VENTILATORY EFFECTS OF MEPTAZINOL AND PETHIDINE IN ANAESTHETIZED PATIENTS

The ventiiatory effects of three doses of mep-tazinol (20 mg,30 mg and 48 mg) were studied in anaesthetized patients andcompared with those of pethidine 20 mg. Minute volume, tidalvolume, ventilatory frequency, inspiratory and expiratory timeswere measured and mean inspiratory flow rates calculated. Eachpatient received a first dose of drug which was followed after5 min by a second identical dose. After the first injectionthe ventilatory effects of meptazinol were dose-dependent andmeptazinol 20 mg had an effect similar to pethidine 20 mg. Followingrepeated injection the effects on ventilation were markedlydifferent between the drugs. Carbon dioxide retention and othercompensatory mechanisms attenuate the ventilatory depressionof meptazinol, but these may be inadequate in the anaesthetizedpatient.