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Anaesthesia for ophthalmic surgery
Anaesthesia for Ophthalmic Surgery
R. W. J o h n s o n
Lid surgery
Ideal conditions for ophthalmic surgery exist when the patient is comfortable and still, with controlled intraocular pressure (IOP) and akinesia of the globe and eyelid. The safest and most appropriate means of providing these conditions varies according to the patient and the procedure to be undertaken, and may be influenced by the preference of the surgeon. Rubin's editorial Anaesthesia for cataract surgery--time for change x publicised a transatlantic difference in practice regarding the relative frequency of use of general (GA) and local anaesthesia (LA) for ophthalmic procedures and discussed possible reasons, some of which were more financial than medical. There is a widely held belief that British patients 'prefer to be asleep' and that the absolute inertia of the eye usually afforded by GA is required for surgery using the microscope. Increasing involvement of anaesthetists in administering ophthalmic LA blocks may improve both safety2 and efficiency of local anaesthetic procedures. Day case surgery for ophthalmic procedures does not exclude the use of GA.
Procedures are usually carried out under direct infiltration LA. However, in children and mentally retarded or nervous adults and for complex ptosis surgery, GA is required. The main anaesthetic consideration is field avoidance, but the aetiology of ptosis must be considered. Myasthenia gravis is likely to have been excluded, but a myopathy which renders the patient susceptible to malignant hyperpyrexia (MH) is possible. Blepharospasm may be treated by the controlled local intramuscular injection of botulinum toxin. 3 Similarly, the toxin may be injected into the extraocular muscles for the treatment of strabismus; GA is sometimes required.
Squint surgery Surgical procedures on the extraocular muscles may be performed on any age group. Although the incidence of MH susceptibility is probably only marginally greater in these patients than in the general population, vigilance is required and temperature monitoring desirable. The commonest problem is the oculocardiac reflex which may occur at any age and presents as bradycardia, nodal rhythm or asystole in response to traction on the extraocular muscles, pressure on the globe or even retrobulbar injection. The afferent pathway is along the ciliary nerves, and the efferent via the vagus. Pre-medication with anticholinergic drugs cannot be relied upon to prevent the reflex; intravenous administration at the time of induction is more reliable, but the reflex may still occur. Immediate treatment is to ask the surgeon to stop the provocative action instantly while intravenous atropine is administered and is given time to exert its protective influence. The
Range of surgical procedures Eye operations may be divided broadly into those performed on intraocular structures where the integrity of the globe must be breached, and those involving extraocular and orbital structures. Surgery is performed on all age groups including premature neonates, and may be planned or emergency in nature.
R. W. Johnson MB, BS, FFARCS, Sir Humphry Davy Department of Anaesthesia, Bristol Royal Infirmary, Bristol BS2 8HW, UK Current Anaesthesia and Critical Care
© 1992LongmanGroupUK Ltd
(1992)3. 17-22
17
18
CURRENT ANAESTHESIA AND CRITICAL CARE
decision regarding controlled or spontaneous ventilation is based on the predicted duration of the procedure and the age of the patient. The smaller the child, and the longer the duration of the operation, the more desirable I consider controlled ventilation to be. Children are frequently irritable after this operation and peri-operative analgesia is a kindness to the patient and the parents.
Intraocular surgery including cataract surgery and corneal grafting Once the decision has been made to provide GA, the precise technique depends on the physical status of the patient. The intention is to provide slightly reduced IOP throughout the operation without significant increases at induction or in the post-operative period. Raised arterial or venous pressures, raised arterial carbon dioxide tension, and the effects of some drugs (notably ketamine and suxamethonium) increase IOP. 4 Factors which predispose to these adverse conditions include inadequate analgesia, clumsy laryngoscopy and intubation, failure to monitor end-tidal carbon dioxide tension, and lack of vigilance regarding the adequacy of neuromuscular blockade. Smooth extubation is desirable, but many surgeons feel that modern suturing techniques make this less important than previously. The author works with a surgeon who pointedly removes the eye dressing and reinspects the section for iris prolapse should he observe the slightest straining at the time of extubation! Spontaneous ventilation is preferred by some, but I believe that the aims are best achieved with controlled ventilation. The place of the laryngeal mask is uncertain, but any airway problem while the operation is in progress could be catastrophic. Opioids, the volatile anaesthetic agents, and nondepolarising neuromuscular blocking drugs tend to reduce IOP. Satisfactory conditions may be achieved in many ways, but the following example is satisfactory. Pre-medication, if given, is with oral temazepam and metoclopramide about l h pre-operatively. After proxygenation, induction is achieved with fentanyl l ~ g kg -1 or alfentanil 10p~g kg -1, and glycopyrrolate 0.2mg is given by some to assist in preservation of cardiovascular stability in the elderly patient. Up to l m g of droperidol may be administered as an antiemetic but lack of psychotropic side effects cannot be guaranteed. Etomidate, thiopentone or propofol are satisfactory induction agents, the choice depending on the age and physical status of the patient. Neuromuscular paralysis may be achieved with any non-depolarising muscle relaxant, but the shorter acting drugs allow well controlled conditions if neuromuscular function is monitored. Following mask ventilation with nitrous oxide and a volatile agent, laryngoscopy and intubation are undertaken gently. The administration of topical local anaesthetic to the larynx and trachea is optional. If it is to be of
use during intubation, time must be allowed for it to work, and further ventilation by mask is necessary before the tube is inserted. Benefit at the time of extubation depends in part on the duration of surgery, and in part on duration of action in the particular patient; it cannot be relied upon. Intubation with a preformed tube such as the RAE pattern improves surgical access. Following intubation, ventilation with nitrous oxide, oxygen and a volatile agent with monitored neuromuscular function and an end-tidal CO2 of approximately 4.5kPa (34mmHg) provides good conditions. Smooth extubation may be achieved in several ways, but restoration of normocapnia and gentle release of air from the tracheal tube cuff before reversal of residual neuromuscular block and withdrawal of anaesthetic agents are contributory. In the author's hands, administration of intravenous lignocaine prior to extubation is unreliable. Post-operative hypoxia is almost invariable in the elderly unless oxygen-enriched air is administered from the moment of extubation. Post-anaesthetic hypertension, which is not uncommon and may be severely detrimental to myocardial oxygenation and function, should be treated with analgesia, sublingual nifedipine, or i.v. hydralazine or [3-blockade depending on the cause and the physical status of the patient. Post-operative pain following cataract surgery is seldom marked unless a rise in IOP occurs, and is usually well controlled with paracetamol. Post-operative nausea is best prevented, but should it occur, metoclopramide, prochlorperazine or acupuncture may be effective.5'6
Surgery for retinal detachment Extraocular procedures for detachment are of variable length and may be performed as a semi-emergency on poorly prepared patients. The anaesthetist is advised to curb the surgeon's enthusiasm for immediate surgery if the patient's proper preparation requires additional time. Although rigid control of IOP is less important than for intraocular procedures, the anaesthetic may be conducted as for cataract surgery, but there will be a requirement for greater intra- and post-operative analgesia. Vitrectomy may form part of detachment surgery (see below).
