A comparison of linear and logarithmic auditory tones in pulse oximeters

Signaling Patient Oxygen Desaturation with Enhanced Pulse Oximetry Tones

Manufacturers could improve the pulse tones emitted by pulse oximeters to support more accurate identification of a patient's peripheral oxygen saturation (SpO2) range. In this article, we outline the strengths and limitations of the variable-pitch tone that represents SpO2 of each detected pulse, and we argue that enhancements to the tone to demarcate clinically relevant ranges are feasible and desirable. The variable-pitch tone is an appreciated and trusted feature of the pulse oximeter's user interface. However, studies show that it supports relative judgments of SpO2 trends over time and is less effective at supporting absolute judgments about the SpO2 number or conveying when SpO2 moves into clinically important ranges. We outline recent studies that tested whether acoustic enhancements to the current tone could convey clinically important ranges more directly, without necessarily using auditory alarms. The studies cover the use of enhanced variable-pitch pulse oximeter tones for neonatal and adult use. Compared with current tones, the characteristics of the enhanced tones represent improvements that are both clinically relevant and statistically significant. We outline the benefits of enhanced tones, as well as discuss constraints of which developers of enhanced tones should be aware if enhancements are to be successful.

Signaling Patient Oxygen Desaturation with Enhanced Pulse Oximetry Tones

Manufacturers could improve the pulse tones emitted by pulse oximeters to support more accurate identification of a patient's peripheral oxygen saturation (SpO2) range. In this article, we outline the strengths and limitations of the variable-pitch tone that represents SpO2 of each detected pulse, and we argue that enhancements to the tone to demarcate clinically relevant ranges are feasible and desirable. The variable-pitch tone is an appreciated and trusted feature of the pulse oximeter's user interface. However, studies show that it supports relative judgments of SpO2 trends over time and is less effective at supporting absolute judgments about the SpO2 number or conveying when SpO2 moves into clinically important ranges. We outline recent studies that tested whether acoustic enhancements to the current tone could convey clinically important ranges more directly, without necessarily using auditory alarms. The studies cover the use of enhanced variable-pitch pulse oximeter tones for neonatal and adult use. Compared with current tones, the characteristics of the enhanced tones represent improvements that are both clinically relevant and statistically significant. We outline the benefits of enhanced tones, as well as discuss constraints of which developers of enhanced tones should be aware if enhancements are to be successful.

The Influence of Audible Alarm Loudness and Type on Clinical Multitasking

In high-consequence industries such as health care, auditory alarms are an important aspect of an informatics system that monitors patients and alerts providers attending to multiple concurrent tasks. Alarms levels are unnecessarily high and alarm signals are uninformative. In a laboratory-based task setting, we studied 25 anesthesiology residents' responses to auditory alarms in a multitasking paradigm comprised of three tasks: patient monitoring, speech perception/intelligibility, and visual vigilance. These tasks were in the presence of background noise plus/minus music, which served as an attention-diverting stimulus. Alarms signified clinical decompensation and were either conventional alarms or a novel informative auditory icon alarm. Both alarms were presented at four different levels. Task performance (accuracy and response times) were analyzed using logistic and linear mixed-effects regression. Salient findings were 1), the icon alarm had similar performance to the conventional alarm at a +2 dB signal-to-noise-ratio (SNR) (accuracy: OR 1.21 (95% CI 0.88, 1.67), response time: 0.04 s at 2 dB (95% CI: -0.16, 0.24), which is a much lower level than current clinical environments; 2) the icon alarm was associated with 27% greater odds (95% CI: 18%, 37%) of correctly addressing the vigilance task, regardless of alarm SNR, suggesting crossmodal/multisensory multitasking benefits; and 3) compared to the conventional alarm, the icon alarm was associated with an absolute improvement in speech perception of 4% in the presence of an attention-diverting auditory stimulus (p = 0.031). These findings suggest that auditory icons can provide multitasking benefits in cognitively demanding clinical environments.

Smooth or Stepped? Laboratory Comparison of Enhanced Sonifications for Monitoring Patient Oxygen Saturation

BACKGROUND

The pulse oximeter (PO) provides anesthesiologists with continuous visual and auditory information about a patient's oxygen saturation (SpO₂). However, anesthesiologists' attention is often diverted from visual displays, and clinicians may inaccurately judge SpO₂ values when relying on conventional PO auditory tones. We tested whether participants could identify SpO₂ value (e.g., "97%") better with acoustic enhancements that identified three discrete clinical ranges by either changing abruptly at two threshold values (stepped-effects) or changing incrementally with each percentage value of SpO₂ (smooth-effects).

METHOD

In all, 79 nonclinicians participated in a between-subjects experiment that compared performance of participants using the stepped-effects display with those who used the smooth-effects display. In both conditions, participants heard sequences of 72 tones whose pitch directly correlated to SpO₂ value, and whose value could change incrementally. Primary outcome was percentage of responses that correctly identified the absolute SpO₂ percentage, ±1, of the last pulse tone in each sequence.

RESULTS

Participants using the stepped-effects auditory tones identified absolute SpO₂ percentage more accurately (M = 53.7%) than participants using the smooth-effects tones (M = 47.9%, p = .038). Identification of range and detection of transitions between ranges showed even stronger advantages for the stepped-effects display (p < .005).

CONCLUSION

The stepped-effects display has more pronounced auditory cues at SpO₂ range transitions, from which participants can better infer absolute SpO₂ values. Further development of a smooth-effects display for this purpose is not necessary.

