The EM0 ether inhaler

Transcription

1 VOL 21 NO 4 ANESTHESIA OCTOBER 1966 The EM0 ether inhaler Clinical experience in a series of a thousand anaesthetics R.A.L. LEATHERDALE, F FA R c s Royal Victoria Hospital, Bournemouth Draw-over vaporizers, using air as the vehicle for conveying the anaesthetic, are as old as anmthesia. John Snow 1 published details in 1848 of an ether inhaler which incorporated a device for regulating the concentration of ether. Subsequently many inhalers working on similar principles were evolved, but the introduction of compressed oxygen and nitrous oxide caused the development of anmthetic apparatus to follow other channels and has resulted in many variants of anresthetic machines, of which the commonest in this country is the Boyle. In Epstein, Macintosh and Mendelssohn2developed the Oxford Ether Vaporizer which enjoyed considerable popularity in war time, particularly in isolated theatres of action where the supply of cylinders of compressed gases was problematical or even impossible. With the return of peace and the great advances in anaesthesia over the past twenty years, techniques based on the use of sucha simple vaporizing unit have again fallen into disuse, particularly in the more sophisticated anaesthetic atmosphere that obtains in the highly developed countries of the world. In 1956, Macintosh and Epstein3 produced an improved version of the Oxford Vaporizer, the EMO Ether Inhaler. In this country, with its relatively high proportion of fully trained specialist anasthetists, the need for such an apparatus has been less obvious and there are few references to it in British literature 4-6. The apparatus is mainly to be found in teaching and research centres, on ships of the mercantile marine and as part of the equipment of obstetric flying squads. It has, however, been exported in considerable numbers and there are many references to it in literature from overseas7-16. It is part of the aniesthetic equipment of over ninety countries outside the British Isles and it has been stock-piled in some countries against the possibility of a thermonuclear war, where the need for a simple and efficient means of anaesthetising large numbers of casualties would arise. It is the purpose of this paper to present a series of one thousand anaesthetics given by the author with this apparatus and to discuss the 504

2 Vol21 ANESTHESIA 505 advantages and limitations that became apparent. It is also suggested that anasthetists should familiarize themselves with this or some similar apparatus as part of their normal training17, not only for its inherent usefulness, but also to be competent to administer anaxthetics under conditions that are currently being commented on by Boulton and Cole The apparatus used has been a standard EMO Ether Inhaler with a spring loaded concertina reservoir bag and a single gravity check valve attached to the vaporizer (Penlon bellows unit). The expiratory valve has been a Ruben20. Although subsequent modifications of the apparatus have been made for use with halothane and azeotropic mixtures of halothane and ether, ether and trichlorethylene (a few cases which will be discussed later) have been the sole volatile anasthetic agents. TABLE 1 Analysis of srrrgery for which anesthetics were administered Major abdominal (including emergencies) D & C, cystoscopy and anal surgery Major dental surgery (impacted wisdom teeth, clearances & etc.) Varicose veins and lower limb orthopaedic surgery Tonsils and Adenoids in children Mastectomies, axillary and upper limb surgery Herniorraphy Ophthalmic surgery (intra & extraocular) Adult tonsillectomy and endoscopic procedures on the respiratory tract and oesophagus Pelvic Floor Repair Thyroidectomy Major orthopaedic Other (manipulations, examinations under anlesthesia & etc.) Standby TOTAL MATERIAL The series has been entirely unselected; details are given in table 1. Some amplification of the last category Standby is necessary. These are cases where the apparatus was not actually used, but where an anasthetic of short duration is given (intravenous thiopentone or methohexitone in a dental surgery or a patient s home are obvious examples) and it is essential to have immediately available the means to inflate and intubate a patient. Such cases have been included since the portability of the apparatus and hence its value in such situations, is one of its most important attributes. TECHNIQUE Prernedication Apart from the invariable use of atropine or scopolamine to counteract the effect of ether on salivation and the bronchial secretions no

