Canadian Journal of Anesthesia, Vol 30, 607-614, Copyright © 1983 by Canadian Anesthesiologists' Society

Chemical Regulation of Ventilation During Isoflurane Sedation and Anaesthesia in Humans

¹ Department of Anaesthesia, University Hospital and University of Western Ontario, London, Canada

Address correspondence to: to: Dr. R.L. Knill, Department of Anaesthesia, University Hospital, P.O. Box 5339, Postal Stn. A., London, Canada N6A 5A5.

To assess the effects of isoflurane on chemical regulation of ventilation, we studied the ventilatory responses to (1) hyperoxic hypercarbia, (2) isocapnic hypoxaemia, and (3) a single half vital capacity breath of carbon dioxide 20 per cent in oxygen in 12 human subjects, awake and sedated or anaesthetized with isoflurane, 0.1 or 1.1 MAC. Sedation did not alter ventilation nor the ventilatory response to hypercarbia but reduced the responses to hypoxaemia and to the half vital capacity breath of CO₂. Anaesthesia reduced ventilation and the response to hypercarbia and nearly abolished the responses to hypoxaemia and to the breath of CO₂. The results indicate that isoflurane reduces ventilatory responses to several chemical drives and that it selectively impairs those responses mediated by peripheral chemoreceptors. In these respects, isoflurane is similar to halo thane and enflurane.

Key Words: ANAESTHETICS, VOLATILE: isoflurane • RECEPTORS: chemoreceptors • VENTILATION: carbon dioxide response, hypoxic response, regulation