Anaesthesia for Ophthalmological Surgery

R. K. Mirakhur and P. Elliott

The article gives a brief description of the physiology of intraocular pressure and the effect

of the commonly used drugs in anaesthesia on it. General and local anaesthetic techniques

for some of the commonly performed operations are discussed.

Although ophthalmic surgery may require to be

performed in all age groups, a large proportion of such operations are performed in the elderly who are steadily increasing as a proportion of the population. It has been estimated that about half the population above the age of 75 years show degenerative changes in the lens.’

Common ophthalmic operations carried out in the elderly include cataract extraction with intraocular lens

implantation (by far the commonest), drainage proce-

dures for glaucoma and detachment and vitreous surgery, surgery on the eyelids, surgery on the lacrimal apparatus

and enucleation or evisceration. Apart from the specific requirements of ophthalmic surgery which include the control of intraocular pressure (IOP) particularly where

the globe has to be opened, absence of vascular conges- tion, immobility of the eye and prevention of the oculo- cardiac reflex, particular attention has to be paid to the physical, functional and the mental state of the patients.

Pre-operative status of patients

Many of the elderly patients presenting for ophthalmic surgery have concurrent diseases of other systems most notable being the presence of hypertension, coronary

insufficiency, incipient cardiac failure, reduction in

respiratory function, late onset diabetes and decreased

R. K. Mirakhur and P. Elliott Department of Anaesthetics, The Queen’s University and the Royal Victoria Hospital, Belfast, N. Ireland

metabolism and excretion of drugs. The treatment of

these conditions needs to be optimised and appropriate therapy continued until the day of surgery and recom- menced soon afterwards. In addition concurrent drug therapy is common in this age group. Of particular concern are agents like levodopa, tricyclic antidepres-

sants. drugs given for the treatment of hypertension, calcium entry blockers, antiarrhythmics. aminophylline etc. Steroid cover for those receiving these needs to be

judged on the basis of duration of therapy and the indica- tion for which these are being used. The anaesthetist has

also to be aware of the systemic effects of some of the drugs instilled into the eye both on a chronic basis and on

acute administration. Drugs like timolol and ecothiopate have important systemic effects. Instillation of phenyle- phrine, adrenaline and other sympathomimetic agents may result in systemic hypertension which is obviously

important in the elderly. These are described in greater detail elsewhere.‘-” This article will concentrate on issues related to ophthalmic surgery only, pre-operative

assessment and preparation being discussed elsewhere in this issue (p 187-192).

It~t~uoc~ular- p~essut’e (IOP)

The normal IOP varies between 10 and 22mmHg exhibiting a diurnal variation of 2-3 mmHg and differing in the two eyes by up to 5 mmHg. The factors that deter- mine the IOP include the volume of various components inside the eye (aqueous, choroidal blood volume, vitreous body) and to a lesser extent the elasticity of the

C,,,IT,1,A,r‘lc.~lllP,locl,ldCl~,,‘~/C~II.C, lYY2) 3, 212-217 Q 1992 Longman Group UK Ltd 212

ANAESTHESIA FOR OPHTHALMOLOGICAL SURGERY 2 13

sclera. Improper use of instruments, forced closure of the

eyelids or the contraction of the extraocular muscles also

has a significant effect on IOP.

Normal IOP is maintained by a balance between the production of the aqueous and its drainage into the canal

of Schlemm. Aqueous humour is a clear fluid produced at

a rate of approximately 2.0pl/min partly as an

ultrafiltrate and partly as a secretion from the ciliary

processes. Reduced drainage of aqueous is the main

reason for an elevated IOP as the production of aqueous is generally constant in healthy people.

Factors affecting intraocular pressure

Arterial pressure: A system of autoregulation exists in

the eye which tends to minimise the changes in IOP in

response to changes in the systemic arterial pressure. A

sudden increase in systemic arterial pressure may

produce a small but transient increase in IOP; however

the decrease in IOP becomes marked as the systolic

arterial pressure decreases below 90mmHg.5*6 The IOP is less than 3-4mmHg at systolic arterial pressures of

below 60mmHg. It is believed that both a reduction in the choroidal blood flow as well as a reduced production

of aqueous are responsible.

