SIGHS AND THEIR EFFECT ON THE BREATHING OF PATIENTS ANAESTHETIZED WITH INFUSIONS OF PROPOFOL

Twenty-one spontaneous sighs were analysed from records of the breathing of 10 patients anaesthetized for 22–42 (mean 28.7) min with propofol infusions. Sighs occurred in eight patients, the rate varying between once in 29 min and four times in 26 min. There was no pattern in breaths preceding sighs, but the succeeding breaths were altered. On the first succeeding breath, tidal volume was reduced by a mean of 32% (95% confidence limits 19–44%; P < 0.01) and inspiratory time by a mean of 15% (95% confidence limits 8–22%; P < 0.01) of the means of the preceding breaths. These effects lasted on average at least 10 breaths. Expiratory time was usually slightly prolonged after a sigh, but this effect was less clear, less consistent and less prolonged. Sighs in patients anaesthetized with propofol reduce the ventilatory drive (in terms of mean inspiratory flow), and alter the timing, of succeeding breaths.