Reliability of pulse oximetry in titrating supplemental oxygen therapy in ventilator-dependent patients

Abstract

Pulse oximetry is widely used in the critical care setting, but few studies have examined its usefulness in clinical decision making. One area where pulse oximetry might be useful is in the titration of fractional inspired O2 concentration (FIO2) in ventilator-dependent patients. Unfortunately, documented guidelines for this use do not exist, and in a survey of directors of intensive care units, we found that they employed a wide range of target O2 saturation (SpO2) values. Consequently, we undertook a study to determine if SpO2 could be reliably substituted for measurements of arterial O2 tension (PaO2) when adjusting FIO2 in ventilator-dependent patients. We examined a number of SpO2 target values in 54 critically ill patients aiming for a PaO2 of greater than or equal to 60 mm Hg, while minimizing the risk of O2 toxicity. In white patients, we found that a SpO2 target of 92 percent was reliable in predicting a satisfactory level of oxygenation. However, in black patients, such a SpO2 reading was commonly associated with significant hypoxemia (PaO2 as low as 49 mm Hg), and a higher SpO2 target, 95 percent, was required. In addition, inaccurate oximetry readings (ie, greater than 4 percent difference between SpO2 and direct SaO2 measurements) were more common in black (27 percent) than in white patients (11 percent, p less than 0.05). In conclusion, a SpO2 target of 92 percent was reliable when titrating supplemental O2 in white patients receiving mechanical ventilation; however, in black patients, such a SpO2 reading was commonly associated with significant hypoxemia, and a higher SpO2 target, 95 percent, was required to ensure a satisfactory level of oxygenation.