Anaesthesia for eye surgery

INTRODUCTION

Eye surgery presents unique challenges to the anaesthetist and the patient. Patients are apprehensive about any form of surgical intervention that may threaten their vision. Although the outcomes from eye surgery are usually excellent, the potential for complications is real and the avoidance of these requires appropriate training and experiencae on the part of the ophthalmologists and the anaesthetists. Special concerns that relate to eye surgery include the patients often being either young or elderly, other coexisting medical problems, patients anxious about their vision and anaesthetic problems such as access to the patients airway and side effects of the local anaesthetic blocks that are used. This section will attempt to outline some of the key issues related to anaesthesia for this type of surgery.

PREOPERATIVE EVALUATION

By nature of the speciality, the patients presenting are often either very young or older and have coexisting medical problems. Infants can have congenital problems that involve the heart and lungs making them rather unwell. Children with squints (strabismus) may also have problems with their muscles placing them at higher risk of complications from anaesthetic drugs. Elderly patients present with high blood pressure, coronary artery disease, lung problems, diabetes, arthritis and cancer.

Fortunately eye surgery carries a low risk and with appropriate teamwork involving physicians, ophthalmologists, anaesthetists and the nursing personal, it can be performed on an outpatient basis. An appropriate medical review must take place before or on the day of the surgery depending on the patient’s circumstances. Most eye surgery is performed under regional or local anaesthesia and for this to take place the patient must be able to lie flat for 45 minutes, have no head or neck tremor, ability to control coughing, no dementia or claustrophobia and have a knowledge of English so they can communicate adequately.

One of the most important contraindications to eye surgery is the use of anti-platelet and anticoagulant drugs (warfarin, clopidogrel). The use of these drugs needs to be appropriately managed before surgery. The other very important issue preoperatively is the management of patient anxiety. It is a challenging experience to have surgery performed on ones eye while you are awake and explaining the procedure is essential to allay a patients fears.

REGIONAL ANAESTHESIA TECHNIQUES

Modern technology has improved the ease with which eye surgery is performed. Cataracts can be extracted using a machine that uses ultrasound to break up the lens which then can be removed through a small incision in the eye. The length of the procedure has decreased to 15 – 30 minutes and the anaesthetic requirements are less. In fact the procedure can sometimes be carried out using only topical local anaesthetic drops. This however can be more difficult for the surgeon as the eye can still move and it may also be bothersome for the patients because of eye sensations and bright lights in the eye. A study performed on patients who were having cataract operations in both eyes were asked to compare the local anaesthesia with a regional anaesthetic used in alternate eyes and most patients preferred the regional anaesthetic.

The regional techniques include various techniques such as Sub-Tenon Anaesthesia, Retrobulbar Blocks and Peribulbar Blocks. In essence they all include the use of a syringe and needle to inject local anaesthetic around the eye. The local anaesthetic works on the nerves to produce loss of sensation and the ability to move the eye for a number of hours. These blocks are similar to injecting local anaesthetic into any other part of a patient and the block can be performed while the patient is awake. This is however a challenging experience for most people and they would prefer not to be aware of what is happening when it is done. This then requires the use of some short acting sedative to facilitate the procedure. There are many different anaesthetic techniques that can be used to sedate a patient for this procedure but the aim remains the same – to give enough sedation so the patient does not remember the eye block being performed.

A small dose of sedative (propofol) being injected via an intravenous cannula

Once the sedation has taken effect, the eye can be cleaned and the local anaesthetic injected. Some anaesthetists will ask the patient to move their eye when the needle is in place to ensure that it has not perforated the eyeball. Although the patient is able to respond to such commands, with adequate sedation on board, there should be no recall of the event.

The eye being cleaned with a Betadine solution

The sedated patient with the eye block being performed

Once the block has been completed the patient is allowed to awaken and the block is tested by assessing eye movements. If the block is working adequately, the eye is unable to move. The patient can then be taken into theatre and the after appropriate preparation, the surgery can be performed. The patient is awake and able to communicate with the surgeon during the procedure although talking is kept to a minimum as the this causes the eye to move and makes the surgery more difficult.

Patient prepared and draped ready for the eye surgery

The anaesthetic machine and the patient monitors

Regional anaesthesia is appropriate for most forms of eye surgery except if the patient is uncooperative, the procedure will take longer than 3 – 4 hours, or if regional block is inappropriate (long eyeball, clotting problems).

COMPLICATIONS OF REGIONAL TECHNIQUES

The complications of regional eye blocks are rare but serious when they happen. Risk factors for complications include inadequate education of the practitioner, inadequate knowledge of the anatomy, an uncooperative patient and failure to adhere to safe techniques.

The complications include:-

(1) Spread of the local anaesthetic solution to the central nervous system (brain) either directly or via an artery/vein which results in a fall in the blood pressure, stopping breathing and convulsions. The practitioner performing the block must be able to respond to and treat these complications.

(2) Damage to the optic nerve from incorrect needle placement

(3) Bleeding behind the eye from damaging an artery

(4) Perforation of the globe. This is more likely to occur in patents who are short sighted and if the eyeball is greater than a certain length, it safer to perform a general anaesthetic. Injection of local anaesthetic into the eyeball will cause serious damage.

(5) Damage to the muscles that move the eye is possible and can result in drooping eyelids and double vision.

CONCLUSION

Anaesthesia for eye surgery is unique and requires excellent communication between the patient, surgeon and anaesthetist to achieve the optimal outcome from eye surgery. Vision is extremely important to people and nothing but the best efforts suffice in trying to achieve this.