Anaesthesia, 1979, Volume 34, pages 526-533.

Normocapnic anaesthesia with trichloroethylene for intraocular surgery A.P. A D A M S , A . F R E E D M A N

General anaesthesia is now popular for cataract extraction in Great Britain. This is because improvements in anaesthetic techniques and anaesthetic drugs have made the operation safer for the patient and reduced the risk of crisessuch as vitreous loss and expulsive haemorrhage -occurring during the surgical procedure. Most cataract surgery now takes longer than when the Graefe knife was in vogue because of the use of the operating microscope and more elaborate suturing techniques. Patients who may be suffering from respiratory and cardiovascular disease may not be able to tolerate local analgesia in the supine position for long periods of time. The advantage of general anaesthesia for the surgeon is that he can enjoy an unhurried and relaxed atmosphere while the apprehension of the patient is completely eliminated. The disadvantages of halothane used in a spontaneously breathing anaesthetic technique are that progressive reductions in arterial pressure are liable to occur; this can be undesirable and even dangerous in elderly patients who are likely to have cardiopulmonary disease and a variety of medications. The use of a minimal halothane and muscle relaxant technique using Intermittent Positive-Pressure Ventilation (IPPV) of the lungs with normocapnia for intraocular surgery has been described by the authors. The advantages of this technique are that there

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is a reliable fall in IOP of about 50% and good lung ventilation is achieved with large tidal volumes but without hypocapnia. This results in good arterial oxygenation during surgery and the prompt resumption of adequate breathing at the end of surgery. However, a second general anaesthetic may be required to be given only a short time after such a first halothane anaesthetic (e.g. for surgery on the other eye or to correct any problem arising as a consequence of the first operation) and the anaesthetist may wish for various reasons to avoid a second halothane anaesthetic. The aim of the present study is to determine whether substitution of 0.5% halothane by 0.5% trichloroethylene will still give satisfactory operating and anaesthetic conditions. There are few accounts of the effects of trichloroethylene on intraocular pressure (IOP) under controlled conditions of Paco2. However, trichloroethylene is reputed to cause a slight increase in IOP ~.~ at constant Pacozand lung v e n t i l a t i ~ n . Other studies in which Pacoz is not controlled suggest that trichloroethylene is associated with a reduction in IOP.4 Although the above concentrations of halothane and trichloroethylene are not equipotent from consideration of their minimum alveolar concentrations, 0.5 % trichloroethylene is that concentration delivered from automatic draw-over Trilene inhalers used for obstetric analgesia when the apparatus is

A.P. Adams, PhD, MB, BS, FFA RCS, Consultant Anaesthetist and Clinical Lecturer, A. Freedman, MA, BM, BCh, FRCS, DO, Consultant Ophthalmologist and J.K.G. Dart, MA, BM, BCh, DO, Senior House Officer in Ophthalmology, Nufield Departments of Anaesthetics and Ophthalmology, Radcliffe Infirmary, and Oxford Eye Hospital, Oxford OX2 6HE.

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0003-2409/79/0600-0S26 $02.00

0 1979 Blackwell Scientific Publications

Anaesthesia for intraoculur surgery adjusted to the ‘strong’ setting. This concentration when used to supplement a nitrous oxide and oxygen inhalational anaesthetic might be expected to produce a sufficient degree of analgesia and anaesthesia yet produce an orientated and awake patient at the end of a surgical procedure lasting up to 40 min. Methods Patients Twelve adult patients with cataracts were admitted for lens extraction under general anaesthesia. Details of these patients are given in the results section. All patients were seen by the anaesthetist pre-operatively and their fitness assessed. No attempt was made to select patients other than to exclude those who were in gross congestive cardiac failure. One patient had had a myocardial infarction 20 years previously, four patients had chronic bronchitis (one of these patients also had asthma), and two patients were diabetic. Some of the patients were receiving medication in the form of phenytoin, diuretics, beta-adrenoreceptor drugs, corticosteroids or insulin. Measuretnents of IOP When the patients arrived in the anaesthetic room the cornea of each patient’s eyes was anaesthetised by the instillation of 1-2 drops of 0.5 % proxymetacaine (Ophthaine) solution. Intraocular pressure was measured using the Alcon applanation* pneumotonograph (Fig. l).s *Alcon Laboratories (U.K.) Ltd, Marlow, Bucks.

