Carbon dioxide response after epidural morphine.

The change in minute volume in response to a rising inspired carbon dioxide concentration was compared in 20 patients who received epidural morphine for postoperative analgesia (the test group), and 18 patients who did not (the control group). The minute volume increase in the test group was depressed at 6 hours but not at 12 hours postoperatively, but the degree of depression as not statistically significant. Control patients had no significant respiratory depression at any time. When the test and control groups were compared with each other, no statistically significant difference between groups was found. Two patients in the test group demonstrated a markedly depressed response to carbon dioxide challenge postoperatively. The incidence of nausea and vomiting was similar in both groups, while the presence of severity of pain was reduced in the test group.