User:Rheatandon/Pulse oximetry

Conditions affecting accuracy

Because pulse oximeter devices are calibrated in healthy subjects, the accuracy is poor for critically ill patients and preterm newborns.

Erroneously low readings may be caused by hypoperfusion of the extremity being used for monitoring (often due to a limb being cold, or from vasoconstriction secondary to the use of vasopressor agents); incorrect sensor application; highly calloused skin; or movement (such as shivering), especially during hypoperfusion. To ensure accuracy, the sensor should return a steady pulse and/or pulse waveform. Pulse oximetry technologies differ in their abilities to provide accurate data during conditions of motion and low perfusion.

Obesity, hypotension (low blood pressure), and some hemoglobin variants can reduce the accuracy of the results. Some home pulse oximeters have low sampling rates which can significantly underestimate dips in blood oxygen levels. The accuracy of pulse oximetry deteriorates considerably for readings below 80%.

Research has suggested that error rates in common pulse oximeter devices may be higher for adults with dark skin color, leading to claims of encoding systemic racism in countries with multi-racial populations such as the United States. The issue was first identified decades ago; one of the earliest studies on this topic occurred in 1976, which reported reading errors in dark-skinned patients that reflected lower blood oxygen saturation values. Further studies indicate that while accuracy with dark skin is good at higher, healthy saturation levels, some devices overestimate the saturation at lower levels, which may lead to hypoxia not being detected. A study that reviewed thousands of cases of occult hypoxemia, where patients were found to have oxygen saturation below 88% per arterial blood gas measurements despite pulse oximeter readings indicating 92% to 96% oxygen saturation, found that Black patients were three times as likely as White patients to have their low oxygen saturation missed by pulse oximeters. Another research study investigated patients in the hospital with COVID-19 and found that occult hypoxemia occurred in 28.5% of Black patients compared to only 17.2% of White patients. There has been research to indicate that black COVID-19 patients were 29% less likely to receive supplemental oxygen in a timely manner and three times more likely to have hypoxemia. A further study, which used a MIMIC-IV critical care dataset of both pulse oximeter readings and oxygen saturation levels detected in blood samples, demonstrated that Black, Hispanic, and Asian patients had higher SpO2 readings than white patients for a given blood oxygen saturation level measured in blood samples. As a result, Black, Hispanic, and Asian patients also received lower rates of supplemental oxygen than white patients. It is suggested that melanin can interfere with the absorption of light used to measure the level of oxygenated blood, often measured from a person’s finger. Further studies and computer simulations show that the increased amounts of melanin found in people with darker skin scatters the photons of light used by the pulse oximeters, decreasing the accuracy of the measurements; as the studies used to calibrate the devices typically oversample people with lighter skin, the parameters for pulse oximeters are set based on information that is not equitably balanced to account for diverse skin colors. This inaccuracy can lead to potentially missing people who need treatment, as pulse oximetry is used for the screening of sleep apnea and other types of sleep-disordered breathing which in the United States are conditions more prevalent among minorities. This bias is a significant concern as a 2% decrease is important for respiratory rehabilitation, studies of sleep apnea, and athletes performing physical efforts; it can lead to severe complications for the patient, requiring an external oxygen supply or even hospitalization.  Another concern regarding pulse oximetry bias is that insurance companies and hospital systems increasingly use these numbers to inform their decisions;  pulse oximetry measurements are used to identify candidates for reimbursement. Similarly, pulse oximetry data is being incorporated into algorithms for clinicians; Early Warning Scores, which provide a record for analyzing a patient’s clinical status and alerting clinicians if needed, incorporate algorithms with pulse oximetry information and can result in misinformed patient records.

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