piston

During this type of measurement the membrane of the instrument and the eye applanate (flatten) each other; the eye is never indented. This instrument had been calibrated over previous weeks by measurements made in the eyes of patients unconnected with the present study by using the Perkins hand-held applanation tonometer for comparison. The over-reading error of the pneumotonograph against the Perkins instrument was constant at 2.5 mmHg. The readings taken with the pneumotonograph were therefore corrected by this amount. The pneumotonograph does not flatten the eye over a n area in excess of that required to make the measurement. However, the sensitivity of the measurement is sufficient to register the intraocular pulse as a rhythmic ripple o n the chart recording. The Alcon pneumotonograph is a combination of a pneumatic and a n electronic system. The pneumatic part provides the means of measuring intraocular pressure. The electronic system translates the measured pressure into an electrical signal which is registered on a paper chart recorder. The measuring head is called an autosensor. This consists basically of an air bearing, a pressure chamber and a hollow piston coupled to a membrane-covered tip assembly. The piston shaft virtually floats without friction on a cushion of gas within the bushing. Dichlorodifluromethane gas, from a canister under pressure, flows in a controlled manner through the air bearing in two directions towards atmosphere when a switch is operated. Some gas goes forwards to the tip of the instrument where a baffle deflects it away from the eye during measurement. The remaining gas passes backwards through the measurement

air bearing I

+gas

in

*to transducer

\

silastic sleeve

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baffle

Fig. 1. Diagram of the principle of operation of the Alcon applanation pneumotonograph.

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A.P. Adams, A. Freedman and J.K.G. Dart

chamber, down the hollow piston and outwards between the tip and the membrane. The pressure in the measurement chamber remains essentially the same as that of the atmosphere as long as the exit path between the tip and the membrane remains unrestricted. As the membrane is brought into contact with the cornea of the eye, the gas flow is restricted and pressure in the measurement chamber begins to increase. This in turn causes the free-floating piston to push outwards so that the membrane applanates the eye and vice versa. The pressure of gas in the measurement chamber continues to rise until it just equals IOP. The increase in pressure is transmitted to a strain-gauge pressure transducer and the signal is suitably processed and recorded. The pneumotonograph has the advantage that it is easy to use with the patient in the supine position and a definite end-point of IOP can always be achieved. All IOP readings were made by the same person (J.D.). Measurements of IOP were made in both eyes just before the induction of general anaesthesia and again 10 min later when full general anaesthesia was established with controlled ventilation of the lungs. Tonometry was also performed on the non-operated eye at the conclusion of surgery while the general anaesthetic was maintained and again immediately spontaneous breathing had returned following withdrawal of the anaesthetic gases and the antagonism of residual neuromuscular block. All IOP measurements were made with the patient in the supine position. Anaesthesia All patients were premedicated with atropine 0.6 mg given intramuscularly about 1 hr before surgery. This is not believed to have any effect on IOP. General anaesthesia was induced with thiopentone 4 mg/kg intravenously. This agent like many induction agents lowers IOP. However the administration of suxamethonium followed by inflation of the lungs with oxygen, laryngoscopy and passage of an endotracheal tube provokes a pressor effect and increases intraocular pressure. *' This undesirable effect on TOP was minimised by administering a Iarge dose of suxamethonium (2.0 mg/kg).2 The beneficial effect of such a large dose is that both the tonic and the phasic fibres of the extraocular muscles are relaxed. Conventional doses

of suxamethonium (0.5-1 *O mg/kg) may produce a tonic contracture of the extra-ocular muscles, squeezing the eyeball and producing a transient rise in IOP.9*10The trachea was intubated with a size 8 or 9 Oxford pattern non-kinking cuffed endotracheal tubeL1after prior spraying of the larynx and upper trachea with 50-100 mg of 10% lignocaine spray from an aerosol canister. Maintenance of anaesthesia and ventilation of the lungs

