Incremental advances will improve medical device alarm sounds.

The March issue contains a laboratory study of auditory perception, which is an unusual topic for this journal. A perspective is provided on how the study relates to recent research on clinical auditory alarms and displays. Techniques used in the study are explored and explained, such as enrolment of non-clinician volunteer participants, use of coordinate response measure phrase stimuli, presentation of sound loudness levels using the decibel scale, and analysis using signal detection theory. Such efforts to improve the safety, efficacy, and tolerability of modern medical device alarms are critical for improved patient safety.

Auditory Sequences Presented With Spearcons Support Better Multiple Patient Monitoring Than Single-Patient Alarms: A Preclinical Simulation.

OBJECTIVE: A study of auditory displays for simulated patient monitoring compared the effectiveness of two sound categories (alarm sounds indicating general risk categories from international alarm standard IEC 60601-1-8 versus event-specific sounds according to the type of nursing unit) and two configurations (single-patient alarms versus multi-patient sequences). BACKGROUND: Fieldwork in speciality-focused high dependency units (HDU) indicated that auditory alarms are ambiguous and do not identify which patient has a problem. We tested whether participants perform better using auditory displays that identify the relevant patient and problem. METHOD: During simulated patient monitoring of four patients in a respiratory HDU, 60 non-clinicians heard either (a) IEC risk categories as single-patient alarm sounds, (b) event-specific categories as single-patient alarm sounds, (c) IEC risk categories in multi-patient sequences or (d) event-specific categories in multi-patient sequences. Participants performed a perceptual-motor task while monitoring patients; after detecting abnormal events, they identified the patient and the event. RESULTS: Participants hearing multi-patient sequences made fewer wrong patient identifications than participants hearing single-patient alarms. Advantages of event-specific categories emerged when IEC risk category sounds indicated more than one potential event. Even when IEC and event-specific sounds indicated the same unique event, spearcons supported better event identification than did auditory icon sounds. CONCLUSION: Auditory displays that unambiguously convey which patient is having what problem dramatically improve monitoring performance in a preclinical HDU simulation. APPLICATION: Time-compressed speech assists development of detailed risk categories needed in specific HDU contexts, and multi-patient sound sequences allow multiple patient wellbeing to be monitored.

Attention to Changes on a Head-Worn Display: Two Preclinical Studies with Healthcare Scenarios.

OBJECTIVE: In two experiments, we examined how quickly different visual alerts on a head-worn display (HWD) would capture participants' attention to a matrix of patient vital sign values, while multitasking. BACKGROUND: An HWD could help clinicians monitor multiple patients, regardless of where the clinician is located. We sought effective ways for HWDs to alert multitasking wearers to important events. METHODS: In two preclinical experiments, university student participants performed a visuomotor tracking task while simultaneously monitoring simulated patient vital signs on an HWD to detect abnormal values. Methods to attract attention to abnormal values included highlighting abnormal vital signs and imposing a white flash over the entire display. RESULTS: Experiment 1 found that participants detected abnormal values faster with high contrast than low contrast greyscale highlights, even while performing difficult tracking. In Experiment 2, a white flash of the entire screen quickly and reliably captured attention to vital signs, but less so on an HWD than on a conventional screen. CONCLUSION: Visual alerts on HWDs can direct users' attention to patient transition events (PTEs) even under high visual-perceptual load, but not as quickly as visual alerts on fixed displays. Aspects of the results have since been tested in a healthcare context. APPLICATION: Potential applications include informing the design of HWD interfaces for monitoring multiple processes and informing future research on capturing attention to HWDs.

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.

Evaluation of an enhanced pulse oximeter auditory display: a simulaion study.

BACKGROUND: We compared anaesthetists' ability to identify haemoglobin oxygen saturation (SpO2) levels using two auditory displays: one based on a standard pulse oximeter display (varying pitch plus alarm) and the other enhanced with additional sound properties (varying pitch plus tremolo and acoustic brightness) to differentiate SpO2 ranges. METHODS: In a counter-balanced crossover study in a simulator, 20 experienced anaesthetists supervised a junior colleague (an actor) managing two airway surgery scenarios: once while using the enhanced auditory display and once while using a standard auditory display. Participants were distracted with other tasks such as paperwork and workplace interruptions, but were required to identify when SpO2 transitioned between pre-set ranges (target, low, critical) and when other vital signs transitioned out of a target range. They also identified the range once a transition had occurred. Visual displays were available for all monitored vital signs, but the numerical value for SpO2 was excluded. RESULTS: Participants were more accurate and faster at detecting transitions to and from the target SpO2 range when using the enhanced display (100.0%, 3.3 s) than when using the standard display plus alarm (73.2%, 27.4 s) (P<0.001 and P=0.004, respectively). They were also more accurate at identifying the SpO2 range once a transition had occurred when using the enhanced display (100.0%) than when using the standard display plus alarm (57.1%; P<0.001). CONCLUSIONS: The enhanced auditory display helps anaesthetists judge SpO2 levels more effectively than current auditory displays and may facilitate 'eyes-free' monitoring.

