Effect of analgesia on respiratory muscle function after upper abdominal surgery

The effects of three methods of analgesia (intravenous morphine, epidural lidocaine and epidural morphine) on vital capacity (VC), forced expiratory volume in 1 s (FEV1) and maximal expiratory and inspiratory pressures (MEP and MIP) at the mouth were studied in 12 high respiratory risk patients following upper abdominal surgery. VC, FEV1, MEP and MIP markedly decreased following laparotomy. VC and FEV1, were partially restored by epidural analgesia and remained unchanged following intravenous morphine. MEP and MIP remained unchanged after each of the three methods of analgesia. This suggests the existence of a non-analgesic dependent dysfunction of inspiratory and expiratory muscles following upper abdominal surgery.