The inferior vena caval compression theory of hypotension in obstetric spinal anaesthesia: studies in normal and preeclamptic pregnancy, a literature review and revision of fundamental concepts

Abstract

Three clinical investigations together with a combined editorial and review of the cardiovascular physiology of spinal anaesthesia in normal and preeclamptic pregnancy form the basis of a thesis to be submitted for the degree of Doctor of Medicine at the University of St Andrews. First, the longstanding consensus that spinal anaesthesia could cause severe hypotension in severe preeclampsia was examined using three approaches. The doses of ephedrine required to maintain systolic blood pressure above predetermined limits were first compared in spinal versus epidural anaesthesia. The doses of ephedrine required were then similarly studied during spinal anaesthesia in preeclamptic versus normal control subjects. The principal outcome of these studies, that preeclamptic patients were resistant to hypotension after a spinal anaesthetic, was then further investigated by studying pulse transit time (PTT) changes in normal versus preeclamptic pregnancy. PTT was explored both as beat-to-beat monitor of cardiovascular function and also as an indicator of changes in arterial stiffness. The cardiovascular physiology of obstetric spinal anaesthesia was then reviewed in the light of the three clinical investigations, developments in reproductive vascular biology and the regulation of venous capacitance. It is argued that the theory of a role for vena caval compression as the single cause of spinal anaesthetic induced hypotension in obstetrics should be revised.