• I C Shaw, G H Mills, and D Turnbull.
• The University Department of Surgical and Anaesthetic Sciences, Department of Anaesthesia, K Floor, The Royal Hallamshire Hospital, Glossop Road, Sheffield, S10 2JF, UK.
• Intensive Care Med. 2002 Jul 1;28(7):891-7.

ObjectivesTo assess the effect of propofol on the change in airway pressure produced by diaphragmatic contraction.Design And SettingProspective, controlled study in patients anaesthetised with propofol in a university hospital.Patients And MethodsWe stimulated the phrenic nerves before and immediately after induction of anaesthesia in 11 subjects, using a pair of 43-mm mean diameter double magnetic coils and measured the change in airway pressure at the mouth (TwPmo) produced by the resulting diaphragmatic contraction. Supramaximality of stimulation was confirmed with electromyogram and pressure measurements. We recorded the change in Resting End Expiratory Position (REEP) using a spirometer. We applied an approximate correction for the effect of lung volume on the amplitude of twitch pressure produced by diaphragmatic contraction.InterventionFollowing the initial stimulations, the patients were anaesthetised with a propofol infusion. Once stable, repeat measurements were made.Measurements And ResultsFollowing induction, REEP fell by mean 0.3 l standard deviation (SD) 0.2 l. TwPmo fell by mean 14.2% SD 14.0% ( P = 0.01), mean 22.3% SD 11.7% corrected ( P < 0.001). Twitch transdiaphragmatic pressure fell by 18.1% and 20.0% (25.8% and 27.7% corrected) in two further subjects studied with oesophageal and gastric balloon catheters.ConclusionPropofol does reduce the effectiveness with which diaphragmatic contraction produces changes of pressure in the airway.

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