Anaesthesia for paediatric eye surgery

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Originally from Update in Anaesthesia | www.wfsahq.org/resources/update-in-anaesthesia

Reprinted with revisions from: Stuart G. Anaesthesia for paediatric eye surgery. Anaesthesia Tutorial of the Week 144 (2009)

Grant Stuart Correspondence email: grant.stuart@gosh.nhs.uk

Summary
Children require general  anaesthesia for  ophthalmic procedures/ surgery, but  can  generally be managed as  day cases.
The oculocardiac  reflex may be induced  during eye surgery and  risks provoking  dangerous bradycardias. Prevent these by  premedicating with  anticholinergic agents.
Postoperative nausea  and vomiting is  common after eye  surgery in children.

Introduction

Unlike adults, children requiring eye surgery do not tolerate sedation or local anaesthetic techniques and therefore almost always require general anaesthesia. T his update will present a general review of the principles of anaesthesia for children undergoing eye surgery and a description of anaesthesia for some specific procedures.

General Principles of Anaesthesia For Paediatric Eye Surgery

Preoperative Considerations

Most children presenting for eye surgery are healthy, ASA I or II and may be managed as day cases. A small number have underlying conditions, often of a chromosomal or metabolic nature, which pose more specific anaesthetic challenges. Examples of these are described in appendix 1.

Ophthalmic Medications

Many children requiring eye surgery receive eye drops. Knowledge of commonly used drugs and potential side effects is useful (See table 1). Medications may be absorbed through the pharyngeal mucosa via the nasolacrimal ducts to cause systemic effects, although this is rarely a significant problem.

Anaesthetic Considerations

Premedication and induction of anaesthesia

The decision to premedicate the child and the choice of induction technique, intravenous (IV) or inhalational, should be tailored to the needs of the child and to the preferences of the anaesthetist. Children with visual impairment should be handled in a careful and sensitive manner.

Airway management

Airway management should be tailored to the procedure. For measurement of intraocular pressure (IOP), spontaneous respiration via a facemask should be used, as intubation will raise the intraocular pressure. For simple procedures such as examination under anaesthesia (EUA) it may be more convenient to maintain spontaneous respiration through a reinforced laryngeal mask airway (LMA), particularly where a sterile field is required.

The reinforced LMA may be used in older children for most eye procedures. It is possible to use controlled ventilation with muscle relaxants, and coughing is reduced at the end of the surgery. Intraocular surgery requires a still eye with low intraocular pressure.  The airway is best managed by intubation with paralysis and controlled ventilation.

Similarly, eye surgery in very young children is best managed with intubation and controlled ventilation to ensure a secure airway. Access to the airway will be restricted during the surgery so it is important to secure the tracheal tube firmly. A preformed south facing RAE tube is ideal, but this may be too long in neonates; a reinforced flexible tracheal tube (ETT) may be preferable in this situation.

Maintenance of anaesthesia

As with induction, the choice of maintenance technique rests largely on the preferences of the anaesthetist and the availability of different agents.

The incidence of dysrhythmias is increased with halothane, particularly if there is hypercapnia and eye preparations containing atropine or adrenaline are used. Isoflurane or sevoflurane may be preferable.

Propofol has anti-emetic effects. Total intravenous anaesthesia (TIVA) with propofol reduces the risk of postoperative nausea and vomiting (PONV). Remifentanil can reduce volatile requirements.

Nitrous oxide is of limited value in eye surgery as it increases PONV and diffuses into gas filled spaces. It should be avoided in vitreoretinal detachment surgery where intraocular gas bubbles of sulphur hexachloride or perfluropropane are introduced into the eye to tamponade detached surfaces as it will cause significant rise in intraocular pressure. It should also be avoided for any patient who has undergone recent vitreoretinal detachment surgery as the bubble may last several weeks. Alternatively, if nitrous oxide was used from the start of the anaesthetic, prior to placement of the gas bubble, it will diffuse out of the bubble on completion of the anaesthetic and increase risk of re-detachment.

Anaesthetic agents and intraocular pressure

Normal intraocular pressure (IOP) ranges from 10 to 20mmHg. Most anaesthetic agents will decrease this. Table 3 describes the effects of commonly used anaesthetic agents on IOP. If serial measurements of IOP are being made, it is important to be consistent with the type of anaesthetic used on different occasions. anaesthetic techniques and intraocular pressure Physical and physiological variables have an important effect on IOP.

