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_o2 ≥99% and Pe′_co2 4.6–5.2 kPa.

Results

TwPdi declined after administration of propofol with gradual recovery. Compared with baseline [20.6 (6.0) cm H₂O], TwPdi decreased by 23.3% (P<0.001) to [15.8 (6.4) cm H₂O]. When the patients regained awareness, TwPdi returned to [19.1 (6.1) cm H₂O], 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.