Accuracy of pulse oximetry in the intensive care unit

Objective: Pulse oximetry (SpO(2)) is a standard monitoring device in inten sive care units (ICUs), currently used to guide therapeutic interventions. Few studies have evaluated the accuracy of SpO(2) in critically ill patient s. Our objective was to compare pulse oximetry with arterial oxygen saturat ion (SaO(2)) in such patients, and to examine the effect of several factors on this relationship. Design: Observational prospective study. Setting: A 26-bed medical ICU in a university hospital. Patients: One hundred two consecutive patients admitted to the ICU in whom one or serial arterial blood gas analyses (ABGs) were performed and a relia ble pulse oximeter signal was present. Interventions: For each ABG, we collected SaO2, SpO(2), the type of pulse o ximeter, the mode of ventilation and requirement for vasoactive drugs. Measurements and results: Three hundred twenty-three data points were colle cted. The mean difference between SpO(2) and SaO(2) was -0.02 % and standar d deviation of the differences was 2.1 %. From one sample to another, the f luctuations in SpO(2) to arterial saturation difference indicated that SaO( 2) could not be reliably predicted from SpO(2) after a single ABG. Subgroup analysis showed that the accuracy of SpO(2) appeared to be influenced by t he type of oximeter, the presence of hypoxemia and the requirement for vaso active drugs. Finally, high SpO(2) thresholds were necessary to detect sign ificant hypoxemia with good sensitivity. Conclusion: Large SpO(2) to SaO(2) differences may occur in critically ill patients with poor reproducibility of SpO(2). A SpO(2) above 94 % appears n ecessary to ensure a SaO(2) Of 90 %.