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Pulse oximetry is a non-invasive method for monitoring a person's O2 saturation. In its most common (transmissive) application mode, a sensor device is placed on a thin part of the patient's body, usually a fingertip or earlobe, or in the case of an infant, across a foot. The device passes two wavelengths of light through the body part to a photodetector. It measures the changing absorbance at each of the wavelengths, allowing it to determine the absorbances due to the pulsing arterial blood alone, excluding venous blood, skin, bone, muscle, fat, and (in most cases) nail polish. Reflectance pulse oximetry may be used as an alternative to transmissive pulse oximetery described above. This method does not require a thin section of the person's body and is therefore well suited to more universal application such as the feet, forehead and chest, but it also has some limitations. Vasodilation and pooling of venous blood in the head due to compromised venous return to the heart, as occurs with congenital cyanotic heart disease patients, or in patients in the Trendelenburg position, can cause a combination of arterial and venous pulsations in the forehead region and lead to spurious SpO2 (Saturation of peripheral oxygen) results.〔Jorgensen JS, Schmid ER, Konig V, Faisst K, Huch A, Huch R. Limitations of forehead pulse oximetry. J Clin Monit. Jul 1995;11(4):253–256.〕 ==History== In 1935, Karl Matthes (German physician 1905–1962) developed the first 2-wavelength ear O2 saturation meter with red and green filters (later switched to red and infrared filters). His meter was the first device to measure O2 saturation. The original oximeter was made by Glenn Allan Millikan in the 1940s. In 1949 Wood added a pressure capsule to squeeze blood out of ear to obtain zero setting in an effort to obtain 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. This method is not used clinically. In 1964 Shaw assembled the first absolute reading ear oximeter by using eight wavelengths of light. Commercialized by Hewlett-Packard, its use was limited to pulmonary functions and sleep laboratories due to cost and size. Pulse oximetry was developed in 1972, by Takuo Aoyagi and Michio Kishi, bioengineers, at Nihon Kohden using the ratio of red to infrared light absorption of pulsating components at the measuring site. Susumu Nakajima, a surgeon, and his associates first tested the device in patients, reporting it in 1975. It was commercialized by Biox in 1981 and Nellcor in 1983. Biox was founded in 1979, and introduced the first pulse oximeter to commercial distribution in 1981. Biox initially focused on respiratory care, but when the company discovered that their pulse oximeters were being used in operating rooms to monitor oxygen levels, Biox expanded its marketing resources to focus on operating rooms in late 1982. A competitor, Nellcor (now part of Covidien, Ltd.), began to compete with Biox for the U.S. operating room market in 1983. Prior to the introduction of pulse oximetry, a patient's oxygenation could only be determined by arterial blood gas, a single-point measurement that takes several minutes for sample collection and processing by a laboratory. In the absence of oxygenation, damage to the brain starts within 5 minutes with brain death ensuing within another 10–15 minutes. The worldwide market for pulse oximetry is over a billion dollars. With the introduction of pulse oximetry, a non-invasive, continuous measure of patient's oxygenation was possible, revolutionizing the practice of anesthesia and greatly improving patient safety. Prior to its introduction, studies in anesthesia journals estimated U.S. patient mortality as a consequence of undetected hypoxemia at 2,000 to 10,000 deaths per year, with no known estimate of patient morbidity. 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 the recovery room, and then into the various 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.〔Lin JC, Strauss RG, Kulhavy JC, et al. Phlebotomy overdraw in the neonatal intensive care nursery. Pediatrics. Aug 2000;106(2):E19.〕 Motion artifact can be a significant limitation to pulse oximetry monitoring resulting in frequent false alarms and loss of data. The reason for this is that 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.〔Barker SJ. "Motion-resistant" pulse oximetry: a comparison of new and old models. Anesth Analg. 2002;95(4):967–972.〕〔Barker SJ, Shah NK. The effects of motion on the performance of pulse oximeters in volunteers (revised publication). Anesthesiology. 1997;86(1):101–108.〕 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〔Jopling MW, Mannheimer PD, Bebout DE. Issues in the laboratory evaluation of pulse oximeter performance. Anesth Analg. Jan 2002;94(1 Suppl):S62–68.〕 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.〔Shah N, Ragaswamy HB, Govindugari K, Estanol L. Performance of three new-generation pulse oximeters during motion and low perfusion in volunteers. J Clin Anesth. May 22.