Anaesthesia and chest wall function.

The effects of anaesthesia and surgery on the chest wall may be responsible for impaired gas exchange and other pulmonary complications during the perioperative period. Current evidence supports the following sequence of events. Anaesthesia changes the shape and motion of the chest wall, either by changing the amount of tonic and phasic activity of the respiratory muscles (anaesthesia with spontaneous breathing) or by eliminating the activity entirely (paralysis with mechanical ventilation). These primary changes in chest wall function lead to secondary changes in lung function, including the formation of dependent lung atelectasis. Recent advances in imaging of the thorax have called into question traditional understanding of the mechanisms by which anaesthesia alters chest wall function. For example, it is now apparent that anaesthesia reduces the functional residual capacity not by changing the position of the diaphragm, but rather by affecting the rib cage, and, perhaps, the volume of intrathoracic blood. The effects of anaesthesia and surgery on postoperative chest wall function may be lessened by regional analgesia and the use of laparoscopic surgical techniques. However, it is not yet clear that this improvement is associated with a reduction in the incidence of pulmonary complications.