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EXTRADURAL ANAESTHESIA IN THE PIG
A TEST OF TWO TYPES OF HALOTHANE VAPORIZER concentration pourrait atteindre 5%, serait utile. Et nous estimons igalement qu'il est inutile, pour la pratique dinique, de poss6der un appareil capable de faire varier la concentration par petites quantites exactement ddterminees: ce serait un luxe inutile et oneieux, pratiquement irrealisable et qui presente le danger, en theorie, de surdosages accidentels massifs. ZWEI
TYPEN
VON HALOTHAN-VERDAMPFERN IM TEST ZUSAMMENFASSUNG
es sich urn ein einfaches, kleines und als Verdampfer ungeniigendes GeraL Der andere Verdampfer ist relativ grofi, kompliziert und aufierordentlich wirksam. Es wird behauptet, daO Bedarf fur eine abgewandelte Version der einfachen Type, mit dem Dampfkonzentrationen bis zu 5 Prozent erzeugt werden konnen, besteht. Es wird weiterhin behauptet, dafi es fur die klinische Praxis nicht erforderlich ist, in der Lage zu sein, die Konzentxationen urn sehr genau bekannte kleine Mengen zu variieren. Die Erzielung solcher Genauigkeit ist ein kostspeiliger und unnotiger Luxus ohne Wert fur die Praxis, und in theoretischer Hinsicht besteht die Gefahr einer unbeabsichtigten Verabfolgung einer erheblichen Doerdosis.
CORRESPONDENCE EXTRADURAL ANAESTHESIA IN THE PIG
Sir,—I read with considerable interest the paper by Dr. Hopcroft on this subject (Brit. J. Anaeuh., 37, 982) but was rather surprised to find no reference to original work on this technique. It is suggested that anaesthesia is a great problem in the pig but no reference is made to the paper by Dawson on the use of halothane anaesthesia in the experimental pig. The technique of epidural anaesthesia is well documented and well known. Two classic papers have appeared in the veterinary literature in the 1930s by Brook and Wright. It is interesting to note that Dr. Hopcroft was able to produce sedation in the pigs with such small doses of pentobarbitone and chlorpromazine. Ritchie has shown that there is a wide variation in response to pentobarbitone sodium and the dose required to produce general anaesthesia in his series of pigs varied from 9 to 56 mg/kg. In view of the fact that a potentially hypotensive drug, chlorpromazine, was used for premedication and a 2 per cent solution of plain lignocaine was employed, it is interesting to note that hypotension did not apparently prove to be a major hazard during surgery. The technique of anterior vena cava puncture which was originally described by Carle and Dewhurst and more recendy by Mackenzie is an extremely useful one which has been used in this department for a number of years. Our experience differs from that of Dr. Hopcroft in that the wall of the vein has been found to be thin-walled and we have never been able to detect a "popping" sensation, although we do, however, keep a syringe attached to the needle and employ a "negative" pressure as soon as the skin has been penetrated. It is not our experience or that of a number of veterinary anaesthetists in this country that respiratory complications are common after anaesthesia and surgery, possibly due to the fact diat our animak are able to walk fairly soon after discontinuing the administration of the volatile anaesthetic agent and antibiotics are administered as a routine. RONAIJD S. JONES
Leahurst REFERENCES
Brook, G. B. (1935). Spinal (epidural) anaesthesia in domestic animals. Vet. rec, 15, 631.
