Respiratory Medicine » Resp failure

Pulse Oximetry

Pulse Oximetry is an easy-to-use and effective method for detecting hypoxaemia when the device recognizes a good pulse wave. It is used routinely for monitoring oxygen saturation; however, it tells nothing about ventilation. A decrease in oxygen saturation to below 90% is an indication of a significant reduction in oxygen partial pressure. The advantages of pulse oximetry are that it is an easy-to-use and reliable instrument and there are fewer sources of error. Also, pain and nervousness during artery sampling cause hyperventilation, which increases oxygen saturation values. and lead to an overestimation of oxygenation. The disadvantages are that pulse oximetry does not give information on acid-base balance. does not detect hypoventilation (increased partial pressure of carbon monoxide) in a patient breathing air with increased concentration of oxygen. In a patient breathing normal air hypoventilation usually reduces oxygen saturation. Pulse oximetry does not thus replace clinical monitoring of respiration. In a critically ill patient the method is unfortunately often unreliable because of peripheral vasoconstriction (the device does not recognize the pulse wave).

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