Dacrocystorhinostomy (DCR) This procedure is undertaken to produce a tear drainage channel by anastomosing the lacrimal sac to the nasal mucosa via a small osteotomy. Many surgeons consider that induced hypotension allowing a relatively bloodless field permits a clearer dissection of the anatomical elements and a better operation. Topical vasoconstrictor, usully cocaine with adrenaline, may be applied to the appropriate part of the nasal mucosa by the anaesthetist before the start of surgery. A pharyngeal pack prevents contamination
ANAESTHESIA FOR OPHTHALMIC SURGERY
of the larynx with blood. It is normal to position the patient with the head elevated. Despite good technique, the occasional DCR results in considerable haemorrhage pre- or post-operatively, and an indwelling i.v. cannula of 18 gauge or larger is a sensible precaution. The procedure can be performed under local anaesthesia.
Tumour surgery Much superficial tumour surgery is performed under local anaesthesia, but occasionally resection of a tumour of the globe is undertaken. Induced hypotension is considered by many to contribute to a good result and should be provided unless contraindicated. It is also believed by some that induced hypotension reduces the risk of tumour dissemination.
Vitreoretinal surgery Vitrectomy is undertaken for a variety of indications including proliferative vascular disease (including that caused by diabetes mellitus), complicated retinal detachments, and for some penetrating eye injuries. Matters of importance to the anaesthetist are preexisting systemic disease, prolonged surgery in a darkened theatre, the use of endo or indirect laser treatment to the retina (the latter requiring the use of protective goggles by theatre staff), and sometimes injection of 'gas' into the eye to produce tamponade to hold the retina against the choroid. One of two poorly diffusible gases is used: sulphur hexafluoride (SF6) or perfluoropropane (C3F8). In both cases, nitrous oxide diffuses freely into the bubble, increasing both volume and pressure. 7 At the end of the anaesthetic, after the surgeon has adjusted the dimensions of the bubble, nitrous oxide diffuses out, rendering the bubble inadequate to fulfil its function. Thus anaesthesia without nitrous oxide is used either throughout surgery, or from about 20min before injection of the bubble. If a circle breathing system is in use, it is essential to increase fresh gas flows, or nitrous oxide washout takes a very long time. Oxygen-enriched air substitutes as the carrier gas and anaesthesia is continued either with an appropriately increased concentration of volatile agent, or with an intravenous infusion of opioid and propofol. The gas remains in the eye for approximately 10 days, and subsequent use of nitrous oxide within this period influences the size of the bubble. The duration of the operation is often in doubt at the start of surgery, and an infusion of a short acting non-depolarising muscle relaxant with neuromuscular junction monitoring avoids embarrassment when surgery ends prematurely. The surgeon may express a preference for the patient's posture following surgery to position the gas bubble most advantageously; this may involve the prone position.
19
Emergency procedures Anaesthesia for a patient with penetrating eye injury presents a number of problems, especially if the patient has eaten recently and if the sight of the uninjured eye is impaired. Frequently, some delay is appropriate, even though gastric emptying is unpredictable following injury. It must also be remembered that the eye injury may not be the only significant trauma and general examination should be undertaken. For other types of emergency surgery the choice lies between rapid sequence induction and intubation with cricoid pressure following preoxygenation using suxamethonium as a rapidly acting muscle relaxant, and awake intubation using local anaesthesia. The theoretical objection to both techniques is that they may increase IOP sufficiently to extrude intraocular contents, leading to permanent loss of vision. A proposed alternative in the patient with a penetrating eye injury is to intubate after a larger than normal dose of non-depolarising relaxant with or without priming. Evidence confirming the objection to the use of suxamethonium is sparse, and the rise in IOP following laryngoscopy in an incompletely paralysed patient is likely to be as great or greater than that associated with an easy intubation after administration of suxamethonium. The consequences of failed intubation in a patient who has a full stomach and who has received a large dose of long-acting relaxant may be dire. Libonati and colleagues8 reported 100 patients in detail and a further 128 in outline who received anaesthesia for penetrating eye injuries at their institution during 1 year. Anaesthetic and surgical records were examined retrospectively with particular reference to the anaesthetic technique and the surgeon's record of pre-anaesthetic and post-intubation status of the eye. No case of vitreous loss initiated during that period of time was noted, independent of the type of anaesthesia used, with or without suxamethonium for intubation. The authors advise production of an adequate depth of anaesthesia prior to the injection of suxamethonium.
