oximetrie

Oximetry is a noninvasive method for estimating the oxygen saturation of arterial blood, typically reported as SpO2. It is based on spectrophotometry, which measures how hemoglobin absorbs light at specific wavelengths.

The most common form, pulse oximetry, uses a sensor placed on a fingertip, toe, or earlobe that emits red and infrared light and detects pulsatile changes in arterial blood to estimate SpO2. Co-oximetry, which can be performed on a blood sample or integrated into analyzers, uses multiple wavelengths to quantify oxyhemoglobin, deoxyhemoglobin, carboxyhemoglobin, and methemoglobin.

Applications: It is widely used for continuous monitoring during anesthesia and in intensive care, emergency medicine, postoperative care, and home monitoring for chronic lung disease. It also serves to screen or monitor patients in sleep medicine and other respiratory conditions.

Interpretation and limitations: Normal SpO2 values at sea level are typically 95–100%. Values below about 90% are often considered hypoxemic. Readings can be affected by poor peripheral perfusion, motion, cold extremities, nail polish or artificial nails, ambient light, skin pigmentation, or severe anemia. Pulse oximetry reflects oxygenation but not ventilation and cannot distinguish different causes of hypoxemia alone. In carbon monoxide exposure, standard pulse oximetry can be falsely high; CO-oximetry or arterial blood gas analysis is needed for accurate assessment.

History and development: Oximetry became widely available in the late 20th century and has since become a standard monitoring modality in many clinical settings due to its noninvasive nature and continuous capability.