Determination Of Total Hemoglobin Mass By Pulse CO-oximetry In Healthy Men And Women

PURPOSE: Carbon monoxide (CO) rebreathing is commonly used to determine total hemoglobin mass (Hbmass), which requires measurement of carboxyhemoglobin saturation (COHb). Pulse CO-oximetry may be an alternative to estimate total Hbmass via measurement of carboxyhemoglobin saturation (SpCO). Previous studies have compared SpCO derived measurement of total Hbmass against COHb-based analyses and agreement results remain equivocal. However, 85% of the subjects in those studies were men. We tested the hypothesis that SpCO derived measurement of total Hbmass has poor agreement with COHb-based analyses in both men and women. METHODS: Following 20 min of supine rest, 45 healthy adults (20 women) completed a modified 2 min CO rebreathing test involving the delivery of 1.0 mL CO per kg body mass into a closed-circuit spirometer connected to a 5 L anesthesia bag filled with 100% O2 and a CO2 scrubber. Capillary blood was taken pre- and 6- and 8-min post-CO rebreathing commencement and analyzed for COHb (OSM3, Radiometer). SpCO was recorded for 1 min before and every 30 s during and following rebreathing using pulse CO-oximetry (Rad-57, Masimo Corp.). RESULTS: Among all subjects, total Hbmass calculated via COHb (890 ± 244 g) vs. SpCO (957 ± 347 g) did not differ (p = 0.100), and COHb and SpCO derived values were positively correlated (r = 0.639, p < 0.001). Bland-Altman plot analyses indicated wide 95% limits of agreement (592 to -458 g) and a bias towards overestimating total Hbmass with SpCO (by 67 ± 268 g), which was greater at higher levels of Hbmass (slope: +0.425, p = 0.004). Similar trends were observed between genders, where total Hbmass calculated via COHb vs. SpCO did not differ (p ≥ 0.150). COHb and SpCO derived Hbmass were correlated in men (r = 0.531, p < 0.009) but not women (r = 0.290, p = 0.191). Wide 95% limits of agreement and a bias towards overestimating total Hbmass with SpCO (by 88 ± 284 g & 45 ± 255 g for men and women) were also observed. The difference between COHb and SpCO derived total Hbmass did not differ between men (-40 ± 136 g/m2) and women (-21 ± 158 g/m2, p = 0.662). CONCLUSIONS: In comparison to COHb measured via blood gas analyses, pulse CO-oximetry overestimates CO rebreathing measures of total Hbmass in healthy adults. The magnitude of such differences persists independent of gender. R01OH011528 & N00014-20-1-2593