Systemic effects of topical medication Ecothiopate is often quoted a s an example of an agent applied topically for its ophthalmic effects which has unwanted systemic actions of anaesthetic significance. Ecothiopate is used for glaucoma and results in inhibition of serum cholinesterase activity, prolonging the action of suxamethonium. However, it is used little in contemporary ophthalmology. The topically applied 13-blocker timolol (also used to treat glaucoma) produces adequate systemic levels to induce bronchospasm in susceptible individuals and also has cardiac effects. Betaxolol is a similar but [3a-selective agent. 10% phenylephrine drops are applied pre-, and occasionally per-operatively to
20
CURRENTANAESTHESIA AND CRITICAL CARE
dilate the pupil and may lead to significant increases in blood pressure. 9 Intra-operative intraocular injection of Miochol (acetylcholine) is probably too evanescent in action to have a significant effect on neuromuscular blocking drugs.
Regional blocks Local anaesthetic techniques for eye surgery have been performed by ophthalmic surgeons since the beginning of local anaesthetic history. Local and systemic complications occur and have been reported. 2 In addition, not all blocks achieve orbicularis paralysis, akinesia of the eye, anaesthesia and controlled IOP. Can the anaesthetist contribute to an improvement in any of these shortcomings?
Complications Systemic complications result from increased concentrations of local anaesthetic drugs in blood or cerebrospinal fluid (CSF), possibly exacerbated by hypercapnia and hypoxaemia. Injection of the appropriate dose of drug in the correct place prevents complications, and recognition of the onset of a problem and prompt corrective measures may avoid disasters.I° The anaesthetist has a good understanding of the pharmacology of the local anaesthetic drugs and is experienced in the preservation of a clear airway, monitoring and resuscitation. Correct placement of the needle requires knowledge of the anatomy of the region, great care, and much practice. The ophthalmic anaesthetist is well placed to provide these.
Making it work The principles are similar to those applied to avoid complications. To these should be added time. Approximately 25rain should elapse between the injection of local anaesthetic and the start of surgery, particularly when using peribulbar block. If the operator is also the anaesthetist (much deplored in other branches of surgery) efficiency will not allow half an hour or so between operations. An anaesthetist with a trained assistant can provide the block, remain with the monitored patient for the critical first 30min (by which time peak blood levels will have been reached) and position the patient safely on the operating table with his assistant providing further observation and communication. He may then start the anaesthetic for the following patient with no loss of surgical time. The following description is of the technique currently used by the author, with alternatives advised by others in brackets.
Anatomy The bony orbit and globe are well described in standard texts.n The orbital connective tissues are of
great significance when considering optimal placement of needles to achieve spread of injected solutions, and those interested in eye blocks should read Koorneef's elegant work. 12 It is essential to maintain a three dimensional concept of the position of the tip of the needle relative to other structures at all times.
Techniques Two drops of topical benoxinate or amethocaine produce corneal and conjunctival anaesthesia. If applied cold, they sting; if warmed to 35°C, they do not. The initial value of the topical anaesthesia is to prevent stinging from the spirit vapour given off by a skin antiseptic containing alcohol. A 25 gauge 11/4" standard bevel needle is introduced through the lower lid (Fig. 1). (A 23 gauge Atkinson short bevel needle is claimed to allow better 'feel' of passage through tissue planes, and to be less traumatic if nerve tissue is contacted; shorter and finer needles are thought to be less traumatic and to avoid the possibility of entering the conus.) Prior intradermal injection of local anaesthetic with a 27 gauge needle is advised if a short bevel needle is used to perform the block. Perconjunctival (rather than percutaneous) injection is used by some as the needle then enters through tissue anaesthetised by the topical agent, and the occasional complication of unsightly lid ecchymosis is avoided. The block needle should pass in a posterior direction following the bony orbital floor and tangential to the globe of the eye as far as the equator of the globe. A finger gently resting on the globe protected by the upper lid helps to detect contact of the needle with the eye. Further evidence is sought by asking the patient to move the eye and noting that the needle remains quite still. After negative aspiration, approximately 3ml of local anaesthetic solution is injected, and a further lml as the needle is withdrawn through the orbicularis muscle. The procedure is repeated at the upper orbital margin, entering the rid inferior to the supraorbital notch (Fig. 2). (The---superior entry point is disliked by some who favour entry through the medial aspect of the caruncle--if this entry point is used the position of the lacrimal drainage apparatus and the medial rectus muscle must be considered. The medial wall of the orbit follows the saggital plane). It is important to note that the roof and floor of the orbit may be very thin and are easily punctured by a needle. The superior relation of the orbit is the brain. With the superior needle in position also adjacent to the equator of the eye, a similar volume of solution is injected, and a further lml is placed in the orbicularis muscle as the needle is withdrawn. Precise volumes vary witl~ the size of the patient and the local anatomy. Conjunctival and lid oedema are usually seen at this stage. The eye is secured carefully in the closed position with atraumatic paper tape and covered with
ANAESTHESIA FOR OPHTHALMIC SURGERY
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21
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\ Periocular block. Thee,inferior (left) and superior (right) injection sites. Postion 1: needle entry; position 2: full needle insertion. Reproduced with permission from: Fry RA, Henderson J. Local anaesthesia for eye surgery. The periocular technique. Anaesthesia 1989; 45: 14-17. Fig. 1 --
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F i g . 2 - - The superior and inferior orbital septa with needles in situ (arrows indicate septa). Reproduced with permission from: Fry RA, Henderson J. Local a n a e s t h e s i a for eye surgery• The periocular technique. Anaesthesia 1989; 45: 14--17.