Carle, B. N., and Dewhurst, W. H. (1942). A method for bleeding swine. J. Amer. vet. med. Ass., 101, 495. Dawson, J. B. (1963). Anaesthesia for the experimental pig. Brit. J. Anaeslh., 35, 736. Mackenzie, A. (1961). Observations on anterior vena cava venepuncture in the pig. Vet. Rec, 73, 895. Ritchie, H. E. (1957). Chlorpromazine: sedation in the pig. Vet. Rec, 69, 895. Wright, J. G. (1939). Spinal (epidural) anaesthesia in the pig. J. com. Path., 52, 1. A copy of Dr. Jones's letter was sent to Dr. Hopcroft, who replied as follows: Sir,—I would like to thank Mr. R. S. Jones for his letter criticizing my paper "Extradural Anaesthesia in the Pig" (Brit. J. Anaeslh., 37, 982). Epidural anaesthesia has been developed in the pig specially in these laboratories to allow renal exposure and operation. In earlier reports it is used only for castration or operation around the hindquarters. We always produce complete motor paralysis and loss of sensation which is not a feature of earlier reports. One of the reasons why we have been so successful in sedating our experimental pigs with such small doses of barbiturates and chlorpromazine is probably due to the fact that these drugs have a very great synergistic effect, and although there is great variation in using each drug singly this variation diminishes when the combination is used I realize that the method developed by Dawson mentioned in your letter exists and am equally sure that it must be very good, but bear in mind the fact that we often perfuse our pigs for several hours. The use of a potentially toxic volatile anaesthetic for such procedures could hardly be considered. In this method when the anaesthetic is given one can forget about it and go on with the experiment. I have given an exact method and description of the anatomy of the area. The earlier reports are concerned with the collection of blood from pigs albeit arterial or venous. I have used the method myself for collecting blood and can say that in a proportion of cases the bicarotid trunk is punctured and arterial blood collected. We have in fact used the bicarotid trunk to cannulate for the purpose of collecting arterial blood samples or intra-arterial perfusion. To do this the needle is
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 22, 2015
Es wurden zwei verschiedene Typen von HalothanVerdampfern verglichen. Bei dem einen handelt
497
498
BRITISH JOURNAL OF ANAESTHESIA
S. C. HOPCROFT
WoodvUle, South Australia
which they occur. I stated quite clearly that "full evaluation . . . must await a more extensive investigation" (1966), and this view has merely been repeated in his letter by Professor Dobkin. It is doubtful whether it would be possible to prove anything very convincing in this field from a study of ten patients, however well controlled. At the most this might yield suggestive evidence that, similarly to that obtained from my study of thirty-five patients, would need to be examined in the light Gf a more extensive investigation. Incidentally, the inference (not assumption) drawn in my paper was not that nitrous oxide has some influence on halothane anaesthesia, but that nitrous oxide per se might produce the changes observed in this study, independently of the action of halothane (or ether, methoxyflurane or trichloroethylene). MAURICE BLOCH
SYSTEMIC EFFECTS OF NITROUS OXIDE WHEN USED WITH HALOTHANE AND OXYGEN ANAESTHESIA AT NORMAL BODY TEMPERATURE
Sir,—In the paper by Dr. Maurice Bloch (Brit. J. Anaesth. (1966), 38, 119) the assumption that nitrous oxide has some influence on halothane anaesthesia would be hard to question, but the data he presented are totally unacceptable as evidence for proving this point, in my opinion. The number of variables interspersed among the few patients he used for his observations preclude drawing valid conclusions. If he re-did this study, even with ten patients of a similar age group, same sex, same premedication and induction agents, no relaxants and same maintenance (in a non-rebreathing system) he might be able to prove what he believes to be true. ALLEN B.
