Determination of hemoglobin saturation in patients with acute sickle chestsyndrome - A comparison of arterial blood cases and pulse oximetry

Study objectives: To evaluate three different methods of measuring oxygen s aturation 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 unde rgo RBC exchange transfusion. Interventions: None. Measurements: Baseline hemoglobin oxygen saturation was determined simultan eously by (1) calculation based on PaO2 and an oxyhemoglobin dissociation c urve algorithm, (2) co-oximetry, and (3) pulse oximetry, These same measure s were repeated after exchange transfusion. Baseline and postexchange hemog lobin electrophoresis was performed in all patients. Results: Baseline calculated saturation overestimated hue saturation (deter mined by co-oximetry) with a baseline mean bias (co-oximetry minus calculat ed 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-oxi metry and calculated saturation (mean difference: -0.17 +/- 1.31% [95% conf idence 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 acu te sickle chest syndrome. This discrepancy abates after exchange transfusio n. Pulse oximetry more closely follows co-oximetry than does calculated sat uration during acute sickle chest syndrome.