Association between preoperative haemoglobin concentration and cardiopulmonary exercise variables: a multicentre study

Background: Preoperative anaemia and low exertional oxygen uptake are both associated with greater postoperative morbidity and mortality. This study reports the association among haemoglobin concentration ([Hb]), peak oxygen uptake (VO2 peak) and anaerobic threshold (AT) in elective surgical patients. Methods: Between 1999 and 2011, preoperative [ Hb] and cardiopulmonary exercise tests were recorded in 1,777 preoperative patients in four hospitals. The associations between [ Hb], VO2 peak and AT were analysed by linear regression and covariance. Results: In 436 (24.5%) patients, [Hb] was < 12 g dl(-1) and, in 83 of these, < 10 g dl(-1). Both AT and VO2 peak rose modestly with increasing [Hb] (r2 = 0.24, P < 0.0001 and r2 = 0.30, P < 0.0001, respectively). After covariate adjustment, an increase in [Hb] of one standard deviation was associated with a 6.7 to 9.7% increase in VO2 peak, and a rise of 4.4 to 6.0% in AT. Haemoglobin concentration accounted for 9% and 6% of the variation in VO2 peak and AT respectively. Conclusions: To a modest extent, lower haemoglobin concentrations are independently associated with lower oxygen uptake during preoperative cardiopulmonary exercise testing. It is unknown whether this association is causative.