Impact of Oxygenation Status on the Noninvasive Measurement of Hemoglobin

Noninvasive monitoring of hemoglobin (SpHgb) via pulse oximetry has the potential to alert caregivers to blood loss. Previous studies have demonstrated that changes in oxygenation may impact accuracy.

Twenty normal volunteers were monitored using SpHgb at sea level, during ascent to 14,000 feet, at 14,000 feet with 100% oxygen delivery, and again at sea level. Each period consisted of 15 minutes of monitoring. SpHgb measurements were compared to a blood sample using Bland Altman analysis. The loss of the SpHgb signal was also recorded.

The mean difference in measured hemoglobin (Hgb) between a venous sample and SpHgb was -2.6 ± 0.96 at 14,000 feet. Ascent to 14,000 feet resulted in a predictable fall in SpO₂ and was associated with loss of the SpHgb signal for half the period of observation (7.4 minutes). In the other three conditions, SpHgb signal was missing 1 to 12.6% of the time. The nadir SpO2 was not predictive of the loss of SpHgb signal.

Changes in oxygenation in normal volunteers are associated with short-term SpHgb signal loss (<10 minutes), but no impact on the measured SpHgb.