24. Anesthesia for Ophthalmic Surgery

Elaine Christiansen¹

(1)

Department of Anaesthesia and Pain Management, Perth Children’s Hospital, Nedlands, WA, Australia

Elaine Christiansen

Email: Elaine.Christiansen@health.wa.gov.au

Keywords

Oculocardiac reflexAnesthesia strabismusPostoperative nausea and vomitingAnesthesia for penetrating eye injury

Children may need general anesthesia for procedures that would be performed awake in adults, such as examination or refraction of the eyes, removal of superficial foreign bodies and cataract repair. Common procedures include strabismus surgery, tear duct surgery and management of the penetrating eye injury. Most of these children are well, but some may be very young or have associated syndromes. Anesthesia depth affects the intraocular pressure and eye position.

24.1 Airway Management

The airway can often be managed with an LMA. Considerations are size of the child, access to the airway should a problem arise during the procedure, duration of the procedure and adequacy of the airway obtained if an LMA is chosen initially. Full-head draping is often used during eye surgery and its removal to urgently access the airway is awkward and introduces the risk of wound infection.

24.2 Oculocardiac Reflex

The oculocardiac reflex is bradycardia, junctional rhythm or even asystole caused by traction on the extraocular muscles or compression of the eyeball. It occurs most commonly during strabismus surgery or enucleation. Anecdotally, the reflex is most likely to be triggered when traction is applied to the medial rectus muscle. The afferent path of the reflex is via the trigeminal nerve to the motor nucleus of the vagus nerve, from which efferent impulses affect the sino-atrial node. The incidence is increased when propofol is used for maintenance of anesthesia.

The oculocardiac reflex is very common, but severe bradycardia (30–40 bpm) is less common. Bradycardia gradually improves over a minute or two and usually resolves quickly if the stimulus is stopped. Sometimes, atropine or glycopyrrolate may be required. Pharmacologic treatment is not always needed and depends on the severity of the bradycardia or arrhythmia and the child’s hemodynamic state. Treatment, particularly with atropine, often results in tachycardia and hypertension unless small, judicious doses are titrated over a short period. Although some would routinely use anticholinergics to prevent the oculocardiac reflex developing, this is not generally necessary due to the potential for side-effects from these drugs and the potential for masking heart rate responses as an indicator of depth of anesthesia or analgesia requirements.

Tip

The oculocardiac reflex can be frightening—there may only be one or two QRS complexes on the ECG screen! Ask the surgeon to stop traction on the muscle and check that there is still a plethysmograph trace from the oximeter to indicate a pulse is present. Prepare to give atropine 10–20 μg/kg if the heart rate does not quickly improve, or if the reflex recurs despite more gentle muscle traction next time.

24.3 Examination Under Anesthesia of the Eyes

Examination of the eyes under general anesthesia (EUA) may be required when a child is too young or uncooperative to allow examination while awake. EUA may be done to assess conditions such as retinoblastoma and congenital cataracts, or to screen for glaucoma or refraction errors. An inhalational technique with spontaneous ventilation is used, and the procedure is usually performed in a darkened room. Most anesthetic drugs, including sevoflurane and propofol, reduce intraocular pressure (IOP) by several mmHg. The effect on IOP is maximal soon after induction, when anesthetic depth is maximal. Some ophthalmologists will allow for this while measuring the IOP and others will measure IOP as the child awakens. Ketamine increases IOP by 2–3 mmHg. It is an alternative for anesthesia because some consider the IOP after ketamine is more reflective of the IOP in the awake child. Ketamine is not an ideal anesthetic agent because it may cause dysphoria and nausea. Children being screened for glaucoma often have multiple check-ups over time, and a pleasant anesthetic experience is important to maintain the child’s cooperation with subsequent anesthetics. Hypoxia and hypercarbia also increase intraocular pressure but mild changes produce clinically insignificant effects.

24.4 Tear Duct Surgery

Blocked lacrimal ducts are relatively common in babies and young children. Patency is restored by probing and syringing the tear duct. This is a short procedure allowing good access to the airway so an LMA is often used. Saline or fluoroscein is used to syringe the duct and enters the pharynx, so this needs to be suctioned away at the end of the procedure. Dacrocystorhinostomy is sometimes performed to create a patent tear duct if attempts at probing fail. It is often a long procedure with fluid and blood entering the pharynx so endotracheal intubation is often used.

24.5 Strabismus Surgery

Strabismus , or squint, is caused by an imbalance of the extraocular muscles so that the visual axes of the two eyes are not parallel. Surgical correction involves shortening or changing the insertion position onto the globe of one or more of the extraocular muscles. The airway can be managed with either an LMA or an ETT, but access to the airway during surgery is limited. The advantages of the LMA include a smoother induction and emergence and less postoperative coughing.

The oculocardiac reflex (OCR) is common in squint surgery. It is a trigeminal (ophthalmic division)-vagal reflex. It most commonly causes a sinus bradycardia, but can also cause junctional or other brady-arrhythmias. It is less likely if traction on the eye muscle by the surgeon is gentle and gradual, and the reflex fades over time. It is more common with anesthetic techniques that are associated with a reduced heart rate, including propofol, remifentanil and fentanyl. It is more likely during light planes of sevoflurane anesthesia compared to deep planes. Atropine given prophylactically causes a tachycardia, making assessment of depth and response to surgery more difficult. If OCR occurs, the surgeon can be asked to temporarily release the muscle, and atropine given if required. Small, incremental doses of atropine are preferable, as larger doses may cause severe hypertension and tachycardia.

Nausea and vomiting (PONV) occur in 50–70% of children when no antiemetic is given, and prophylaxis is routinely given. The greater the number of eye muscles repaired, the greater the likelihood of PONV. Ondansetron 0.15 mg/kg with dexamethasone 0.15 mg/kg decreases the incidence of PONV (Fig. 24.1). Propofol anesthesia is as effective as the administration of dexamethasone and ondansetron in the prevention of PONV, but the incidence of the oculocardiac reflex is higher in propofol-based techniques. In practice, the oculocardiac reflex is not a great problem, and propofol anesthesia together with antiemetics and IV fluids facilitate day-stay strabismus surgery.