Determination of Hemoglobin Saturation in Patients With Acute Sickle Chest Syndrome

Study objectives To evaluate three different methods of measuring oxygen saturation in patients suffering from acute sickle chest syndrome. Design A prospective, descriptive study of 9 months’ duration. Setting A tertiary care university hospital. Patients Adult patients with acute sickle chest syndrome scheduled to undergo RBC exchange transfusion. Interventions None. Measurements Baseline hemoglobin oxygen saturation was determined simultaneously by (1) calculation based on Pa o 2 and an oxyhemoglobin dissociation curve algorithm, (2) co-oximetry, and (3) pulse oximetry. These same measures were repeated after exchange transfusion. Baseline and postexchange hemoglobin electrophoresis was performed in all patients. Results Baseline calculated saturation overestimated true saturation (determined by co-oximetry) with a baseline mean bias (co-oximetry minus calculated saturation) of −6.78 ± 2.63% (95% confidence interval for bias: −8.37% to −5.19%). Pulse oximetry was not different than co-oximetry at baseline with a baseline bias of+ 1.86 ± 3.25% (95% confidence interval: −0.1% to 3.82%). After exchange transfusion, there was no bias between either co-oximetry and calculated saturation (mean difference: −0.17 ± 1.31% [95% confidence interval: −0.95% to 0.61%]), or co-oximetry and pulse oximetry (mean difference: +0.3 ± 1.53% [95% confidence interval:− 0.62% to 1.22%]). Conclusions Calculated saturation overestimates true saturation during acute sickle chest syndrome. This discrepancy abates after exchange transfusion. Pulse oximetry more closely follows co-oximetry than does calculated saturation during acute sickle chest syndrome.