Anesthesiology 2009; 111:1217–26 Copyright © 2009, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins, Inc. Intraoperative Hypotension and 1-Year Mortality after Noncardiac Surgery Jilles B. Bijker, M.D.,* Wilton A. van Klei, M.D., Ph.D.,† Yvonne Vergouwe, Ph.D.,‡ Douglas J. Eleveld, Ph.D.,§ Leo van Wolfswinkel, M.D., Ph.D.,† Karel G. M. Moons, Ph.D.,‡ Cor J. Kalkman, M.D., Ph.D.# This article has been selected for the ANESTHESIOLOGY CME Program. Learning objectives and disclosure and ordering information can be found in the CME section at the front of this issue. Background: Intraoperative hypotension (IOH) is frequently associated with adverse outcome such as 1-yr mortality. How- ever, there is no consensus on the correct definition of IOH. The authors studied a number of different definitions of IOH, based on blood pressure thresholds and minimal episode durations, and their association with 1-yr mortality after noncardiac surgery. Methods: This cohort study included 1,705 consecutive adult patients who underwent general and vascular surgery. Data on IOH and potentially confounding variables were obtained from electronic record-keeping systems. Mortality data were col- lected up to 1 yr after surgery. The authors used two different techniques to reduce the influence of confounding variables, multivariable Cox proportional hazard regression modeling and classification and regression tree analysis. Results: The mortality within 1 yr after surgery was 5.2% (88 patients). After adjustment for confounding, the Cox regression analysis did not show an association between IOH and the risk of dying within 1 yr after surgery (hazard ratio around 1.00 with high P values for different definitions of IOH). Additional clas- sification and regression tree analysis identified IOH as a pre- dictor for 1-yr mortality in elderly patients. When the blood pressure threshold for IOH was decreased, the duration of IOH at which this association was found was decreased as well. Conclusions: This observational study showed no causal re- lation between IOH and 1-yr mortality after noncardiac surgery for any of the definitions of IOH. Nevertheless, additional anal- ysis suggested that for elderly patients, the mortality risk in- creases when the duration of IOH becomes long enough. The length of this duration depends on the designated blood pres- sure threshold, suggesting that lower blood pressures are tol- erated for shorter durations. The effect of IOH on 1-yr mortality remains debatable, and no firm conclusions on the lowest accept- able intraoperative blood pressures can be drawn from this study. IN recent years, there has been an increased interest in a possible causal effect of intraoperative hypotension (IOH) on adverse outcomes after noncardiac surgery, such as myocardial infarction, stroke, slow graft function after liver or kidney transplantation, and even 1-yr mor- tality. 1–6 However, almost 50 different definitions of IOH were used in the recent anesthesia literature, resulting in widely varying incidences of IOH when applied to ac- tual patient data. 7 Obviously, these different inci- dences of IOH influence the estimated association between IOH and adverse outcome. Therefore, it is not surprising that several studies did not show an association between IOH and adverse outcomes. 8,9 A recent meta-analysis even provided support for the notion that “moderate” hypotension during orthope- dic surgery might improve outcome by reducing blood loss and transfusion requirements. 10 The ability of a particular patient to tolerate episodes of hypotension also depends on other factors, such as the indication for surgery, age, and comorbidity. If blood pressure becomes low enough for a duration that is long enough, organ perfusion will be compromised. This in turn might result in end-organ damage or death. How- ever, what exactly constitutes “too low” or what is “too long” is unknown. We hypothesized that the association between IOH and 1-yr all-cause mortality depends on a series of se- lected threshold values for IOH and associated durations of IOH episodes. To explore this hypothesis, a series of frequently used IOH definitions— comprising different threshold values and minimal episode durations of IOH—were studied for their associations with 1-yr mor- tality in a cohort of general and vascular surgery patients. Materials and Methods Study Design This study was an observational cohort study. Patients were selected from a previously conducted prospective cohort study: the Outpatient Preoperative Evaluation by Nurses study. 11 In brief, all consecutive adult patients (aged 18 yr or older) who visited the outpatient preoperative This article is featured in “This Month in Anesthesiology.” Please see this issue of ANESTHESIOLOGY, page 9A.  This article is accompanied by an Editorial View. Please see: Kheterpal S, Woodrum DT, Tremper KK: Too much of a good thing is wonderful: Observational data for perioperative re- search. ANESTHESIOLOGY 2009; 111:1183– 4.  * Resident in Anesthesiology, † Anesthesiologist, # Professor of Anesthesiol- ogy, Department of Perioperative Care and Emergency Medicine, ‡ Epidemiolo- gist, Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, The Netherlands. § Research Engineer, Department of Anes- thesiology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands. Received from the Division of Perioperative Care and Emergency Medicine, Department of Anesthesiology, University Medical Center Utrecht, Utrecht, The Netherlands. Submitted for publication May 11, 2008. Accepted for publication July 28, 2009. Support was provided solely from institutional and/or departmen- tal sources. Presented in part at the Annual Meeting of the American Society of Anesthesiologists, Atlanta, Georgia, October 22–26, 2005. Address correspondence to Dr. Bijker: University Medical Center Utrecht, Department of Perioperative Care and Emergency Medicine Q.04.2.313, P.O. Box 85500, 3508 GA Utrecht, The Netherlands. j.b.bijker@umcutrecht.nl. This article may be accessed for personal use at no charge through the Journal Web site, www.anesthesiology.org. Anesthesiology, V 111, No 6, Dec 2009 1217 Downloaded from anesthesiology.pubs.asahq.org by guest on 06/06/2020