EPIDURAL-ANESTHESIA INFLUENCES OXYGEN-CON SUMPTION AFTER MAJOR ABDOMINAL-SURGERY

In the postoperative period patients are at risk of excessive oxygen c onsumption (VO2). However, patients suffering from cardiovascular dise ase may be unable to increase their oxygen transport capacity sufficie ntly and may be especially vulnerable to tissue hypoxia as part of the reaction to intraoperative stress. During the last 10 years conflicti ng results concerning the benefits of a combined epidural and light ge neral anaesthesia have been published. Some of the results indicate th at postoperative catabolism may be depressed and that the neuroendocri ne response to stress may be inhibited by such a combined technique. W e studied the effect of a combined epidural and light general anaesthe sia on VO2 in the early postoperative period. Patients and methods. Th ree groups of patients were studied: group 1 contained 10 patients sch eduled for major urological procedures of at least 3 h duration who re ceived a combined epidural and light general anaesthesia. Group 2 cont ained 17 patients with procedures comparable to group 1 but received a standard general anaesthesia with isoflurane, N2O and fentanyl. In ad dition, 13 patients undergoing minor urological procedures of less tha n 2 h duration and undergoing standard general anaesthesia were includ ed in the study as a control group (group 3). All patients gave inform ed consent. Preoperative management was the same in the three groups. Perioperative risk was assessed according to the ASA classification. I n group 1 patients, an epidural catheter was placed preoperatively at the L3/4 interspace and tested for correct poitioning using 4 ml of 2% mepivacaine with epinephrine 1:200000. After induction of anaesthesia an epidural block was established with 0.5% bupivacaine for intraoper ative analgesia and 0.25% bupivacaine for postoperative pain relief. T he initial dosage was determined (according to Bromage's method) to re ach a sensory level of T-6. Two-thirds of the initial dose was the giv en on two occasions, each 90 min after the dose before. End-tidal isof lurane concentrations ranged between 0.3 and 0.6 vol % in this group. In groups 2 and 3, end-tidal isoflurane concentrations of 1.0 to 1.5 v ol % were applied. Postoperative analgesia was achieved in these group s using repeated doses of 7.5 mg piritramide i.v. Oxygen consumption w as 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 co ntinuously using pulse oximetry. Data acquisition was started within 1 0 min after extubation and continued for at least 60 min until a stead y 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 extu bation). Results. Patients in the three groups were comparable in age, height and body weight (Table 1). The duration of procedures in group s 1 and 2 ranged between 4 and 7 h. Groups 1 and 2 were further compar able 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 ox ygen consumption in patients of groups 1, 2, and 3. The readings in th e group 1 patient as well as in-the group 3 patients were stable throu ghout the observation period. Oxygen consumption was in the physiologi cal range. In contrast, in the group 2 patients during the early posto perative period, increased values of VO2 (approx. 50% above normal) we re observed. These findings were highly significant in our study. In t he 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.m in-1 was measured (P<0.01). During steady state (45-60 min) VO2 was th e same in all patients (Table 4). Discussion. During the past 10 years several studies have compared combined epidural and light general ana esthesia with conventional anaesthesiological techniques. The results of these studies are controversial. Authors who found the combination of doubtful value have suggested that cardiovascular instability may a rise from the synergy between epidural sympathetic block on the one ha nd and cardiovascular depression due to general anaesthesia on the oth er. In contrast, those who came out in support of a combined epidural and general anaesthesia found a faster return to normal in gut functio n, satisfactory postoperative analgesia, a lower stress response, and a reduction in overall postoperative complications. The latter factors may have contributed to the reduction in oxygen consumption in our gr oup 1 patients. Our results demonstrate that a combined technique of g eneral and epidural anaesthesia prevents excessive oxygen consumption postoperatively. Patients suffering from cardiovascular disease who ma y not be able to increase their oxygen transport capacity sufficiently (therefore developing tissue hypoxia postoperatively) may benefit fro m the addition of an epidural block. The risk of costs of this epidura l anaesthesia are almost certainly outweighed by an improvement in ove rall patient safety.