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Open Access Highly Accessed Research article

The accuracy of pulse oximetry in emergency department patients with severe sepsis and septic shock: a retrospective cohort study

Ben J Wilson1*, Hamish J Cowan2, Jason A Lord34, Dan J Zuege13 and David A Zygun356

Author Affiliations

1 Department of Medicine, University of Calgary, (1403 - 29th Street NW), Calgary, (T2N 2T9), Canada

2 Faculty of Medicine, University of Calgary, (1403 - 29th Street NW), Calgary, (T2N 2T9), Canada

3 Department of Critical Care Medicine, University of Calgary, (1403 - 29th Street NW), Calgary, (T2N 2T9), Canada

4 Division of Emergency Medicine, University of Calgary, (1403 - 29th Street NW), Calgary, (T2N 2T9), Canada

5 Department of Clinical Neurosciences, University of Calgary, (1403 - 29th Street NW), Calgary, (T2N 2T9), Canada

6 Department of Community Health Sciences, University of Calgary, (1403 - 29th Street NW), Calgary, (T2N 2T9), Canada

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BMC Emergency Medicine 2010, 10:9  doi:10.1186/1471-227X-10-9

Published: 5 May 2010

Abstract

Background

Pulse oximetry is routinely used to continuously and noninvasively monitor arterial oxygen saturation (SaO2) in critically ill patients. Although pulse oximeter oxygen saturation (SpO2) has been studied in several patient populations, including the critically ill, its accuracy has never been studied in emergency department (ED) patients with severe sepsis and septic shock. Sepsis results in characteristic microcirculatory derangements that could theoretically affect pulse oximeter accuracy. The purposes of the present study were twofold: 1) to determine the accuracy of pulse oximetry relative to SaO2 obtained from ABG in ED patients with severe sepsis and septic shock, and 2) to assess the impact of specific physiologic factors on this accuracy.

Methods

This analysis consisted of a retrospective cohort of 88 consecutive ED patients with severe sepsis who had a simultaneous arterial blood gas and an SpO2 value recorded. Adult ICU patients that were admitted from any Calgary Health Region adult ED with a pre-specified, sepsis-related admission diagnosis between October 1, 2005 and September 30, 2006, were identified. Accuracy (SpO2 - SaO2) was analyzed by the method of Bland and Altman. The effects of hypoxemia, acidosis, hyperlactatemia, anemia, and the use of vasoactive drugs on bias were determined.

Results

The cohort consisted of 88 subjects, with a mean age of 57 years (19 - 89). The mean difference (SpO2 - SaO2) was 2.75% and the standard deviation of the differences was 3.1%. Subgroup analysis demonstrated that hypoxemia (SaO2 < 90) significantly affected pulse oximeter accuracy. The mean difference was 4.9% in hypoxemic patients and 1.89% in non-hypoxemic patients (p < 0.004). In 50% (11/22) of cases in which SpO2 was in the 90-93% range the SaO2 was <90%. Though pulse oximeter accuracy was not affected by acidoisis, hyperlactatementa, anemia or vasoactive drugs, these factors worsened precision.

Conclusions

Pulse oximetry overestimates ABG-determined SaO2 by a mean of 2.75% in emergency department patients with severe sepsis and septic shock. This overestimation is exacerbated by the presence of hypoxemia. When SaO2 needs to be determined with a high degree of accuracy arterial blood gases are recommended.