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تعريف جهاز pulse oximeter

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    belal-alsharaa
    belal-alsharaa غير متواجد حالياً

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    تاريخ التسجيل: Mar 2007
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    تعريف جهاز pulse oximeter

    السلام عليكم ورحمة الله وبركاته ....... شرح عن جهاز ال pulse oximeter والتعريف به وعن تاريخه....... أتمنى أن ينال اعجابكم ...



    .
    Introduction Pulse Oximetry :
    Pulse oximetry is useful method of monitoring patient in many circumstances, and in the face of limited resources, the pulse oximeter may represent a wise choice of monitor as with training it allows for the assessment of several different patient parameters.
    Pulse oximeter are non-invasive now a standard part of per operative monitoring which give the operator a non-invasive indication of the patient cardio-respiratory status . having been successfully used in invasive care, the recovery room during anesthesia they have been introduced in other areas of medicine such as general wards apparently without staff undergoing adequate training and it is possible that patient safety may be compromised with untrained staff. This article is therefore intended for occasional user of pulse oximetry .
    Pulse oximeters measure the arterial oxygen saturated of hemoglobin . the technology involved is complicated but there are two basic physical principles .
    First , the absorption of light at two different wavelengths by hemoglobin differs depending on the degree of oxygenation of hemoglobin .
    Second , the light signal following transmission through the tissues has a pulsatile component, resulting from the changing volume of arterial blood with each pulse beat . this can be distinguished by the microprocessor from the non-pulsatile component resulting from venous , capillary and tissue light absorption .
    The function of a pulse oximeter is affected by many variables , including :
    Ambient light ; shivering ; abnormal hemoglobin’s ; pulse rate and rhythm ; vasoconstriction and cardiac function .
    A pulse oximeter gives no indication of a patient’s ventilation , only of their oxygenation , and thus can give a false sense of security if supplemental oxygen is being given . in addition , there may be delay between the occurrence of a potentially hypoxic event such as respiratory obstruction detecting low oxygen saturation . however, oximetry is a useful non-invasive monitor of a patient’s cardio-respiratory system ,which has undoubtedly improved patient safety in many circumstances.
    What does a pulse oximeter measure ?
    1. the oxygen saturation of hemoglobin in arterial blood – which is a measure of the average amount of oxygen bound to each hemoglobin molecule .the percentage saturation is given as a digital read out together with am audible signal varying in pitch depending on the oxygen saturation
    2. the two pulse rate –in beats per minute , averaged over 5 to 20 seconds .
    A pulse oximeter gives no information on any of these other variables:
    . the oxygen ******* of the blood
    . the amount of oxygen dissolved in the blood
    . the respiratory rate or tidal volume i.e. ventilation
    . the cardiac out put or blood pressure
    systolic blood pressure can be estimated by nothing the pressure at which the plethysmograph trace reappears during deflation of a proximal non-invasive blood pressure cuff
    .[IMG]file:///C:/DOCUME%7E1/PC2%7E1/LOCALS%7E1/Temp/msohtml1/01/clip_image002.jpg[/IMG]
    Today there are many manufacturers of pulse oximeters. All offer a variety of different oximeter boxes with SpO2 (oxyhemoglobin) and pulse rate readings, waveform displays, alarms, etc. While the boxes and the displays may differ, they use a similar method of measuring oxyhemoglobin saturation by two wavelengths of light in the red and infrared range. But while the two-wavelength method is used to start the SpO2 measurement process, the way the signals are processed after that point, play a major role on how accurate the readings will be, especially through motion and low perfusion. During the late 1990's and into the next decade, 'new generation' pulse oximeters have been introduced that have elevated the accuracy of pulse oximeter readings significantly.
    Note: When arterial oxyhemoglobin saturation is measured by an arterial blood gas it is referred to as SaO2. When arterial oxyhemoglobin saturation is measured non-invasively by pulse oximetry, it is referred to as SpO2.
    Principles of modern pulse oximetry :