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.

Comparison of Standard and Enhanced Pulse Oximeter Auditory Displays of Oxygen Saturation: A Laboratory Study With Clinician and Nonclinician Participants.

BACKGROUND: When engaged in visually demanding tasks, anesthesiologists depend on the auditory display of the pulse oximeter (PO) to provide information about patients' oxygen saturation (SpO2). Current auditory displays are not always effective at providing SpO2 information. In this laboratory study, clinician and nonclinician participants identified SpO2 parameters using either a standard auditory display or an auditory display enhanced with additional acoustic properties while performing distractor tasks and in the presence of background noise. METHODS: In a counterbalanced crossover design, specialist or trainee anesthesiologists (n = 25) and nonclinician participants (n = 28) identified SpO2 parameters using standard and enhanced PO auditory displays. Participants performed 2 distractor tasks: (1) arithmetic verification and (2) keyword detection. Simulated background operating room noise played throughout the experiment. Primary outcomes were accuracies to (1) detect transitions to and from an SpO2 target range and (2) identify SpO2 range (target, low, or critical). Secondary outcomes included participants' latency to detect target transitions, accuracy to identify absolute SpO2 values, accuracy and latency of distractor tasks, and subjective judgments about tasks. RESULTS: Participants were more accurate at detecting target transitions using the enhanced display (87%) than the standard display (57%; odds ratio, 7.3 [95% confidence interval {CI}, 4.4-12.3]; P < .001). Participants were also more accurate at identifying SpO2 range using the enhanced display (86%) than the standard display (76%; odds ratio, 2.7 [95% CI, 1.6-4.6]; P < .001). Secondary outcome analyses indicated that there were no differences in performance between clinicians and nonclinicians for target transition detection accuracy and latency, SpO2 range identification accuracy, or absolute SpO2 value identification. CONCLUSIONS: The enhanced auditory display supports more accurate detection of target transitions and identification of SpO2 range for both clinicians and nonclinicians. Despite their previous experience using PO auditory displays, clinicians in this laboratory study were no more accurate in any SpO2 outcomes than nonclinician participants.

The Impact of Head-Worn Displays on Strategic Alarm Management and Situation Awareness.

OBJECTIVE: To investigate whether head-worn displays (HWDs) help mobile participants make better alarm management decisions and achieve better situation awareness than alarms alone. BACKGROUND: Patient alarms occur frequently in hospitals but often do not require clinical intervention. Clinicians may become desensitized to alarms and fail to respond to clinically relevant alarms. HWDs could make patient information continuously accessible, support situation awareness, and help clinicians prioritize alarms. METHOD: Experiment 1 ( n = 76) tested whether nonclinicians monitoring simulated patients benefited from vital sign information continuously displayed on an HWD while they performed a secondary calculation task. Experiment 2 ( n = 13) tested, across three separate experimental sessions, how effectively nursing trainees monitored simulated patients' vital signs under three different display conditions while they assessed a simulated patient. RESULTS: In Experiment 1, participants who had access to continuous patient information on an HWD responded to clinically important alarms 25.9% faster and were 6.7 times less likely to miss alarms compared to participants who only heard alarms. In Experiment 2, participants using an HWD answered situation awareness questions 18.9% more accurately overall than when they used alarms only. However, the effect was significant in only two of the three experimental sessions. CONCLUSION: HWDs may help users maintain continuous awareness of multiple remote processes without affecting their performance on ongoing tasks. APPLICATION: The outcomes may apply to contexts where access to continuous streams of information from remote locations is useful, such as patient monitoring or clinical supervision.

Using a Sequence of Earcons to Monitor Multiple Simulated Patients.

OBJECTIVE: The aim of this study was to determine whether a sequence of earcons can effectively convey the status of multiple processes, such as the status of multiple patients in a clinical setting. BACKGROUND: Clinicians often monitor multiple patients. An auditory display that intermittently conveys the status of multiple patients may help. METHOD: Nonclinician participants listened to sequences of 500-ms earcons that each represented the heart rate (HR) and oxygen saturation (SpO2) levels of a different simulated patient. In each sequence, one, two, or three patients had an abnormal level of HR and/or SpO2. In Experiment 1, participants reported which of nine patients in a sequence were abnormal. In Experiment 2, participants identified the vital signs of one, two, or three abnormal patients in sequences of one, five, or nine patients, where the interstimulus interval (ISI) between earcons was 150 ms. Experiment 3 used the five-sequence condition of Experiment 2, but the ISI was either 150 ms or 800 ms. RESULTS: Participants reported which patient(s) were abnormal with median 95% accuracy. Identification accuracy for vital signs decreased as the number of abnormal patients increased from one to three, p < .001, but accuracy was unaffected by number of patients in a sequence. Overall, identification accuracy was significantly higher with an ISI of 800 ms (89%) compared with an ISI of 150 ms (83%), p < .001. CONCLUSION: A multiple-patient display can be created by cycling through earcons that represent individual patients. APPLICATION: The principles underlying the multiple-patient display can be extended to other vital signs, designs, and domains.

