Comparative Evaluation of Accuracy of Pulse Oximeters and Factors Affecting Their Performance in a Tertiary Intensive Care Unit

Abstract

Introduction: Pulse oximetry is a widely used tool, unfortunately there is a paucity of data investigating its accuracy in Intensive Care Units (ICU) and if they are able to meet mandated FDA criteria as claimed by them in critically ill patients.

Aim: To assess bias, precision and accuracy of pulse oximeters used in ICU and factors affecting them.

Materials and methods: A prospective cohort study, including 129 patients admitted to the ICU of a tertiary referral centre. Pulse oximetry and blood gas were done simultaneously. Pulse oximetry was done using two pulse oximetres: Nonin and Philips. All physiological variables like haemoglobin, lactate, use of vasopressors and blood pressure were recorded. Bland Altman curves were constructed to determine bias and limits of agreement. Effect of physiological variables on bias and difference between performance characteristics of bias was determined using SPSS.

Results: Pulse oximetry overestimated arterial oxygen saturation (SaO₂) by 1.44%. There was negative correlation between bias and SaO₂ (r=-0.32) and positive correlation with lactate (r=0.16). The Philips pulse oximeter had significant higher bias and variability than Nonin pulse oximeter. (2.49±2.99 versus 0.46±1.68, mean difference = 1.98, 95% C.I. = 1.53 - 2.43, p-value <0.001).

Conclusion: Pulse oximetry overestimates SaO₂. Bias tends to increase with rising lactate and hypoxia. There is heterogeneity in performance of various pulse oximetry devices in ICU.

Keywords: Critical care; Oxygen saturation; Pulse oximetry.

[Table/Fig-3]:

Bland Altman plot depicting mean difference (Bias) - central line and upper and lower limits of agreement between pulse oximeter oxygen saturation and arterial oxygen saturation.

[Table/Fig-4]:

Regression lines depicting relation between bias and oxygen saturation for Nonin and Philips pulse oximeters.