Perioperative comparison of the agreement between a portable fingertip pulse oximeter v. a conventional bedside pulse oximeter in adult patients (COMFORT trial)
Background. Low-cost, portable fingertip pulse oximeters are widely available to health professionals and the public. They are often not tested to International Organization for Standardization standards, or only undergo accuracy studies in healthy volunteers under ideal laboratory conditions.
Objectives. To pragmatically evaluate the agreement between one such device and a conventional bedside pulse oximeter in a clinical setting, in patients with varied comorbidities and skin pigmentations.
Methods. A single-centre equipment comparison study was conducted. Simultaneous measurements were obtained in 220 patients with both a Contec CMS50D Fingertip Pulse Oximeter and a Nihon Kohden Life Scope MU-631 RK conventional bedside monitor. Peripheral oxygen saturations (SpO2) and pulse rates were documented, and patients’ skin tone was recorded using the Fitzpatrick scale. Data were assessed using a Bland-Altman analysis with bias, precision and limits of agreement (LOA) calculated with 95% confidence intervals (CIs). A priori acceptability for LOA was determined to be 3%, in keeping with international standards.
Results. The mean difference (therefore bias) between the conventional and fingertip oximeters for all data was –0.55% (95% CI –0.73 - –0.36). Upper and lower limits of agreement were 2.16% (95% CI 1.84 - 2.47) and –3.25% (95% CI –3.56 - –2.94). Regression analysis demonstrated worsening agreement with decreasing SpO2. When samples were separated into ‘normal’ (SpO2 ≥93%) and ‘hypoxaemic’ (SpO2 <93%) groups, the normal range displayed acceptable agreement between the two oximeters (bias –0.20% with LOA 2.20 - –2.27), while the hypoxaemic group fell outside the study’s a priori limits. Heart rate measurements had a mean difference of –0.43 bpm (LOA –5.61 - 4.76). The study was not powered to detect differences among the skin tones, but demonstrated no trend for this parameter to alter the SpO2 measurements.
Conclusions. During normoxia, portable fingertip pulse oximeters are reliable indicators of SpO2 and pulse rates in patients with various comorbidities in a pragmatic clinical context. However, they display worsening agreement with conventional pulse oximeters during hypoxaemia. Skin tones do not appear to affect measurements adversely.