Anaesthesia for colonic surgery : studies of the effects of anaesthetic techniques and other perioperative factors on colonic anastomoses and colonic blood flow
The disruption of an anastomosis is the most significant single cause of morbidity and mortality following colonic surgery. A number of factors are known to increase the risk of anastomotic breakdown in the colon, and these are reviewed. The physiology of the intestines is discussed, with particular emphasis on the effects on the bowel of anaesthetic drugs, techniques employed during anaesthesia, and other factors pertaining to the peri-operative period. A retrospective clinical study of patients who had undergone colonic anastomosis either during spinal nerve block with a light general anaesthetic or under conventional general anaesthesia is pre¬ sented and the findings discussed. There appeared to be a trend sugg¬ esting that spinal nerve block might result in a rather lower incid¬ ence of anastomotic breakdown. Because oxygen delivery is an important factor in wound heal¬ ing, and because anastomotic healing is known to be impaired by an inadequate blood flow, an animal model was developed for the measure¬ ment of colonic blood flow. The model was designed in such a way that the integrity of the nerve and blood supply was maintained, and was validated by comparison with other techniques. The effects of a number of factors of relevance to the peri-op¬ erative period were investigated using the model. Hypocapnia was found to reduce colonic blood flow, and hypercapnia to increase it. The increase in flow associated with hypercapnia diminished over a 60 min period. Moderate hypovolaemia decreased blood flow to the colon. Spinal nerve block and halothane both resulted in increased flow, al¬ though i.v. methoxamine or hypovolaemia during spinal nerve block produced substantial reductions. The clinical relevance of these findings is discussed.