〕 In 2004, a jury found that Nellcor infringed several Masimo patents related to measure-through motion and low perfusion signal processing technology. In 2005, the appellate court affirmed the infringement findings against Nellcor, and instructed the District Court to enter a permanent injunction against Nellcor’s pulse oximeters (e.g., N-395, N-595) that were found to infringe. In January 2006, Masimo and Nellcor entered into a settlement agreement, where Nellcor, among other things, agreed to discontinue shipment of the pulse oximeters that were found to infringe Masimo’s patents. Published papers have compared signal extraction technology to other pulse oximetry technologies and have demonstrated consistent favorable results for signal extraction technology.〔Barker SJ. "Motion-resistant" pulse oximetry: a comparison of new and old models. Anesth Analg 2002;95:967–72〕〔Shah N, Ragaswamy HB, Govindugari K, Estanol L. Performance of three new-generation pulse oximeters during motion and low perfusion in volunteers. J Clin Anesth 2012〕〔Hay WW, Jr., Rodden DJ, Collins SM, Melara DL, Hale KA, Fashaw LM. Reliability of conventional and new pulse oximetry in neonatal patients. J Perinatol 2002;22:360–6.〕 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.〔Castillo A, Deulofeut R, Critz A, Sola A. Prevention of retinopathy of prematurity in preterm infants through changes in clinical practice and SpO(2)technology. Acta Paediatr 2010;100:188–92.〕 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.〔Durbin CG, Rostow SK. More reliable oximetry reduces the frequency of arterial blood gas analyses and hastens oxygen weaning after cardiac surgery: A prospective, randomized trial of the clinical impact of a new technology. Crit Care Med 2002;30:1735–40〕 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 clinicians using signal extraction technology pulse oximetry on the general floor were able to decrease rapid response team activations, ICU transfers, and ICU days.〔Taenzer AH, Pyke JB, McGrath SP, Blike GT. Impact of pulse oximetry surveillance on rescue events and intensive care unit transfers: a before-and-after concurrence study. Anesthesiology 2010;112:282–7.〕 In 2011, an expert workgroup recommended newborn screening with pulse oximetry to increase the detection of critical congenital heart disease (CCHD). 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.〔()〕 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. 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. 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.〔()〕 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.〔() 〕〔() 〕 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.〔Chung F, Liao P, Elsaid H, Islam S, Shapiro CM, Sun Y. Oxygen desaturation index from nocturnal oximetry: a sensitive and specific tool to detect sleep-disordered breathing in surgical patients. Anesth Analg;114:993–1000.〕 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,〔De Felice C, Leoni L, Tommasini E, Tonni G, Toti P, Del Vecchio A, Ladisa G, Latini G. Maternal pulse oximetry perfusion index as a predictor of early adverse respiratory neonatal outcome after elective cesarean delivery. ''Pediatric Critical Care Medicine'' 2008;9:203–8.〕〔De Felice C, Latini G, Vacca P, Kopotic RJ. The pulse oximeter perfusion index as a predictor for high illness severity in neonates. Eur J Pediatr 2002;161:561–2.〕〔De Felice C, Goldstein MR, Parrini S, Verrotti A, Criscuolo M, Latini G. Early dynamic changes in pulse oximetry signals in preterm newborns with histologic chorioamnionitis. ''Pediatric Critical Care Medicine'' 2006;7:138–42.〕 predict low superior vena cava flow in very low birth weight infants,〔Takahashi S, Kakiuchi S, Nanba Y, Tsukamoto K, Nakamura T, Ito Y. The perfusion index derived from a pulse oximeter for predicting low superior vena cava flow in very low birth weight infants. J Perinatol;30:265–9〕 provide an early indicator of sympathectomy after epidural anesthesia,〔Ginosar Y, Weiniger CF, Meroz Y, Kurz V, Bdolah-Abram T, Babchenko A, Nitzan M, Davidson EM. Pulse oximeter perfusion index as an early indicator of sympathectomy after epidural anesthesia. Acta Anaesthesiol Scand 2009;53:1018–26.〕 and improve detection of critical congenital heart disease in newborns.〔Granelli AW, Ostman-Smith I. Noninvasive peripheral perfusion index as a possible tool for screening for critical left heart obstruction. Acta Paediatr 2007;96:1455–9.〕 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.〔Zimmermann M, Feibicke T, Keyl C, Prasser C, Moritz S, Graf BM, Wiesenack C. Accuracy of stroke volume variation compared with pleth variability index to predict fluid responsiveness in mechanically ventilated patients undergoing major surgery. Eur J Anaesthesiol 2009;27:555–61〕〔Cannesson M, Desebbe O, Rosamel P, Delannoy B, Robin J, Bastien O, Lehot JJ. Pleth variability index to monitor the respiratory variations in the pulse oximeter plethysmographic waveform amplitude and predict fluid responsiveness in the operating theatre. Br J Anaesth 2008 Aug;101(2):200–6〕〔Forget P, Lois F, de Kock M. Goal-Directed Fluid Management Based on the Pulse Oximeter-Derived Pleth Variability Index Reduces Lactate Levels and Improves Fluid Management. Anesth Analg 2010.〕 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. 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.〔() 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pulse oximetry」の詳細全文を読む スポンサード リンク
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