How Well Can Anaesthetists Discriminate Pulse Oximeter Tones?

Enhanced Neonatal Pulse Oximetry Sounds for the First Minutes of Life: A Laboratory Trial

OBJECTIVE

Auditory enhancements to the pulse oximetry tone may help clinicians detect deviations from target ranges for oxygen saturation (SpO2) and heart rate (HR).

BACKGROUND

Clinical guidelines recommend target ranges for SpO2 and HR during neonatal resuscitation in the first 10 minutes after birth. The pulse oximeter currently maps HR to tone rate, and SpO2 to tone pitch. However, deviations from target ranges for SpO2 and HR are not easy to detect.

METHOD

Forty-one participants were presented with 30-second simulated scenarios of an infant's SpO2 and HR levels in the first minutes after birth. Tremolo marked distinct HR ranges and formants marked distinct SpO2 ranges. Participants were randomly allocated to conditions: (a) No Enhancement control, (b) Enhanced HR Only, (c) Enhanced SpO2 Only, and (d) Enhanced Both.

RESULTS

Participants in the Enhanced HR Only and Enhanced SpO2 Only conditions identified HR and SpO2 ranges, respectively, more accurately than participants in the No Enhancement condition, ps < 0.001. In the Enhanced Both condition, the tremolo enhancement of HR did not affect participants' ability to identify SpO2 range, but the formants enhancement of SpO2 may have attenuated participants' ability to identify tremolo-enhanced HR range.

CONCLUSION

Tremolo and formant enhancements improve range identification for HR and SpO2, respectively, and could improve clinicians' ability to identify SpO2 and HR ranges in the first minutes after birth.

APPLICATION

Enhancements to the pulse oximeter tone to indicate clinically important ranges could improve the management of oxygen delivery to the neonate during resuscitation in the first 10 minutes after birth.

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.

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.

Supporting multiple patient monitoring with head-worn displays and spearcons

In hospitals, clinicians often need to monitor several patients while performing other tasks. However, visual displays that show patients' vital signs are in fixed locations and auditory alarms intended to alert clinicians may be missed. Information such as spearcons (time-compressed speech earcons) that 'travels' with the clinician and is delivered by earpiece and/or head-worn displays (HWDs), might overcome these problems. In this study, non-clinicians monitored five simulated patients in three 10-min scenarios while performing a demanding tracking task. Monitoring accuracy was better for participants using spearcons and a HWD (88.7%) or a HWD alone (86.2%) than for participants using spearcons alone (74.1%). Participants using the spearcons and HWD (37.7%) performed the tracking task no differently from participants using spearcons alone (37.1%) but participants using the HWD alone performed worse overall (33.1%). The combination of both displays may be a suitable solution for monitoring multiple patients.

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.

Audible capnometric cues with end-tidal carbon dioxide improve the quality of patient monitoring

The importance of capnometry and end-tidal carbon dioxide (ETCO₂) has been underscored in recent years by guidelines as a method to continuously monitor adequacy of ventilation during sedation and anesthesia. Guidelines for cardiopulmonary resuscitation (CPR) recommend attempts to improve CPR quality if ETCO₂ is lower than 10 mmHg. ETCO₂ is thus a time-critical parameter that may benefit from being delivered in real time to health care providers. We performed a pilot study to investigate whether the addition of audible capnometric cues after each breath enhanced providers' ability to maintain appropriate ventilation over conventional capnography. The addition of audible cues was confirmed to enhance control of ETCO₂ during manual ventilation. We subsequently developed five distinct audible capnometric cues corresponding to different levels of ETCO₂. We performed a study using ten random simulated test cases to confirm whether changes between levels as well as the direction of change could be distinguished using these audible cues. Audible cues were found to be easily distinguishable. 16 evaluators correctly identified presence and direction of change in ETCO₂ with an average pass rate of 89%. It is anticipated that this "ETCO₂ Audible Cue" feature will be able to improve the quality of patient monitoring, as well help improve the quality of CPR.

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.

A comparison of linear and logarithmic auditory tones in pulse oximeters

This study compared the ability of forty anaesthetists to judge absolute levels of oxygen saturation, direction of change, and size of change in saturation using auditory pitch and pitch difference in two laboratory-based studies that compared a linear pitch scale with a logarithmic scale. In the former the differences in saturation become perceptually closer as the oxygenation level becomes higher whereas in the latter the pitch differences are perceptually equivalent across the whole range of values. The results show that anaesthetist participants produce significantly more accurate judgements of both absolute oxygenation values and size of oxygenation level difference when a logarithmic, rather than a linear, scale is used. The line of best fit for the logarithmic function was also closer to x = y than for the linear function. The results of these studies can inform the development and standardisation of pulse oximetry tones in order to improve patient safety.

The multimodal world of medical monitoring displays

A vision of the future of intraoperative monitoring for anesthesia is presented-a multimodal world based on advanced sensing capabilities. I explore progress towards this vision, outlining the general nature of the anesthetist's monitoring task and the dangers of attentional capture. Research in attention indicates different kinds of attentional control, such as endogenous and exogenous orienting, which are critical to how awareness of patient state is maintained, but which may work differently across different modalities. Four kinds of medical monitoring displays are surveyed: (1) integrated visual displays, (2) head-mounted displays, (3) advanced auditory displays and (4) auditory alarms. Achievements and challenges in each area are outlined. In future research, we should focus more clearly on identifying anesthetists' information needs and we should develop models of attention in different modalities and across different modalities that are more capable of guiding design.