Influence of thoracic epidural anaesthesia on intestinal blood supply
Abstract
Background: To date research has demonstrated that the use of general anaesthesia in combination with thoracic epidural anaesthesia (TEA) protects the patient against surgical stress. There is disagreement, however, concerning the effect of TEA on intestinal blood supply. In order to determine the influence of TEA on intestinal blood flow, partial O2 pressure (pO2) and pH were determined in the portal blood that drains blood from intestine, just before liver resection. These values were compared with those measured in the superior caval vein which drains blood from the upper part of the body, region not directly affected by TEA.
Methods: Forty patients included in our prospective randomized study were divided into two groups, i.e. a group of 20 patients given TEA in combination with general anaesthesia, and a group of 20 patients receiving only general anaesthesia. They were premedicated with midazolam 1.5–3.0 mg i. v. Immediately after introduction of an epidural catheter at T11– T12, 15 ml of 0.25% local anaesthetic bupivacain or 15 ml of 0.9% NaCl was injected into the thoracic epidural space in the TEA group and in the control group, respectively. Anaesthesia was initiated by intravenous opioid analgesic fentanyl 0.1–0.2 mg, thiopentone 4.0 mg/kg body weight, and muscle relaxant vecuronium 0.1 mg/kg body weight. The patients were intubated and controlled ventilation was started with a 45 to 55 per cent oxygen-air mixture with addition of the volatile agent isoflurane 0.8–1.5 vol %. Muscle relaxation was maintained with vecuronium at a dose of 2–4 mg i. v. Central venous pressure was maintained at a low normal limit, i.e. 6 ± 2 mmHg. Just before liver resection, blood samples were obtained from the portal vein and superior caval vein. Intestinal blood supply was evaluated by measuring pO2 and pH in the portal vein, and the results were compared with the values obtained in the superior caval vein in each patient and in the two groups.
Results: In both groups, pO2 levels in the portal vein were significantly higher than those in the superior caval vein (TEA group: 7.8 kPa in the portal vein vs. 6.0 kPa in the superior caval vein; p < 0.001; control group: 7.5 kPa in the portal vein vs. 6.1 kPa in the superior caval vein; p < 0.01). No significant differences were found between the groups (p > 0.05). In both groups, portal venous pH was significantly higher than pH determined in the superior caval vein (TEA group: 7.41 in the portal vein vs. 7.39 in the superior caval vein; p < 0.001; control group: 7.41 in the portal vein vs. 7.39 in the superior caval vein; p < 0.05), yet they were within the range of normal. There was no statistically significant difference between the groups (p > 0.05). In the TEA groups, a statistically significant negative correlation was found between the portal venous pH and pO2 levels (r = –4.7) (p < 0.05). No such correlation was observed for the control group (r = 0.058; p > 0.05).
Conclusions: The observed negative correlation between pO2 and pH levels in the portal blood of TEA group suggests that the use of TEA in combination with general anaesthesia with a central venous pressure of 6 ± 2 mmHg affords a more constant intestinal blood flow pattern than general anaesthesia alone.
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References
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