Are Anesthesiology Providers Good Guessers? Heart Rate and Oxygen Saturation Estimation in a Simulation Setting

Background

Anesthesia providers may need to interpret the output of vital sign monitors based on auditory cues, in the context of multitasking in the operating room. This study aims to evaluate the ability of different anesthesia providers to estimate heart rate and oxygen saturation in a simulation setting.

Methods

Sixty anesthesia providers (residents, nurse anesthetics, and anesthesiologists) were studied. Four scenarios were arranged in a simulation context. Two baseline scenarios with and without waveform visual aid, and two scenarios with variation of heart rate and/or oxygen saturation were used to assess the accuracy of the estimation made by the participants.

Results

When the accurate threshold for the heart rate was set at less than 5 beats per minute, the providers only had a correct estimation at two baseline settings with visual aids (p=0.22 and 0.2237). Anesthesia providers tend to underestimate the heart rate when it increases. Providers failed to accurately estimate oxygen saturation with or without visual aid (p=0.0276 and 0.0105, respectively). Change in recording settings significantly affected the accuracy of heart rate estimation (p < 0.0001), and different experience levels affected the estimation accuracy (p=0.041).

Conclusion

The ability of anesthesia providers with different levels of experience to assess baseline and variations of heart rate and oxygen saturation is unsatisfactory, especially when oxygen desaturation and bradycardia coexist, and when the subject has less years of experience.

A Novel Auditory Display for Neonatal Resuscitation: Laboratory Studies Simulating Pulse Oximetry in the First 10 Minutes After Birth

OBJECTIVE

We tested whether enhanced sonifications would improve participants' ability to judge the oxygen saturation levels (SpO₂) of simulated neonates in the first 10 min after birth.

BACKGROUND

During the resuscitation of a newborn infant, clinicians must keep the neonate's SpO₂ levels within the target range, however the boundaries for the target range change each minute during the first 10 min after birth. Resuscitation places significant demand on the clinician's visual attention, and the pulse oximeter's sonification could provide eyes-free monitoring. However, clinicians have difficulty judging SpO₂ levels using the current sonification.

METHOD

In two experiments, nonclinicians' ability to detect SpO₂ range and direction-while performing continuous arithmetic problems-was tested with enhanced versus conventional sonifications. In Experiment 1, tremolo signaled when SpO₂ had deviated below or above the target range. In Experiment 2, tremolo plus brightness signaled when SpO₂ was above target range, and tremolo alone when SpO₂ was below target range.

RESULTS

The tremolo sonification improved range identification accuracy over the conventional display (81% vs. 63%, p < .001). The tremolo plus brightness sonification further improved range identification accuracy over the conventional display (92% vs. 62%, p <.001). In both experiments, there was no difference across conditions in arithmetic task accuracy ( p >.05).

CONCLUSION

Using the enhanced sonifications, participants identified SpO₂ range more accurately despite a continuous distractor task.

APPLICATION

An enhanced pulse oximetry sonification could help clinicians multitask more effectively during neonatal resuscitations.

Improving the detectability of oxygen saturation level targets for preterm neonates: A laboratory test of tremolo and beacon sonifications

Recent guidelines recommend oxygen saturation (SpO2) levels of 90%-95% for preterm neonates on supplemental oxygen but it is difficult to discern such levels with current pulse oximetry sonifications. We tested (1) whether adding levels of tremolo to a conventional log-linear pulse oximetry sonification would improve identification of SpO2 ranges, and (2) whether adding a beacon reference tone to conventional pulse oximetry confuses listeners about the direction of change. Participants using the Tremolo (94%) or Beacon (81%) sonifications identified SpO2 range significantly more accurately than participants using the LogLinear sonification (52%). The Beacon sonification did not confuse participants about direction of change. The Tremolo sonification may have advantages over the Beacon sonification for monitoring SpO2 of preterm neonates, but both must be further tested with clinicians in clinically representative scenarios, and with different levels of ambient noise and distractions.

Novel Pulse Oximetry Sonifications for Neonatal Oxygen Saturation Monitoring: A Laboratory Study

OBJECTIVE

We aimed to test whether the use of novel pulse oximetry sounds (sonifications) better informs listeners when a neonate's oxygen saturation (SpO2) deviates from the recommended range.

BACKGROUND

Variable-pitch pulse oximeters do not accurately inform clinicians via sound alone when SpO2 is outside the target range of 90% to 95% for neonates on supplemental oxygen. Risk of blindness, organ damage, and death increase if SpO2 remains outside the target range. A more informative sonification may improve clinicians' ability to maintain the target range.

METHOD

In two desktop experiments, nonclinicians' ability to detect SpO2 range and direction of change was tested with novel versus conventional sonifications of simulated patient data. In Experiment 1, a "shoulder" sonification used larger pitch differences between adjacent saturation percentages for SpO2 values outside the target range. In Experiment 2, a "beacon" sonification used equal-appearing pitch differences, but when SpO2 was outside the target range, a fixed-pitch reference tone from the center of the target SpO2 range preceded every fourth pulse tone.

RESULTS

The beacon sonification improved range identification accuracy over the control display (85% vs. 60%; p < .001), but the shoulder sonification did not (55% vs. 52%).

CONCLUSION

The beacon provided a distinct auditory alert and reference that significantly improved nonclinical participants' ability to identify SpO2 range.

APPLICATION

Adding a beacon to the variable-pitch pulse oximeter sound may help clinicians identify when, and by how much, a neonate's SpO2 deviates from the target range, particularly during patient transport situations when auditory information becomes essential.