Pulse oximeter
337320
224704481
2008-07-10T01:19:04Z
Scientificone
7451265
[[Image:R7C_total_hemoglobin_screen.jpg|frame|thumbnail|50px|A modern pulse oximeter that also provides pulse co-oximetry, a noninvasive way to measure several blood constituents that previously required invasive procedures and time-consuming laboratory tests.]]
[[Image:saturometre_1.jpg|thumb|A portable saturometer (for emergencies)]]
[[Image:saturometre_2.jpg|thumb|Typical measurement through the fingernail]]
[[Image:oximeter.jpg|thumb|A portable pulse oximeter registering a satisfactory saturation reading]]
A '''pulse oximeter''' is a [[medical device]] that indirectly measures the oxygen saturation of a patient's [[blood]] (as opposed to measuring oxygen saturation directly through a blood sample) and changes in blood volume in the skin, producing a [[photoplethysmograph]]. It is often attached to a [[medical monitor]] so staff can see a patient's oxygenation at all times. Most monitors also display the heart rate. Portable, battery operated pulse oximeters are also available for home blood oxygen monitoring. The original oximeter was made by Milliken in the 1940s. The precursor to today's modern pulse oximetrer was developed in 1972, by Aoyagi at Nihon Kohden using the ratio of red to infrared light absorption of pulsating components at the measuring site. It was commercialized by Biox in 1981. The device did not see wide adoption in the United States until the late 1980's.
== Function ==
A blood-oxygen monitor displays the percentage of arterial [[hemoglobin]] in the [[oxyhemoglobin]] configuration. Acceptable normal ranges are from 95 to 100 percent, although values down to 90% are common. For a patient breathing room air, at not far [[Above mean sea level|above sea level]], an estimate of arterial pO<sub>2</sub> can be made from the blood-oxygen monitor SpO<sub>2</sub> reading.
A pulse oximeter is a particularly convenient [[non-invasive]] measurement instrument. Typically it has a pair of small [[light-emitting diode]]s (LEDs) facing a [[photodiode]] through a translucent part of the patient's body, usually a fingertip or an earlobe. One LED is red, with [[wavelength]] of 660 nm, and the other is [[infrared]], 905, 910, or 940 nm. Absorption at these wavelengths differs significantly between [[oxyhemoglobin]] and its deoxygenated form, therefore from the ratio of the absorption of the red and infrared light the oxy/deoxyhemoglobin ratio can be calculated. The absorbance of oxyhemoglobin and deoxyhemoglobin is the same ([[isosbestic point]]) for the wavelengths of 590 and 805 nm; earlier oximeters used these wavelengths for correction for hemoglobin concentration.[http://www.frca.co.uk/article.aspx?articleid=332]
The monitored signal bounces in time with the [[Heart rate|heart beat]] because the arterial [[blood vessel]]s expand and contract with each heartbeat. By examining only the varying part of the [[absorption spectrum]] (essentially, subtracting minimum absorption from peak absorption), a monitor can ignore other tissues or nail polish[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=12212998] and discern only the absorption caused by arterial blood. Thus, detecting a pulse is essential to the operation of a pulse oximeter and it will not function if there is none.
A recent use has been found for the pulse oximeter, in the area of detecting blood loss. Kirk Shelley, a Yale University anesthesiologist, through gathering pulse oximeter data for over seven years, developed an algorithm that turns absorption changes into accurate estimates of blood volume. [http://www.technologyreview.com/Biotech/16019/ Technology Review]
==Advantages==
A pulse oximeter is useful in any setting where a patient's [[oxygenation]] is unstable, including [[intensive care]], operating, recovery, emergency and hospital ward settings, [[pilots]] in unpressurized aircraft, for assessment of any patient's oxygenation, and determining the effectiveness of or need for supplemental [[oxygen]]. Assessing a patient's need for oxygen is the most essential element to life; no human life thrives in the absence of oxygen (cellular or gross). Although a pulse oximeter is used to monitor oxygenation, it cannot determine the metabolism of oxygen, or the amount of oxygen being used by a patient. For this purpose, it is necessary to also measure [[carbon dioxide]] (CO<sub>2</sub>) levels. It is possible that it can also be used to detect abnormalities in ventilation. However, the use of a pulse oximeter to detect [[hypoventilation]] is impaired with the use of supplemental oxygen, as it is only when patients breathe room air that abnormalities in respiratory function can be detected reliably with its use. Therefore, the routine administration of supplemental oxygen may be unwarranted if the patient is able to maintain adequate oxygenation in room air, since it can result in hypoventilation going undetected.