22
CURRENT ANAESTHESIA AND CRITICAL CARE
an eye pad. A device producing local and controlled pressure over the orbit is then applied to disperse the injected solution and reduce orbital pressure. A Honan balloon is suitable and allows the pressure applied to be measured; alternatively, a small bag containing mercury rested over the orbit is satisfactory, and others use the Super Pinky--a foam rubber ball of suitable size and resistance held over the orbit by a strap applied around the head. The device is removed after 10min and eye movement and orbicularis activity are tested. With experience, the operator can judge whether a good block is developing, and will either close the eye and reapply the pressure device, or supplement the block by a further low volume injection, usually at the inferior entry point. If orbicularis is active, a modified Van Lindt facial block may be performed, entering the skin through the same point. Ten min later, the pressure device is removed and the patient placed on the operating table. The nature of the local anaesthetic agent used varies enormously. There is a growing feeling that undiluted 0.75% bupivacaine may result in prolonged ptosis and extraocular muscle paresis. The author uses a solution containing equal volumes of 2% lignocaine and 0.75% bupivacaine with 150 units of hyalase in 10ml of solution (with no adrenaline) and achieves reasonably consistent results. Good objective studies to ascertain the ideal solution are notoriously difficult because technique probably matters more than the precise nature of the solution. It is claimed that the procedure is more comfortable if all solutions are warmed to 35°C, and if the needle tracks are first infiltrated with local anaesthetic diluted considerably with balanced salt solution. Attention to comfort of the patient on the operating table is rewarded. An empty bladder, hips and knees held slightly flexed by a soft pillow under the knees, arms supported on foam rests and cool oxygen-enriched air wafted over the face with the drapes supported to avoid irritation and claustrophobia usually remove the need for sedation which may cause confusion, unpredictable arousal and movement, loss of airway and hypoxia, a3 If sedation is used, it should be titrated carefully against state of consciousness and given well in advance of the start of surgery so that a steady state has been reached. Monitoring should be by direct observation of the airway and state of consciousness with the addition of standard methods of displaying blood pressure, heart rate, oxygen saturation and electrocardiograph. If an automated device is used to measure blood pressure, it should be set to operate in the manual mode and the patient should be warned verbally before each cuff inflation to avoid movement occasioned by surprise.
Summary Provision of a proper anaesthetic service to an eye surgery unit may improve safety, quality of anaesthesia and efficiency. It is an enjoyable and challenging activity and assists in improvement of quality of life of patients. The role of the anaesthetist in care of ophthalmic regional blocks has probably been underused in Great Britain and should expand. There remains an appropriate place for combined general and regional anaesthesia in ophthalmic surgery. Some anaesthetists may consider that ophthalmic local blocks are not best suited to their particular skills, and they should certainly not be attempted by unsupervised novices.
References 1. Rubin AP. Editorial. Anaesthesia 1990; 45:717-718 2. Nicoll JMV, Acharya PA, Ahlen K, Bagueid S, Edge KR. Central nervous system complications after 6000 retrobulbar blocks. Anesth Analg 1987; 66:1298-1302 3. Lee JP, Hogg C. Botulinum toxin therapy for squint and other ocular motility disorders. In: Easty DL ed. Current Ophthalmic Surgery. Balliere Tindall 1990; 163-171 4. Murphy DF. Anesthesia and intraocular pressure. Anesth Analg 1985; 64:520-530 5. VanDen Berg AA, Lambourne A, Yazji NS, Laghari NA. Vomiting after ophthalmic surgery. Anaesthesia 1987; 42: 270-276 6. Ghaly RG, Fitzpatrick KTJ, Dundee JW. Antiemetic studies with traditional Chinese acupuncture. Anaesthesia 1987; 42: 1108-1110 7. Eger EI. Nitrous Oxide. Amsterdam, Elsevier, 1985; 93-110 8. Libonati MM, Leahy J J, Ellison N. The use of succinylcholine in open eye surgery. Anesthesiology 1985; 62: 637-640 9. Fraunfelder FT, Scafidi AF. Adverse effects from topical ocular 10% phenylephrine. Amer J Ophthalmol 1978; 85: 447-453 10. Covino BG. Clinical pharmacology of local anesthetic agents. In: Cousins MJ, Bridenbaugh PO eds. Neural Blockade. Lippincon 1988; 120-134 11. Feitl ME, Krupin T. Neural blockade for ophthalmologic surgery. In: Cousins MJ, Bridenbaugh PO eds. Neural Blockade. Lippincott 1988; 577-592 12. Koornneef L. Sectional anatomy of the orbit. Aeolus Press, Amsterdam: 1881 13. Bailey, PL, Pace NL, Ashburn MA, Moll JWB, East KA, Stanley TH. Frequent hypoxemia and apnea after sedation with midazolam and fentanyl. Anesthesiology 1990; 73: 826830
Further reading Barker JP, Robinson PN, Vafidis GC, Hart GR, Sapsed-Byrne S, Hall GM. Local analgesia prevents the cortisol and glycaemic responses to cataract surgery. Br J Anaesth 1990; 64:442-445 Mercereau DA. Brain-stem anesthesia complicating retrobulbar block. Can J Ophthalmol 1989; 24:159-161 Biebyck JF. Perioperative management of surgical patients with diabetes mellitus. Anesthesiology 1991; 74:346-359 Gainey SP, Robertson DM, Fay W, Ilstrup D. Ocular surgery on patients receiving long-term warfarin therapy. Am J Ophthalmol 1989; 108:142-146
R. W. J o h n s o n
Lid surgery
Ideal conditions for ophthalmic surgery exist when the patient is comfortable and still, with controlled intraocular pressure (IOP) and akinesia of the globe and eyelid. The safest and most appropriate means of providing these conditions varies according to the patient and the procedure to be undertaken, and may be influenced by the preference of the surgeon. Rubin's editorial Anaesthesia for cataract surgery--time for change x publicised a transatlantic difference in practice regarding the relative frequency of use of general (GA) and local anaesthesia (LA) for ophthalmic procedures and discussed possible reasons, some of which were more financial than medical. There is a widely held belief that British patients 'prefer to be asleep' and that the absolute inertia of the eye usually afforded by GA is required for surgery using the microscope. Increasing involvement of anaesthetists in administering ophthalmic LA blocks may improve both safety2 and efficiency of local anaesthetic procedures. Day case surgery for ophthalmic procedures does not exclude the use of GA.
