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.

    7/30 page 256
    dioxide is rather readily abolished; and with fairly deep anaesthesia, but not so deep as to itself threaten life, the administration of 5 per cent carbon dioxide may actually stop the animal breathing. The implication of this, bearing in mind that one always has to extrapolate from animals to man with some degree of caution, is that one ought to take seriously the danger, not merely of unconscious¬ ness or of a reduced response to carbon dioxide, but of frank respiratory depression by this gas. Many anaesthetists of course, are aware of this. But it also seems to be important that the effect of a given underventilation may vary appreciably with the anaesthetic, and no doubt also with the other ancillary agents which are used. Oxygen lack, one imagines, could only occur when the anaesthetic apparatus has been removed from the patient in the post-anaesthetic period. Then, perhaps, a depressed minute volume while inhaling air could give rise to anoxaemia. Under these conditions of course, damage to the respiratory centre can take place, and the patient would be reduced to that state of moribundity discussed above. OVERVENTILATION This is a familiar possible cause of apnoea. The mechanism usually in¬ voked is that with overbreathing carbon dioxide is washed out from the blood so that the respiratory centre and chemoreceptors are driven only by the stimulus of anoxaemia. So long as oxygen continues to be breathed the apnoea may tend to be somewhat persistent. One might have thought that there would be little difficulty in determining whether continuing overventilation is the cause of an apnoea, and that merely suspending the respiration for one or two minutes would be enough to restore normal breathing if this was the cause. I think it is worth noting, however, that there seems to be quite an important variation in individual susceptibility to the effects of overventilation. Mills8 made some interesting studies on voluntary hyperventilation in conscious volunteers. In some subjects apnoea could not be produced; when the test over-breathing period was completed, they continued to overbreathe. For some of this group he attributed the continuance of overbreathing to a reflex response to reflex of blood into the thorax, blood which had been driven out by the previous hyperpnoeic effort. In others of these cases no satisfactory cause of the hyperpncea was identified. Now this is a different point from our present concern. But it shows that individuals can vary considerably and that some are more prone to apnoea following hyperventilation than others. I would also say from animal experience, that it is easy to be seriously deceived by an animal in whom a slight but persistent overventilation has oc¬ curred; the apnoea which follows the overventilation before normal breathing returns is often so long as to make one hesitate to allow it to
    digitised image 1
    digitised image 2
    digitised image 3