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MATERNAL AWARENESS
Br.J. Anaesth. (1986), 58, 1198-1208
CORRESPONDENCE
C. E. BLOGG J. EDMUNDS-SEAL
Oxford D. BKIGHOUSE P. I. E. JONES
London F. P. BUCKLEY
Washington, U.S.A. D. M. JACKSON
Swindon M. STYLES
Northampton
REFERENCES Crawford, J. S., James, F. M. in, Davies, P., and Crawley, M. (1976). A further study of general anaesthesia for Caesarean section. Br.J. Anaesth., 48, 661. Lewis, M., and Davies, P. (1985). Maternal and neonatal responses related to the volatile agent used to maintain anaesthesia at Caesarean section. Br. J. Anaesth., 57, 482. Moir, D. D. (1970). Anaesthesia for Caesarean section. Evaluation of a method using low concentrations of halothane and 50% oxygen. Br. J. Anaesth., 42, 136. Tunstall, M. E. (1979). The reduction of amnesic wakefulness during Caesarean section Anaesthesia, 34, 674. (1980). On being aware by request. Br. J. Anaesth., 52, 1049. Sir,—Thank you for the opportunity to reply to this splendidly spirited letter. As your correspondents will certainly know, during the past several decades a multitude of studies have been undertaken in an attempt to define a technique of general anaesthesia for Caesarean section which will provide for safety and—if possible—comfort for the mother whilst guarding against any observable degree of drug-induced neonatal depression. My own efforts in this field have resulted in at least six successive "refinements" of a basic technique. Examination of the potential value of each refinement has usually been conducted— I believe advisably— in the mode of a comparison with the previously adopted technique. Such was the procedure in the study to which Dr Blogg and his colleagues have taken exception. I re-iterate that we are interested in the condition of both mother and infant. It is only in very recent years that many obstetric anaesthetists (including myself) have begun to form the opinion that, in certainly the great majority of cases, a slight and probably evanescent degree of neonatal depression caused by the transplacental accretion of a volatile anaesthetic agent is of virtually no consequence to the well-being of that infant, and that thus the elimination, as far as is possible, of maternal discomfort should be the more important objective. Incidentally, it is worth recording that, internationally, many neonatologists do not accept the former contention. Our objective in this study was thus to determine whether or not, by providing a higher concentration of the volatile agent, we could reduce significantly the previously encountered incidence of "maternal awareness plus unpleasant dreams" (which wat, by the way, 2.5% among the total group of mothers given 0.2% trichloroethylene) without promoting an unacceptable increase in the incidence of drug-induced neonatal depression. In our previous study (Crawford et al., 1976) to which your correspondents refer, we compared the use of 0.1 % trichloroethylene (which, before the start of the investigation had, for some time, been our standard choice) with that of the 0.2% concentration. As a m u l t of that investigation the use of 0.2% became our routine. When the study under review was designed, we chose to include, in randomized fashion, the
Downloaded from http://bja.oxfordjournals.org/ at Ryerson University on September 8, 2015
MATERNAL AWARENESS Sir,—The recent account of maternal and neonatal responses by Crawford, Lewis and Davies (1985) cannot be allowed to pass unchallenged. An open study is reported of 777 mothers who were, prospectively and randomly, given various concentrations of trichloroethylene (0.2 or 0.3%) or halothane (0.2, 0.3, 0.4 or 0.5%) in nitrous oxide 4 litre min~> and oxygen 8 litre min"1 "to maintain anaesthesia (the term coined by Oliver Wendell Holmes for the state of " insensibility ") at Caesarean section ". The authors have previously demonstrated (Crawford et al., 1976) that low concentrations of inhalation agents under similar circumstances carry an appreciable incidence (5%) of unpleasant awareness. In this study, the use of 0.2% trichloroethylene (even in 40% nitrous oxide) is difficult to justify (9.6% aware) when trichloroethylene was approved by the Central Midwives' Board, to be used in higher concentrations in air by awake patients in labour. Similarly, it appears unwarranted to use very low concentrations of halothane when 0.4 % halothane in 33 % nitrous oxide can result in awareness (Tunstall, 1980), and 0.5% halothane had been shown 15 years previously to be safe and not to be associated with recall (Moir, 1970). The likelihood of awareness was apparently not even considered until the day following operation, although patients in the lowest concentration groups required considerably greater total doses of suxamethonium—indicative of the possibility of the horrific combination of paralysit with awareness. On the following day the patients were initially merely asked if they had had any dreams during the operation, this despite methods being available for many years to determine, at the time of operation, whether the patient is experiencing wakefulness (Tunstall, 1979). Other aspects of this study are equally disquieting: no local ethics committee approval was sought; informed consent was not obtained. There is nothing to suggest that these patients were made to understand that many of them stood a considerable chance of awareness. The authors admit to conducting an open study in which the incidence of awareness plus unpleasant dreams was unacceptably high, but it should not have taken 26 of 264 patients to demonstrate that awareness is unacceptable when concentrations (0.4-0.5 %) of halothane sufficient to reduce wakefulness to justifiable levels do not carry undue hazard. Publication of such a report does credit only to the fortitude of the patients.