    Oxygen is carried in the bloodstream mainly bounded to hemoglobin .one molecule of hemoglobin can carry up to four molecules of oxygen , which is then100% saturated with oxygen . the average percentage saturation of a population of hemoglobin molecules in a blood sample is the oxygen saturation of blood .in addition ,a very small quantity of oxygen is carried dissolved in the blood , which can become important if the hemoglobin levels are extremely low. The latter ,however ,is not measured by pulse oximetry
    [IMG]file:///C:/DOCUME%7E1/PC2%7E1/LOCALS%7E1/Temp/msohtml1/01/clip_image006.jpg[/IMG]
    Calibration and Performance :
    Oximeters are calibrated during manufacture and automatically check their internal circuits when they are turned on. They are accurate in the range of oxygen saturations of 70 to 100% (+/-2%), but less accurate under 70%. The pitch of the audible pulse signal falls with reducing values of saturation.
    The size of the pulse wave (related to flow) is displayed graphically. Some models automatically increase the gain of the display when the flow decreases and in these the display may prove misleading. The alarms usually respond to a slow or fast pulse rate or an oxygen saturation below 90%. At this level there is a marked fall in PaO2 representing serious hypoxia.
    In the following situations the pulse oximeter readings may not be accurate:
    1.A reduction in peripheral pulsatile blood flow produced by peripheral vasoconstriction (hypovolaemia, severe hypotension, cold, cardiac failure, some cardiac arrhythmias) or peripheral vascular disease. These result in an inadequate signal for analysis.
    2.Venous congestion, particularly when caused by tricuspid regurgitation, may produce venous pulsations which may produce low readings with ear probes. Venous congestion of the limb may affect readings as can a badly positioned probe. When readings are lower than expected it is worth repositioning the probe. In general, however, if the waveform on the flow trace is good, then the reading will be accurate.
    3.Bright overhead lights in theatre may cause the oximeter to be inaccurate, and the signal may be interrupted by surgical diathermy. Shivering may cause difficulties in picking up an adequate signal.
    4.Pulse oximetry cannot distinguish between different forms of hemoglobin. Carboxy hemoglobin (hemoglobin combined with carbon monoxide) is registered as 90% oxygenated haemoglobin and 10% desaturated hemoglobin - therefore the oximeter will overestimate the saturation. The presence of methaemoglobin will prevent the oximeter working accurately and the readings will tend towards 85%, regardless of the true saturation.
    5.When methylene blue is used in surgery to the parathyroid’s or to treat methemoglobinaemia a short lived reduction in saturation estimations is registered.
    6.Nail varnish may cause falsely low readings. However the units are not affected by jaundice, dark skin or anemia.
    The oxygen saturation should always be above 95%. In patients with long standing respiratory disease or those with cyanotic congenital heart disease readings may be lower and reflect the severity of the underlying disease. Oximeters give no information about the level of CO2 and therefore have limitations in the assessment of patients developing respiratory failure due to CO2 retention. On rare occasions oximeters may develop faults and like all monitoring the reading should always be interpreted in association with the patient's clinical condition. Never ignore a reading which suggests the patient is becoming hypoxic. There is no doubt that pulse oximetry is the greatest advance in patient monitoring for many years and it is hoped that their use will eventually become routine during anesthesia and surgery world wide.
    Principles of Pulse Oximetry Technology:
    The principle of pulse oximetry is based on the red and infrared light absorption characteristics of oxygenated and deoxygenated hemoglobin. Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. Deoxygenated (or reduced) hemoglobin absorbs more red light and allows more infrared light to pass through. Red light is in the 600-750 nm wavelength light band. Infrared light is in the 850-1000 nm wavelength light band.
    [IMG]file:///C:/DOCUME%7E1/PC2%7E1/LOCALS%7E1/Temp/msohtml1/01/clip_image008.jpg[/IMG]
    Pulse oximetry uses a light emitter with red and infrared LEDs that shines through a reasonably translucent site with good blood flow. Typical adult/pediatric sites are the finger, toe, pinna (top) or lobe of the ear. Infant sites are the foot or palm of the hand and the big toe or thumb. Opposite the emitter is a photo detector that receives the light that passes through the measuring site.

