How accurate are pulse oximeters in patients with acute exacerbations of chronic obstructive airways disease?

The aim of this study was to determine the extent of correlation and agreem ent between arterial oxygen saturation and oxygen saturation as recorded by transcutaneous pulse oximetry. with a view to identifying whether pulse ox imetry can be used as an alternative to arterial values in the clinical man agement of patients with acute exacerbations of chronic obstructive airways disease (COAD) in the emergency department. It also aims to determine whet her there is a cut-off level of oxygen saturation by pulse oximetry that ca n screen for significant systemic hypoxia in this group. This prospective study of patients with acute exacerbations of GOAD who Eve rt: deemed by their treating doctor to require an arterial blood gas analys is to determine their ventilatory status; compared arterial oxygen saturati on with simultaneously recorded oxygen saturation measured by transcutaneou s pulse oximetry. Data were analysed using Pearson correlation. bias plot ( Bland-Altman) methods for agreement and the receiver operator characteristi c (ROC) curve method for determination of a screening cut-off. Sixty-four sample-pairs were analysed for this study. Nine (14%) had signif icant hypoxia (arterial PO2 less than 60 mmHg). The correlation coefficient was 0(.)91. The bias (Bland-Altman) plot shows a constant bias of -0(.)758 % and only fair agreement, with 95% limits for agreement of -8(.)2 to +6(.) 7%. With respect to the ROC curve analysis, the 'best' cut-off for detectio n of hypoxia was at oxygen saturation by pulse oximetry of 92% (sensitivity 100%. specificity 86%). In conclusion, there is not sufficient agreement for oxygen saturation meas ured by pulse oximetry to replace analysis of on arterial blood gas sample in the clinical evaluation of oxygenation in emergency patients with GOAD. However. oxygen saturation by pulse oximetry may be an effective screening test for systemic hypoxia, with the screening cut-off of 92% having sensiti vity for the detection of systemic hypoxia of 100% with specificity of 86%.