Laryngoscopy, coughing, straining, crying, bucking and the process of tracheal extubation may all cause a rise in IOP. This effect may be attenuated by lidocaine 1mg.kg^-1 IV 3 minutes prior to intubation or extubation. Use of the LMA allows smoother induction and emergence from anaesthesia and has much less effect on IOP.

Hypoxia and hypercapnia both increase IOP.

Hypocapnia and hypothermia decrease IOP.

The Oculocardiac Reflex

The oculocardiac reflex is common during eye surgery in children, and is seen in up to 60% of children undergoing strabismus surgery. It is essential to use continuous heart rate monitoring with an ECG during eye surgery in children. The reflex takes its afferent innervations from the ophthalmic division of the trigeminal nerve, relays via the sensory nucleus in the 4th ventricle, with the efferent impulse passing through the vagus nerve.

Surgical traction on the extra-ocular eye muscles or pressure on the globe causes a sinus bradycardia, and occasionally junctional rhythms, atrioventricular block, atrial ectopics or ventricular ectopics. The reflex is most commonly induced by traction on the medial rectus muscle, rather than the smaller lateral rectus muscle. The bradycardia resolves almost immediately after the stimulus has been removed and weakens with repetition of the stimulus.

Atropine 20mcg.kg^-1 IV or glycopyrrolate 10mcg.kg^-1 IV at induction will block the oculocardiac reflex. If not given at induction, it is important to have the drugs drawn up and ready to administer if bradycardia should occur.

The reflex may be attenuated by application of topical local anaesthetic agents to the eye (such as tetracaine eye drops), or by blocking the afferent limb of the reflex with a peribulbar block, although this block is not usually used in children due to the risk of globe perforation.

The oculocardiac reflex is less common with sevoflurane compared to halothane, and less common with deep anaesthesia compared to light anaesthesia. The likelihood of significant bradycardia is doubled if hypercarbia is present, so controlled ventilation should be considered. The oculocardiac reflex is more likely to occur with rocuronium compared to atracurium.

Children who exhibit the oculocardiac reflex are more likely to develop PONV and should receive an antiemetic during anaesthesia.

Extubation and emergence from anaesthesia

It is important to avoid coughing and bucking on the tracheal tube at the end of surgery, particularly for children who have undergone intraocular surgery. For this reason, many anaesthetists use a laryngeal mask airway for eye surgery. If a tracheal tube has been used, the child should be extubated deep, if possible. If deep extubation is contraindicated, for instance if the child has a full stomach, lidocaine 1mg.kg^-1 IV can be given to reduce rises in IOP.

Principles of pain relief and postoperative care

Pain after eye surgery is usually mild to moderate and can be managed with simple analgesics such as paracetamol, NSAIDS and topical local anaesthetic agents. These may be given pre-emptively as oral preparations preoperatively or rectally/IV at induction.

Squint surgery, evisceration and vitreoretinal surgery is associated with more severe pain. Analgesia should include an opioid such as fentanyl IV, paracetamol, NSAIDs, and topical local anaesthetic if possible. Multimodal analgesia should be continued into the postoperative period, with the addition of codeine phosphate or tramadol, escalating to morphine if required. The use of opioids increases the risk of PONV and antiemetics are essential.

PONV is extremely common after paediatric eye surgery, and for strabismus surgery can be as high as 60% if no prophylaxis is given. The combination of ondansetron 0.15mg.kg^-1 IV , and dexamethasone 0.1-0.2mg.kg^-1 IV reduces PONV to 10% in strabismus surgery. It is wise to leave the IV cannula in place postoperatively where PONV may be a problem so that further antiemetics and IV fluids can be given.

Ketamine is associated with emergence phenomena and the child should be recovered in a quiet area with minimal stimulation.

Most paediatric eye procedures are treated as day cases and children may resume oral intake as soon as they are able. Occasionally PONV results in an unplanned overnight admission.

Anaesthesia For Specific Ophthalmic Conditions and Procedures

EUA and measurement of IOP

For an examination of the eyes under anaesthesia, either an inhalational or intravenous induction technique and airway maintenance with a facemask will suffice. It may be technically easier to place an LMA for a longer EUA.

