Documented intraoperative hypotension according to the three most common definitions does not match the application of antihypotensive medication.

This observational study investigated which of the three most common definitions of intraoperative hypotension (IOH), reported in a published systematic literature review, were associated best with anaesthetists' administration of antihypo tensive medication (AHM). IOH and AHM use in anaesthetic procedures in a mixed surgical population (n = 2350) were also reviewed. The definitions were: arterial systolic blood pressure (SBP) < 100 mmHg or a fall in SBP of > 30% of the preoperative SBP baseline; arterial SBP < 80 mmHg; a fall in SBP of > 20% of the preoperative SBP. Accuracy of predicting AHM using these three definitions was 67%, 54% and 65%, respectively. Prediction by a new fourth definition, using an optimal threshold of minimal SBP falling to < 92 mmHg or by > 24% of preoperative baseline, was 68% accurate. In multivariate logistic analysis, age, volatile versus intravenous anaesthetics, medical history of arterial hypertension and all four definitions of IOH were associated with intraoperative AHM, however IOH was not associated with postoperative in-patient stay. The three original definitions correlated poorly with the anaesthetist's judgement about applying AHM. Anaesthetists make complex decisions regarding the relevance of IOH, considering various perioperative factors in addition to SBP. Age, physical status and duration and type of surgery showed better correlations with postoperative in-patient stay than IOH.