Читать книгу Management of Complications in Oral and Maxillofacial Surgery - Группа авторов - Страница 18

Pulse oximeters are designed to estimate the peripheral arterial blood oxygen saturation as measured/estimated by the pulse oximeter (SpO₂) and work via measurements of infrared energy transmission. In smokers, pulse oximetry readings may be artificially increased due to the level of carboxyhemoglobin present in the circulation. This is especially true for those who have smoked tobacco within a few hours of the anesthetic procedure. The pulse oximeter cannot distinguish between carboxyhemoglobin and oxygen‐carrying hemoglobin in the blood of smokers and thus provides an overestimate of the true blood oxygen saturation. Nail polish or cold extremities may interfere with the function of the pulse oximeter.

The reading provided by pulse oximetry (SpO₂) is a good approximation of arterial oxygen saturation (SaO₂), and a 90% SpO₂ level is the standard cutoff value below which desaturation begins to have noticeable clinical effects. At an SpO₂ of 90%, the SaO₂ is approximately 60% (oxyhemoglobin dissociation curve), and that is why the low SpO₂ alarm on the pulse oximeter should be set at or above the 92% range. There is a time delay between a patient's true oxygen saturation and the pulse oximeter reading, and many oximetry machines will sound an alarm when a patient's oxygen saturation reading drops below 93% or 94% to account for this. Most healthy adults will have an SpO₂ between 98% and 100% on room air, but occasionally patients with underlying respiratory compromise will have a baseline O₂ saturation of 94–95%. It can be important to know this prior to beginning a procedure to avoid the erroneous assumption that a patient with a low baseline O₂ saturation is experiencing respiratory depression as a result of anesthesia.