Recovery of ventilatory response to carbon dioxide after thiopentone, morphine and fentanyl in man

FOLLOWING GENERAL ANAESTHESIA, the return of spontaneous ventilation may be delayed. Frequently, this can be attributed to a relative drug overdose, or an unanticipated drug sensitivity or reaction; however, there are occasions when such a delay cannot be so explained. It is possible that differences in the operation of respiratory control mechanisms among patients may account for variation in the rate of recovery of spontaneous ventilation after anaesthesia. The ventilatory response to an increasing concentration of inspired carbon dioxide is recognized as a sensitive index of respiratory control and is known to vary widely among normal people. 1,2 Anaesthetics and other central nervous depressant drugs decrease the response in a quantitative dose-related manner. 3-7 Furthermore, it has been postulated that low respiratory sensitivity to carbon dioxide may render people more susceptible to ventilatory depressant effects of anaesthetic drugs, s but, to our knowledge, this idea has not been tested formally. If this suggestion is true, then it supports the hypothesis that differences in recovery of control of breathing may have a physiological (in addition to a pharmacological) basis. In this study, we measured ventilatory response to carbon dioxide after infusions of thiopentone, fentanyl, morphine and saline in healthy men, to shed light on these problems. METHODS