In these patients, the oxygen saturation remains above 90% for the duration of the study. The first pattern is seen in healthy individuals without underlying cardiopulmonary issues. How is overnight pulse oximetry useful in OSA?įrom a practical point of view, waveforms can be classified into one of three distinct patterns. 5, 6 Analyzing the oxygen saturation waveform after OPO for specific patterns can reveal information regarding the patient’s overnight oxygenation status. 4 Continuous pulse oximetry measures three parameters these include the pulse rate, the oxygen saturation, and lastly, the time spent with an oxygen saturation below 90% during the duration of the study (T-90). OPO has been extensively studied in sleep studies and the American Academy of Sleep Medicine has classified it as a type 4 monitoring device. 3 Any decrease below this value can indicate to a health care provider that the patient may possibly have an underlying derangement in his or her cardiopulmonary status. In general, healthy patients have an overnight oxygen saturation of 96%. Since continuous monitoring is generally done overnight, this technology is commonly referred to as overnight pulse oximetry (OPO). The advantage of continuous monitoring is that practitioners are able to evaluate changes in oxygen saturation in real-time. Traditional pulse oximetry is useful in its ability to capture a snapshot of a patient’s oxygen saturation at a moment in time. This technology has advanced over the years to the point that continuous monitoring is possible. This component is capable of measuring the amount of light that is transmitted through the tissue. The lights are emitted from the diodes on one end of the device and pass through the vascular tissue before being detected by a component on the other side. The first, at 660 nm, appears as red light and the second, at 940 nm, is infrared light. Most pulse oximeters emit light at two distinct wavelengths. Most commercially available pulse oximeters are placed on bodily areas that are rich in blood vessels such as the fingertip or the earlobe. 1)įigure 1 – absorbance patterns of oxyhemoglobin and deoxyhemoglobin 2 It is well documented that oxyhemoglobin absorbs near-infrared light and dissipates red light. Using simple spectrophotometry, this technology allows us to detect differences in the absorption spectra of oxyhemoglobin and deoxyhemoglobin as blood passes through the body in a pulsatile fashion. It has even been called the “fifth vital sign”. Pulse oximetry has been used to measure oxygen status for more than 40 years. As such, it is important that respiratory therapists acquaint themselves with this technology and its uses. This technology provides adequate information regarding a patient’s oxygenation and respiratory patterns, aiding in the assessment of a patient’s cardiopulmonary dysfunction. Overnight pulse oximetry (OPO) is a straightforward testing modality that carries the potential to screen for patients with moderate to severe obstructive sleep apnea (OSA). A less intrusive screening test like overnight pulse oximetry would likely increase adherence to study protocols. ![]() Consequently, patients may be unwilling to undergo these procedures. ![]() Both of these evaluations are at times cumbersome. 1 Currently, either an at-home sleep test or overnight polysomnographic test is necessary to diagnose sleep apnea. Sleep apnea, with an estimated incidence between three and seven percent in the general population, is a common disorder.
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