Pulse Oximeters Used in Hospitalized Patients Have Moderate Accuracy

Pulse oximeters used in stable patients hospitalized in an intensive care unit (ICU) had moderate accuracy when compared to arterial blood gas measurements, according to study findings published in Respiratory Care.

The Oxygap study evaluated the accuracy and biases of 4 pulse oximeters that are frequently used in clinical practice by comparing the SpO₂ values generated by these instruments with SaO₂ values measured via drawing arterial blood gases.

Participants were adult patients admitted to an ICU in Quebec City, Canada, from March 24 to September 17, 2021. All patients were stable regarding oxygen administration parameters (ie, no change in fraction of inspired oxygen [FiO₂] and oxygen flow for the last 30 minutes) and hospitalized with an arterial catheter in place.

The oximeters that were assessed were: (1) Nonin in the FreeO₂ device (Oxynov); (2) Masimo (nontouch screen, Radical-7); (3) Philips (FAST); and (4) Nellcor (N-600). SpO₂ values for each pulse oximeter were obtained concomitantly to the arterial blood gas. The primary outcomes were SpO₂ values for each pulse oximeter and SaO₂ values from the measurement of arterial blood gases.

A total of 211 sets of concomitant oxygen saturation measurements (with each set including 1 SaO₂ value and 4 SpO₂ values, 1 for each of the 4 pulse oximeters) were obtained from 193 participants. Of those sets of measurements, 153 (73%) were from men and 58 (27%) were from women. The patients had a mean (SD) age of 66 (11) years, and most had “light skin,” noted the researchers (ie, 96.2% had Fitzpatrick scale type 1 or 2 skin pigmentation).

The participants had a mean SaO₂ value of 93.6% (2.2%). The Philips oximeter had a positive bias of 0.9%. Negative biases were observed for the Nonin, Nellcor, and Masimo oximeters (-3.1%, -0.3%, and -0.2%, respectively).

Compared with the concomitant SaO₂ measurements, SpO₂ was underestimated in 55% of cases. Among the 4 pulse oximeters evaluated, an overall frequency of positive and negative differences of 4% or more between SaO₂ vs SpO₂ measurements were found in 35.2%, 2.4%, 8.6%, and 9.5% of the Nonin, Nellcor, Masimo, and Philips pulse oximeter measurements, respectively.

Regarding accuracy, the pulse oximeters showed large random errors. The Nellcor, which had an R² coefficient value of 0.5148, was found to have slightly greater accuracy than the other pulse oximeters, which had R² coefficients of 0.4306 (Nonin), 0.4328 (Masimo), and 0.4387 (Philips).

The pulse oximeters’ ability to identify hypoxemia varied. Among cohort participants, 19 patients had a PaO₂ value from 55 mmHg to 60 mmHg, and 12 had SaO₂ values from 86% to 90%, indicating moderate hypoxemia. The Nonin pulse oximeter was the most sensitive for detecting hypoxemia, detecting 100% of the states of moderate hypoxemia, whereas the Philips pulse oximeter detected 11%, the Masimo detected 37%, and the Nellcor detected 26% of hypoxemic events.

Study limitations include the low diversity of skin pigmentation in study participants and the lack of accounting for bias introduced by dark skin pigmentation in some of the results; small sample size; and a limited number of patients with SaO₂ values of less than 90%.

“Oximeters should be used knowing their limits, and when SpO₂ is used by clinicians to target the oxygen flow or FiO₂, the oxygenation targets should probably be adapted based on the oximeter and skin pigmentation,” stated the researchers.

Disclosure: Some of the study authors declared affiliations with a medical equipment manufacturer. Please see the original reference for a full list of authors’ disclosures.

This article originally appeared on Pulmonology Advisor