Interest in two-wavelength classic, that is, nonpulse, oximetry began early in the 20th century. Noninvasive in vivo measurements of oxygen saturation showed promise, but the methods were beset by several problems. The pulse oximetry technique, by focusing on the pulsatile arterial component, neatly circumvented many of the problems of the classic nonpulse arterial approach. Today's pulse oximeter owes a good measure of its success to the technologic advances in light emission and detection and the ready availability of microcomputers and their software. Many clinicians have recognized how valuable the assessment of the patient's oxygenation in real time can be. This appreciation has propelled the use of pulse oximeters into many clinical fields, as well as nonclinical fields such as sports training and aviation. Understanding how and what pulse oximetry measures, how pulse oximetry data compare with data derived from laboratory analysis, and how the pulse oximeter responds to dyshemoglobins, dyes, and other interfering conditions must be understood for the correct application and interpretation of this revolutionary monitor.
Pulse oximetry is an important diagnostic and patient monitoring tool. However, motion can induce considerable error into pulse oximetry accuracy, resulting in loss of data, inaccurate readings, and false alarms. We will discuss how motion artifact affects pulse oximetry accuracy, the clinical consequences of motion artifact, and the methods used by various technologies to minimize the impact of the motion noise.
The technological strategies implemented in Masimo SET pulse oximetry effectively permit continuous monitoring of SpO2 during challenging clinical conditions of motion and poor tissue perfusion.
Pulse oximetry, utilizing spectrophotometric principles and normalized absorption of red and infrared light, provides vital information concerning patients' arterial oxygen saturation, pulse rate and perfusion level. Conventional pulse oximeters, incorporating conventional filters, are hampered by artifact interference from motion, electrical and ambient light and other conditions producing weak signals. Masimo introduced mathematically and physiologically based designs along with adaptive filtering and what it calls DST (Discrete Saturation Transform) as a solution to monitoring patients even during times of severe and unpredictable noise interference. This combined with 4 other alternative calculations, revolutionized pulse oximetry performance. This new technology is called Signal Extraction Pulse Oximetry or Masimo SET pulse oximetry. Sensitivity and specificity of signal extraction technology, was first tested extensively in the lab on volunteers under conditions designed to simulate varying physiology, including controlled desaturations, combined with severe patient motion, and low perfusion conditions. Conventional pulse oximeters demonstrated very low sensitivity and specificity while pulse oximeters with SET showed sensitivity and specificity of over 95% under the same conditions. Clinical testing was then performed on an extensive variety of patients in the hospital environment demonstrating similar performance, validating the significant advance resulting from the use of SET. False alarms due to motion artifact and low perfusion have been reduced from up to 90% to less than 5%.
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