    .
    Pulse Oximetry Test Results :
    Pulse oximeter results must be accompanied by the percentage of oxygen the person is breathing, and their respiratory rate, for the results to be meaningful. A fit, healthy person should have an oxygen saturation between 95% and 99%. Results lower than 90% may be caused by excessive bleeding, lung problems, cigarette smoking, blood vessel problems, lung diseases such as COPD. Percentages above 99% may indicate that the testing was performed outside the pulse oximeter's limitations; re-testing may be needed.



    Monitoring
    with pulse oximetry might improve patient outcome by enabling an early diagnosis and, consequently, correction of per operative events that might otherwise cause postoperative complications or even death. The aim of the study was to clarify the effect of per operative monitoring with pulse oximetry and to identify the adverse outcomes that might be prevented or improved by its use. Trials were identified by computerized searches of the Cochrane Library, MEDLINE, EMBASE, and by checking the reference lists of trials and review articles. All controlled trials that randomized patients to either pulse oximetry or no pulse oximetry during the per operative period, including in the operating and recovery room, were included in the study.
    Features :
    • Oxygen Saturation (SpO2)
    • Heart Rate
    • Quick assessment and continuous measurements
    • Colored textual, pulse quality warnings
    • Audible warning of abnormal saturation levels and heart rates
    • Internal and external direct, result and trend printouts


    The pulse waveforms are continuously displayed in green, yellow or red. Textual and audible warnings are available to ensure that abnormal saturation, heart rates and pulse artifact are immediately indicated. Analysis of the results from a continuous test is also possible and printout formats, both internal and direct A4 are selectable.
    The instrument makes Pulse Oximetry quick and simple in supporting other respiratory investigations, vital in the management of COPD and other cardio respiratory disease.
    Purpose :
    To determine the utility of pulse oximetry as a routine fifth vital sign in acute pediatric assessment.
    Design :
    Prospective study using pulse oximetry to measure oxygen saturation in children presenting to emergency department triage. Saturation values were disclosed to clinicians only after they had completed medical evaluations and were ready to discharge or admit each child. We measured changes in medical treatment and diagnoses initiated after the disclosure of pulse oximetry values.
    Setting and Participants :
    The study included 2127 consecutive children presenting to triage at a university emergency department.
    Measurements :
    Changes in select diagnostic tests: chest radiography, complete blood count, spirometry, arterial blood gases, pulse oximetry, and ventilation-perfusion scans; treatments: antibiotics, -agonists, supplemental oxygen; and hospital admission and final diagnoses that occurred after disclosure of triage pulse oximetry values.
    Signal acquisition challenge :
    the resistor-feedback amplifier circuit shown in this figure is the most common bioelectric trans impedance circuit.
    With the amplifier used in the inverting configuration ,the light shining on a photodiode produces a small current that
    Runs to the amplifier summing junction and through the feedback resistor .
    Given the very large feedback resistor value ,this circuit is extremely sensitive to changes in light intensity .
    In this example configuration , an input light signal of just 0.001 uW will produce afull-swing out put.
    Depending on design requirements, it can be very useful to achieve out put swing down to or below ground .
    The medical pulse integrator :
    Summary points
    ØPulse oximeters give non-invasive estimation of arterial hemoglobin oxygen saturation .
    ØUseful in anesthesia , recovery , intensive care ,patient transport.
    ØTwo principles involved :
    1.differential light absorption by hemoglobin and oxyhemoglobin.
    2.identification of pulsatile component of signal .
    Øno direct indication of a patient’s ventilation , only of their oxygenation .
    Ølag monitor –time delay between potentially hypoxic event such as respiratory obstruction and a pulse oximeter detecting low oxygen saturation .
    Øinaccuracies :ambient light shivering and vasoconstriction ;abnormal hemoglobin ; and alterations in pulse rate rhythm
    advances in microprocessor have led to improved signal processing.




    مع تحيات أبواسكندر

  2. [2]
    Biomedical
    Biomedical غير متواجد حالياً
    عضو متميز
    الصورة الرمزية Biomedical


    تاريخ التسجيل: Dec 2005
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