Venous pressure and posture: IOP follows the changes in venous pressure very closely (Fig. 1)’ An

increase in venous pressure has a much greater effect in raising the IOP than an increase in arterial pressure.8

Coughing which increases the venous pressure may raise

the IOP by as much as 40 mm Hg. Similar effects on IOP

are exerted by straining on a tracheal tube. A head up tilt is associated with a reduction in IOP and is a useful

adjunct in keeping the IOP low during surgery. The effects of posture are probably due to changes in the

venous pressure. Curhorl dioxide tension: Changes in arterial carbon

dioxide tension have a direct relationship with IOP

(Fig. 1). A reduction in IOP has been shown by hyper-

mmHg 90/50 lOW55 85145

60-15

1 *,/A- C-A \

A’ I \

40- 1 opG-FJ&

O-01 0 5 1015 202530Min

Fig. 1 - Relationship of intraocular pressure to central venous pressure and carbon dioxide tension (with the permission of the authors and the publisher)

ventilation in both animals and man.’ The effects are

mediated via changes in the choroidal blood flow which

is very sensitive to changes in the arterial Pco,. The reduction in IOP on hyperventilation is much more

marked and rapid than is the increase due to hypoventila- tion making controlled hyperventilation a very useful

tool in the control of IOP during surgery. Variations in

the arterial oxygen tension have much less influence on

the IOP unless oxygen is used under hyperbaric condi- tons.

Effect of drugs: Although orally administered diazepam has no effect on IOP, its intravenous adminis-

tration lowers the IOP. Opioid drugs produce a moderate decrease in IOP. Systemically administered anticholin-

ergic agents have no significant effect on IOP.

All the intravenous induction agents with the excep-

tion of ketamine reduce the IOP. This includes the

neuroleptanaesthetic combination of fentanyl and

droperidol. The newer intravenous anaesthetic propofol has been observed to reduce the IOP even more than is

observed with thiopentone.“’ Currently used volatile agents halothane, enflurane and

isoflurane all reduce IOP. Although it was thought that these agents produced a dose-related reduction in

IOP, recent studies have shown that there is a limit to their IOP reducing effect.“.” Nitrous oxide is believed

to increase the IOP.‘” The effects of both the

intravenous and volatile anaesthetics are thought to be

mediated by their central effects, relaxation of the extraocular muscles and by altering the outflow of the

aqueous.‘s Of the muscle relaxants, suxamethonium is well

documented to cause an increase in intraocular pressure

(IOP). The rise in pressure occurs within l-2 min of the administration of suxamethonium, peaks at about 2-4 min and is back to normal by 6 min. The reason for

the increase in IOP following suxamethonium is a

contracture-like state of the extraocular muscles which contain both fast and slow fibres. It is also thought that

dilatation of the choroidal vessels is an additional mecha-

nism. Tracheal intubation quite often exaggerates the rise

in IOP seen with suxamethonium. Various methods have

been suggested to attenuate the increase in IOP due to suxamethonium. These have been reviewed elsewhere and include slow administration of suxamethonium,

immediate addministration of suxamethonium after

thiopentone, prior administration of small doses of nondepolarising relaxants, pretreatment with benzodiazepines, a small self-taming dose of suxametho-

nium, and administration of lignocaine or acetazolamide.‘*i” It is however known that none is

compeletely reliable.

Nondepolarising relaxants in general either produce no change in IOP or reduce it significantly. Significant effects have not been shown following administration of

pancuronium, gallamine, alcuronium and atracurium during steady state anaesthesia but a reduction has been reported with tubocurarine and vecuronium. The effects of more recent relaxants pipecuronium, doxacurium, mivacurium and rocuronium which are still under inves-

2 14 CURRENT ANAESTHESIA AND CRITICAL CARE

tigation, are yet to be investigated regarding effects on

IOP. The carbonic anhydrase inhibitor, acetazolamide, is

often used either orally of intravenously for reduction of

IOP and acts by decreasing aqueous production by inter- fering with the secretory activity of the ciliary body.

