[Measurement of respiratory effects of propofol by indirect spirometry]

The effects of a continuous steady rate infusion of propofol on spontaneous ventilation were studied in eight unpremedicated ASA 1 male patients. All were non smokers, aged 29 +/- 8 years, and weighed 67 +/- 9 kg. After an initial 1 mg.kg-1 bolus, they received 10 mg.kg-1.h-1 propofol for 10 min, followed by 8 mg.kg-1.h-1 for a further 10 min, and then 6 mg.kg-1.h-1 during the whole study period. Endotracheal intubation was carried out using lidocaine for local anaesthesia. Spontaneous ventilation was assessed during three periods of five minutes: in the awake subject, using indirect spirometry (measurement of variations in chest circumference) and direct spirometry separately, and then, in the anaesthetized subject, using both methods simultaneously. This study aimed: a) to compare the results obtained with the two methods, b) to characterize the effects of propofol anaesthesia on chest wall mechanics using the partitioning of ventilation between rib cage and abdomen provided by the non-invasive method, and c) to assess abdominal compliance by means of a gastric balloon catheter. There was an increase in rib cage ventilation in the awake state, induced by the apparatus for direct spirometry (mouth piece, nose clip). This explained that the ventilatory depression induced by propofol anaesthesia was more pronounced when measured by the direct method. The major determinant of this depression was a shortened inspiratory time, and, to a lesser extent, a decreased mean inspiratory flow rate. By contrast to inhalational anaesthesia, rib cage ventilation was preserved during propofol anaesthesia. The decrease in abdominal ventilation was partly related to a lowered abdominal compliance, suggesting recruitment of the abdominal muscles.