• J Bartoszko, K E Thorpe, A Laupacis, D N Wijeysundera, METS Study Investigators, International and National Coordinators, Central Project Office Operations Committee, CPET Methods Committee, Outcome Adjudication Committee, and International Steering Committee.
• Department of Anesthesia, University of Toronto, Toronto, ON, Canada; Institute of Health Policy Management and Evaluation, University of Toronto, Toronto, ON, Canada.
• Br J Anaesth. 2019 Aug 1; 123 (2): 161-169.

BackgroundPreoperative anaemia is associated with elevated risks of postoperative complications. This association may be explained by confounding related to poor cardiopulmonary fitness. We conducted a pre-specified substudy of the Measurement of Exercise Tolerance before Surgery (METS) study to examine the associations of preoperative haemoglobin concentration with preoperative cardiopulmonary exercise testing performance (peak oxygen consumption, anaerobic threshold) and postoperative complications.MethodsThe substudy included a nested cross-sectional analysis and nested cohort analysis. In the cross-sectional study (1279 participants), multivariate linear regression modelling was used to determine the adjusted association of haemoglobin concentration with peak oxygen consumption and anaerobic threshold. In the nested cohort study (1256 participants), multivariable logistic regression modelling was used to determine the adjusted association of haemoglobin concentration, peak oxygen consumption, and anaerobic threshold with the primary endpoint (composite outcome of death, cardiovascular complications, acute kidney injury, or surgical site infection) and secondary endpoint (moderate or severe complications).ResultsHaemoglobin concentration explained 3.8% of the variation in peak oxygen consumption and anaerobic threshold (P<0.001). Although not associated with the primary endpoint, haemoglobin concentration was associated with moderate or severe complications after adjustment for peak oxygen consumption (odds ratio=0.86 per 10 g L-1 increase; 95% confidence interval, 0.77-0.96) or anaerobic threshold (odds ratio=0.86; 95% confidence interval, 0.77-0.97). Lower peak oxygen consumption was associated with moderate or severe complications without effect modification by haemoglobin concentration (P=0.12).ConclusionHaemoglobin concentration explains a small proportion of variation in exercise capacity. Both anaemia and poor functional capacity are associated with postoperative complications and may therefore be modifiable targets for preoperative optimisation.Copyright © 2019 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.

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