![]() Non-arterial pulses may be detected if the probe is secured too tightly, creating venous pulsations in the finger. Patients who are cold but not hypothermic may have vasoconstriction in their fingers and toes that may also compromise arterial flow (Carroll, 1997). Patients most at risk of low perfusional states are those with hypotension, hypovolaemia and hypothermia and those in cardiac arrest. ![]() ![]() If the patient has a weak or absent peripheral pulse, pulse oximeter readings will not be precise. In order for a pulsatile flow to be detected, there must be sufficient perfusion in the monitored area. Patient condition - To calculate the difference between full and empty capillaries, oximetry measures light absorption over a number of pulses, usually five (Harrahill, 1991). Factors which affect accuracy of readings All staff using the pulse oximeter must be aware of its functions and correct usage.Īrterial blood gas analysis is more accurate however, pulse oximetry is considered sufficiently accurate for most clinical purposes, having recognised that there are limitations. Selection depends on the setting in which it is used. Most provide a visual digital waveform display, an audible display of arterial pulsations and heart rate, and a variety of sensors to accommodate individuals regardless of age, size or weight. There are various makes and models of pulse oximeters available (Lowton, 1999). The result is processed into a digital display of oxygen saturation on the oximeter screen, which is symbolised as SpO2 (Jevon, 2000). The oxygen saturation of the blood determines the degree of light absorption. Pulsatile arterial blood during systole causes an influx of oxyhaemoglobin to the tissue, absorbing more infrared light, and allowing less light to reach the photodetector. Infrared light is absorbed by the oxyhaemoglobin red light by the reduced haemoglobin. The probe is placed on a suitable part of the body, usually a fingertip or ear lobe, and the LEDs transmit light wavelengths through pulsating arterial blood to a photodetector on the other side of the probe. The oximeter probe has two light-emitting diodes (LEDs), one red and one infrared, located on one side of the probe. Arterial oxygenated blood is red due to the quality of oxyhaemoglobin it contains, causing it to absorb light of certain wavelengths. Pulse oximeters measure the absorption of specific wavelengths of light in oxygenated haemoglobin as compared with that of reduced haemoglobin. This paper aims to promote a greater awareness of the importance of having an appropriate knowledge base before using pulse oximetry and to provide a source of education and reference for teaching purposes. However, staff are reported to have limited education in the operation of the device and limited knowledge of how it works and what factors may affect the readings (Stoneham et al, 1994 Casey, 2001). It has been suggested that the increase in the use of pulse oximeters in general wards could see it becoming as commonplace as the thermometer. They do, however, provide an opportunity for deviations from a patient’s oxygen baseline to be noticed immediately, as an early warning signal to clinicians to help prevent the consequences of desaturation and detect hypoxaemia before it produces cyanosis. Pulse oximeters do not offer information about haemoglobin concentration, cardiac output, efficiency of oxygen delivery to the tissues, oxygen consumption, sufficiency of oxygenation, or adequacy of ventilation.
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