Control of breathing after fentanyl and Innovar anaesthesia

Ventilation (VI), end-tidal (PCO2), mixed venous (PvCO2) and the ventilatory response to carbon dioxide were measured before surgery, and during the first 4 h of recovery in 18 adult patients who underwent elective limb surgery under fentanyl or Innovar anaesthesia. End-tidal and mixed venous PCO2 were increased significantly in the first 150 min after the last dose of drug (P less than 0.001, P less than 0.01), but had returned to control values by 4 h. Ventilation and ventilatory response to carbon dioxide were significantly depressed in all patients (P less than 0.001), but returned to near control values at 4 h. Fentanyl and Innovar anaesthesia displaced the carbon dioxide response to the right, but no correlation was found between either the magnitude of the displacement of the response curve or the alteration in slope and the control values. This suggests that patients with a low value of VI/PCO2 are not more susceptible to the ventilatory depressed action of narcotic anaesthetics. Recovery of ventilatory responsiveness towards normal during the 4 h after anaesthesia, occurred in a graded and progressive manner, there was no evidence of a biphasic pattern of recovery.