Procedures are usually carried out under direct infiltration LA. However, in children and mentally retarded or nervous adults and for complex ptosis surgery, GA is required. The main anaesthetic consideration is field avoidance, but the aetiology of ptosis must be considered. Myasthenia gravis is likely to have been excluded, but a myopathy which renders the patient susceptible to malignant hyperpyrexia (MH) is possible. Blepharospasm may be treated by the controlled local intramuscular injection of botulinum toxin. 3 Similarly, the toxin may be injected into the extraocular muscles for the treatment of strabismus; GA is sometimes required.
Squint surgery Surgical procedures on the extraocular muscles may be performed on any age group. Although the incidence of MH susceptibility is probably only marginally greater in these patients than in the general population, vigilance is required and temperature monitoring desirable. The commonest problem is the oculocardiac reflex which may occur at any age and presents as bradycardia, nodal rhythm or asystole in response to traction on the extraocular muscles, pressure on the globe or even retrobulbar injection. The afferent pathway is along the ciliary nerves, and the efferent via the vagus. Pre-medication with anticholinergic drugs cannot be relied upon to prevent the reflex; intravenous administration at the time of induction is more reliable, but the reflex may still occur. Immediate treatment is to ask the surgeon to stop the provocative action instantly while intravenous atropine is administered and is given time to exert its protective influence. The
Range of surgical procedures Eye operations may be divided broadly into those performed on intraocular structures where the integrity of the globe must be breached, and those involving extraocular and orbital structures. Surgery is performed on all age groups including premature neonates, and may be planned or emergency in nature.
R. W. Johnson MB, BS, FFARCS, Sir Humphry Davy Department of Anaesthesia, Bristol Royal Infirmary, Bristol BS2 8HW, UK Current Anaesthesia and Critical Care
© 1992LongmanGroupUK Ltd
(1992)3. 17-22
17
18
CURRENT ANAESTHESIA AND CRITICAL CARE
decision regarding controlled or spontaneous ventilation is based on the predicted duration of the procedure and the age of the patient. The smaller the child, and the longer the duration of the operation, the more desirable I consider controlled ventilation to be. Children are frequently irritable after this operation and peri-operative analgesia is a kindness to the patient and the parents.
Intraocular surgery including cataract surgery and corneal grafting Once the decision has been made to provide GA, the precise technique depends on the physical status of the patient. The intention is to provide slightly reduced IOP throughout the operation without significant increases at induction or in the post-operative period. Raised arterial or venous pressures, raised arterial carbon dioxide tension, and the effects of some drugs (notably ketamine and suxamethonium) increase IOP. 4 Factors which predispose to these adverse conditions include inadequate analgesia, clumsy laryngoscopy and intubation, failure to monitor end-tidal carbon dioxide tension, and lack of vigilance regarding the adequacy of neuromuscular blockade. Smooth extubation is desirable, but many surgeons feel that modern suturing techniques make this less important than previously. The author works with a surgeon who pointedly removes the eye dressing and reinspects the section for iris prolapse should he observe the slightest straining at the time of extubation! Spontaneous ventilation is preferred by some, but I believe that the aims are best achieved with controlled ventilation. The place of the laryngeal mask is uncertain, but any airway problem while the operation is in progress could be catastrophic. Opioids, the volatile anaesthetic agents, and nondepolarising neuromuscular blocking drugs tend to reduce IOP. Satisfactory conditions may be achieved in many ways, but the following example is satisfactory. Pre-medication, if given, is with oral temazepam and metoclopramide about l h pre-operatively. After proxygenation, induction is achieved with fentanyl l ~ g kg -1 or alfentanil 10p~g kg -1, and glycopyrrolate 0.2mg is given by some to assist in preservation of cardiovascular stability in the elderly patient. Up to l m g of droperidol may be administered as an antiemetic but lack of psychotropic side effects cannot be guaranteed. Etomidate, thiopentone or propofol are satisfactory induction agents, the choice depending on the age and physical status of the patient. Neuromuscular paralysis may be achieved with any non-depolarising muscle relaxant, but the shorter acting drugs allow well controlled conditions if neuromuscular function is monitored. Following mask ventilation with nitrous oxide and a volatile agent, laryngoscopy and intubation are undertaken gently. The administration of topical local anaesthetic to the larynx and trachea is optional. If it is to be of
use during intubation, time must be allowed for it to work, and further ventilation by mask is necessary before the tube is inserted. Benefit at the time of extubation depends in part on the duration of surgery, and in part on duration of action in the particular patient; it cannot be relied upon. Intubation with a preformed tube such as the RAE pattern improves surgical access. Following intubation, ventilation with nitrous oxide, oxygen and a volatile agent with monitored neuromuscular function and an end-tidal CO2 of approximately 4.5kPa (34mmHg) provides good conditions. Smooth extubation may be achieved in several ways, but restoration of normocapnia and gentle release of air from the tracheal tube cuff before reversal of residual neuromuscular block and withdrawal of anaesthetic agents are contributory. In the author's hands, administration of intravenous lignocaine prior to extubation is unreliable. Post-operative hypoxia is almost invariable in the elderly unless oxygen-enriched air is administered from the moment of extubation. Post-anaesthetic hypertension, which is not uncommon and may be severely detrimental to myocardial oxygenation and function, should be treated with analgesia, sublingual nifedipine, or i.v. hydralazine or [3-blockade depending on the cause and the physical status of the patient. Post-operative pain following cataract surgery is seldom marked unless a rise in IOP occurs, and is usually well controlled with paracetamol. Post-operative nausea is best prevented, but should it occur, metoclopramide, prochlorperazine or acupuncture may be effective.5'6
Surgery for retinal detachment Extraocular procedures for detachment are of variable length and may be performed as a semi-emergency on poorly prepared patients. The anaesthetist is advised to curb the surgeon's enthusiasm for immediate surgery if the patient's proper preparation requires additional time. Although rigid control of IOP is less important than for intraocular procedures, the anaesthetic may be conducted as for cataract surgery, but there will be a requirement for greater intra- and post-operative analgesia. Vitrectomy may form part of detachment surgery (see below).