3 ANESTHESIA voz 21 standard premedication was employed. The age distribution (from neonates to nonogenarians) and the varying clinical condition of the patients rendered this impossible. For the same reasons no statistical analysis of the incidence of post-operative vomiting could be attempted. Induction In adults a short acting intravenous agent (thiopentone sodium, methohexitone sodium or propanidid) was followed by suxamethonium hydrochloride and inflation with ether and air. In very young children and infants ethyl chloride on an open mask was used. In such cases the material difference from the rag and bottle technique is that the concentration of ether vapour is precisely controlled after the induction with ethyl chloride. The transition from induction to maintenance. This is an artificial concept, but may loosely be defined in the present context as the period during which the amsthetic agent is changed from the intravenous agent to the volatile agent. Inflation with 15-20% ether was employed during the period of apnoea following the administration of succinylcholine until the first or second plane of surgical anasthesia was reached. Clinical observation supports the evidence of Hart and Bryce-Smith** that the inflation of an apnoeic patient with 15-20% ether has a negligible effect on the pulse. Certainly in none of the patients in this series was there any cause for worry on this score during the induction of anasthesia. Maintenaiice Ansesthesia beyond this point depended on the type of surgery being performed, and may be considered under two headings. First, operations where spontaneous respiration was required and, second, operations where muscular relaxation and controlled respiration were necessary. Maintenance with spontarieous respiration. In these cases the concentration of ether was steadily reduced and in the majority of patients it was found that after a period of ten minutes or so a steady and satisfactory level of anasthesia using 6-8 % ether was obtained. Maintenance with controlled ventilation. In this group the concentration of ether was also steadily reduced, usually at a somewhat faster rate and narcosis was invariably adequate using a concentration of 3-4 ether. Relaxation in these patients was obtained in the normal way with intermittent suxamethonium, d-tubocurarine or gallamine triethiode, the length of the operation being virtually the sole criterion as to which relaxant was used.

4 Vol 21 ANESTHESIA 507 It is important that the practice of siting the inflating bellows on the inlet side of the EMO Inhaler should be avoided. It is possible under these circumstances that the inspired gases may pass over the vaporizing chamber more than once before reaching the patient and thus contain eventually a far higher concentration of ether than that indicated by the machine. Clementsen21 has stressed this in relation to the use of an Ambu bag and Ruben valve being placed on the inlet side of the EMO. Air as the carrier gas Since air is the vehicle for inflation and conveying the anasthetic the dangers of hypoxaemia and cyanosis are much more immediate than when oxygen is used for inflation. The duration of any period of complete apnoea inflicted on the patient must be carefully watched. The practice of holding one s own breath coincidentally with the apnoea gives a good rough clinical guide if accurate timing is not practicable. Weitzner et a122 state that the arterial oxygen tension after inflation with air in an apnoeic patient falls to 78 % in one minute and to 60% after one and a half minutes. Such considerations apply particularly during endotracheal intubation and also when engaged in passing a Ryle s tube or setting up an intravenous drip, though in the latter two instances it is nearly always possible to choose a time most convenient to the anasthetist. It is essential when endotracheal intubation is to be carried out that everything necessary is ready and immediately to hand before starting the anxsthetic. In practice, of course, the time available for passing an endotracheal tube is more than enough, but where any difficulty arises during the manoeuvre the shorter time available before re-inflating the patient must be borne in mind. Failure of the technique could be defined as inability to prevent cyanosis in the anasthetized patient. Such a state did not arise in any patients who were paralyzed and on controlled ventilation, though, naturally, the problems associated with the very obese patient and those with large abdominal tumours required that more vigorous ventilation than usual was practised. In those patients who were respiring spontaneously maintenance of anasthesia needed as much if not more care than those on controlled respiration. Occasional incidents of cyanosis did occur, though these were brief and were always immediately correctable by assisting the respiration. Cole and Parkhouses and Ikezono et al. 23 have investigated blood oxygen saturation during spontaneous respiration under these conditions and advocate assisting the respiration. The incidents of cyanosis in this series were all in earlier patients ; it subsequently became the author s practice to assist the respiration inany operation lasting more than ten to fifteen minutes, When this was done no evidence of clinical hypoxia

5 508 ANESTHESIA Vol21 was seen. In no case in the series did cyanosis develop to an extent where it caused any concern either during the operation or in the form of post-operative complications. Recovery It is still commonly held that recovery from ether anasthesia is inevitably protracted. With experience, and particularly experience in working frequently with individual surgeons, it is to be expected that at the end of the operation the patient s protective reflexes will be fully established, even after anasthetics lasting an hour or more. The level of consciousness is usually less than that to be expected after an anasthetic using the nitrous oxide - oxygen - relaxant sequence and the period of amnesia is often quite pronounced. In the author s view this is an advantage; it does not for example seem to be in the best interests of the patient if he is awake and fully conscious of pain within five minutes of the end of an operation of gastrectomy. The restoration of the protective reflexes is a far more important landmark in the recovery; it has been the rule in the present series that the patient is rational and able to answer questions within minutes of the end of the operation. Prior to this perseveration in response to commands has been very common, if the patient is told to put his tongue out he does so, but leaves it protruding until he is told to put it back. For a smooth and satisfactory recovery the skills of the anasthetists who practised before relaxant drugs and intravenous inductions are necessary. Post-operative ~~orirititig It has been indicated earlier in the paper that a statistical analysis of the present series would be valueless. Nevertheless, among those patients of the year old group, who were undergoing cold surgery for procedures such as hernia repair, varicose veins and minor orthopaedic surgery, the clinical impression of the author strongly supports Holmes24 that vomiting is no commoner after ether air anasthesia than after other anasthetic techniques. The association of ether and vomiting, particularly in the lay mind, is very strong and must date from the days when ether was the sole anasthetic agent used for both narcosis and abdominal relaxation. The essence of the technique described is that the minimum amounts of ether are given. On more than one occasion a patient has commented that they were always sick after ether on previous occasions; no mention of the anasthetic drugs to be employed has been made and ether has been given with no nausea or vomiting post-operatively. Conversely it is quite frequent to encounter a patient who states that they are always sick after anasthetics and transforms his words into actions whatever anas-