Ventilation of the lungs was at first manually controlled using a mixture of 33% oxygen and 0.5 % trichloroethylene in nitrous oxide. The trichloroethylene was delivered from a calibrated Tritec vaporiser; however, refractometry revealed that 0.4% trichloroethylene was in fact delivered at the 05% setting. The gas mixture was fed into the delivery tube of the Penlon version of the Bain anaesthetic breathing circuit.12 The fresh-gas flow was set on the Rotameters of a BOC-Medishield Boyle International anaesthetic machine to as close to 70 ml/kg per min as the flowmeter etchings permitted. This flowrate of fresh gas has been shown to produce a Pacol within the normal range during IPPV."*'* Gallamine triethiodide (Flaxedil) in a dose of 2 mg/kg, but not exceeding 120 mg, was given intravenously in a single dose immediately it was apparent that the muscle relaxation obtained by the suxamethonium was wearing off. The purpose of this dose of gallamine was to facilitate the patient's ventilation with the automatic ventilator (Cape TC50 ventilator) but to limit the dose so that gross effects did not remain at the end of the operation and which could create problems in this elderly group of patients. It should be emphasized that this dose of gallamine is insufficient to permit tracheal intubation without the patient reacting and hence provoking a rise in IOP. Intermittent positive-pressure ventilation of the lungs was maintained by use of a Cape TC 50 ventilator which was adjusted to give a respiratory frequency of 12 cycleslmin and a tidal volume of 10-15 ml/kg (Fig. 2). These values were coniirrned using a Wright's electronic respirometer inserted at the catheter mount; this sensor was removed once the required ventilation had been established at the start of the anaesthetic.

Anaesthesia for intraocular surgery

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FRESH ANAESTHETIC GASES PENLON CO-AXIAL VALVE 'CLOSED'

SAFETY VALVE I

PATlENT EXPIRATION

.Oh ORRUGATEDANAESTHETIC OSE

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Fig. 2. Diagram of co-axial anaesthetic breathing circuit connected to the Cape TCSO Ventilator.

Intermittent positive-pressure ventilation of the lungs with the anaesthetic mixture unchanged was continued throughout the duration of surgery. It was not found necessary to give any further muscle relaxant although in two patients (both of whom were obese) a slight delay in re-establishing IPPV after moving the patient from the anaesthetic room into the operating theatre caused desynchronisation of the patient with the ventilator just before surgery began. This problem resolved spontaneously over a few minutes. Towards the end of the operation metoclopramide 10 mg was given intravenously as a prophylactic against sickness in the postoperative period. In the concluding phase of the operation arterial blood was sampled from the radial artery. The 2 ml syringes containing the samples were transported in iced-water to the blood-gas laboratory where analysis was performed within 30 min using a Radiometer ABL 1 bloodgas system. Standard corrections were applied to these results for storage time.15 At the end of the operation the IOP was measured in the non-operated eye while the anaesthetic and ventilation of the lungs was continued. After this measurement had been made residual neuromuscular blockade was reversed with 0.6 mg atropine (or 1.2 mg atropine if the tachycardia from the gallamine had worn off) and 2.5 mg neostigmine, secretions

in the pharynx were aspirated and the endotracheal tube was removed. Oxygen was administered through an anaesthetic face mask, taking care not to press on the eyes, and spontaneous breathing was regained within a few minutes. At this point IOP was again determined. The patient was then turned on to one side and given oxygen-enriched air to breathe from a plastic disposable face mask for a period of 10 min. The patient was then returned to the ward having gained complete consciousness.

Results

Patients There were twelve patients of whom six were male in the series. Their mean age was 68.3 years (range 48-82 years) and their mean weight was 66.2 kg (range 50.1-83.2 kg).

Anaesthesia The mean total fresh gas flow (Vf) set on the anaesthetic machine flowmeters was 4.87 I/min (s.e. mean0.03 I/min), i.e. 73.6 ml/kg, mean body weight. The mean expired minute volume (VE) was 11.3 I/min, i.e. 170 ml/kg per min at a set frequency of ventilation of 12 cycles/min giving a mean tidal volume of 939 ml or 14.2 ml/kg.

