Reference range for tissue oxygen saturation in pregnancy using near-infrared spectroscopy

OBJECTIVE: To estimate the reference range of tissue oxygen saturation (StO2) values in pregnancy. Near-infrared spectroscopy-derived StO2 is a noninvasive continuous measure used to predict hypoperfusion. Normal StO2 values have not been established in pregnant women.

STUDY DESIGN: We enrolled 154 healthy pregnant women from an obstetric and gynecology resident clinic. Three sequential measurements were taken after securing the StO2 probe to the thenar eminence of one hand. One-way ANOVA was used to test for differences between trimesters and non-parametric methods to establish a reference range with 95% CI on the limits.

RESULTS: The reference interval for the entire cohort of pregnant women is 73% (95% CI 72-75) to 92% (95% CI 89-93), similar to the normal range in the general population. We found no statistically significant difference in StO2 measurements between trimesters. Due to inadequate sample sizes we could not estimate a valid reference range for each trimester.

CONCLUSION: We estimated a reference range for StO2 values in normal pregnant women. This information may contribute to the study of StO2 monitoring to predict impending shock in the obstetric patient.