6 Vol21 ANESTHESIA 509 thetic drugs have been used. Discussion of these points is as much in the realms of psychology as anxsthetics, but post-operative vomiting is an unpleasant experience and one that remains firmly fixed in the patient s mind. Phenothiazine compounds certainly have reduced the incidence and were employed in the majority of adult patients in this series. Further practical points in the use of the EM0 The use of trichlorethylene with the EMO. This has been carried out by attaching a Rowbotham s vaporizer to the apparatus and has provided fully satisfactory anasthesia though it has been the rule that this has had to be supplemented by relaxants in the majority of cases. Prior to the introduction of methohexitone, the apparatus, using trichlorethylene, has been employed in the dental surgery to give anasthetics for up to an hour for conservation work.this has involved intubation and packing off the pharynx, but it has been very interesting to see how little relaxant in the form of intermittent suxamethonium has been required, mg has been sufficient. Patients have been able to leave the surgery (accompanied) within 30 minutes of the end of the operation. It is not intended to advocate this practice, methohexitone is obviously a far more satisfactory agent, but it was interesting to see what was capable of being carried out with trichlorethylene and air using this apparatus. Use of oxygen with the EMO. At the start of the series the author had an attachment made so that oxygen could be administered if necessary. This has not been used. The inspired air can be supplemented with oxygen simply if somewhat crudely by taping the end of the pressure tubing from an oxygen cylinder to the inlet port of the EMO and turning the supply of oxygen well on. Intravenous technique. A Mitchell25 needle has been introduced into a vein on the dorsum of the hand as a standard practice while using the EMO. This was obviously essential in any operation requiring full muscular relaxation, but was found to be less so, as experience was gained in patients who were respiring spontaneously or who were being assisted. This was most noticeable in the dental operations. Inflation with % ether in air following a sleep dose of thiopentone and 100mg of suxamethonium nearly always produced a patient whose reflexes were adequately obtunded by the time spontaneous respiration returned; though this obviously depended on the robustness and general condition of the patient as well as on the premedication. The use of the EMO, for unasthesiu for tonsillectomy and rrdeiioidectomy in children. A Royle Davis gag without an endotracheal tube was invariably used. The gag had a built-in attachment for insufflating

7 510 ANESTHESIA voz 21 gases into the pharynx and this was attached to the catheter mount coming from the expiratory side of the Ruben valve. If necessary a right angled connection with 19-2 inch length of the appropriate sized endotracheal tube was interposed between the catheter mount and the nozzle on the Boyle Davis gag. Insufflation was then carried out in the usual m y with the concertina bellows. In view of relative inefficiency and wastefulness of this method of anzsthesia it was found to be impractical to lower the concentration of ether below about 8% if a satifactory level of anaesthesia was to be maintained. DISCUS S I 0 N The advantages The main advantages of the EMO Ether Inhaler are simplicity, portability and cheapness. The virtues of simplicity in anzsthesia have been stated by Macintosh26 and in the editorial in Anasthesia previously quoted 17. If, through force of circumstances, anasthetics have to be administered by personnel less highly trained than is the case in this country, or where one trained person has to supervise more than one anmthetic, the advantages are obvious. A further advantage of its simplicity is that servicing is less complicated and is needed less frequently. As a corollary to simplicity one may thus add reliability as a characteristic. The portability of the apparatus does not appear to be of much import in this country where few of the population live so far from a hospital that it is preferable to take the services to the patient. Nevertheless there are occasions when anzsthetics have to be administered in such situations and a portable anasthetic machine is essential. In the present economic circumstances it might well be argued that the cheapness of the EMO both as regards capital outlay and running costs, could well be an important factor; but the almost universal training in anzsthesia in this country being based on the Boyle s machine, the cost of a change to a draw-over apparatus might well negative the financial advantages. The capital cost is approximately a quarter of the standard Boyle s apparatus. For the advantages in running costs it is necessary again to refer to conditions overseas. Compressed oxygen and nitrous oxide are both relatively cheap in this country, but when the transport costs are added in countries which do not themselves manufacture them, the relative cheapness of the FMO is better appreciated. Three overseas authors have particularly stressed thissp 10,12. TI? e disadvat i tages From the experience gained in this series it was felt that the only substantial disadvantage was the shortened time available for endo-

