General anesthesia is almost always required because children do not tolerate sedation and local analgesia for eye surgery.
Intraocular surgery and surgery of the nasolacrimal duct and eyelids require a bloodless field. Although induced hypotension is seldom indicated for these operations, all measures should be taken to ensure that the anesthetic does not increase bleeding. Smooth, general anesthesia—with optimal airway, good positioning of the child, and quiet emergence without coughing or straining—is important.
The oculocardiac reflex (OCR) is powerful in children but is readily blocked by intravenous atropine (0.01 to 0.02 mg/kg) at induction of anesthesia. Do not rely on atropine given intramuscularly or on local anesthetic (retrobulbar) blocks to prevent this reflex. Monitor the heart rate carefully during manipulation of the eyes and extraocular muscles. In the rare event that atropine is contraindicated, remember that the oculocardiac reflex is more likely to be triggered by a sudden pull than by a gradually applied progressive traction on the extraocular muscles. The reflex usually fatigues rapidly; that is, a second pull does not elicit the same powerful effect.
Some children may be taking medications that have significant side effects ( Table 9-1 ).
Echothiophate iodide (phospholine iodide), (long-acting plasma cholinesterase inhibitor)
Nausea, vomiting, abdominal pain, prolonged apnea after administration of succinylcholine
Timolol maleate topical (ß-blocking agent)
Bradycardia refractory to atropine, bronchospasm, Exacerbation of the disease in asthmatics
Acetazolamide (Diamox) (Carbonic anhydrase inhibitor)
Metabolic acidosis, and depletion of sodium, potassium, and water. It may also rarely trigger anaphylaxis, Stevens-Johnson syndrome, and bone marrow depression.
Dorzolamine (Carbonic anhydrase inhibitor)
Medications that are applied to the conjunctivas or injected into the eye during surgery may have important systemic effects or significant implications ( Table 9-2 ).
Potential Adverse Effects and Implications
Hypertension and arrhythmias (especially dangerous during halothane anesthesia). Epinephrine eye drops are specifically contraindicated in children with tetralogy of Fallot because they may precipitate a cyanotic “tet” spell. Phenylephrine drops cause fewer problems, especially if the concentration is limited to 2.5%; but if instilled on a hyperemic conjunctiva, they may cause severe hypertension. Monitor the heart rate and blood pressure carefully after drug instillation. Ensure that you know what is being instilled: 10% phenylephrine drops should not be used in children; cardiac arrest may occur.
Ataxia, disorientation, psychosis, and convulsions, especially if a 2% solution is used. A 0.5% solution should be used for infants, and a 1% solution for children
Behavior disturbance, psychotic reactions, and rarely, vasomotor collapse.
Scopolamine eye drops
Excitation, disorientation, possible psychosis; may be treated with physostigmine 0.01 mg/kg IV.
Hypertension, tachycardia, bronchospasm, nausea, vomiting, and diarrhea.
Intraocular injection of acetylcholine
Increased secretions, salivation, bronchospasm, and bradycardia. Treat with IV atropine (to produce miosis after lens extraction).
Sulfur hexafluoride gas or air injection to globe (to assist in retinal reattachment surgery)
Discontinue N 2 O 20 minutes beforehand to prevent an increase in intraocular pressure (IOP) followed by an even more dangerous decrease in IOP as the N 2 O is withdrawn; this could damage the retinal reattachment
The effects of anesthetic drugs and techniques on IOP must be remembered:
Atropine (by any route) causes only a very slight increase in IOP. Its use as a premedicant is not contraindicated in children with glaucoma.
All potent inhalation anesthetic agents, intravenous agents (i.e., propofol, thiopental) and nondepolarizing relaxants decrease IOP; effect may be dose related.
Intravenous succinylcholine may cause a transient increase in IOP that is not reliably prevented by pretreatment with a nondepolarizing relaxant drug. The increase in IOP occurs within 30 seconds after administration but abates quickly, returning to normal within 6 minutes. Succinylcholine is usually avoided in children undergoing intraocular surgery. The increase in IOP may be less in those in whom the IOP is already increased (i.e., glaucoma), but it seems prudent to omit succinylcholine in such children, especially if IOP is to be measured. The use of succinylcholine in children with penetrating eye trauma has been controversial. Although it was originally contraindicated, it has been shown to be safe in at least one very large series. Indeed, when given after thiopental in a rapid sequence induction, succinylcholine does not increase in IOP. However, with the intermediate duration, relatively rapid-acting nondepolarizing relaxants (i.e., rocuronium), there are alternatives to succinylcholine for RSI in children with penetrating eye injury.
Ketamine, originally thought to increase IOP, probably has little effect.
Diuretic drugs decrease IOP, and chronic diuretic therapy may reduce the increase in IOP after succinylcholine administration.
Pressure on the globe from a facemask increases IOP, avoid compressing the eyes; use of a contoured mask (i.e., Rendell-Baker-Soucek mask) in small children makes it easier to do this. Laryngoscopy and endotracheal intubation may increase IOP; this effect can be modified by the administration of lidocaine 1 mg/kg IV, preferably 3 minutes before intubation. The insertion of a LMA causes a smaller increase in IOP than tracheal intubation, and its removal may be associated with less coughing and straining. Therefore, the LMA may be useful for children undergoing elective eye surgery.
Coughing, bucking, crying, and straining all markedly increase IOP. Smooth extubation with reduced risk of coughing can be effected by prior administration of lidocaine 1 to 2 mg IV, a small dose of propofol (1 mg/kg) immediately before removal of the tracheal tube, or by deep extubation (contraindicated in the presence of a full stomach).
Hypercapnia increases IOP, and hypocapnia decreases it.
