Which device is used to monitor oxygen saturation continuously during anesthesia?

• A. Stethoscope
• B. Thermometer
• C. Capnograph
• D. Pulse oximeter

Answer: (D)

Monitoring oxygen saturation continuously during anesthesia is done with a pulse oximeter. It noninvasively estimates the percentage of hemoglobin bound with oxygen by sending light through a capillary bed (usually at the finger, toe, or ear) and detecting changes as the arterial pulse beats. This yields a real-time SpO2 reading along with a plethysmographic waveform, allowing immediate detection of hypoxemia and rapid intervention, such as increasing inspired oxygen or adjusting ventilation.

The other devices don’t provide continuous oxygen saturation: a stethoscope is for listening to breath and heart sounds but doesn’t give a numerical oxygen saturation; a thermometer only measures temperature; a capnograph tracks end-tidal CO2 and ventilation status rather than oxygen saturation.