8 Vol21 ANESTHESIA 51 1 tracheal intubation and other manoeuvres in an apnoeic patient, compared with similar circumstances when oxygen was used for inflation. This was only apparent when a particularly difficult situation arose in relation to the manoeuvre being carried out. The exclusion of other volatile anasthetic agents and the dependence on ether and occasionally trichlorethylene, cannot be considered a disadvantage since the apparatus has been adapted for halothane and azeotropic mixtures of halothane and ether. This limitation was deliberate in order to introduce some standardization into the technique and to reduce anaesthesia to as simple a level as was practical. CONCLUSION The surgery carried out in the present series is by no means completely representative, no neurosurgery or thoracic surgery was undertaken. Both these specialties are referred to by authors abroad and Poppelbaum2 7 reviewed 250 thoracic operations carried out under ether-air anasthesia. No anasthetic apparatus can claim to be universally suitable or ideal under all conditions, or for all types of surgery. A simple draw-over vaporizing apparatus, dependent on air for conveying the anaesthetic, does provide completely satisfactory anasthesia and even in the advanced state of modern anasthesia should be taught to all those training in the specialty. SUMMARY The successful use of ether-air anasthesia in lo00 cases using them0 Inhaler is reported. The advantages and disadvantages of the technique are reviewed and a plea is made for teaching the use of the apparatus to all anasthetists. References ISNOW, J. (1848). Lancet, I, 179 ~MACINTOSH, R.R. and MENDELSSOHN, K. (1941).Lancet, 2,61 3EPSTEIN, H.G. and MACINTOSH, R.R. (1956). Anesthesia, II,83 ICOLE, P.V. and PARKHOUSE, J. (1963). Postgrad. med. J., 39,476 5STEPHENS, K.F. (1958). Jl. R. Army med. cps, 104,159 P COLE, P.V. and PARKHOUSE, J. (1961). Br. J. Ancesth., 33,265 IBOYAN, c. (1963). N. Y. St. J. Med., 63,829 ~GHOSE, R. (1964). Ethiopian med. J., 2,221 gprior, F.N. (1964).J. Christ. med. Ass. of India, Burms, Ceylon, 39,49 ~OO CONNOR, A.P. (1961). Zr. J.med. Sci., 421, 1 FARMAN AN, J.V. (1961). WestAfr. rned.j., 10, CASTRO, ~ ~ B. (1962). Proc. Asian and Australasian Congress of Anesthesiology, Manila 1 ~MAKLARY, E. (1964). Proc. 1st European Congress of Anesthesiology, Vienna, ,154 ~~LAU, L.F. (1964). W. Indian med. J., 1412

9 512 ANBSTHESIA Vol21 lsparkhouse, J. (1960). Der AnUesfhesiSt, 9, TEMMERMAN, ~ ~ P. (1960). Acta belg. Antemed. Pharm. milit., 113,131 17Editorial. (1959). Anesthesia, 14,111 ~*BOULTON, T.B. and COLE, P.V. (1966). Anresthesia, 21,268 19BOULTON, T.B. and COLE, P.V. (1966). Annsthesia, 21,379 ~ORUBEN, H. (1955). Anesthesiology, 16,643 CLEMENTSE SEN, H. J. (1963). Br.med. J.,2,1409 ~~WEITZNER, s.w., KING, B.D. and IKEZONO, E. (1959). Anesthesiology, 20, 624 Z3IKEZONO, E., HARMEL, M. H. and KING, B.D. (1959). Anesthesiology, 20,597 24HOLMES, C. MCK. (1965). Anesthesia, 20,199 25MITCHELL, J.V. (1952). Anesthesia, 7,258 ~~MACINTOSH, R.R. (1955). Br. med. J., 2,1054 Z7POPPELBAUM, H.F. (1960). PrOC. R. SOC. Med., 53,289 HA HART, S.M. and BRYCE-SMITH, R. (1963). Anesthesia, 18,311