Osmotic agents such as mannitol and sucrose reduce IOP by withdrawing fluid from the vitreous body and their

effects last for 4-6 h. The anaesthetist is in a position to manipulate many of

the factors such as the arterial carbon dioxide tension and arterial blood pressure to produce a soft eye with a low

intraocular pressure, particularly when the eye is opened. The principal ways of sustaining a low IOP are given in

the Table.

Table Methods of controlling intraocular pressure

Smooth induction of anaesthesia Use of propofol for induction Use of vecuronium for relaxation Adequate depth of anaesthesia Moderate hyperventilation Control of arterial pressure 10-15” head-up tilt use of osmotic diuretics

The choice of method of anaesthesia

Until recently the decision as to the type of anaesthesia

the patient was given was dictated to a large extent by the condition of the patient and the availability of an anaes- thetist. However factors such as the length of hospital

stay, absence of complications, and the decision to operate on more patients on a day stay basis now need

greater consideration. Cataract surgery on a day case

basis has been advocated for some time.14 Although Vernon and Cheng15 reported a greater incidence of surgery related complications in those discharged home

on the first postoperative day (in patients operated under

general anaesthesia), it is likely that refinements in surgical techniques now ensure better results. Even

general anaesthesia is not considered contraindicated for lens extractions on a day stay basis with proper patient selection.‘6 However there are no large properly carried

out prospective studies comparing general and local anaesthesia for ophthalmic and in particular cataract

surgery.

General anaesthesia

General anaesthesia has the advantage of a good control

of IOP and the ease with which it can be manipulated to suit the surgical requirements.

Prior to administration of anaesthesia it is important to remember that the response to drugs may be altered in the elderly.’ The circulation time is slow and thus an overdose of drugs such as the induction agents may easily occur resulting in greater cardiovascular depres- sion. In addition the effect of drugs such as muscle relax- ants may last longer. The effect of benzodiazepines and

opiates may last well into the postoperative period with

the possibility of arterial oxygen desaturation and hypox-

aemia. Anaesthesia can be induced with intravenous agents

such as thiopentone or propofol. Propofol has the advan- tage of producing a greater reduction in IOP. Although

suxamethonium can be used to facilitate intubation, because any rise in IOP with its use is usually dissipated

by the time the eye is opened, a nondepolarising relaxant

is more commonly employed for this purpose. Single doses of atracurium and vecuronium are suitable. It has

been shown that whether suxamethonium or a nondepo-

larising relaxant is used, there is an increase in IOP due to

the manoeuvres of laryngoscopy and tracheal intubation.

This may be of little consequence in patients with normal

IOP but may be important in patients with acute conges-

tive glaucoma. The methods that might be employed to reduce the intraocular hypertensive response due to

suxamethonium have already been mentioned. More recently, it has been found that administration of an

additional small dose of propofol prior to laryngoscopy and intubation can control the increase in IOP conse-

quent upon laryngoscopy and intubation. This is irrespec-

tive of whether suxamethonium or a nondepolarising

agent such as vecuronium has been used to facilitate intubation.“,‘s It is also important to try to control exces-

sive increases in systematic arterial pressure in elderly

patients who may be already hypertensive and may have associated coronary artery disease. Use of the additional

dose of propofol keeps a good control of arterial pressure as well. The induction dose should however be carefully

titrated in the elderly to prevent an excessive decrease in arterial pressure. Following tracheal intubation.

controlled ventilation is employed and any of the commonly used volatile agents can be used to maintain

anaesthesia. A moderate degree of hyperventilation is

useful in keeping the eye soft and avoiding any forward movement of the anterior vitreous face. Neuromuscular

block is antagonised at the end with an anticholinesterase agent prior to extubation.

