Date:
December 7, 2011
Promotors: Prof. C.J. Kalkman, MD, PhD
Prof. K.G.M. Moons, MD, PhD
Co-promotor:
W.A. van Klei, MD, PhD
Intraoperative hypotension is a frequent and common side effect of anesthesia. The incidence of intraoperative hypotension is however dependent on the chosen definition. A wide variety of definitions could be found in the recent anesthesia literature, and also self-reported definitions by anesthesia personnel differ widely. Furthermore, in daily clinical practice, intraoperative hypotension is not always treated according to the self-reported definitions.
Thus, there is much discussion on the associations between intraoperative hypotension and adverse outcome after surgery, which is highly dependent on the chosen definition of intraoperative hypotension. Previously, a relation between intraoperative hypotension and one-year mortality was described. Furthermore, an association between intraoperative hypotension and the occurrence of a postoperative stroke was suggested. In this thesis two studies are presented that studied the relation between intraoperative hypotension and adverse outcome. No causal association could be found between intraoperative hypotension and one-year mortality. Nevertheless, the risk of dying within one year after surgery was increased for elderly patients when the duration of low blood pressure became long enough. Lower blood pressures are tolerated for shorter durations.
A postoperative stroke is mostly described to be caused by an embolism. The role of intraoperative hypotension remains debatable, but one could hypothesize that intraoperative hypotension can compromise collateral blood flow to ischemic areas, even in embolic strokes. Support could be found fot this hypothesis in a study, described in this thesis, showing an increased risk of a postoperative stroke when the blood pressure decreased below 30% of the baseline blood pressure.
Based on the studies presented in this thesis, it seems appropriate to define intraoperative hypotension according to thresholds relative to a baseline blood pressure and keeping the blood pressure above 30% of the baseline blood pressure. Associations between intraoperative hypotension and adverse outcome is however also dependent on patient and surgery related factors and no firm conclusions on lowest acceptable intraoperative blood pressures can be drawn based on this thesis.