EFFECTS OF INCREMENTAL DOSES OF ALFENTANIL AND PROPOFOL ON THE BREATHING OF ANAESTHETIZED PATIENTS

Incremental doses of alfentanil and propofol were given to anaesthetizedhealthy patients undergoing routine orthopaedic surgery. Ventilationwas recorded by respiratory inductance plethysmography and analysedby microcomputer. Alfentanil affected primarily expiratory time.The onset of effect lasted 82 s (range 25–173 s); offsetwas exponential, with a half-life of 146 s (range 62–260s). Alfentanil also reduced tidal volume, but the effect wasless obvious and less consistent. Propofol affected primarilytidal volume. The onset of effect lasted 34 s (range 17–69s); offset was linear, with a time to 50% recovery of 92 s (range47–161 s). Propofol had little effect on expiratory time.The drugs had little effect on inspiratory time. Three patientsshowed periods when the distribution of expiratory times wasbimodal; the mechanism for this is unknown.