Accuracy and Response Time of a Portable Pulse Oximeter

Abstract

We studied the performance of a portable pulse oximeter in 123 consecutive adult patients by spot-checking with a finger probe and by spectrophotometry of oxygen saturation on a simultaneous arterial blood sample. 88 patients were overtly hypoxemic (HbO₂ < 90%) and 26 showed severe hypoxemia (HbO₂ 36–70%). The differences between the two methods showed a skewed distribution with a positive tail due to the over-estimation of lower saturation values by the pulse oximeter. Overall, the 95% confidence interval for the median difference ranged from -0.6 to +0.5%. The limits of agreement (distribution-free 95% confidence interval for the sample) were -5.8 to +11.6%. Pulse oximetry can be recommended as a first assessment of the respiratory balance only if a cut-off value of HbO₂ equal to 90% in nonsmoking, air-breathing subjects is acceptable. The finger probe implies a response delay of approximately 30 s, making the instrument rather insensitive to short hypoxemic transients. With a predictive value around 90%, the pulse oximeter may be a useful portable screening tool

BTS guideline for emergency oxygen use in adult patients

“…In one study of 123 adult patients who had simultaneous measurements of pulse oximetry and arterial oxygen saturation measured in arterial blood gases, the 95% confidence interval for the median difference ranged from −0.6 to +0.5% 148. It has been estimated that an oxygen saturation of 92% or above measured by pulse oximetry has a sensitivity of 100% and specificity of 86% for excluding hypoxaemia defined as an arterial oxygen saturation below 60 mm Hg (8 kPa) 151…”

ThoracicSociety ofAustralia andNewZealand oxygen guidelines for acute oxygen use in adults: ‘Swimming between the flags’

“… Pulse oximetry should be available in all clinical situations in which oxygen is used . [Grade C] Practice point: There is variable accuracy of pulse oximetry to predict SaO 2 in acutely ill patients, with SaO 2 measurements by pulse oximeter (SpO 2 ) both over and underestimating SaO 2 , with wide limits of agreement . The accuracy of SpO 2 may worsen with increasingly severe hypoxaemia .…”

“…[Grade C] Practice point: There is variable accuracy of pulse oximetry to predict SaO 2 in acutely ill patients, with SaO 2 measurements by pulse oximeter (SpO 2 ) both over and underestimating SaO 2 , with wide limits of agreement . The accuracy of SpO 2 may worsen with increasingly severe hypoxaemia . Clinicians need to be aware of the variable accuracy of SpO 2 in the utilization of pulse oximetry in clinical practice.…”

“…Proposed mechanisms for oxygen‐induced hypercapnia include increased ventilation perfusion mismatch due to reduced hypoxic pulmonary vasoconstriction, reduced ventilatory drive, atelectasis and the Haldane effect, with the contribution of each likely to depend on the clinical situation There is variable accuracy of pulse oximetry to predict SaO 2 in acutely ill patients, with SpO 2 measurements both over and under estimating SaO 2 , with wide limits of agreement . Clinicians need to be aware of the variable accuracy of SpO 2 in the utilization of pulse oximetry in clinical practice.…”

“…Clinicians need to be aware of the variable accuracy of SpO 2 in the utilization of pulse oximetry in clinical practice. Factors that might affect the accuracy of pulse oximetry include severe hypoxaemia, carboxyhaemoglobin and methaemoglobin levels, anaemia, dark skin, low perfusion, excessive ambient light and nail polish The use of high flow oxygen in an attempt to protect against subsequent hypoxaemia in the event of deterioration has the potential to delay the recognition of such a deterioration .…”