DOBKIN
Syracuse, New York The above letter was forwarded to Dr. Bloch, who replied as follows: Sir,—Thank you for permitting me to see Professor Dobkin's letter. My two papers on nitrous oxide refer to observations made in the absence of surgery, at normal and at reduced body temperature (Brit. J. Anaesth. (1963), 35, 631), and during thirty-five routine operations pirformed at normal body temperature (Brit. J. Anaesth. (1966), 38, 119). In a proportion of patients increase in concentration of nitrous oxide in the inspired gas mixture was followed by decrease in arterial pressure, heart rate and tidal volume, and increase in respiratory rate. These changes became reversed following withdrawal of nitrous oxide, whether the latter was replaced by air or by oxygen (1963). Oxygen concentration did not fall below 70-80 per cent at any time during anaesthesia. These were observed events. They are not assumptions, and I suggest Professor Dobkin would be hard put not to accept them as evidence that nitrous oxide has "some influence" on halothane anaesthesia, whatever the coincidental variables. It must be obvious, the observations having once been made, that they must be compared with the results of an extensive and rigidly controlled study in order to confirm them, to understand how these effects are brought about, and to establish the frequency with
London THE CHARLES KING COLLECTION OF HISTORICAL ANAESTHETIC APPARATUS
Sir,—The Association of Anaesthetists has done me the honour of appointment as Curator of the Charles King Collection of historical anaesthetic apparatus which Mr. King presented to the Association some years ago, and which now is housed in the Royal College of Surgeons of England, through the courtesy of the President and Council, and of the Curator of Instruments, Sir Eric Riches. This is a fine basic collection of antique apparatus, supplemented by several beautiful replicas (for instance, John Snow's ether apparatus) made by Charles King himself. I feel that the time is opportune to ask anaesthetists not to discard any older anaesthetic apparatus without first considering its historical value. The rebuilding of hospitals and removal of anaesthetic departments with clearance of old stores make it likely that much which may be valuable and interesting will come to light, and I would urge senior anaesthetists either to establish their own collections for teaching purposes, or to consider donation of suitable material to supplement the King Collection. Needless to say, considerations of display and storage space may make it difficult to accept larger apparatus, but I should be most grateful to hear of any pieces which might be available and which might otherwise be destroyed. Items of any period, even to modern times, would be welcome, even though it might be n;cessary to store them for some time. All members of the specialty will have heard with regret of the recent death of Charles A. King, to whom anaesthesia in this country owes a larger debt than many anaesthetists realize. One can only be sorry that he did not live to see his collection housed in the way he intended, but I am sure that with this as a nucleus, and with the help of anaesthetists everywhere, the collection can be increased to be a worthwhile possession of the Association, and a tribute to the memory of the friendly, courteous and gifted gendeman who commenced it. K. BRYN THOMAS
Primed in Great Briuin by John Sberntt & Son Ltd.. Park Rotd. Ahrlncham
Reading
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 22, 2015
driven in until it strikes the trachea, it is then withdrawn 0.5 cm and directed in the same direction as the trachea. Figure 3 in the article makes this point easier to follow. It is possible then to have a bicarotid and a superior vena caval cannula in the one animal. I am interested to hear that little postoperative respiratory trouble occurs in experimental pigs in England. This is probably related to better husbandry in that country. Most of our pigs are purchased from farms outside our establishment; this means, of course, that we have no control of parisitism, endemic infections, etc. The use of non-volatile anaesthetic becomes more important under these conditions.
TYPEN
VON HALOTHAN-VERDAMPFERN IM TEST ZUSAMMENFASSUNG
es sich urn ein einfaches, kleines und als Verdampfer ungeniigendes GeraL Der andere Verdampfer ist relativ grofi, kompliziert und aufierordentlich wirksam. Es wird behauptet, daO Bedarf fur eine abgewandelte Version der einfachen Type, mit dem Dampfkonzentrationen bis zu 5 Prozent erzeugt werden konnen, besteht. Es wird weiterhin behauptet, dafi es fur die klinische Praxis nicht erforderlich ist, in der Lage zu sein, die Konzentxationen urn sehr genau bekannte kleine Mengen zu variieren. Die Erzielung solcher Genauigkeit ist ein kostspeiliger und unnotiger Luxus ohne Wert fur die Praxis, und in theoretischer Hinsicht besteht die Gefahr einer unbeabsichtigten Verabfolgung einer erheblichen Doerdosis.