Succinylcholine causes contracture of the extraocular smooth muscles and interferes with forced duction testing that is performed within 15 minutes after its administration.
The depth of anesthesia for ophthalmology surgery must be sufficient to ensure that the eyes are immobile and fixed centrally; during light anesthesia the eyes often “roll up” cephalad. Ketamine is generally unsatisfactory for ophthalmic surgery because of the associated nystagmus.
Postoperative pain may be troublesome after eye operations, but nonsteroidal antiinflammatory drugs such as rectal acetaminophen (35 to 45 mg/kg administered postinduction) may be sufficient after minor surgery. Immediately after intraocular surgery or trauma repair a retrobulbar block placed during anesthesia may be very effective. Topical analgesics (i.e., tetracaine ophthalmic drops) may significantly reduce postoperative discomfort.
Postoperative nausea and vomiting are common. It may be reduced by the use of propofol as the primary anesthetic, and it may be further reduced by the intraoperative administration of intravenous ondansetron (0.1 mg/kg), dexamethasone (0.0625 to 0.15 mg/kg), dimenhydrinate (0.5 mg/kg), or metoclopramide (0.15 mg/kg). Avoid dimenhydrinate which produces sedation if adjustable sutures are being used.
Be very cautious when using facemask anesthesia for surgery of the eyelids and similar operations (e.g., chalazion excision). Do not use high concentrations of oxygen, which might leak around the mask when the surgeon uses cautery; serious facial burns may occur if the drapes catch fire. An air or helium/oxygen mixture is preferred. Avoid N 2 O.
CORRECTION OF STRABISMUS
Correction of strabismus is the most common eye operation in children.
Malignant hyperthermia is very rare, but strabismus may be an associated condition.
Special Anesthesia Problems
Oculocardiac reflex—Severe bradycardia and even cardiac arrest can occur as a result of traction on the extraocular muscles (see previous discussion).
“Oculogastric reflex”—vomiting after eye muscle surgery is very common and should be prevented as outlined previously. Vomiting may also be precipitated by “pushing” oral fluids postoperatively and by early ambulation. It is our recommendation that children only ingest clear fluids when they express the desire to drink.
Postoperative pain after strabismus may be considerable in older children.
If adjustable sutures are used, the child must be assessable postoperatively; excessive sedation should not be ordered. If a second anesthetic might be required to adjust the sutures, an intravenous line or a heparin lock should be left in place to facilitate induction of a second anesthetic. Do not use droperidol as an antiemetic in such children because they may be too drowsy to cooperate; the combination of ondansetron and dexamethasone is preferred (see later discussion).
Do not give heavy sedation.
The surgeon may wish to examine the child immediately before the operation.
Oral midazolam (0.5 to 0.75 mg/kg for children 1 to 6 years of age) is an effective premedication with rapid onset.
Clonidine (4 μg/kg PO) is effective as a premedication although it must be given 60 to 90 minutes before surgery. The latter may cause bradycardia, hypotension, and postoperative sedation but does provide postoperative analgesia.
Give atropine, preferably intravenously, at induction. If not administered it must be readily available, drawn up in a syringe, in case the OCR is elicited.
Induction is accomplished either by inhalation of sevoflurane or halothane in nitrous oxide or by intravenous propofol or thiopental followed by a relaxant.
If induction includes halothane, consider IV atropine before the start of surgery.
After a sevoflurane induction, a dose of propofol (up to 3 mg/kg IV) facilitates tracheal intubation and permits spontaneous respiration during surgery. After an intravenous induction and a muscle relaxant, maintain anesthesia with an inhaled agent and spray the larynx well with lidocaine before tracheal intubation. In both instances, intubate with an oral RAE tube. Alternatively, in suitable children, use a well-lubricated LMA.
Maintain anesthesia with N 2 O/O 2 /isoflurane or sevoflurane; allow spontaneous ventilation (provided the duration of surgery is not excessive).
From the start of surgery, listen to the child’s heart sounds continuously via a precordial stethoscope and monitor the electrocardiogram. If bradycardia occurs, ask the surgeon to discontinue traction, additional intravenous atropine may be given; alternatively repeated gentle traction on the muscle may fatigue the reflex.
Give ondansetron (0.1 mg/kg) plus dexamethasone or dimenhydrinate (0.5 mg/kg) intravenously to reduce postoperative vomiting, or metoclopramide (0.15 mg/kg) immediately after the operation. Avoid opioids intraoperatively.
Provide for postoperative analgesia. IV ketorolac decreases postoperative pain and is associated with less PONV than opioids. Tetracaine eye drops instilled by the surgeon provide analgesia as does subtenon injection of bupivacaine or ropivacaine.
To prevent subconjunctival hemorrhage, the trachea must be extubated or the LMA removed without causing coughing and straining by the child. Extubate while the child is still deeply anesthetized, and allow the child to awaken smoothly while supporting the airway and administering oxygen by mask. Intravenous lidocaine (1.5 mg/kg) or low-dose propofol (0.5 to 1 mg/kg) administered before extubation may reduce coughing during emergence.
Provide analgesics for pain as indicated, avoid opioids where possible.
Intravenous rehydration during surgery should obviate the need for early oral ingestion in the postanesthesia care unit. Delaying ingestion of oral fluids decreases the incidence of poststrabismus vomiting. Do not attempt to mobilize the child rapidly; there is a motion sickness component to PONV after strabismus surgery. Beware that vomiting may occur en route to home in outpatients. These children tend to sleep more than most in part because they have double vision in the immediate postoperative period. It is reasonable to inform parents that their child will be quite sleepy the rest of the day.
If nausea and/or vomiting occur, order additional antiemetic therapy and continue with intravenous fluids.