Respiration and circulation after total hip replacement surgery. A comparison between parenteral analgesics and continuous lumbar epidural block.

The cardiopulmonary effects of two different types of postoperative analgesic regimes were compared in 31 cardiorespiratorily healthy patients subjected to total hip replacement surgery. The investigation was performed preoperatively on the morning of the day of surgery and during the first 3 days postoperatively. All patients received continuous lumbar epidural analgesia preoperatively, during surgery and up to the end of the first measurement period, which started 2.5 h after surgery. Ten patients were subseuqently given pentazocine (Fortalgesic) intramuscularly on demand for pain relief throughout the investigation, while 14 patients received 0.4% plain lidocaine (Xylocain), and seven patients 0.4% lidocaine with adrenaline (1/400,000) as a continuous lumbar epidural drip for analgesia thorughout the investigation. It was confirmed that the operative procedure itself did not significantly influence the postoperative arterial oxygenation, while the type of postoperative analgesic regimen was of considerable importance in this respect. Thus, patients given pentazocine showed a significant increase in pulmonary venous admixture, due both to an increase in true shunt and to an increase in ventilation/perfusion disturbances. This pattern of poor pulmonary function still persisted on the third postoperatively. In patients given an epidural block no significant changes in pulmonary venous admixture were noted postoperatively, and thus there was no reduction in PaO2. All patients, irrespective of the type of analgesic regimen used, had a significantly increased cardiac index and oxygen uptake postoperatively, although patients given an epidural block showed a greater increase in cardiac index, and thus a tendency towards a more hyperkinetic circulation than those given pentazocine.