Most anaesthetic agents decrease IOP, which may potentially mask a high IOP.

Some anaesthetists advocate the use of ketamine 1–2mg.kg^-1 IV or 5–10mg.kg^-1 IM for IOP measurements, as it does not drop IOP. Although it may slightly raise IOP, this may be safer than having a falsely low reading. Ketamine increases secretions so should be given with either atropine 20mcg.kg^-1 IV or glycopyrolate 10mcg.kg^-1 IV.  Airway reflexes are maintained and instrumentation of the airway is rarely required.

Alternatively, inhalational induction may be used. The ophthalmologist should be present in the room so that the IOP can be measured as soon as the child is still. The child should not be too deeply anaesthetised, the eyes should be central and the facemask must not press on the eyes.

Regardless of the technique used, the IOP should always be measured before laryngoscopy or LMA insertion, although there is little evidence to prove that the latter significantly raises IOP. A consistent technique should be ensured if serial measurements of IOP are to be made.

Syringing and probing of nasolacrimal ducts

Children with blocked nasolacrimal ducts will usually present early in life with increased tearing. Most respond to probing of their nasolacrimal ducts, which is a short procedure for which an LMA will suffice.

Should simple probing fail, the surgeon might place a silicone catheter through the duct where it is secured for a few weeks. Alternatively the inferior turbinate bone may be fractured to relieve the obstruction.

Dacrocystorhinostomy is a more extensive procedure that involves exposure of the duct and creation of a new opening into the nasal cavity.

Anaesthetic considerations

The main problem is bleeding from the nasal mucosa:

• Topical vasoconstrictors reduce bleeding from the nasal mucosa.
• Hypotensive anaesthesia may be required to reduce bleeding, for instance, relatively deep anaesthesia with moderate head up tilt.
• The airway should be protected from blood, ideally with a throat pack, and the nasopharynx should be suctioned before extubation.
• Opioids may be required for analgesia for this procedure.

Strabismus surgery

Squint is a common problem that affects 3 – 5% of the population, making strabismus surgery the most commonly performed eye operation in children. It affects males and females equally.

Squints are usually idiopathic, but may also be secondary to intracerebral space occupying lesions, trauma, infection or inflammation causing muscle palsies. Most patients are healthy, but occasionally squints may be associated with a family history, prematurity, and disorders of the central nervous system such as cerebral palsy, hydrocephalus and myelomeningocoele. Patients may have occult myopathies and there is a threefold increase in the incidence of masseter spasm. Anecdotal evidence of an increased association with malignant hyperpyrexia remains unproven.

Squint correction is achieved by lengthening (recession), shortening or tightening (resection) or transposition of any of the four rectus and two oblique extra-ocular muscles, or combinations of any of the above.

Surgeons may use forced duction testing to distinguish a paretic muscle from one that has restricted motion. Botulinum toxin may be injected into the extra-ocular muscle for minor abnormalities.

This requires electromyelogram (EMG) control and muscle relaxants should be avoided.

In older children an adjustable suture may be used that allows fine adjustments to be made 24 to 48 hours postoperatively under topical local anaesthetic once the patient is awake.

Anaesthetic considerations

• Induction technique, the method of airway control and choice of ventilation may be guided by the preference of the anaesthetist.
• TIVA with propofol reduces PONV. Alternatively, anaesthesia may be maintained with a volatile agent and air/oxygen.
• Consider atropine 20mcg.kg^-1 IV or glycopyrolate 10mcg.kg^-1 IV to block the oculocardiac reflex.
• PONV is common postoperatively, up to 50–75%. Give two anti-emetic agents such as ondansetron 0.1mg.kg^-1 IV and  dexamethasone 0.1-0.2 mg.kg^-1 IV.
• Extubate the child deep if possible.
• Analgesia should include topical tetracaine or oxybuprocaine, NSAIDS such as ibuprofen or diclofenac and paracetamol,  unless contraindicated.
• Intraoperative opioids should be avoided if possible
• A peribulbar block is effective for analgesic requirements and reduces PONV, possibly by blocking the ophthalmic division of  the trigeminal nerve that passes to the vomiting centre in the medulla. The risk of globe perforation in children makes most  practitioners cautious of this.
• A sub-Tenon block performed intraoperatively by the surgeon provides effective analgesia.