Ventilatory effects of meptazinol and pethidine in anaesthetized patients.

The ventilatory effects of three doses of meptazinol (20 mg, 30 mg and 48 mg) were studied in anaesthetized patients and compared with those of pethidine 20 mg. Minute volume, tidal volume, ventilatory frequency, inspiratory and expiratory times were measured and mean inspiratory flow rates calculated. Each patient received a first dose of drug which was followed after 5 min by a second identical dose. After the first injection the ventilatory effects of meptazinol were dose-dependent and meptazinol 20 mg had an effect similar to pethidine 20 mg. Following repeated injection the effects on ventilation were markedly different between the drugs. Carbon dioxide retention and other compensatory mechanisms attenuate the ventilatory depression of meptazinol, but these may be inadequate in the anaesthetized patient.