A recent development has been the use of a laryngeal mask airway in place of tracheal intubation in patients

undergoing ophthalmic surgery. The laryngeal mask airway is now recognised as a suitable alternative to intubation in patients undergoing elective surgery. The advantages of the use of laryngeal mask airway for

ophthalmic surgery are, the observation of a much smaller increase in IOP in comparison to the placement

of a tracheal tube.i9 The use of the laryngeal mask airway

has also been found to be associated with a much lower incidence of postoperative coughing, straining and breath-holding and diminished pressor response in contrast to tracheal intubation.‘“-” It should however be remembered that the laryngeal mask does not provide reliable protection against regurgitation and aspiration.

A more recently described anaesthetic technique for the removal of cataracts is the use of total intravenous anaesthesia using propofo12’ An induction dose of propofol in the region of 1.0-l .5 mg/kg is followed by the use of a continuous infusion of propofol starting

ANAESTHESIA FOR OPHTHALMOLOGICAL SURGERY 2 15

initially at a rate on lOmg/kg/h and reducing at 10 min

intervals to 8 and 6mg/kg/h.23 The rate may be reduced

further if feasible. Ventilation may be with oxygen enriched air or a nitrous oxide-oxygen mixture.

Ventilation is facilitated using vecuronium and additional analgesia is provided by a small dose of

fentanyl ( 1.0-l .5 pg/kg). Using propofol for induction alone or for induction and maintenance of anaesthesia is

associated with a good and early recovery with a’low

incidence of postoperative nausea and vomiting, factors

which are of importance in intraocular surgery.

Local anaesthesia

Although as pointed out earlier that most of ophthalmic

surgery in this country has been performed under general

anaesthesia, there is a trend for more use of local anaes-

thesia in ophthalmic surgery particularly for those under-

going cataract extraction. 24 In a comparison of general

and local anaesthesia for eye surgery, Pearce observed no

great differences between the two techniques in terms of

patient morbidity.‘5 Local anaesthesia has generally been administered by

the surgeons themselves and has consisted usually of a retrobulbar block combined with block of the facial

nerve. Part of the reason why anaesthetists have tended not to give local blocks in the eye has been the fear of

producing a retrobulbar haemorrhage, perforation of the

globe or damage to the surrounding nerves and blood

vessels. Although there are other complications of a

retrobulbar block such as the spread of anaesthesia to the

brain stem resulting in respiratory arrest, anaesthetists are

perhaps better equipped than others to deal with the situa-

tion effectively. However, the recent popularity of the peribulbar method of producing ocular anaesthesia has encouraged more anaesthetists to give blocks.z6.‘7

The largest series of cataract extraction and intraocular

lens implantations using local anaesthesia has been recorded by Hamilton et a1.2h They described 12 000

consecutive operations in which they evolved a

technique of local anaesthesia starting with a retrobulbar and seventh nerve injection, and finally deciding on the use of a combined peribulbar and retrobulbar blocking

technique. In their experience, retrobulbar block was associated with the highest incidence of brain stem

anaesthesia and retrobulbar haemorrhage. These compli- cations were low in those given the peribulbar block. All

local blocks were given by anaesthetists in this series.

They based their success on the use of fine gauge needles

and slow administration of injections into the orbit. Fry and Henderson have described their experience of more

than 800 cases using the periocular (peribulbar) technique without any complications and only one

partial failure which required additional anaesthetic infiltration.27 Another advantage of the peribulbar

technique is the absence of discomfort to the patient due to a facial nerve block which has to be done in conjunc- tion with a retrobulbar injection.

The peribulbar technique involves using somewhat

larger quantities of local anaesthetic solution and

volumes of up to 20 ml may be used. The commonly used

local anaesthetic mixture consists of 2% lignocaine

Fig. 2 - Needle insertion points for a peribulbar block.

