Effect of propofol on twitch diaphragmatic pressure evoked by cervical magnetic stimulation in patients

Abstract

Background: Several studies have demonstrated the inhibitory effect of propofol on diaphragmatic contractility in laboratory animals, but there have been few studies in humans. We have investigated the effect of a single bolus injection of propofol on twitch diaphragmatic pressure (TwPdi) evoked by cervical supramaximal magnetic stimulation, and its impact on diaphragmatic contractility.

Methods: In 16 patients scheduled for elective operation, TwPdi was evoked bilaterally at the cervical phrenic nerves with supramaximal magnetic stimulations using a 140 mm diameter magnetic coil. Changes of TwPdi were monitored dynamically before and during general anaesthesia induced by single bolus of propofol 2 mg kg (-1). During the study, all patients breathed 100% oxygen by a face mask, maintaining Sp(O(2)) > or = 99% and PE'(CO(2)) 4.6-5.2 kPa.

Results: TwPdi declined after administration of propofol with gradual recovery. Compared with baseline [20.6 (6.0) cm H(2)O], TwPdi decreased by 23.3% (P<0.001) to [15.8 (6.4) cm H(2)O]. When the patients regained awareness, TwPdi returned to [19.1 (6.1) cm H(2)O], close to baseline (P=0.063). The time from starting the propofol infusion to the lowest TwPdi was [240 (86) s]. Total time course of stimulation lasted [363 (89) s].

Conclusions: A single bolus propofol depressed TwPdi evoked by cervical magnetic stimulation, demonstrating inhibitory effects of propofol on diaphragmatic contractility in patients during general anaesthesia.