Mass spectrometric measurements of oxygen uptake during epidural analgesia combined with general anesthesia

Oxygen uptake was measured using a mass spectrometer system in 12 patients scheduled for abdominal surgery who intraoperatively were mechanically ventilated with 50% nitrous oxide and given continuous intravenous infusions of methohexital (3.5 mg.kg-1.h-1) plus repeated epidural injections of lidocaine. At the end of the surgical procedure, meperidine (0.7 mg/kg) was epidurally injected in six patients (group A). The other six patients (group B) received no epidural injections during the first 2 h after surgery. Intraoperatively, oxygen uptake decreased in both groups by an average of 28%. Within the first two postoperative hours, clear-cut differences among the two groups arose. Patients in group A had smoother increases in oxygen uptake and core temperatures, greater cardiovascular stability as reflected by the rate-pressure product, and no visible shivering. We suggest that epidural meperidine given immediately at the end of a surgical procedure might be beneficial, especially, perhaps, in patients with impaired cardiac function.