The accuracy of pulse oximetry in the emergency department

Division of Emergency Medicine, University of Utah Medical Center, Salt Lake City, USA.
American Journal of Emergency Medicine (Impact Factor: 1.27). 08/2000; 18(4):427-31. DOI: 10.1053/ajem.2000.7330
Source: PubMed


The objective of this retrospective study was to identify factors affecting the accuracy of pulse oximetry in the ED. Over a 3-year period, 664 consecutive emergency department (ED) patients had simultaneous arterial blood gas (ABG) and pulse oximeter readings taken. Pulse oximeter saturations (SpO2) were compared with ABG CO-oximeter saturations (SaO2) for accuracy. Multiple variables including age, sex, hemoglobin, bicarbonate, pH, and carboxyhemoglobin (COHb) were analyzed to see if they affected SpO2 accuracy. ROC curves were used to determine the best pulse oximeter threshold for detecting hypoxia. Using multivariate analysis, COHb was the only statistically significant factor affecting the accuracy of pulse oximetry. In patients with COHb <2%, SpO2 overestimated SaO2 by more than 4% in 8.4% of cases. In patients with COHb > or = 2%, SpO2 overestimated SaO2 by more than 4% in 35% of cases. The best pulse oximetry threshold for detecting hypoxia is 92%. At this threshold, if COHb is <2%, pulse oximetry has a sensitivity of 0.92 and specificity of 0.90. If COHb is > or =2%, sensitivity is 0.74 and specificity is 0.84. For patients likely to have a COHb < 2, pulse oximetry is an effective screening tool for detecting hypoxia. However, more caution must be exercised when using pulse oximetry in patients likely to have a COHb > or = 2%.

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    • "Both the degree of inaccuracy, or bias, and its direction has been inconsistent [1-3,5,7-9]. In addition, while certain studies of critically ill patients have demonstrated that hypoxemia [1], anemia [10], requirement for vasoactive drugs [7], and acidosis [8] influence the accuracy of pulse oximetry, others have not [2,6]. Data on the effects of other physiologic derangements, such as hyperlactatemia and bacteremia, are absent. "
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    ABSTRACT: 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. 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. 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. 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.
    Full-text · Article · May 2010 · BMC Emergency Medicine
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    • "La fotopletismografía [1] [2] es una técnica basada en principios ópticos, que se emplea para monitorizar la frecuencia cardiaca. La pulsioximetría [3] [4] combina la fotopletismografía y las características de absorción de la hemoglobina [5] [6] a través del análisis de señales luminosas de longitudes de onda específicas, para determinar el grado de oxigenación periférica. Los dispositivos clásicos emplean dos diodos electroluminiscentes (LEDs) con emisiones en las zonas del rojo (630-660 nm) y del infrarrojo (880-940 nm) del espectro óptico como fuentes de luz. "
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    ABSTRACT: El principal problema al monitorizar la frecuencia cardiaca mediante fotopletismografía durante el ejercicio son los artefactos por movimiento. Hemos registrado fotopletismogramas por transmisión en atletas durante pruebas de esfuerzo máximo en tapiz rodante, con un nuevo sistema sensor basado en tres diodos láser con emisiones en longitudes de onda del infrarrojo cercano. Los valores de frecuencia cardiaca obtenidos con un algoritmo de procesamiento desarrollado para este fin, coinciden los de electrocardiografía.
    Full-text · Conference Paper · Jul 2005
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    • "Accurate calibration, in particular, is a significant challenge because no reliable calibration method currently exists other than empirical methods. A reliable calibration algorithm would be especially useful for the application of pulse oximetry to saturations below 70% where current empirical approaches perform poorly (i.e., standard error for 50% saturation can be up to 20%, while in the 80%–100% range it is usually 1%–2%) [3], [4]. Pulse oximetry at low saturations, e.g., in the 10%–70% range, though rarely needed in adults, would be very useful in other emerging applications such as monitoring of the fetus during labor and delivery [5]–[8]. "
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    ABSTRACT: Pulse oximetry is a widely used technique in biomedical optics, but currently available pulse oximeters rely on empirical calibration approaches, which perform poorly at low saturations. We present an exact solution for pulse oximetry and show how this can be used as the basis for the development of a semiempirical calibration approach that may be useful, especially at low saturations and variable probe geometries. This new approach was experimentally tested against traditional empirical calibration techniques on transmission pulse oximetry for monitoring of fetal sheep using a minimally invasive spiral probe. The results open the way for the development of more accurate pulse oximetry.
    Preview · Article · Jun 2004 · IEEE Transactions on Biomedical Engineering
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