Canadian Journal of Anesthesia, Vol 23, 449-458, Copyright © 1976 by Canadian Anesthesiologists' Society

Components of Respiratory Depression after Narcotic Premedication in Adolescents

¹ Department of Anaesthesia, University of Western Ontario, London, Ontario
² Canadian Cystic Fibrosis Foundation
³ Department of Paediatrics, University of Toronto, and the Research Institute, The Hospital for Sick Children, Toronto, Ontario

The effects of narcotics on ventilatory control were assessed in 13 adolescents and young adults. Both a narcotic and narcotic-phenothiazine significantly depressed the CO₂ response curve. Using an occlusion pressure technique (P_m100) to evaluate those neuromuscular processes that generate forces acting on the ventilatory pump, it was found that narcotic agents reduced neuromuscular drive. In most subjects, narcotics had an additional action that contributed to the overall ventilatory depression. Using carbon dioxide to vary neuromuscular drive before and after drug administration at constant levels of neuromuscular drive the drugs reduced tidal-volume responsiveness of the pump. We conclude that narcotics impair ventilation through a combination of two effects; first, reduced neuromuscular drive, most probably due to central depression, and second, increased impedance of the ventilatory pump, most probably due to a decrease in chest-wall compliance.