Changes in intragastric pressure on induction of anaesthesia

Intragastric pressure was measured in 20 patients before, and immediately after, the induction of anaesthesia with thiopentone. Intragastric pressure decreased in patients whose weights were the same as or less than expected, and increased in five of seven patients whose weights were greater than expected (P = 0.0013). These findings suggest that the decrease in FRC known to occur on the induction of anaesthesia is caused by a decrease in inspiratory muscle tone in the diaphragm and other muscles.