CORRESPONDENCE EXTRADURAL ANAESTHESIA IN THE PIG
Sir,—I read with considerable interest the paper by Dr. Hopcroft on this subject (Brit. J. Anaeuh., 37, 982) but was rather surprised to find no reference to original work on this technique. It is suggested that anaesthesia is a great problem in the pig but no reference is made to the paper by Dawson on the use of halothane anaesthesia in the experimental pig. The technique of epidural anaesthesia is well documented and well known. Two classic papers have appeared in the veterinary literature in the 1930s by Brook and Wright. It is interesting to note that Dr. Hopcroft was able to produce sedation in the pigs with such small doses of pentobarbitone and chlorpromazine. Ritchie has shown that there is a wide variation in response to pentobarbitone sodium and the dose required to produce general anaesthesia in his series of pigs varied from 9 to 56 mg/kg. In view of the fact that a potentially hypotensive drug, chlorpromazine, was used for premedication and a 2 per cent solution of plain lignocaine was employed, it is interesting to note that hypotension did not apparently prove to be a major hazard during surgery. The technique of anterior vena cava puncture which was originally described by Carle and Dewhurst and more recendy by Mackenzie is an extremely useful one which has been used in this department for a number of years. Our experience differs from that of Dr. Hopcroft in that the wall of the vein has been found to be thin-walled and we have never been able to detect a "popping" sensation, although we do, however, keep a syringe attached to the needle and employ a "negative" pressure as soon as the skin has been penetrated. It is not our experience or that of a number of veterinary anaesthetists in this country that respiratory complications are common after anaesthesia and surgery, possibly due to the fact diat our animak are able to walk fairly soon after discontinuing the administration of the volatile anaesthetic agent and antibiotics are administered as a routine. RONAIJD S. JONES
Leahurst REFERENCES
Brook, G. B. (1935). Spinal (epidural) anaesthesia in domestic animals. Vet. rec, 15, 631.
Carle, B. N., and Dewhurst, W. H. (1942). A method for bleeding swine. J. Amer. vet. med. Ass., 101, 495. Dawson, J. B. (1963). Anaesthesia for the experimental pig. Brit. J. Anaeslh., 35, 736. Mackenzie, A. (1961). Observations on anterior vena cava venepuncture in the pig. Vet. Rec, 73, 895. Ritchie, H. E. (1957). Chlorpromazine: sedation in the pig. Vet. Rec, 69, 895. Wright, J. G. (1939). Spinal (epidural) anaesthesia in the pig. J. com. Path., 52, 1. A copy of Dr. Jones's letter was sent to Dr. Hopcroft, who replied as follows: Sir,—I would like to thank Mr. R. S. Jones for his letter criticizing my paper "Extradural Anaesthesia in the Pig" (Brit. J. Anaeslh., 37, 982). Epidural anaesthesia has been developed in the pig specially in these laboratories to allow renal exposure and operation. In earlier reports it is used only for castration or operation around the hindquarters. We always produce complete motor paralysis and loss of sensation which is not a feature of earlier reports. One of the reasons why we have been so successful in sedating our experimental pigs with such small doses of barbiturates and chlorpromazine is probably due to the fact that these drugs have a very great synergistic effect, and although there is great variation in using each drug singly this variation diminishes when the combination is used I realize that the method developed by Dawson mentioned in your letter exists and am equally sure that it must be very good, but bear in mind the fact that we often perfuse our pigs for several hours. The use of a potentially toxic volatile anaesthetic for such procedures could hardly be considered. In this method when the anaesthetic is given one can forget about it and go on with the experiment. I have given an exact method and description of the anatomy of the area. The earlier reports are concerned with the collection of blood from pigs albeit arterial or venous. I have used the method myself for collecting blood and can say that in a proportion of cases the bicarotid trunk is punctured and arterial blood collected. We have in fact used the bicarotid trunk to cannulate for the purpose of collecting arterial blood samples or intra-arterial perfusion. To do this the needle is
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 22, 2015
Es wurden zwei verschiedene Typen von HalothanVerdampfern verglichen. Bei dem einen handelt
497
498
BRITISH JOURNAL OF ANAESTHESIA
S. C. HOPCROFT
WoodvUle, South Australia
which they occur. I stated quite clearly that "full evaluation . . . must await a more extensive investigation" (1966), and this view has merely been repeated in his letter by Professor Dobkin. It is doubtful whether it would be possible to prove anything very convincing in this field from a study of ten patients, however well controlled. At the most this might yield suggestive evidence that, similarly to that obtained from my study of thirty-five patients, would need to be examined in the light Gf a more extensive investigation. Incidentally, the inference (not assumption) drawn in my paper was not that nitrous oxide has some influence on halothane anaesthesia, but that nitrous oxide per se might produce the changes observed in this study, independently of the action of halothane (or ether, methoxyflurane or trichloroethylene). MAURICE BLOCH
SYSTEMIC EFFECTS OF NITROUS OXIDE WHEN USED WITH HALOTHANE AND OXYGEN ANAESTHESIA AT NORMAL BODY TEMPERATURE
Sir,—In the paper by Dr. Maurice Bloch (Brit. J. Anaesth. (1966), 38, 119) the assumption that nitrous oxide has some influence on halothane anaesthesia would be hard to question, but the data he presented are totally unacceptable as evidence for proving this point, in my opinion. The number of variables interspersed among the few patients he used for his observations preclude drawing valid conclusions. If he re-did this study, even with ten patients of a similar age group, same sex, same premedication and induction agents, no relaxants and same maintenance (in a non-rebreathing system) he might be able to prove what he believes to be true. ALLEN B.