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Table 1. Mean IOP and arterial pressures+ s.e. mean, before, during and after trichloroethylene anaesthesia. Ranges in parentheses. Student’s r-test was used to test the mean differences between groups for the null hypothesis. IOP: Group A cf. group B, P 0.01). However, the fall in diastolic pressure from a mean value of 92 mmHg to 83 mmHg was not significant. Arterial pressures remained constant throughout the operation; systolic, diastolic and mean arterial pressures rose slightly after the end of the operation when the residual neuromuscular blockade had been reversed with neostigmine and atropine, the nitrous oxide and trichloroethylene had been withdrawn and spontaneous breathing re-established on oxygen.

Arterial blood gases

The mean arterial carbon dioxide tension (Paco,) of blood taken towards the end of surgery during IPPV of the lungs was 38.6 mmHg (s.e. mean 1.24 mmHg). The mean arterial oxygen tension (Pao,) at this time was 148.5 (s.e. mean 10.0 mmHg), the mean arterial pH was 7.35 (calculated from individual values of hydrogen in concentration) and the mean in vivo base deficit was 2.9 mmol/l.

Postoperative problem

All patients recovered consciousness and clinically adequate pulmonary ventilation within 5-7 min of the end of the anaesthetic. There were no systemic or ophthalmic complications in any of the patients studied.

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Discussion In the anaesthetic technique described a reduction in intraocular pressure should occur by the use of thiopentone and the muscle relaxant gallamine. However, non-depolarizing muscle relaxants generally have only a small effect on IOP consequent upon the relaxation of the extraocular muscles and the orbicularis ~ c u l i . ~ ~Tubocurarine ." may have a greater effect due to its hypotensive action, although pancuronium, which has mild stimulatory effects on the circulation, has no effect.'" Gallamine was chosen for this study because its short duration of action matched the time of the operation. Suxamethonium is reputed to increase IOP. However, contracture of the extra-ocular muscles is not the only effect produced as section of these muscles does not completely abolish the rise in IOP.'9-20 Suxamethonium may cause an increase in IOP through an action of choroidal blood f l ~ ~ . This ~ ~rise. in~ ~ . ~ IOPcannot be entirely prevented by prior administration of small doses of p a n c u r o n i ~ m . ~ ~ * ~ ~ Joshi & Bruce" showed that large doses of suxamethonium such as were used in the present study are not associated with increases in IOP. The other factors used in this anaesthetic technique which might be expected to increase IOP are laryngoscopy and tracheal intubation, and any increase in central venous pressure produced by the large tidal volumes used. The use of such tidal volumes helped synchronise the patient with the ventilator and produced good arterial oxygenation in this group of elderly patients.25s26However, the avoidance of hypocapnia lessens the tendency to a reduced cardiac ~ ~ t p and ~ the t ~avoidance ~ * ~of ~ depletion of carbon dioxide from the body stores means that postoperative hypoxaemia caused by hypoventilation does not O C C U ~ . ~ ~ , ~ " Magora & Collins4 reported a fall in IOP during trichloroethylene anaesthesia but controlled carbon dioxide levels were not obtained in their study. Direct measurements in monkeys3 showed a rise in IOP with trichloroethylene anaesthesia. AI-Abrak & Samuel2 studied the effects of IPPV with 1 % trichloroethylene in a mixture of nitrous oxide and oxygen at constant end-tidal carbon dioxide concentrations in eight urological patients and found that IOP was increased. The rise in IOP in those studies

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A.P. Adam, A. Freedman and J.K.G. Dart

