Intra-Operative Hypotension and Postoperative Stroke: A Case Control Study among 30,000 Patients Johannes A. de Jager, M.D., Jilles B. Bijker, M.D., Suzanne Persoon, M.D., Cor J. Kalkman, M.D., Ph.D., Wilton A. van Klei, M.D., Ph.D. Anesthesiology, Univ Med Center Utrecht, Netherlands Background Stroke after noncardiac surgery is a rare but clinically important complication.1 Intraoperative hypotension (IOH) was sometimes reported to be associated with perioperative stroke. However, there are many definitions of IOH in use and the incidence of IOH varies with the chosen definition.2 It is therefore likely that the association between IOH and stroke depends on the chosen threshold value. In the present study we hypothesized that postoperative stroke was associated with type of surgery and IOH, but that this association is dependent on the chosen threshold value for IOH. Methods This nested Case-Control study was performed among a cohort of 30,088 adult patients operated on between 1-1-2002 and 28-02-2007. Patients having undergone cardiac and neuro surgery were excluded. All preoperative demographic and co-morbidity data and intraoperative data on vital signs (blood pressures) were available from the electronic patient and anesthesia record keeping systems. These systems store data with unique hospital and case identifiers and include time stamps. The data was merged with the hospital administrative database to identify patients who had had a 'CT brain' within 10 days after surgery. The 165 (0.5%) CT reports found were read and patients with a definite stroke and / or where there was clear clinical evidence for a stroke from the request to the radiologist were selected. In total 47 (0.2%) postoperative strokes were found (Cases). These Cases were matched for surgical procedure and age with otherwise randomly chosen Control subjects fom the same cohort in a 1:4 ratio (table 1). IOH was defined as an absolute decrease in systolic blood pressure below 80, 60 and 50 mmHg for at least one minute and as a relative decrease in systolic blood pressure with 30% and 50% from preoperative baseline for at least one minute. The relationship between IOH and stroke was adjusted for known risk factors for stroke (surgical procedure, gender, age, smoking, hypertension, previous stroke and medications) using conditional logistic regression analysis (conditional on the matching). Carotid surgery procedures were analyzed seperately, as postoperative stroke after these procedures might have a different pathophysiology.[table1]Results In univariable analysis, postoperative stroke was associated with a previous stroke, with a preoperative diagnosis of hypertension and with the use of beta-blockers. After adjustment, stroke was never associated with IOH nor with any of the other variables in carotid surgery. For the other procedures, stroke was associated with absolute IOH threshold values below 80 mm Hg (OR 5.0; 95% CI: 1.0-28; p=0.05). The relative IOH thresholds revealed comparable results but at higher p-values. Postoperative stroke was further associated with a previous stroke (OR 9.0; 95% CI: 1.8-40; p < 0.01). Conclusion This Case-Control study showed that in procedures other than cardiac, neuro and carotid surgery, postoperative stroke was significantly associated with intraoperative systolic blood pressures below 80 mm Hg and with a previous stroke. 1 NEJM 2007;356:706-13. 2 Anesthesiology 2007;107:213-20. Anesthesiology 2008; 109 A215 Matching results, data are numbers (%) Cases (N=47) Controls (N=188) Mean age (SD) 66 (12) 65 (13) Carotid surgery 22 (47) 93 (50) Other vascular surgery 6 (13) 19 (10) Neck dissection 5 (11) 20 (11) Other surgery 14 (30) 56 (30)
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