Clearance and action of insulin during general or epidural anaesthesia

Surgery performed under general anaesthesia induces impaired glucose tolerance together with comparatively low levels of insulin. This contrasts with the normal glucose tolerance and normal insulin levels found in patients operated upon under epidural anaesthesia. The aim of this study was to investigate insulin clearance and insulin action during surgery. Sixteen non-diabetic patients admitted for elective inguinal herniorrhaphy were operated under general anaesthesia (thiopentone, N2O/O2 (2/1), fentanyl, pancuronium bromide) or after high epidural blockade with mepivacaine. The clearance and hypoglycemic action of insulin were determined after a 2.5 min infusion of a physiologic dose of insulin. All patients were studied the day before operation and during surgery. The hypoglycemic action of insulin, expressed as % decrement from the pre-test blood glucose level, was unchanged during epidural anaesthesia but reduced during general anaesthesia (22.4 +/- 1.8% pre-operatively vs 7.5 +/- 1.3% intra-operatively, p < 0.01). The insulin resistance during general anaesthesia was associated with a decreased clearance of insulin (20.3 +/- 0.8 ml min(-1) kg(-1) pre-operatively vs 12.7 +/- 1.1 ml min(-1) kg(-1) intra-operatively, p < 0.01), whereas insulin clearance was normal during epidural anaesthesia. It is concluded that general anaesthesia, but not epidural anaesthesia, induces a reduction in both clearance and hypoglycemic action of insulin.