Possible causes of prolonged apnœa / by W.D.M. Paton.

  • William Paton
Date:
[1958]
Catalogue details

Licence: In copyright

Credit: Possible causes of prolonged apnœa / by W.D.M. Paton. Source: Wellcome Collection.

    3/30 page 254
    as anaesthesia has become increasingly skilful and increasingly safe, steadily poorer risk patients come under treatment. Under these circumstances, patients whose survival is in question, whatever is done or not done, must inevitably come to receive anaesthesia. Such cases are obviously very unsuitable for studying the normal risk of an anaesthetic procedure. In particular it seems unprofitable to use cases, whose survival is anyway in peril, as evidence about the nature of action of, say, muscle relaxants, just as no pharmacologist should use a moribund animal to analyse the normal action of drugs. Perhaps, indeed, one should take the question the other way; it might be worth¬ while to use the reaction to the anaesthetic procedure in seriously ill patients as an indication of what the threat to their life is. But for our immediate point I wish simply to suggest that any patient whose survival was in question before the operation began should be set in a category by himself in analysing the causes of prolonged apnoea. OVER-ANES THETIS ATI ON Next we must consider whether, even with ordinary practice, oc¬ casional patients might receive too much anaesthetic. Immediately one recalls that, with every drug, individuals vary in their response to it. For cardiac glycosides the range of doses which covers the majority of patients runs over a threefold range, say for digoxin, from 0.5mg in the sensitive to 1.5mg in the resistant for roughly equal effects. With sodium amytal anaesthesia, the range is wider - roughly from 5 to 25mg/kg, given by intravenous infusion12. Studies on variability in re¬ sponse to drugs have shown that in the main the distribution of sensi¬ tivities has the properties of a normal distribution; if the proportion reacting to a dose is plotted against the dose or the logarithm of the dose, one obtains one of the characteristic distribution curves. The implications of a distribution of sensitivity are far-reaching. In the first place, we must expect similar differences with the common anaes¬ thetics; and probably the range over which patients will distribute themselves in their reactions will be of the order of 3-4 fold. But there is a second point. The investigations of variability have usually been on groups of tens, possibly a hundred or so subjects. In relation to clinical practice these are tiny numbers. But if the groups are made much larger - say the sensitivity of one million subjects to thiopentone is studied - then we will expect to run into a number of extraordinary sensitivities, if the laws of distribution continue to operate. It is the same with tossing pennies; with any reasonable number of trials, say up to one hundred, more than six or seven heads in succession would be unlikely; but in 5,000 trials a series of fifteen heads could be ex¬ pected - and have indeed been observed. Similarly, for the situation when ninety-five out of a hundred patients come into a range of
    No text description is available for this image
    No text description is available for this image
    No text description is available for this image