were associated with rises in central venous pressure when trichloroethylene was introduced although systolic arterial pressure remained fairly constant. The present study also employs IPPV but maintains Pacol within the normal range by fractional re-breathing in the co-axial circuit. In all twelve patients a significant reduction in IOP and in systolic and mean (but not diastolic) arterial pressures occurred after the induction of anaesthesia. Thereafter there was a tendency for IOP to rise (Fig. I), to an extent such that at the end of surgery the IOP in the non-operated eye was not significantly different from that obtained before the induction of anaesthesia. However, arterial pressure remained constant for the duration of the operation. Systolic and mean (but not diastolic) pressures at the end of surgery were significantly different from the pressures before the induction of anaesthesia. Although the IOP reduction with 0.4% trichloroethylene was not as great as that found in an exactly similar study using 0.5% halothane,' the fall in arterial pressure was also not marked. Ten minutes after the induction of anaesthesia the IOP in the eye to be operated upon is reduced by 48% in the halothane study' with an associated reduction in systolic arterial pressure of 25%. However, the comparable figures in the present trichloroethylene study shows reductions in IOP of 28% and in systolic arterial pressure of 17%. These differences produced between the two anaesthetics are more obvious when the IOP and systolic arterial pressures are compared before the induction of the anaesthetic and at the end of anaesthesia. Halothane, 0.5%, is associated with reductions of 26% in systolic arterial pressure and 52% in IOP' while 0.4% trichloroethylene is associated with reductions of 16% in arterial pressure and 13% in IOP. Halothane 0.5 % therefore clearly shows a greater reduction in IOP than can be achieved by trichloroethylene 0.4%at comparable levels of systolic arterial pressure. The fact that IOP tended to rise during the trichloroethylene anaesthetic although systolic and mean arterial pressures continued to remain stable suggests that trichloroethylene does increase IOP. However, the effect appears to be dose-dependent and large rises in IOP described by other wo r k e d may be avoided by maintaining the concentration of trichloroethylene at 0.4% under the conditions given in this study.

In conclusion, it appears that trichloroethylene is a satisfactory agent to use in the manner described for anaesthesia in cataract surgery, although the reduction in IOP is not as great as that produced by halothane. A controlled concentration of 0.4% trichloroethylene may therefore be a satisfactory substitute for halothane should the latter agent need to be avoided.

Summary Measurements of intraocular pressure (IOP) by applanation tonometry in twelve. patients undergoing lens extraction showed that a normocapnic anaesthetic technique using 0.4% trichloroethylene with controlled ventilation of the lungs (IPPV) with large tidal volumes (14 ml/kg) reduced IOP by 13-20%. There was only a small reduction in arterial pressure. Normocapnia was easy to achieve by use of the singlelimb co-axial Penlon (Bain type) anaesthetic breathing circuit in conjunction with an electrically-driven, small and inexpensive lung ventilator. The anaesthetic technique described using trichloroethylene is suitable for lens extraction surgery when it is desired to avoid a halothane anaesthetic for any reason. Key words

ANAESTHETICS, VOLATILE; trichloroethylene. EYES; intraocular pressure. MEASUREMENT TECHNIQUES; applanation tonometry. References 1. ADAMS,A.P., FREEDMAN.A. &HENvILLE,J.D.(~~~~)

Normocapnic anaesthesia for intraocular surgery. British Journal of Ophthalmology, 63,204-210. J.R. (1973) Effects of AL-ABRAK,M.H. & SAMUEL, general anaesthesia on the intraocular pressure in man. Trichloroethylene in nitrous oxide and oxygen. British Journal of Ophthalmology, 59, 107-1 10. SCHREUDER, M. & LINSSEN,G.H.(1972) Intraocular pressure and anaesthesia. Direct measurements by needling the anterior chamber in the monkey. Anaesthesia, 27, 165-1 70. F. & COLLINS,V.J. (1961) The influence MAGORA, of general anaesthesia agents on intraocular pressure in man. Archives of Ophthalmology, 66,806-81 1. QUIGLEY,H.A. & LANGHAM,M.E. (1975) Comparative intraocular pressure measurements with

