Pulse oximetry

Pulse oximeter fingertip reading of SpO2 (monitoring your oxygen saturation level), perfusion index value display and pulse rate.

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Pulse oximetry is a noninvasive method for monitoring a person’s oxygen saturation (SO2). Its reading of SpO2 (peripheral oxygen saturation) is not always identical to the reading of SaO2 (arterial oxygen saturation) from arterial blood analysis, but the two are correlated well enough that the safe, convenient, noninvasive, inexpensive pulse oximetry method is valuable for measuring oxygen saturation.

Pulse Rate
Range : 30-254 BPM
Resolution : ±1bpm
Accuracy : ±2bpm

Environmental
Operating Temperature : 0’C-50’C
Storage Temperature : -10’C – 60’C
Operating Humidity : 15%RH – 95%RH

Storage Humidity : 10%RH – 95%RH

In its most common (transmissive) application mode, a sensor device is placed on a thin part of the patient’s body, usually a finger or earlobe. The device passes two wavelengths of light through the body part to a photodetector. It measures the changing absorbance at each of the wavelenghts, 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.

Less commonly, reflectance pulse oximetry is 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 a 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 can cause a combination of arterial and venous pulsations in the forehead region and lead to spurious SpO2 results.

A blood-oxygen monitor displays the percentage of blood that is loaded with oxygen. More specifically, it measures what percentage of hemoglobin, the protein in blood that carries oxygen, is loaded. For a patient breathing room air at or near sea level, an estimate of arterial pO2 can be made from the blood-oxygen monitor saturation peripheral oxygen (SpO2) reading.

Absorption of light at these wavelengths differs significantly between blood loaded with oxygen and blood lacking oxygen. Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through. Deoxygenated hemoglobin allows more infrared light to pass through and absorbs more red light.

 

In contrast, blood gas levels must otherwise be determined in a laboratory on a drawn blood sample. Pulse oximetry 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. 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.

Because of their simplicity of use and the ability to provide continuous and immediate oxygen saturation values, pulse oximeters are of critical importance in emergency and are also very useful for patients with respiratory or cardiac problems, or for diagnosis of some sleep disordees such as apnea and hypopnea.

Portable pulse oximeters are also useful for mountain climbers and athletes whose oxygen levels may decrease at high altitudes or with exercise. Some portable pulse oximeters employ software that charts a patient’s blood oxygen and pulse, serving as a reminder to check blood oxygen levels.