Journal of clinical monitoring
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Oximetry, the measurement of hemoglobin oxygen saturation in either blood or tissue, depends on the Lambert-Beer relationship between light transmission and optical density. Shortly after Bunsen and Kirchhoff invented the spectrometer in 1860, the oxygen transport function of hemoglobin was demonstrated by Stokes and Hoppe-Seyler, who showed color changes produced by aeration of hemoglobin solutions. In 1932 in Göttingen, Germany, Nicolai optically recorded the in vivo oxygen consumption of a hand after circulatory occlusion. ⋯ Shaw devised an eight-wavelength ear oximeter. Nakajima and co-workers invented the pulse oximeter, which avoids the need for calibration with only two wavelengths by responding only to the pulsatile changes in transmitted red and infrared light. Lübbers developed catheter tip and cuvette fiberoptic sensors for oxygen tension, carbon dioxide tension, and pH.
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One hundred and five children with congenital heart disease were monitored by pulse oximetry during cardiac catheterization. Excellent correlation (r = 0.95) was found between oxygen saturation values obtained with pulse oximetry and those obtained from arterial blood in 133 data pairs. ⋯ The clinical usefulness of pulse oximetry in the early recognition of decreased pulmonary blood flow or partial airway obstruction was demonstrated. Early diagnosis of changes in oxygenation was especially helpful in children with cyanotic congenital heart disease, in whom small changes in arterial oxygen tension may cause large changes in oxygen saturation.
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Comparative Study
An electronic stethoscope is judged better than conventional stethoscopes for anesthesia monitoring.
A prototype electronic monitoring stethoscope was constructed from readily available, high-quality components. It consisted of a conventional precordial or esophageal probe connected to a microphone by a rubber adapter. The microphone was connected by lightweight wire to an amplifier and headphones. ⋯ The electronic device was perceived to be louder, clearer in sound reproduction, more efficacious for monitoring, and easier to use continuously, and its headphones were considered more comfortable than the conventional earpiece. Based on our results, we conclude that amplified stethoscopes have the potential to improve monitoring. Further development of electronic stethoscope monitoring seems warranted and is continuing.
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The first biologic use of a platinum cathode for oxygen monitoring was reported in 1938 by Blinks and Skow, who was studying photosynthesis. Their report led to the tissue oxygen studies of Davies, Brink, and Bronk. Clark, by covering cathode and anode with a polyethylene membrane, changed the polarographic cathode from a sensor of oxygen availability by diffusion to a measure of oxygen tension (PO2) in the solution and thereby facilitated an enormous expansion of the study of the respiratory physiology of blood oxygen after 1956. ⋯ By reducing the cathode diameter, Staub and others eliminated the need for stirring the blood samples. Concurrent research with amperometric or polarographic oxygen measurement led Hersch to develop the means of determining oxygen content by coulometry in large cells that consumed all the injected oxygen. Methods of applying noninsulating, but protein impermeable, membranes to cathodes and of recessing cathodes into glass permitted measurement of PO2 in tissues and fluids with microelectrodes.