[Show abstract][Hide abstract] ABSTRACT: Several methods are available to measure splanchnic blood flow and gut ischaemia. Tonometry is most practical for peri-operative use. Epidural blockade from T5 to T11 causes mesenteric arteriovenous vasodilation and may increase splanchnic blood flow. This study assesses the ability of tonometry to measure differential effects of opiate and epidural analgesia on splanchnic blood flow. Forty patients for elective colorectal surgery were randomly allocated to receive epidural infusion or intravenous morphine. Gastric mucosal PCO2, pHi, standard pHi, PCO2 gap and pH gap were measured after induction and on termination of surgery. These parameters were within normal limits at the end in most cases and there was no significant difference between the groups. The complication rate was similar in both groups and was not correlated with low pHi, but was correlated with blood loss. We were unable to demonstrate a difference in splanchnic perfusion, as assessed by gastric tonometry, between the two groups.