Dacrocystorhinostomy (DCR) This procedure is undertaken to produce a tear drainage channel by anastomosing the lacrimal sac to the nasal mucosa via a small osteotomy. Many surgeons consider that induced hypotension allowing a relatively bloodless field permits a clearer dissection of the anatomical elements and a better operation. Topical vasoconstrictor, usully cocaine with adrenaline, may be applied to the appropriate part of the nasal mucosa by the anaesthetist before the start of surgery. A pharyngeal pack prevents contamination
ANAESTHESIA FOR OPHTHALMIC SURGERY
of the larynx with blood. It is normal to position the patient with the head elevated. Despite good technique, the occasional DCR results in considerable haemorrhage pre- or post-operatively, and an indwelling i.v. cannula of 18 gauge or larger is a sensible precaution. The procedure can be performed under local anaesthesia.
Tumour surgery Much superficial tumour surgery is performed under local anaesthesia, but occasionally resection of a tumour of the globe is undertaken. Induced hypotension is considered by many to contribute to a good result and should be provided unless contraindicated. It is also believed by some that induced hypotension reduces the risk of tumour dissemination.
Vitreoretinal surgery Vitrectomy is undertaken for a variety of indications including proliferative vascular disease (including that caused by diabetes mellitus), complicated retinal detachments, and for some penetrating eye injuries. Matters of importance to the anaesthetist are preexisting systemic disease, prolonged surgery in a darkened theatre, the use of endo or indirect laser treatment to the retina (the latter requiring the use of protective goggles by theatre staff), and sometimes injection of 'gas' into the eye to produce tamponade to hold the retina against the choroid. One of two poorly diffusible gases is used: sulphur hexafluoride (SF6) or perfluoropropane (C3F8). In both cases, nitrous oxide diffuses freely into the bubble, increasing both volume and pressure. 7 At the end of the anaesthetic, after the surgeon has adjusted the dimensions of the bubble, nitrous oxide diffuses out, rendering the bubble inadequate to fulfil its function. Thus anaesthesia without nitrous oxide is used either throughout surgery, or from about 20min before injection of the bubble. If a circle breathing system is in use, it is essential to increase fresh gas flows, or nitrous oxide washout takes a very long time. Oxygen-enriched air substitutes as the carrier gas and anaesthesia is continued either with an appropriately increased concentration of volatile agent, or with an intravenous infusion of opioid and propofol. The gas remains in the eye for approximately 10 days, and subsequent use of nitrous oxide within this period influences the size of the bubble. The duration of the operation is often in doubt at the start of surgery, and an infusion of a short acting non-depolarising muscle relaxant with neuromuscular junction monitoring avoids embarrassment when surgery ends prematurely. The surgeon may express a preference for the patient's posture following surgery to position the gas bubble most advantageously; this may involve the prone position.
19
Emergency procedures Anaesthesia for a patient with penetrating eye injury presents a number of problems, especially if the patient has eaten recently and if the sight of the uninjured eye is impaired. Frequently, some delay is appropriate, even though gastric emptying is unpredictable following injury. It must also be remembered that the eye injury may not be the only significant trauma and general examination should be undertaken. For other types of emergency surgery the choice lies between rapid sequence induction and intubation with cricoid pressure following preoxygenation using suxamethonium as a rapidly acting muscle relaxant, and awake intubation using local anaesthesia. The theoretical objection to both techniques is that they may increase IOP sufficiently to extrude intraocular contents, leading to permanent loss of vision. A proposed alternative in the patient with a penetrating eye injury is to intubate after a larger than normal dose of non-depolarising relaxant with or without priming. Evidence confirming the objection to the use of suxamethonium is sparse, and the rise in IOP following laryngoscopy in an incompletely paralysed patient is likely to be as great or greater than that associated with an easy intubation after administration of suxamethonium. The consequences of failed intubation in a patient who has a full stomach and who has received a large dose of long-acting relaxant may be dire. Libonati and colleagues8 reported 100 patients in detail and a further 128 in outline who received anaesthesia for penetrating eye injuries at their institution during 1 year. Anaesthetic and surgical records were examined retrospectively with particular reference to the anaesthetic technique and the surgeon's record of pre-anaesthetic and post-intubation status of the eye. No case of vitreous loss initiated during that period of time was noted, independent of the type of anaesthesia used, with or without suxamethonium for intubation. The authors advise production of an adequate depth of anaesthesia prior to the injection of suxamethonium.
