The Sounds of Saturation

Abstract

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.

The effectiveness of pulse oximetry sonification enhanced with tremolo and brightness for distinguishing clinically important oxygen saturation ranges: a laboratory study

“…Suggested remedies have included multisensory training and the use of better mappings of SpO 2 to pitch . Commercial pulse oximeters map linear increments of SpO 2 to either fixed or percentage increments in sound frequency (perceived as pitch); the former results in a linear mapping, whereas the latter results in a logarithmic mapping . A logarithmic scale creates approximately equal‐appearing pitch intervals .…”

Audio spectrum and sound pressure levels vary between pulse oximeters

“…Our results on the tones generated are consistent with those of Santamore and Cleaver. 3 They found, using simulator technology to generate oxygen saturation levels, that each of the different models of variable pitch pulse oximeters tested had different frequencies at the oxygen saturation levels measured. We used brief occlusions of the digital arteries to achieve the relevant oxygen saturations, which we think is more physiological.…”

“…Several of these properties have been researched previously. [3][4][5][6][7] For example, noise levels in the operating room have been systematically measured [4][5][6][7] as has the hearing acuity of anesthesiologists. 8 However, an audio spectrum and sound pressure level analysis of the monitoring beeps produced by common variable-pitch pulse oximeters has not been reported.…”

Accuracy of detecting changes in auditory heart rate in a simulated operating room environment*

“…The sonification (transfer of information by the use of sound) of heart rate (by a change in the interval between tones) and oxygen saturation (by a change in pitch) is used to augment information transfer to anaesthetists. This multimodal information transfer assists clinical performance during periods of high cognitive workload [2].The transfer of precise values of oxygen saturation using sonification has been shown to be poor, and of greater concern is that a 8% change in oxygen saturation was required before 95% of anaesthetists noticed a change [3]. In an abstract [4], the threshold for detecting a change in heart rate sonification has been described as 8 beats per minute (bpm), a rate at which < 50% of anaesthestists could correctly identify changes.…”

“…The transfer of precise values of oxygen saturation using sonification has been shown to be poor, and of greater concern is that a 8% change in oxygen saturation was required before 95% of anaesthetists noticed a change [3]. In an abstract [4], the threshold for detecting a change in heart rate sonification has been described as 8 beats per minute (bpm), a rate at which < 50% of anaesthestists could correctly identify changes.…”