Because of their simplicity and speed, pulse oximeters are of critical importance in [[emergency medicine]] and are also very useful for patients with respiratory or cardiac problems, or for diagnosis of some [[sleep disorders]] such as [[apnea]] and [[hypopnea]]. Portable, battery operated pulse oximeters are useful for pilots operating in a non-pressurized aircraft above 10,000 feet (12,500 feet in the US[http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/0/BA9AFBF96DBC56F0852566CF006798F9?OpenDocument&Highlight=oxygen]), where supplemental oxygen is required. Prior to the oximeter's invention, many complicated [[blood test]]s needed to be performed. Portable pulse oximeters are also useful for mountain climbers and athletes whose oxygen levels may decrease at high [[altitudes]] or with exercise.
==Limitations and Advancements==
Oximetry is not a complete measure of respiratory sufficiency. A patient suffering from [[hypoventilation]] (poor [[gas exchange]] in the [[lung]]s) given 100% oxygen can have excellent blood oxygen levels while still suffering from [[respiratory acidosis]] due to excessive [[carbon dioxide]].
It is also not a complete measure of circulatory sufficiency. If there is insufficient [[Circulatory system|bloodflow]] or insufficient hemoglobin in the blood ([[anemia]]), tissues can suffer [[Hypoxia (medical)|hypoxia]] despite high [[oxygen saturation]] in the blood that does arrive.
A higher level of [[methemoglobin]] will tend to cause a pulse oximeter to read closer to 85% regardless of the true level of oxygen saturation. It also should be noted that the inability of two-wavelength saturation level measurement devices to distinguish [[carboxyhemoglobin]] due to [[carbon monoxide]] inhalation from oxyhemoglobin must be taken into account when diagnosing a patient in emergency rescue, e.g., from a fire in an apartment. A Pulse [[CO-oximeter]] measures absorption at additional wavelengths to distinguish CO from O<sub>2</sub> and determines the blood oxygen saturation more reliably. In 2005 [http://www.masimo.com Masimo Corporation] introduced the first FDA-approved pulse oximeter to monitor carbon monoxide levels noninvasively.[http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfPMN/pmn.cfm?ID=25620]. Masimo Pulse CO-oximeters can now measure total [[hemoglobin]], [[oxygen content]],[[methemoglobin]] and PVI, in addition to carboxyhemoglobin. [http://www.masimo.com Masimo Corporation]
PVI has been shown in initial clinical studies to provide clinicians with a new method for noninvasive and automatic assessment of patient fluid volume status. [http://www.bio-medicine.org/medicine-news-1/Breaking-Study-3A-Masimo-Pleth-Variability-Index--28PVI-29-Shown-Effective-in-Noninvasive-Detection-of-Changes-in-Ventricular-Preload-and-Fluid-Volume-3719-1/] Appropriate fluid levels are vital to reducing postoperative risks and improving patient outcomes as fluid volumes that are too low (under hydration) or too high (over hydration) have been shown to decrease wound healing, increase risk of infection and cardiac complications. [http://www.unboundmedicine.com/medline/ebm/record/870721/full_citation/Comparisons_of_body_fluid_volumes_plasma_renin_activity_hemodynamics_and_pressor_responsiveness_between_juvenile_and_aged_patients_with_essential_hypertension_]
==See also==
*[[Arterial blood gas]]
*[[Medical equipment]]
*[[Medical monitor]]
*[[Pulse_oximetry |Pulse oximetry]]
*[[Capnography]], measuring of carbon dioxide (CO2) in the respiratory gases
Pulse oximetry is the most important safety development in anesthesia.
==External links==
* [http://www.oximetry.org/pulseox/principles.htm Principles of Pulse Oximetry Technology]
* [http://www.nda.ox.ac.uk/wfsa/html/u05/u05_003.htm How Pulse Oximetry Works]
[[Category:Medical testing equipment]]
[[Category:Oxygen]]
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