CORRESPONDENCE
C. E. BLOGG J. EDMUNDS-SEAL
Oxford D. BKIGHOUSE P. I. E. JONES
London F. P. BUCKLEY
Washington, U.S.A. D. M. JACKSON
Swindon M. STYLES
Northampton
REFERENCES Crawford, J. S., James, F. M. in, Davies, P., and Crawley, M. (1976). A further study of general anaesthesia for Caesarean section. Br.J. Anaesth., 48, 661. Lewis, M., and Davies, P. (1985). Maternal and neonatal responses related to the volatile agent used to maintain anaesthesia at Caesarean section. Br. J. Anaesth., 57, 482. Moir, D. D. (1970). Anaesthesia for Caesarean section. Evaluation of a method using low concentrations of halothane and 50% oxygen. Br. J. Anaesth., 42, 136. Tunstall, M. E. (1979). The reduction of amnesic wakefulness during Caesarean section Anaesthesia, 34, 674. (1980). On being aware by request. Br. J. Anaesth., 52, 1049. Sir,—Thank you for the opportunity to reply to this splendidly spirited letter. As your correspondents will certainly know, during the past several decades a multitude of studies have been undertaken in an attempt to define a technique of general anaesthesia for Caesarean section which will provide for safety and—if possible—comfort for the mother whilst guarding against any observable degree of drug-induced neonatal depression. My own efforts in this field have resulted in at least six successive "refinements" of a basic technique. Examination of the potential value of each refinement has usually been conducted— I believe advisably— in the mode of a comparison with the previously adopted technique. Such was the procedure in the study to which Dr Blogg and his colleagues have taken exception. I re-iterate that we are interested in the condition of both mother and infant. It is only in very recent years that many obstetric anaesthetists (including myself) have begun to form the opinion that, in certainly the great majority of cases, a slight and probably evanescent degree of neonatal depression caused by the transplacental accretion of a volatile anaesthetic agent is of virtually no consequence to the well-being of that infant, and that thus the elimination, as far as is possible, of maternal discomfort should be the more important objective. Incidentally, it is worth recording that, internationally, many neonatologists do not accept the former contention. Our objective in this study was thus to determine whether or not, by providing a higher concentration of the volatile agent, we could reduce significantly the previously encountered incidence of "maternal awareness plus unpleasant dreams" (which wat, by the way, 2.5% among the total group of mothers given 0.2% trichloroethylene) without promoting an unacceptable increase in the incidence of drug-induced neonatal depression. In our previous study (Crawford et al., 1976) to which your correspondents refer, we compared the use of 0.1 % trichloroethylene (which, before the start of the investigation had, for some time, been our standard choice) with that of the 0.2% concentration. As a m u l t of that investigation the use of 0.2% became our routine. When the study under review was designed, we chose to include, in randomized fashion, the
Downloaded from http://bja.oxfordjournals.org/ at Ryerson University on September 8, 2015
MATERNAL AWARENESS Sir,—The recent account of maternal and neonatal responses by Crawford, Lewis and Davies (1985) cannot be allowed to pass unchallenged. An open study is reported of 777 mothers who were, prospectively and randomly, given various concentrations of trichloroethylene (0.2 or 0.3%) or halothane (0.2, 0.3, 0.4 or 0.5%) in nitrous oxide 4 litre min~> and oxygen 8 litre min"1 "to maintain anaesthesia (the term coined by Oliver Wendell Holmes for the state of " insensibility ") at Caesarean section ". The authors have previously demonstrated (Crawford et al., 1976) that low concentrations of inhalation agents under similar circumstances carry an appreciable incidence (5%) of unpleasant awareness. In this study, the use of 0.2% trichloroethylene (even in 40% nitrous oxide) is difficult to justify (9.6% aware) when trichloroethylene was approved by the Central Midwives' Board, to be used in higher concentrations in air by awake patients in labour. Similarly, it appears unwarranted to use very low concentrations of halothane when 0.4 % halothane in 33 % nitrous oxide can result in awareness (Tunstall, 1980), and 0.5% halothane had been shown 15 years previously to be safe and not to be associated with recall (Moir, 1970). The likelihood of awareness was apparently not even considered until the day following operation, although patients in the lowest concentration groups required considerably greater total doses of suxamethonium—indicative of the possibility of the horrific combination of paralysit with awareness. On the following day the patients were initially merely asked if they had had any dreams during the operation, this despite methods being available for many years to determine, at the time of operation, whether the patient is experiencing wakefulness (Tunstall, 1979). Other aspects of this study are equally disquieting: no local ethics committee approval was sought; informed consent was not obtained. There is nothing to suggest that these patients were made to understand that many of them stood a considerable chance of awareness. The authors admit to conducting an open study in which the incidence of awareness plus unpleasant dreams was unacceptably high, but it should not have taken 26 of 264 patients to demonstrate that awareness is unacceptable when concentrations (0.4-0.5 %) of halothane sufficient to reduce wakefulness to justifiable levels do not carry undue hazard. Publication of such a report does credit only to the fortitude of the patients.