Pressure-volume relationships in the lung during laparoscopy.

Pressure-volume relationships for the total respiratory system and for the lung were recorded in anaesthetized and paralysed patients, during deflation from an airway pressure of 3 kPa to FRC at a rate of 2 litre min-1. Pleural pressure was estimated by means of an oesophageal balloon. A group of nine female patients (mean age 32.7 yr) about to undergo laparoscopy were each studied in four successive states: supine, 15 degrees head down tilt, tilt and lithotomy position, and again in this position after abdominal inflation with nitrous oxide to a pressure of 0.8(-1) kPa. Compliance values were calculated from the curves. Mean total compliance was increased significantly by moving to the lithotomy position, and reduced markedly after inflation of the abdomen, because of a large reduction in thoracic compliance. Mean lung compliance was unaltered, except for a slight but statistically significant increase on moving from the supine to the Trendelenburg position. Measurement of FRC by helium dilution in a group of seven patients showed that abdominal inflation caused a mean decrease of 19%. Airway closure manoeuvres were carried out using a helium bolus technique from FRC in five patients, but closing volume could be measured in only one patient, in the supine position. The absence of an inflexion in the slope of the pressure-volume curves for the other patients supported this negative finding.