Respiratory effects of extradural analgesia after lower abdominal surgery.

Blood-gas tensions, FRC and volume of trapped gas (VTG) in the lung were measured in patients on the day before lower abdominal gynaecological surgery, and twice on the day following surgery, before and after establishing lumbar extradural block (EDB) using 0.5% bupivacaine to provide analgesia after operation. FRC and VTG were measured with the closed-circuit helium-dilution technique. Mean VTG was 175 ml before operation and 275 ml after operation. PaO2 decreased significantly after operation, and the changes in FRC and VTG that occurred were related qualitatively. EDB did not significantly alter FRC, VTG or PaO2. Individual changes in FRC could not be related to changes in VTG or PaO2. Although EDB provided effective analgesia, the variables measured did not indicate that EDB conferred an immediate respiratory advantage.