Pulse oximetry

History[edit]

In 1935, German physician Karl Matthes (1905–1962) developed the first two-wavelength ear O₂ saturation meter with red and green filters (later red and infrared filters). It was the first device to measure O₂ saturation.^[45]


The original oximeter was made by Glenn Allan Millikan in the 1940s.^[46] In 1943^[47] and as published in 1949,^[48] Earl Wood added a pressure capsule to squeeze blood out of the ear so as to obtain an absolute O₂ saturation value when blood was readmitted. The concept is similar to today's conventional pulse oximetry, but was difficult to implement because of unstable photocells and light sources; today this method is not used clinically. In 1964 Shaw assembled the first absolute reading ear oximeter, which used eight wavelengths of light.


The first pulse oximetry was developed in 1972 by Japanese bioengineers Takuo Aoyagi and Michio Kishi at Japanese medical electronic equipment manufacturer Nihon Kohden, using the ratio of red to infrared light absorption of pulsating components at the measuring site. Nihon Kohden manufactured the first pulse oximeter, Ear Oximeter OLV-5100. Surgeon Susumu Nakajima and his associates first tested the device in patients, reporting it in 1975.^[49] However, Nihon Kohden suspended the development of pulse oximetry and did not apply for a basic patent of pulse oximetry except in Japan, which facilitated further development and utilization of pulse oximetry later in U.S. In 1977, Minolta commercialized the first finger pulse oximeter OXIMET MET-1471. In the U.S., the first pulse oximetry was commercialized by Biox in 1980.^[49][50][51]


By 1987, the standard of care for the administration of a general anesthetic in the U.S. included pulse oximetry. From the operating room, the use of pulse oximetry rapidly spread throughout the hospital, first to recovery rooms, and then to intensive care units. Pulse oximetry was of particular value in the neonatal unit where the patients do not thrive with inadequate oxygenation, but too much oxygen and fluctuations in oxygen concentration can lead to vision impairment or blindness from retinopathy of prematurity (ROP). Furthermore, obtaining an arterial blood gas from a neonatal patient is painful to the patient and a major cause of neonatal anemia.^[52] Motion artifact can be a significant limitation to pulse oximetry monitoring, resulting in frequent false alarms and loss of data. This is because during motion and low peripheral perfusion, many pulse oximeters cannot distinguish between pulsating arterial blood and moving venous blood, leading to underestimation of oxygen saturation. Early studies of pulse oximetry performance during subject motion made clear the vulnerabilities of conventional pulse oximetry technologies to motion artifact.^[18][53]


In 1995, Masimo introduced Signal Extraction Technology (SET) that could measure accurately during patient motion and low perfusion by separating the arterial signal from the venous and other signals. Since then, pulse oximetry manufacturers have developed new algorithms to reduce some false alarms during motion,^[54] such as extending averaging times or freezing values on the screen, but they do not claim to measure changing conditions during motion and low perfusion. So there are still important differences in performance of pulse oximeters during challenging conditions.^[19] Also in 1995, Masimo introduced perfusion index, quantifying the amplitude of the peripheral plethysmograph waveform. Perfusion index has been shown to help clinicians predict illness severity and early adverse respiratory outcomes in neonates,^[55][56][57] predict low superior vena cava flow in very low birth weight infants,^[58] provide an early indicator of sympathectomy after epidural anesthesia,^[59] and improve detection of critical congenital heart disease in newborns.^[60]


Published papers have compared signal extraction technology to other pulse oximetry technologies and have demonstrated consistently favorable results for signal extraction technology.^[18][19][61] Signal extraction technology pulse oximetry performance has also been shown to translate into helping clinicians improve patient outcomes. In one study, retinopathy of prematurity (eye damage) was reduced by 58% in very low birth weight neonates at a center using signal extraction technology, while there was no decrease in retinopathy of prematurity at another center with the same clinicians using the same protocol but with non-signal extraction technology.^[62] Other studies have shown that signal extraction technology pulse oximetry results in fewer arterial blood gas measurements, faster oxygen weaning time, lower sensor utilization, and lower length of stay.^[63] The measure-through motion and low perfusion capabilities it has also allow it to be used in previously unmonitored areas such as the general floor, where false alarms have plagued conventional pulse oximetry. As evidence of this, a landmark study was published in 2010 showing that clinicians at Dartmouth-Hitchcock Medical Center using signal extraction technology pulse oximetry on the general floor were able to decrease rapid response team activations, ICU transfers, and ICU days.^[64] In 2020, a follow-up retrospective study at the same institution showed that over ten years of using pulse oximetry with signal extraction technology, coupled with a patient surveillance system, there were zero patient deaths and no patients were harmed by opioid-induced respiratory depression while continuous monitoring was in use.^[65]


In 2007, Masimo introduced the first measurement of the pleth variability index (PVI), which multiple clinical studies have shown provides a new method for automatic, noninvasive assessment of a patient's ability to respond to fluid administration.^[41][66][67] Appropriate fluid levels are vital to reducing postoperative risks and improving patient outcomes: fluid volumes that are too low (under-hydration) or too high (over-hydration) have been shown to decrease wound healing and increase the risk of infection or cardiac complications.^[68] Recently, the National Health Service in the United Kingdom and the French Anesthesia and Critical Care Society listed PVI monitoring as part of their suggested strategies for intra-operative fluid management.^[69][70]


In 2011, an expert workgroup recommended newborn screening with pulse oximetry to increase the detection of critical congenital heart disease (CCHD).^[71] The CCHD workgroup cited the results of two large, prospective studies of 59,876 subjects that exclusively used signal extraction technology to increase the identification of CCHD with minimal false positives.^[72][73] The CCHD workgroup recommended newborn screening be performed with motion tolerant pulse oximetry that has also been validated in low perfusion conditions. In 2011, the US Secretary of Health and Human Services added pulse oximetry to the recommended uniform screening panel.^[74] Before the evidence for screening using signal extraction technology, less than 1% of newborns in the United States were screened. Today, The Newborn Foundation has documented near universal screening in the United States and international screening is rapidly expanding.^[75] In 2014, a third large study of 122,738 newborns that also exclusively used signal extraction technology showed similar, positive results as the first two large studies.^[76]


High-resolution pulse oximetry (HRPO) has been developed for in-home sleep apnea screening and testing in patients for whom it is impractical to perform polysomnography.^[77][78] It stores and records both pulse rate and SpO₂ in 1 second intervals and has been shown in one study to help to detect sleep disordered breathing in surgical patients.^[79]