The sounds of saturation

Audible pulse tones, based on a variable-pitch frequency scale, allow the anesthesiologist to determine the patient's oxygen saturation without constant visual examination of the monitor display. The ability to reliably detect oxygen saturation levels based on audible pulse tones may be compromised when multiple pulse oximeter systems are used. The goal of this observational study was to examine the pitch frequency scales from several different pulse oximeter manufacturers. Using simulator technology, incremental oxygen saturations between 80% and 100% were created. The frequencies of various pulse tones in this range were measured with an oscilloscope. From this data, the relationship between oxygen saturation and corresponding pulse tone frequency was examined. Diagrammed results showed wide variation in the pulse frequency scales used by the pulse oximeters tested. At any oxygen saturation level between 80% and 100%, none of the monitors had the same pulse tone frequency. With such variation among systems, the ability to accurately determine oxygen saturation from a pulse tone may be hindered. In locations where different pulse oximeter systems are encountered, the potential for confusion exists. Anesthesiologists need to be aware of these differences, and should familiarize themselves with the audible frequency scale of a particular pulse oximeter model before its use.