The safety of one, or repeated, vital capacity maneuvers during general anesthesia

A vital capacity maneuver (VCM) (inflating the lungs to 40 cm H2O for 15 s) is effective in relieving atelectasis during general anesthesia or after cardiopulmonary bypass (CPB). The study was undertaken to investigate the safety of one or repeated VCM. Five groups of six pigs were studied. Two groups had general anesthesia for 6 h and one group received a VCM every hour. Three other groups received CPB. VCM was performed after CPB in two of these groups. VCM was then repeated every hour in one of the groups. Lung damage was evaluated by extravascular lung water (EVLW) measurement, light microscopy, and the half-time (T-1/2) of disappearance from the lung of a nebulized aerosol containing Tc-99m-DTPA. No changes were noted in extravascular lung water. The pigs subjected to VCM decreased their T-1/2. In the groups exposed to repeated VCM, T-1/2 remained lowered (CPB pigs) or decreased over time (non-CPB pigs). No lung damage could be seen on the morphology study. These results suggest that one VCM is a safe procedure. The increase in lung clearance of Tc-99m-DTPA not associated with an increase in lung water when VCM is repeated may have been caused by an increase in lung volume. Therefore, repeated VCM also appears to be safe.