & identification of other congenital abnl (echo to rule out endocardial cushion defects)

•  Anesthesia management: A-line usually placed

• Position pt on 30° wedge to avoid passive aspiration of gastric fluid

• Induction techniques: Should minimize aspiration risk (awake intubation, RSI)

• Avoid PPV prior to intubation

• May cause significant gastric distention, diaphragmatic elevation, & hypoxia

• Prophylactic gastrostomy may prevent accumulation of gastric air

•  Deliberate R-sided mainstem intubation → limit transmission of air across fistula

• Pass ETT distal to fistula, then withdraw until bilateral breath sounds obtained

•  Lung isolation indirectly achieved by surgical compression of nondependent lung

• May be poorly tolerated (V./Q. mismatch); consider intermittent lung reinflation

• Hypotension may occur → mediastinal structures distortion & ↓ venous return

•  Extubate stable pts (with good pain control) to avoid pressure on tracheal suture line

• If pt remains intubated, only suction with a premeasured catheter that does not extend beyond distal tip of ETT

Gastroschisis & Omphalocele

•  Involve defects of anterior abdominal wall with herniation of visceral components

•  Cover exposed viscera to avoid evaporative heat loss & limit infection

• Large fluid shifts occur; fluids should be aggressively replaced

• Serial electrolyte & glucose monitoring important (place A-line/CVP)

•  Anesthetic technique

• Awake intubation or RSI; avoid N₂O

•  Defect closure may → ↑ intra-abdominal pressures which may cause → ↑ peak airway press, ↓ venous return, hypotension, lower extremity ischemia

•  Postop: Usually require mech vent support

Necrotizing Enterocolitis

•  Etiology multifactorial: Pts usually present with bowel distention & bloody feces

• Preterm infants <2 wks’ gestational age → highest risk

•  Intestinal hypoperfusion & ischemia → weakened intestinal wall → may perforate

•  Anesthesia management: Place A-line & CVP

• Resuscitation should include crystalloid & blood products

• Monitor urine output, avoid N₂O

• DIC, thrombocytopenia may occur

•  Pts often return for reexploration

Pediatric Congenital Syndromes

NEONATAL & PEDIATRIC RESUSCITATION

Figure 26-2. Neonatal resuscitation algorithm.

Neonatal Resuscitation Algorithm

Note: The following summary is not to be a substitute for completion of the Neonatal Resuscitation course as administered by a certified instructor.

•  ∼10% of newborns require direct assistance to achieve cardiopulmonary stability during transition to extrauterine life. <1% require extensive efforts

•  Term neonates with adequate breathing/crying and tone should be dried and kept warm. All others require rapid assessment and the following sequential interventions

•  Dry and keep warm, position, airway check, stimulate to breathe

•  Ambu-bag ventilation, oximetry monitoring, possible intubation

•  Chest compressions

•  Medications and volume expansion

New recommendations since 2010:

•  Initial evaluation now followed by simultaneous assessment of heart and respirations. Oximetry monitoring should be used early

•  For full-term babies, resuscitation should begin with air rather than 100% FiO₂

•  Supplemental oxygen should be blended with air and delivered concentration guided by oximetry

•  Current evidence neither supports nor contradicts the routine endotracheal suctioning of infants born in the presence of meconium-stained amniotic fluid

•  Neonatal chest compression–ventilation ratio should remain 3:1, higher ratio to be applied if neonatal arrest due to cardiac etiology

•  Therapeutic hypothermia may be considered for term/near-term infants with evolving hypoxic-ischemic encephalopathy

•  It is appropriate to consider cessation of resuscitation efforts if no detectable heart rate for 10 min

•  Delay cord clamping for at least 1 min in babies NOT requiring resuscitation