Total haemoglobin mass, but not haemoglobin concentration, is associated with preoperative cardiopulmonary exercise testing-derived oxygen-consumption variables

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Abstract

Background.

Cardiopulmonary exercise testing (CPET) measures peak exertional oxygen consumption (Symbol) and that at the anaerobic threshold (Symbol at AT, i.e. the point at which anaerobic metabolism contributes substantially to overall metabolism). Lower values are associated with excess postoperative morbidity and mortality. A reduced haemoglobin concentration ([Hb]) results from a reduction in total haemoglobin mass (tHb-mass) or an increase in plasma volume. Thus, tHb-mass might be a more useful measure of oxygen-carrying capacity and might correlate better with CPET-derived fitness measures in preoperative patients than does circulating [Hb].

Methods.

Before major elective surgery, CPET was performed, and both tHb-mass (optimized carbon monoxide rebreathing method) and circulating [Hb] were determined.

Results.

In 42 patients (83% male), [Hb] was unrelated to Symbol at AT and Symbol (r=0.02, P=0.89 and r=0.04, P=0.80, respectively) and explained none of the variance in either measure. In contrast, tHb-mass was related to both (r=0.661, P<0.0001 and r=0.483, P=0.001 for Symbol at AT and Symbol, respectively). The tHb-mass explained 44% of variance in Symbol at AT (P<0.0001) and 23% in Symbol (P=0.001).

Conclusions.

In contrast to [Hb], tHb-mass is an important determinant of physical fitness before major elective surgery. Further studies should determine whether low tHb-mass is predictive of poor outcome and whether targeted increases in tHb-mass might thus improve outcome.

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