oximeters

An oximeter is a device that noninvasively estimates the oxygen saturation of hemoglobin in arterial blood, typically reporting SpO2 and pulse rate. It is widely used in medical settings and at home to monitor oxygenation in patients with respiratory or cardiovascular conditions.

The most common form is the pulse oximeter, which is usually a fingertip or earlobe sensor connected to a small monitor. These devices emit light at red and infrared wavelengths and measure how much light is absorbed by the blood. The ratio of absorbed light at the two wavelengths correlates with the percentage of hemoglobin saturated with oxygen (SpO2). Some devices also provide a plethysmographic waveform to track pulse rate. A co-oximeter is a laboratory or anesthesia monitor that uses multiple wavelengths to distinguish different forms of hemoglobin, including carboxyhemoglobin and methemoglobin.

Applications and interpretation: used during surgery, in critical care, ambulances, and for home sleep apnea or chronic respiratory disease monitoring. Normal SpO2 in healthy individuals is typically around 95–100%. Readings markedly lower than normal may indicate hypoxemia, but readings can be affected by poor perfusion, movement, ambient light, nail polish, skin pigmentation, or anemia. Certain conditions, such as carbon monoxide exposure or methemoglobinemia, can distort readings, especially with CO-oximeters or low-hemoglobin states.

History and regulation: pulse oximetry was developed in the late 20th century, with Takuo Aoyagi credited as a key inventor. In most countries, consumer and clinical pulse oximeters are regulated as medical devices and require safety and accuracy standards. While useful for rapid assessment, oximeters estimate arterial oxygen saturation rather than measuring it directly, and must be interpreted in clinical context.