Airway management and mode of ventilation

It is considered good practice to intubate and ventilate the patient to ensure a secure airway (the surgical field is in close proximity) and to facilitate mild hypocarbia (this reduces intra-ocular pressure). The laryngeal mask airway is a popular choice for airway management for elective eye surgery in the UK. Laryngeal mask insertion avoids the pressor response to laryngoscopy and intubation causing raised intra-ocular pressure. The laryngeal mask does not protect against aspiration of gastric contents. Its use in emergency anaesthesia is therefore limited. 

Analgesia and control of nausea and vomiting

It is possible to manage pain in the majority of patients after eye surgery with oral analgesia. Avoiding opioids if possible helps prevent nausea and vomiting. Regular doses of paracetamol (acetominophen) and a non steroidal anti-inflammatory drug (ibuprofen, diclofenac, ketoprofen) should be prescribed. Codeine phosphate can also be added. These drugs are best accepted by children if given as an elixir (syrup). Some analgesic drugs are listed in the table below.

In patients having surgery with general anaesthesia it is a good idea to ask the surgeon to perform a local anaesthetic block before waking up the patient. If stronger analgesia is required this is best given as small intravenous doses of morphine or pethidine.

Nausea and vomiting after emergency eye anaesthesia can be a major problem in some patients. Anti-emetic prophylaxis may help prevent this. Some patients may benefit from a regular anti-emetic in the post-operative period. There is a vast number of anti-emetic drugs available. Most have a limited efficacy. Using a combination of small doses of anti-emetic drugs from different pharmacological classes may enhance efficacy and reduce side effects. Some anti-emetic drugs are listed in the table below.

A practical approach to emergency eye anaesthesia

1. Assess the indication for emergency anaesthesia in discussion with the surgeon. Can surgery be deferred until normal working hours and to allow adequate fasting?
2. Carry out a full preoperative assessment including a history and examination.
3. Are there any medical/trauma issues that need addressing first?
4. Decide on choice of anaesthetic technique. Provide the patient with a full explanation. Tell the patient what to expect if a local anaesthetic technique is to be used.
5. If a general anaesthesia is chosen decide if the patient has a full stomach and is at risk of aspiration.
6. If the patient has a full stomach a rapid sequence induction technique should be used. They should be preoxygenated with 100% oxygen. Pressure on the affected eye from the mask must be avoided. The patient should then be induced with an intravenous anaesthetic agent (eg thiopentone 4-7mg/kg) and a rapid onset muscle relaxant (suxamethonium 1-1.5mg/kg is currently the only realistic option). While the patient is being induced cricoid pressure should be applied by an assistant (Sellick's manouvre) thus occluding the oesophagus behind. The patient's trachea should be intubated after which the cricoid pressure can be removed. Note that the endotracheal tube tie should not be tight around the neck as this impedes venous drainage and raises intra-ocular pressure.
7. Choice of maintenance depends on local availability e.g. 40% O2, 60% N2O and an inhalational agent. Note that all inhalational agents reduce intra-ocular pressure.
8. Control ventilation during the procedure aiming for low to normal end-tidal carbon dioxide. This may require the use of a longer acting muscle relaxant (e.g. vecuronium 0.1mg/kg). A slight head up tilt helps reduce intra-ocular pressure.
9. At the end of the procedure the patient should beextubated on their side and once airway protective reflexes have returned. In patients not deemed atrisk of aspiration extubation with the patient deepand breathing spontaneously may prevent coughing. Severe coughing and straining needs to be avoided as this increases the risk of ocular haemorrhage.
10. If the patient does not have a full stomach and is not deemed at risk of aspiration, general anaesthesia should proceed as for an elective patient.
    Pre-oxygenate the patient for safety and induce with an intravenous agent. Give a long acting muscle once ability to hand ventilate is established. Laryngoscopy should be performed gently. Consider spraying the vocal cords with lignocaine to minimise the pressorresponse to intubation. This may also decrease the risk of coughing on intubation. Intubate, ventilate and maintain anaesthesia as above.
11. Post operatively nausea, vomiting and pain should be kept to a minimum as they can cause rises in intra-ocular pressure. Prescribe regular oral analgesia and an anti-emetic. Some patients may need stronger analgesia early after surgery. Titrate small doses of intravenous opioid (morphine, pethidine) to control pain. 

References

1. Mcgoldrick KE. The open globe: is an alternative to succinylcholine necessary? J Clin Anaesth 1993, 5: 1-4.

   This article argues that suxamethonium is probably still the best muscle relaxant for the real emergency. It also discusses the use of pretreatment.

2. Libonati MM, Leahy JJ, Ellison N: The use of succinylcholine in open eye surgery. Anaesthesiology 1985, 62: 637-40.

   This paper studied 100 patients needing "open eye" surgery with suxamethanium. 

This article contained links to the following further information:

 Anaesthesia for Opthalmic Surgery - Part 1: Regional Techniques

 Anaesthesia for Opthalmic Surgery - Part 2: General Anaesthesia

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