Use of pulse oximetry to monitor venous saturation during extracorporeal life support.

OBJECTIVE

To assess the ability of two different pulse oximeters to display continuous venous oxygen saturation through an extracorporeal bypass circuit with a degree of accuracy comparable to direct in-line oximetry.

DESIGN

Prospective, comparison study of pulse oximeters (test oximeter 1 or test oximeter 2) and an in-line oximeter (test oximeter 3).

SETTING

A tertiary care neonatal intensive care unit.

PATIENTS

Sixty-five consecutive neonates with severe cardiorespiratory failure undergoing extracorporeal life support.

INTERVENTIONS

The accuracy of the oximeters was determined by simultaneously comparing the saturation displayed by the pulse oximeters (test oximeters 1 and 2) and/or the in-line oximeter (test oximeter 3) with the measured fractional venous oxygen saturation obtained at regular intervals from the extracorporeal circuit.

MAIN OUTCOME MEASURES

Venous oxygen saturation was the criterion standard used to determine accuracy. Bias was defined as the mean difference between observed pulse oximeter or in-line oximeter values and the measured venous oxygen saturation. Mean biases were calculated for venous oxygen saturation measurements between 55% and 99% at intervals of 10%. Precision (the standard deviation of the bias) was calculated for low (55% to 75%), medium (76% to 81%), and high (82% to 99%) venous oxygen saturation values. A total of 983 venous oxygen saturation measurements were made and compared with simultaneous oximeter readings from test oximeter 1 (n = 600), test oximeter 2 (n = 478), and test oximeter 3 (n = 587).

RESULTS

Test oximeter 1 was the most precise instrument at each level of venous oxygen saturation (SD, 4.0 to 4.8). Test oximeter 3 demonstrated the most consistent mean bias (range, 8), but was the most inaccurate oximeter across all levels of venous oxygen saturation.

CONCLUSIONS

In addition to its known clinical usefulness, pulse oximetry may serve as an adequate substitute for in-line oximetry during extracorporeal life support.