Systemic effects of topical medication Ecothiopate is often quoted a s an example of an agent applied topically for its ophthalmic effects which has unwanted systemic actions of anaesthetic significance. Ecothiopate is used for glaucoma and results in inhibition of serum cholinesterase activity, prolonging the action of suxamethonium. However, it is used little in contemporary ophthalmology. The topically applied 13-blocker timolol (also used to treat glaucoma) produces adequate systemic levels to induce bronchospasm in susceptible individuals and also has cardiac effects. Betaxolol is a similar but [3a-selective agent. 10% phenylephrine drops are applied pre-, and occasionally per-operatively to
20
CURRENTANAESTHESIA AND CRITICAL CARE
dilate the pupil and may lead to significant increases in blood pressure. 9 Intra-operative intraocular injection of Miochol (acetylcholine) is probably too evanescent in action to have a significant effect on neuromuscular blocking drugs.
Regional blocks Local anaesthetic techniques for eye surgery have been performed by ophthalmic surgeons since the beginning of local anaesthetic history. Local and systemic complications occur and have been reported. 2 In addition, not all blocks achieve orbicularis paralysis, akinesia of the eye, anaesthesia and controlled IOP. Can the anaesthetist contribute to an improvement in any of these shortcomings?
Complications Systemic complications result from increased concentrations of local anaesthetic drugs in blood or cerebrospinal fluid (CSF), possibly exacerbated by hypercapnia and hypoxaemia. Injection of the appropriate dose of drug in the correct place prevents complications, and recognition of the onset of a problem and prompt corrective measures may avoid disasters.I° The anaesthetist has a good understanding of the pharmacology of the local anaesthetic drugs and is experienced in the preservation of a clear airway, monitoring and resuscitation. Correct placement of the needle requires knowledge of the anatomy of the region, great care, and much practice. The ophthalmic anaesthetist is well placed to provide these.
Making it work The principles are similar to those applied to avoid complications. To these should be added time. Approximately 25rain should elapse between the injection of local anaesthetic and the start of surgery, particularly when using peribulbar block. If the operator is also the anaesthetist (much deplored in other branches of surgery) efficiency will not allow half an hour or so between operations. An anaesthetist with a trained assistant can provide the block, remain with the monitored patient for the critical first 30min (by which time peak blood levels will have been reached) and position the patient safely on the operating table with his assistant providing further observation and communication. He may then start the anaesthetic for the following patient with no loss of surgical time. The following description is of the technique currently used by the author, with alternatives advised by others in brackets.
Anatomy The bony orbit and globe are well described in standard texts.n The orbital connective tissues are of
great significance when considering optimal placement of needles to achieve spread of injected solutions, and those interested in eye blocks should read Koorneef's elegant work. 12 It is essential to maintain a three dimensional concept of the position of the tip of the needle relative to other structures at all times.
Techniques Two drops of topical benoxinate or amethocaine produce corneal and conjunctival anaesthesia. If applied cold, they sting; if warmed to 35°C, they do not. The initial value of the topical anaesthesia is to prevent stinging from the spirit vapour given off by a skin antiseptic containing alcohol. A 25 gauge 11/4" standard bevel needle is introduced through the lower lid (Fig. 1). (A 23 gauge Atkinson short bevel needle is claimed to allow better 'feel' of passage through tissue planes, and to be less traumatic if nerve tissue is contacted; shorter and finer needles are thought to be less traumatic and to avoid the possibility of entering the conus.) Prior intradermal injection of local anaesthetic with a 27 gauge needle is advised if a short bevel needle is used to perform the block. Perconjunctival (rather than percutaneous) injection is used by some as the needle then enters through tissue anaesthetised by the topical agent, and the occasional complication of unsightly lid ecchymosis is avoided. The block needle should pass in a posterior direction following the bony orbital floor and tangential to the globe of the eye as far as the equator of the globe. A finger gently resting on the globe protected by the upper lid helps to detect contact of the needle with the eye. Further evidence is sought by asking the patient to move the eye and noting that the needle remains quite still. After negative aspiration, approximately 3ml of local anaesthetic solution is injected, and a further lml as the needle is withdrawn through the orbicularis muscle. The procedure is repeated at the upper orbital margin, entering the rid inferior to the supraorbital notch (Fig. 2). (The---superior entry point is disliked by some who favour entry through the medial aspect of the caruncle--if this entry point is used the position of the lacrimal drainage apparatus and the medial rectus muscle must be considered. The medial wall of the orbit follows the saggital plane). It is important to note that the roof and floor of the orbit may be very thin and are easily punctured by a needle. The superior relation of the orbit is the brain. With the superior needle in position also adjacent to the equator of the eye, a similar volume of solution is injected, and a further lml is placed in the orbicularis muscle as the needle is withdrawn. Precise volumes vary witl~ the size of the patient and the local anatomy. Conjunctival and lid oedema are usually seen at this stage. The eye is secured carefully in the closed position with atraumatic paper tape and covered with