DOBKIN
Syracuse, New York The above letter was forwarded to Dr. Bloch, who replied as follows: Sir,—Thank you for permitting me to see Professor Dobkin's letter. My two papers on nitrous oxide refer to observations made in the absence of surgery, at normal and at reduced body temperature (Brit. J. Anaesth. (1963), 35, 631), and during thirty-five routine operations pirformed at normal body temperature (Brit. J. Anaesth. (1966), 38, 119). In a proportion of patients increase in concentration of nitrous oxide in the inspired gas mixture was followed by decrease in arterial pressure, heart rate and tidal volume, and increase in respiratory rate. These changes became reversed following withdrawal of nitrous oxide, whether the latter was replaced by air or by oxygen (1963). Oxygen concentration did not fall below 70-80 per cent at any time during anaesthesia. These were observed events. They are not assumptions, and I suggest Professor Dobkin would be hard put not to accept them as evidence that nitrous oxide has "some influence" on halothane anaesthesia, whatever the coincidental variables. It must be obvious, the observations having once been made, that they must be compared with the results of an extensive and rigidly controlled study in order to confirm them, to understand how these effects are brought about, and to establish the frequency with
London THE CHARLES KING COLLECTION OF HISTORICAL ANAESTHETIC APPARATUS
Sir,—The Association of Anaesthetists has done me the honour of appointment as Curator of the Charles King Collection of historical anaesthetic apparatus which Mr. King presented to the Association some years ago, and which now is housed in the Royal College of Surgeons of England, through the courtesy of the President and Council, and of the Curator of Instruments, Sir Eric Riches. This is a fine basic collection of antique apparatus, supplemented by several beautiful replicas (for instance, John Snow's ether apparatus) made by Charles King himself. I feel that the time is opportune to ask anaesthetists not to discard any older anaesthetic apparatus without first considering its historical value. The rebuilding of hospitals and removal of anaesthetic departments with clearance of old stores make it likely that much which may be valuable and interesting will come to light, and I would urge senior anaesthetists either to establish their own collections for teaching purposes, or to consider donation of suitable material to supplement the King Collection. Needless to say, considerations of display and storage space may make it difficult to accept larger apparatus, but I should be most grateful to hear of any pieces which might be available and which might otherwise be destroyed. Items of any period, even to modern times, would be welcome, even though it might be n;cessary to store them for some time. All members of the specialty will have heard with regret of the recent death of Charles A. King, to whom anaesthesia in this country owes a larger debt than many anaesthetists realize. One can only be sorry that he did not live to see his collection housed in the way he intended, but I am sure that with this as a nucleus, and with the help of anaesthetists everywhere, the collection can be increased to be a worthwhile possession of the Association, and a tribute to the memory of the friendly, courteous and gifted gendeman who commenced it. K. BRYN THOMAS
Primed in Great Briuin by John Sberntt & Son Ltd.. Park Rotd. Ahrlncham
Reading
Downloaded from http://bja.oxfordjournals.org/ at The University of British Colombia Library on June 22, 2015
driven in until it strikes the trachea, it is then withdrawn 0.5 cm and directed in the same direction as the trachea. Figure 3 in the article makes this point easier to follow. It is possible then to have a bicarotid and a superior vena caval cannula in the one animal. I am interested to hear that little postoperative respiratory trouble occurs in experimental pigs in England. This is probably related to better husbandry in that country. Most of our pigs are purchased from farms outside our establishment; this means, of course, that we have no control of parisitism, endemic infections, etc. The use of non-volatile anaesthetic becomes more important under these conditions.