[Modification of oxygen consumption following major abdominal surgery by epidural anesthesia]

In the postoperative period patients are at risk of excessive oxygen consumption (VO2). However, patients suffering from cardiovascular disease may be unable to increase their oxygen transport capacity sufficiently and may be especially vulnerable to tissue hypoxia as part of the reaction to intraoperative stress. During the last 10 years conflicting results concerning the benefits of a combined epidural and light general anaesthesia have been published. Some of the results indicate that postoperative catabolism may be depressed and that the neuroendocrine response to stress may be inhibited by such a combined technique. We studied the effect of a combined epidural and light general anaesthesia on VO2 in the early post-operative period. PATIENTS AND METHODS. Three groups of patients were studied: group 1 contained 10 patients scheduled for major urological procedures of at least 3 h duration who received a combined epidural and light general anaesthesia. Group 2 contained 17 patients with procedures comparable to group 1 but received a standard general anaesthesia with isoflurane, N2O and fentanyl. In addition, 13 patients undergoing minor urological procedures of less than 2 h duration and undergoing standard general anaesthesia were included in the study as a control group (group 3). All patients gave informed consent. Preoperative management was the same in the three groups. Perioperative risk was assessed according to the ASA classification. In group 1 patients, an epidural catheter was placed preoperatively at the L3/4 interspace and tested for correct positioning using 4 ml of 2% mepivacaine with epinephrine 1:200,000. After induction of anaesthesia an epidural block was established with 0.5% bupivacaine for intraoperative analgesia and 0.25% bupivacaine for postoperative pain relief. The initial dosage was determined (according to Bromage's method) to reach a sensory level of T-6. Two-thirds of the initial dose was the given on two occasions, each 90 min after the dose before. End-tidal isoflurane concentrations ranged between 0.3 and 0.6 vol% in this group. In groups 2 and 3, endtidal isoflurane concentrations of 1.0 to 1.5 vol% were applied. Postoperative analgesia was achieved in these groups using repeated doses of 7.5 mg piritramide i.v. Oxygen consumption was measured in the recovery room using the Deltatrac (Datex) metabolic monitor. Measurements were performed with a canopy room air dilution technique. Arterial oxygen saturation of the patients was monitored continuously using pulse oximetry. Data acquisition was started within 10 min after extubation and continued for at least 60 min until a steady state of oxygen consumption was reached. We recorded the average VO2 during the initial 5 min of the measurement period and during another 5-min period after the steady state was reached (45-60 min after extubation). RESULTS. Patients in the three groups were comparable in age, height and body weight (Table 1). The duration of procedures in groups 1 and 2 ranged between 4 and 7 h. Groups 1 and 2 were further comparable in terms of intraabdominal procedures, intraoperative blood loss, fluid replacement, and fall in body temperature during the operation (Table 2). Heart range was significantly higher in group 2 during the 5-min test interval (Table 3). Figure 1 shows the typical course of oxygen consumption in patients of groups 1, 2, and 3. The readings in the group 1 patient as well as in the group 3 patients were stable throughout the observation period. Oxygen consumption was in the physiological range. In contrast, in the group 2 patients during the early postoperative period, increased values of VO2 (approx. 50% above normal) were observed. These findings were highly significant in our study. In the early postoperative period (5 min) patients in group 1 showed a VO2 or 3.6 +/- 0.4 ml.kg-1.min-1. This was the same as in group 3 (3.5 +/- 0.3 ml.kg-1.min-1). In contrast, in group 2 a VO2 of 5.3 +/- 0.7 ml.kg-1.min-1