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

Abstract

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 (V˙O2 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], V˙O2 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 V˙O2 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 V˙O2 peak, and a rise of 4.4 to 6.0% in AT. Haemoglobin concentration accounted for 9% and 6% of the variation in V˙O2 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.

Figure 1

Linear regression between unadjusted$\dot{\mathbf{V}}{\mathbf{O}}_{\mathbf{2}}$peak (ml min ^-1 ) and haemoglobin concentration ([Hb]), n = 1,774.

Figure 2

Linear regression between unadjusted oxygen uptake at anaerobic threshold (AT) (ml min ^-1 ) and haemoglobin concentration ([Hb]), n = 1,631.

Figure 3

Allometrically scaled oxygen uptake (ml kg^-0.83 min^-1) across [Hb] group (<10 g dl^-1, 10 to 12 g dl^-1, >12 g dl^-1);$\dot{\mathbf{V}}{\mathbf{O}}_{\mathbf{2}}$peak (A) and at the anaerobic threshold (AT) (B). Mean +/- SD values adjusted for weight, testing site, age, sex, revised cardiac risk index, diabetes, creatinine and operation category. P <0.0001 (ANOVA) and trend (P <0.0001) for both measures. Hb, haemoglobin concentration.