2 16 CURRENT ANAESTHESIA AND CRITICAL CARE

and 0.5% bupivacaine with 1:200,000 adrenaline and 500

units of hyaluronidase. The patient is prepared as for general anaesthesia and placed in a supine position and

the eye cleaned with antiseptic solution. The injection

may be made either through the skin or through the conjunctiva after topical application of the local anaes-

thetic solution. The number and the positions through which the local

anaesthetic solution is placed around the globe may vary but three injections give consistently good result. Two

injections are usually given over the lower border of the orbit just lateral to the medial canthus and about 1.0 cm

medial to the lateral canthus and one injection is made

just below the upper orbital border just medial to the

supraorbital notch (Fig. 2). An Atkinson or an ordinary 1 inch long 23 SWG needle is advanced towards the

equator of the eye keeping more towards the orbit than towards the globe and 5-6ml of the local anaesthetic

solution deposited at each site at a depth of 0.75-1.0 inch. One may deposit a larger volume of the solution (8-10ml) at the first injection and use smaller volumes

for others. The first injection provides some analgesia for the subsequent injections. Some amount of proptosis, and

oedema of the lids and the conjunctiva is almost always

noticed. Following completion of the injections a

pressure bulb inflated to 30-40mm Hg is placed on the eye for 15-20 minutes. The method takes slightly

longer than the retrobulbar technique for producing anaesthesia and may take anything from 10 to 20min.

However, with the anaesthetist carrying out the block, this is only marginally longer than the time taken for administering a well-planned general anaesthetic. In

either case the anaesthetist is free to be able to prepare the patient. The pain due to administration of the local

solution may be reduced by warming the solution to body temperature.

Sedation if required may be provided by I-2mg of

midazolam but is better given after the local block has been instituted and observed to be satisfactory. It is

probably better to maintain verbal contact with the patient. For those patients who fear injection to the eye

one might consider the use of 0.75-l.Omg/kg of propofol prior to the local anaesthetic injection, a practice which is common in the USA. The patient must however be completely awake before commencement of surgery.

The advantages of carrying out this type of surgery under local anaesthesia have been highlighted in a recent

editorial which remarks on the simplicity, success and excellent operating conditions provided by local anaes- thetic methods, particularly the peribulbar technique.24 In addition, the complications are less and the patient is able to return to their environment much earlier and without disturbance. It is also advantageous in terms of attenua- tion of the endocrine and metabolic response in compar- ison to general anaesthesia. ** It is considered to be an excellent technique for carrying out this type of surgery on a day to day basis. Although complications has been described more often with the retrobulbar block, globe perforation has been described with the use of peribulbar

block as well.29 There are reports of perforation of the globe leading to blindness; attention to detail is thus very

important.

Anaesthesia for detachment and vitreous surgery

Although this type of surgery has been carried out using

local anaesthesia,30 patients may be uncomfortable because of having to lie in one position over a long

period of time. Most surgeons hence prefer general anaesthesia for detachment and vitreous surgery.

The requirements of anaesthesia for vitrectomy have

been previously described.” Vitrectomy involves a large

amount of bulky equipment in the theatre. In addition,

quite a large part of surgery is carried out with the theatre

in complete darkenss, thus full monitoring technique is

required as a standard procedure. Fluid gas exchange involving the instillation of sulphur hexafluoride and air

into the eye means avoidance of nitrous oxide from the

anaesthetic mixture because of the great solubility of nitrous oxide which increases the volume of the intravit-

real bubble during surgery and shrinks the bubble when nitrous oxide is withdrawn at the end of surgery. It is

essential that nitrous oxide be discontinued about 20 min

prior to the fluid gas exchange, or better still not used at

all. Anaesthesia can be induced with an intravenous

anaesthetic and maintained with a volatile agent in oxygen-enriched air, muscle relaxants being used to

facilitate ventilation. An alterative technique which is associated with a quicker recovery and a low incidence of nausea and vomiting is the use of total intravenous anaes-

thesia employing propofol and fentanyl.“’ A similar three-stage propofol infusion as described earlier, can be used for this type of surgery as well although a larger

dose of analgesics may be required.

Most of the surgery on the eyelids can be carried out using infiltration of local anaesthesia.

Postoperative pain relief following ophthalmic surgery

is usually provided by oral analgesics such as parac- etamol with or without codeine or with a non-steroidal analgesic.

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