Self Reported Definitions of Hypotension and Actual Treatment Thresholds for Low Blood Pressure Jilles B. Bijker, M.D., Wilton A. van Klei, M.D., Ph.D., Peter L. Houweling, M.D., Ph.D., Cor J. Kalkman, M.D., Ph.D. Anesthesia, UMC Utrecht, Netherlands Introduction Many definitions of intraoperative hypotension (IOH) can be found in the literature, resutling in widely varying incidences.1 In the present study we aimed to study the difference between self reported definitions of IOH and the actual treatment threshold for low blood pressure (BP) in the OR. Furthermore, it was hypothesized that this treatment threshold was different for general and spinal anesthesia. Methods Definitions of IOH were collected using a questionnaire amongst Dutch anesthesiologists, residents and nurse anesthetists in the UMC Utrecht (1042 beds university hospital) and the Diakonessenhuis Utrecht (627 beds general hospital). Subsequently, all adult patients undergoing a knee arthroscopy in these two hospitals in the period from 2000 untill 2007 who received a bolus of ephedrine for low BP were selected. Patients who recieved inotropics other than ephedrine were exluded. Baseline BP was defined as the mean of all BP's before induction of anesthesia. The mean of the 2 BP's preceding ephedrine administration (the 'accepted' and 'treated' BP respectively) was taken as the treatment threshold for low BP. Results In total 41 different definitions of IOH were collected from 169 questionnaires. The most frequently reported definitions were a mean blood pressure (MBP) < 60 mmHg (N=35) and a decrease in MBP > 20-30% from baseline (N=73). The characteristics of the cohort (N= 906) are presented in table 1.[table1]Both the absolute and relative treatment thresholds were not normally distributed (tested with Kolmogorov-Smirnov goodness of fit test), so median MBP thresholds were compared in stead of means. The median MBP treatment thresholds for patients receiving general anesthesia was 62 mmHg corresponding with a 37% decrease from baseline. For patients receiving spinal anesthesia this was 74 mmHg and 30% respectively. Conclusion Anesthesia personnel does not use a universal definition of IOH. The most frequently used definition is a MBP < 60 mmHg or a decrease in MBP > 20-30% from baseline. Patients receiving general anesthesia are treated at a MBP threshold of 62 mmHg, corresponding well with the reported definition. However, this threshold corresponds with a 37% decrease relative to baseline, which is more than the reported definition. In patients receiving spinal anesthesia, the MBP treatment threshold is 74 mmHg, much higher than the reported definition. This corresponds with a relative decrease of 30%, which is consistent with the self reported definition. It seems that anesthesia personnel is preferably treating absolute BP values in stead of decreases relative to baseline. Treatment thresholds for patients under spinal anesthesia are higher, possibly due to treatment indicated by other patient factors such as nausea or dizzyness. 1 Anesthesiology 2007;107:213-20. Anesthesiology 2008; 109 A45 Characteristics of the cohort (N=906) general anesthesia (N=112) spinal anesthesia (N=794) mean age (SD) 51.5 (13.4) 47.3 (15.5) male gender 51 (45.5) 472 (59.4) hospital - UMCU 35 (31.3) 84 (10.6) - Diakonessenhuis 77 (68.7) 710 (89.4) ASA class - 1 56 (50.0) 557 (70.2) - 2 20 (17.9) 129 (16.2) - 3 0 (0) 4 (0.5) - unknown 36 (32.1) 104 (13.1) median procedure duration in minutes (SD) 71.2 (44.8) 72.0 (25.3) Values are numbers (%) unless otherwise indicated. ASA = American Society of Anesthesiologists, UMCU = University Medical Center Utrecht
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