ANAESTHESIA FOR OPHTHALMIC SURGERY
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\ Periocular block. Thee,inferior (left) and superior (right) injection sites. Postion 1: needle entry; position 2: full needle insertion. Reproduced with permission from: Fry RA, Henderson J. Local anaesthesia for eye surgery. The periocular technique. Anaesthesia 1989; 45: 14-17. Fig. 1 --
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CURRENT ANAESTHESIA AND CRITICAL CARE
an eye pad. A device producing local and controlled pressure over the orbit is then applied to disperse the injected solution and reduce orbital pressure. A Honan balloon is suitable and allows the pressure applied to be measured; alternatively, a small bag containing mercury rested over the orbit is satisfactory, and others use the Super Pinky--a foam rubber ball of suitable size and resistance held over the orbit by a strap applied around the head. The device is removed after 10min and eye movement and orbicularis activity are tested. With experience, the operator can judge whether a good block is developing, and will either close the eye and reapply the pressure device, or supplement the block by a further low volume injection, usually at the inferior entry point. If orbicularis is active, a modified Van Lindt facial block may be performed, entering the skin through the same point. Ten min later, the pressure device is removed and the patient placed on the operating table. The nature of the local anaesthetic agent used varies enormously. There is a growing feeling that undiluted 0.75% bupivacaine may result in prolonged ptosis and extraocular muscle paresis. The author uses a solution containing equal volumes of 2% lignocaine and 0.75% bupivacaine with 150 units of hyalase in 10ml of solution (with no adrenaline) and achieves reasonably consistent results. Good objective studies to ascertain the ideal solution are notoriously difficult because technique probably matters more than the precise nature of the solution. It is claimed that the procedure is more comfortable if all solutions are warmed to 35°C, and if the needle tracks are first infiltrated with local anaesthetic diluted considerably with balanced salt solution. Attention to comfort of the patient on the operating table is rewarded. An empty bladder, hips and knees held slightly flexed by a soft pillow under the knees, arms supported on foam rests and cool oxygen-enriched air wafted over the face with the drapes supported to avoid irritation and claustrophobia usually remove the need for sedation which may cause confusion, unpredictable arousal and movement, loss of airway and hypoxia, a3 If sedation is used, it should be titrated carefully against state of consciousness and given well in advance of the start of surgery so that a steady state has been reached. Monitoring should be by direct observation of the airway and state of consciousness with the addition of standard methods of displaying blood pressure, heart rate, oxygen saturation and electrocardiograph. If an automated device is used to measure blood pressure, it should be set to operate in the manual mode and the patient should be warned verbally before each cuff inflation to avoid movement occasioned by surprise.
Summary Provision of a proper anaesthetic service to an eye surgery unit may improve safety, quality of anaesthesia and efficiency. It is an enjoyable and challenging activity and assists in improvement of quality of life of patients. The role of the anaesthetist in care of ophthalmic regional blocks has probably been underused in Great Britain and should expand. There remains an appropriate place for combined general and regional anaesthesia in ophthalmic surgery. Some anaesthetists may consider that ophthalmic local blocks are not best suited to their particular skills, and they should certainly not be attempted by unsupervised novices.
References 1. Rubin AP. Editorial. Anaesthesia 1990; 45:717-718 2. Nicoll JMV, Acharya PA, Ahlen K, Bagueid S, Edge KR. Central nervous system complications after 6000 retrobulbar blocks. Anesth Analg 1987; 66:1298-1302 3. Lee JP, Hogg C. Botulinum toxin therapy for squint and other ocular motility disorders. In: Easty DL ed. Current Ophthalmic Surgery. Balliere Tindall 1990; 163-171 4. Murphy DF. Anesthesia and intraocular pressure. Anesth Analg 1985; 64:520-530 5. VanDen Berg AA, Lambourne A, Yazji NS, Laghari NA. Vomiting after ophthalmic surgery. Anaesthesia 1987; 42: 270-276 6. Ghaly RG, Fitzpatrick KTJ, Dundee JW. Antiemetic studies with traditional Chinese acupuncture. Anaesthesia 1987; 42: 1108-1110 7. Eger EI. Nitrous Oxide. Amsterdam, Elsevier, 1985; 93-110 8. Libonati MM, Leahy J J, Ellison N. The use of succinylcholine in open eye surgery. Anesthesiology 1985; 62: 637-640 9. Fraunfelder FT, Scafidi AF. Adverse effects from topical ocular 10% phenylephrine. Amer J Ophthalmol 1978; 85: 447-453 10. Covino BG. Clinical pharmacology of local anesthetic agents. In: Cousins MJ, Bridenbaugh PO eds. Neural Blockade. Lippincon 1988; 120-134 11. Feitl ME, Krupin T. Neural blockade for ophthalmologic surgery. In: Cousins MJ, Bridenbaugh PO eds. Neural Blockade. Lippincott 1988; 577-592 12. Koornneef L. Sectional anatomy of the orbit. Aeolus Press, Amsterdam: 1881 13. Bailey, PL, Pace NL, Ashburn MA, Moll JWB, East KA, Stanley TH. Frequent hypoxemia and apnea after sedation with midazolam and fentanyl. Anesthesiology 1990; 73: 826830
Further reading Barker JP, Robinson PN, Vafidis GC, Hart GR, Sapsed-Byrne S, Hall GM. Local analgesia prevents the cortisol and glycaemic responses to cataract surgery. Br J Anaesth 1990; 64:442-445 Mercereau DA. Brain-stem anesthesia complicating retrobulbar block. Can J Ophthalmol 1989; 24:159-161 Biebyck JF. Perioperative management of surgical patients with diabetes mellitus. Anesthesiology 1991; 74:346-359 Gainey SP, Robertson DM, Fay W, Ilstrup D. Ocular surgery on patients receiving long-term warfarin therapy. Am J Ophthalmol 1989; 108:142-146