The reliability of continuous measurement of mixed venous oxygen saturation during exercise in patients with chronic heart failure

Continuous assessment of mixed venous oxygen saturation (cSvO₂) during exercise using a fiber optic pulmonary artery catheter can provide valuable information on the physiological determinants of the exercise capacity in patients with chronic heart failure (CHF). Since its accuracy is not well established during exercise, this study evaluated the reliability of a fiber optic pulmonary artery catheter for measuring SvO₂ during exercise in CHF patients. Ten patients with stable CHF performed steady-state exercise tests at 30 and 80% of the ventilatory threshold and consequently a symptom-limited incremental exercise test. During the tests, SvO₂ was monitored continuously using a fiber optic pulmonary artery catheter (CCOmbo, Edwards Lifesciences, Irvine, CA, USA) and by oximetric analysis of mixed venous blood samples obtained at rest (n = 26), steady state (n = 17) and peak exercise (n = 8). There was a significant correlation between oximetrically determined SvO₂ and cSvO₂ values (r = 0.97). The bias between both methods was 0.6% with limits of agreement from −8 to 9%. The limits of agreement for SvO₂ values <30% (n = 16) were slightly wider than for SvO₂ values >30% (n = 35) (from −10 to 12% and from −7 to 8%, respectively). In conclusion, continuous measurement of SvO₂ during exercise using a fiber optic pulmonary catheter is reliable in patients with CHF, with somewhat less accurate measurements of SvO₂ below 30%.