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A COMPARISON OF THE ACUTE HAEMODYNAMIC EFFECTS OF THIOPENTONE, METHOHEXITONE AND PROPANIDID IN THE DOG
990
BRITISH JOURNAL OF ANAESTHESIA
Tunstall, M. E. (1963). Effect of cooling on pre-mixed gas mixtures for obstetric analgesia. Brit. med. J., 2, 915.
DENTALE ANASTHESIE DURCH A N W E N D U N G VORGEMISCHTER GASE
ANESTHESIE DENTAIRE AVEC DES GAZ PREALABLEMENT MELANGES
Eine klinische Prufung wird beschrieben, in deren Verlauf zahnarztlich verwendete Anasthetika verglichen werden, die entweder in Form von vorgemischten Gasen und Halothan oder mit dem konventionellen Narkoseapparat appliziert wurden, der mit einem kalibrierten Halothanzerstauber ausgeriistet ist und die Abgabe des Narkosemittels bei Bedarf erfolgt. Es wird demonstriert, dafi 50prozentige Mischungen von Stickoxydul und Sauerstoff die gleiche Wirkung besitzen wie Mischungen mit einem Gehalt von 20 Prozent Sauerstoff.
ZUSAMMENFASSUNG
SOMMAIRE
Description d'un essai clinique comparatif des anesthesiques administrcs dans la chaise dentaire sous forme d'un melange gazeux predetermind et d'autre part l'halothane et l'appareil usuel qui fournit les gaz a la demande. On demontre que des melanges a 50% de protoxyde d'azote et d'oxygene sont aussi efficaces que des melanges contenant 20% d'oxygene.
A COMPARISON OF THE ACUTE HAEMODYNAMIC EFFECTS OF THIOPENTONE, METHOHEXITONE AND PROPANIDID IN THE DOG
Sir,—It was a great sorrow to read the painstaking article by Drs. Conway, Ellis and King (Brit. J. Anaesth. (1968), 40, 736), because I believe that the authors used disproportionately large doses of propanidid to obtain their comparisons. I use propanidid for induction of anaesthesia almost exclusively, and agree with Clarke and associates (.Brit. J. Anaesth. (1968), 40, 593), that mg for mg it is only marginally less potent than thiopentone as a hypnotic for induction, i.e., 450 mg of thiopentone is equivalent to about 500 mg of propanidid. I'm sure that the formers' estimate, that 250 mg of thiopentone is equivalent to 500 mg of propanidid, is unrealistic and thus invalidates their carefully gleaned data. Also concerning propanidid, this agent has been said to prolong the action of suxamethonium, and to diminish the incidence of muscle pains following suxamethonium as compared with thiopentone and methohexitone. I would like to extend these observations to say that propanidid interferes with the action of suxamethonium as if it were a competitive inhibitor by delaying the onset of maximum relaxation due to n fixed dose of suxamethonium, by making the maximal effect of that dose of suxamethonium less profound, by diminishing the incidence and severity of muscle fasciculations and postoperative pains, and by potentiating the length of action of suxamethonium. Thus the undoubted value of propanidid as an induction agent is tarnished by this interference with the normal action of suxamethonium, rendering it a less than perfect induction agent in a known "difficult intubation" and in a patient in whom aspiration into the lungs is a real hazard. JOHN S.
MATHER
Birmingham Sir,—Dr. Mather's sorrows are well founded, but not for the reasons he states. The dose ratios of induction agents used in our study are of secondary importance, and in no way invalidate the data. Reference to figure 3
of our article would have shown Dr. Mather that, weight for weight, propanidid had 2.86 times the effect of thiopentone upon systolic pressure in our dogs, and this value would be applicable to the ratio of doses of these agents that he uses. In planning our study we were well aware of the different views held on the comparative potencies of these drugs as anaesthetic agents. The reasons for our choice of the dose ratios of agents used are fully discussed in our paper and do not need reiteration. That propanidid in the doses used had a much greater effect upon systolic pressure than the other agents only became apparent after the start of the trial. It must, however, be stressed that this in no way affects the validity of the comparison. The use of smaller doses of propanidid may have reduced the variance of the data and thus reduced the confidence limits of the dose response curves, but, assuming a linear log doseresponse curve, would have led to identical comparative results. Dr. Mather's letter continues with a number of ambiguously worded, totally unsubstantiated, and in part mutually exclusive statements, none of which are relevant to our paper. Unsupported statements and clinical impressions are no substitute for careful observation and controlled trials: Dr. Mather should have quoted his evidence when presenting his unorthodox V1CWS
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C. M. CONWAY D. N.
B. E I X I S W. KING
London ACKNOWLEDGEMENT
Sir,— I regret that in the two papers by Miss Helen W. Y. Hooi and myself on aspects of drug-binding, which appeared in the October and November issues of the Journal (pp. 723 and 825), I inadvertently failed to acknowledge the handsome financial assistance provid:d by the Sir Halley Stewart Trust. Please allow me, therefore, to repair that omission herewith, and to express our gratitude to the Trust for their very valuable aid. J. SELWYN CRAWFORD
Birmingham
Downloaded from http://bja.oxfordjournals.org/ at University of Victoria on August 27, 2015
CORRESPONDENCE
BRITISH JOURNAL OF ANAESTHESIA
Tunstall, M. E. (1963). Effect of cooling on pre-mixed gas mixtures for obstetric analgesia. Brit. med. J., 2, 915.
