Otto JM, Plumb JOM, Wakeham D, Clissold E, Loughney L, Schmidt W, Montgomery HE, Grocott MPW, Richards

Br J Anaesth. 2017 May 1;118(5):747-754. doi: 10.1093/bja/aew445.
Comment in Br J Anaesth. 2017 May 1;118(5):655-657.
Comment on Eur J Appl Physiol. 2013 May;113(5):1181-8.

Background: Cardiopulmonary exercise testing (CPET) measures peak exertional
oxygen consumption ( V˙O2peak ) and that at the anaerobic threshold ( V˙O2 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 V˙O2 at AT and V˙O2peak
( 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 V˙O2 at AT and V˙O2peak , respectively). The
tHb-mass explained 44% of variance in V˙O2 at AT ( P <0.0001) and 23% in V˙O2peak
( 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.