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the pneuniotonograph and Goldmann tonometer. American Journal of Ophthalmology, 80, 266-273. TAYLOR,T.H., MULCAHY,M. & NIGHTINGALE, D.A. (1968) Suxamethonium chloride in intraocular surgery. British Journal of Anesthesia, 40, 1 1 3118. PANDEY,K., BADOLA,R.P. & KUMAR,S. (1972) Time course of intraocular hypertension produced by suxamethonium. British Journalof Ophthalmology 44, 191-196. JOSHI,C. & BRUCE,D.L. (1975) Thiopental and succinylcholine action on intraocular pressure. Anesthesia and Analgesia: Current Researches, 54, 471-475. WISLICKI, L. (1976) Factors affecting intraocular pressure. Proceedings of the Royal Society of Medicine, 69, 952. GIBB, D.B. (1974) Suxamethonium-a review. Pharmacological actions of suxamethonium apart’ from its neuroniuscular blocking effect. Anaesthesia and Intensire Care, 2, 9-26. DUCKWORTH, S.I. (1962) The Oxford non-kinking endotracheal tube: results of its use in about 18,000 cases. Anaesthesia, 17, 208-214. HENVILLE, J.D. & ADAMS,A.P. (1976) A co-axial breathing circuit and scavenging valve. Anesthesia, 31, 257-258. BAIN,J. & SPOEREL,W.E. (1973) Flow requirements for a modified Mapleson D system during controlled ventilation. Canadian Anaesthetists’ Society Joirrnal, 20, 629-636. HENVILLE, J.D. & ADAMS,A.P. (1976) The Bain anaesthetic system. An assessment during controlled ventilation. Anaesthesia, 31, 247-256. KELMAN, G.R. & NUNN,J.F. (1966) Nomograms for correction of blood POZ. P c o ~ ,pH and base excess for time and temperature. Journal of Applied Physiology, 21, 1484-1490. DUNCALF,D. & FOLDES,F.F. (1973) Effect of anaesthetic drugs and muscle relaxants on intraocular pressure. International Ophthalmology Clinics, 13 (2), 21-33. ERIKSEN,S ., BRAMSEN, T. & HOMMELGAARD, P. (1977) Some aspects of ocular function after precurarization. Act4 Anaesthesiologica Scandinavica, 1, 385-389. AL-ABRAK,M.H. & SAMUEL, J.R. (1974) Further observations on the effects of general anaesthesia on

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intraocular pressure in man: comparisons of tubocurarine and pancuronium in nitrous oxide and oxygen. British Journal of Ophthalmology, 58, 806-810. CRAYTHORNE, N.W.B., ROTTENSTEIN,H.S. & DRIPPS, R.D. (1960) Effect of succinylcholine on intraocular pressure in adults, infants and children during general anesthesia. Anesthesiology, 21, 5963. ADAMS,A.K. & BARNETT, K.C. (1966) Anesthesia and intraocular pressure. Anaesthesia, 21, 202-210. WAHLIN, A. (1960) Clinical and experimental studies on effects of succinylcholine. Act4 Anaesthesiologica Scandinauica, Supplement 5 , 1-24. WILSON,T.M., LE MAY, M., HOLLOWAY, K.B., STRANG,R. & MCKENZIE,E. (1974) Experimental and clinical study of factors influencing choroidal blood flow. Transactions of the Ophthalmological Societies of the United Kingdom, 94, 378-382. MILLER, R.D., WAY, W.L. & HICKEY,R.F. (1968) Inhibition of succinylcholine-induced intraocular pressure by non-depolarising muscle relaxants. Anesthesiology, 29, 123-126. BOWEN,D.J., MCGRAND,J.C. & PALMER,R.J. (1976) Intraocular pressures after suxamethonium and endotracheal intubation in patients pretreated with pancuronium. British Journal of Anaesthesia, 48, 1201-1205. PRYS-ROBERTS, C., KELMAN, G.R., GREENBAUM, R. & ROBINSON, R.H. (1967) Circulatory influences of artificial ventilation during nitrous oxide anaesthesia in man. I1 Results: the relative influence of mean intrathoracic pressure and arterial carbon dioxide tension. British Journal of Anaesthesia, 39, 533-548. HEWITT, P.B., CHAMBERLAIN, J.H. & SEED, R.F. (1973) The effect of carbon dioxide o n cardiac output in patients undergoing mechanical ventilation following open heart surgery. British Journal of Anaesthesia, 45, 1035-1042. SALVATORE, A.J., SULLIVAN, S.F. & PAPPER,E.M. (1969) Postoperative hypoventilation and hypoxaemia after hyperventilation. New England Journal of Medicine, 280, 267-470. SULLIVAN, S.F., PATTERSON, R.W. & PAPPER, E.M. (1966) Arterial COz tension adjustment following hyperventilation. Journal of Applied Physiology, 21, 247-250.

Normocapnic anaesthesia with trichloroethylene for intraocular surgery.

Anaesthesia, 1979, Volume 34, pages 526-533. Normocapnic anaesthesia with trichloroethylene for intraocular surgery A.P. A D A M S , A . F R E E D M...
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