DENTALE ANASTHESIE DURCH A N W E N D U N G VORGEMISCHTER GASE
ANESTHESIE DENTAIRE AVEC DES GAZ PREALABLEMENT MELANGES
Eine klinische Prufung wird beschrieben, in deren Verlauf zahnarztlich verwendete Anasthetika verglichen werden, die entweder in Form von vorgemischten Gasen und Halothan oder mit dem konventionellen Narkoseapparat appliziert wurden, der mit einem kalibrierten Halothanzerstauber ausgeriistet ist und die Abgabe des Narkosemittels bei Bedarf erfolgt. Es wird demonstriert, dafi 50prozentige Mischungen von Stickoxydul und Sauerstoff die gleiche Wirkung besitzen wie Mischungen mit einem Gehalt von 20 Prozent Sauerstoff.
ZUSAMMENFASSUNG
SOMMAIRE
Description d'un essai clinique comparatif des anesthesiques administrcs dans la chaise dentaire sous forme d'un melange gazeux predetermind et d'autre part l'halothane et l'appareil usuel qui fournit les gaz a la demande. On demontre que des melanges a 50% de protoxyde d'azote et d'oxygene sont aussi efficaces que des melanges contenant 20% d'oxygene.
A COMPARISON OF THE ACUTE HAEMODYNAMIC EFFECTS OF THIOPENTONE, METHOHEXITONE AND PROPANIDID IN THE DOG
Sir,—It was a great sorrow to read the painstaking article by Drs. Conway, Ellis and King (Brit. J. Anaesth. (1968), 40, 736), because I believe that the authors used disproportionately large doses of propanidid to obtain their comparisons. I use propanidid for induction of anaesthesia almost exclusively, and agree with Clarke and associates (.Brit. J. Anaesth. (1968), 40, 593), that mg for mg it is only marginally less potent than thiopentone as a hypnotic for induction, i.e., 450 mg of thiopentone is equivalent to about 500 mg of propanidid. I'm sure that the formers' estimate, that 250 mg of thiopentone is equivalent to 500 mg of propanidid, is unrealistic and thus invalidates their carefully gleaned data. Also concerning propanidid, this agent has been said to prolong the action of suxamethonium, and to diminish the incidence of muscle pains following suxamethonium as compared with thiopentone and methohexitone. I would like to extend these observations to say that propanidid interferes with the action of suxamethonium as if it were a competitive inhibitor by delaying the onset of maximum relaxation due to n fixed dose of suxamethonium, by making the maximal effect of that dose of suxamethonium less profound, by diminishing the incidence and severity of muscle fasciculations and postoperative pains, and by potentiating the length of action of suxamethonium. Thus the undoubted value of propanidid as an induction agent is tarnished by this interference with the normal action of suxamethonium, rendering it a less than perfect induction agent in a known "difficult intubation" and in a patient in whom aspiration into the lungs is a real hazard. JOHN S.
MATHER
Birmingham Sir,—Dr. Mather's sorrows are well founded, but not for the reasons he states. The dose ratios of induction agents used in our study are of secondary importance, and in no way invalidate the data. Reference to figure 3
of our article would have shown Dr. Mather that, weight for weight, propanidid had 2.86 times the effect of thiopentone upon systolic pressure in our dogs, and this value would be applicable to the ratio of doses of these agents that he uses. In planning our study we were well aware of the different views held on the comparative potencies of these drugs as anaesthetic agents. The reasons for our choice of the dose ratios of agents used are fully discussed in our paper and do not need reiteration. That propanidid in the doses used had a much greater effect upon systolic pressure than the other agents only became apparent after the start of the trial. It must, however, be stressed that this in no way affects the validity of the comparison. The use of smaller doses of propanidid may have reduced the variance of the data and thus reduced the confidence limits of the dose response curves, but, assuming a linear log doseresponse curve, would have led to identical comparative results. Dr. Mather's letter continues with a number of ambiguously worded, totally unsubstantiated, and in part mutually exclusive statements, none of which are relevant to our paper. Unsupported statements and clinical impressions are no substitute for careful observation and controlled trials: Dr. Mather should have quoted his evidence when presenting his unorthodox V1CWS
-
C. M. CONWAY D. N.
B. E I X I S W. KING
London ACKNOWLEDGEMENT
Sir,— I regret that in the two papers by Miss Helen W. Y. Hooi and myself on aspects of drug-binding, which appeared in the October and November issues of the Journal (pp. 723 and 825), I inadvertently failed to acknowledge the handsome financial assistance provid:d by the Sir Halley Stewart Trust. Please allow me, therefore, to repair that omission herewith, and to express our gratitude to the Trust for their very valuable aid. J. SELWYN CRAWFORD
Birmingham
Downloaded from http://bja.oxfordjournals.org/ at University of Victoria on August 27, 2015
CORRESPONDENCE