The Sounds of Desaturation: A Survey of Commercial Pulse Oximeter Sonifications.

BACKGROUND: The pulse oximeter has been a standard of care medical monitor for >25 years. Most manufacturers include a variable-pitch pulse tone in their pulse oximeters. Research has shown that the acoustic properties of variable-pitch tones are not standardized. In this study, we surveyed the properties of pulse tones from 21 pulse oximeters, consisting of 1 to 4 instruments of 11 different models and 8 brands. Our goals were to fully document the sounds over saturation values 0% to 100%, test whether tones become quieter at low saturation values, and create a public repository of pulse oximeter recordings for future use. METHODS: A convenience sample of commercial pulse oximeters in use at one hospital was studied. Audiovisual recordings of each pulse oximeter's display and sounds were taken while it monitored a simulator starting at a saturation of 100% and slowly decreasing in 1% steps until the saturation reached 0%. Recorded pulse tones were analyzed for spectral frequency and total power. Audio files for each pulse oximeter containing 100 pulse tones, one at every saturation value, were created for inclusion in the repository. RESULTS: Recordings containing 509 to 1053 pulse tones were made from the 21 pulse oximeters. Fundamental frequencies at 100% saturation ranged from 479 to 921 Hz, and fundamental frequencies at 1% saturation ranged from 38 to 404 Hz. The pulse tones from all but one model pulse oximeter contained harmonics. Pulse tone step sizes were linear in 6 models and logarithmic in 6 models. Only 6 pulse oximeter models decreased the pulse tone pitch at every decrease in saturation; all others decreased the pitch at only select saturation thresholds. Five pulse oximeter models stopped decreasing pitch altogether once the saturation reached a certain lower threshold. Pulse tone power (perceived as loudness) changed with saturation level for all pulse oximeters, increasing above baseline as saturation decreased from 100% and decreasing to levels below baseline at low saturation values. CONCLUSIONS: Current pulse oximeters use different techniques to address the competing goals of (1) using pitch steps that are large enough to be readily perceived, and (2) conveying saturation values from 0 to 100 within a limited range of sound frequencies. From a clinical perspective, 2 techniques for increasing perceivability (increasing the frequency range and using ratio step sizes) have no drawback, but 2 techniques (not changing pitch at every saturation change and using a lower saturation cutoff) do have potential clinical drawbacks. On the basis of our findings, we have made suggestions for clinicians and manufacturers.

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.

Attention capture by own name decreases with speech compression.

Auditory stimuli that are relevant to a listener have the potential to capture focal attention even when unattended, the listener's own name being a particularly effective stimulus. We report two experiments to test the attention-capturing potential of the listener's own name in normal speech and time-compressed speech. In Experiment 1, 39 participants were tested with a visual word categorization task with uncompressed spoken names as background auditory distractors. Participants' word categorization performance was slower when hearing their own name rather than other names, and in a final test, they were faster at detecting their own name than other names. Experiment 2 used the same task paradigm, but the auditory distractors were time-compressed names. Three compression levels were tested with 25 participants in each condition. Participants' word categorization performance was again slower when hearing their own name than when hearing other names; the slowing was strongest with slight compression and weakest with intense compression. Personally relevant time-compressed speech has the potential to capture attention, but the degree of capture depends on the level of compression. Attention capture by time-compressed speech has practical significance and provides partial evidence for the duplex-mechanism account of auditory distraction.

The risk and outcomes of epidural hematomas after perioperative and obstetric epidural catheterization: a report from the Multicenter Perioperative Outcomes Group Research Consortium.

BACKGROUND: In this study, we sought to determine the frequency and outcomes of epidural hematomas after epidural catheterization. METHODS: Eleven centers participating in the Multicenter Perioperative Outcomes Group used electronic anesthesia information systems and quality assurance databases to identify patients who had epidural catheters inserted for either obstetrical or surgical indications. From this cohort, patients undergoing laminectomy for the evacuation of hematoma within 6 weeks of epidural placement were identified. RESULTS: Seven of 62,450 patients undergoing perioperative epidural catheterizations developed hematoma requiring surgical evacuation. The event rate was 11.2 × 10(-5) (95% confidence interval [CI], 4.5 × 10(-5) to 23.1 × 10(-5)). Four of the 7 had anticoagulation/antiplatelet therapy that deviated from American Society of Regional Anesthesia guidelines. None of 79,837 obstetric patients with epidural catheterizations developed hematoma (upper limit of the 95% CI, 4.6 × 10(-5)). The hematoma rate in obstetric epidural catheterizations was significantly lower than in perioperative epidural catheterizations (P = 0.003). CONCLUSIONS: In this series, the 95% CI for the frequency of epidural hematoma requiring laminectomy after epidural catheter placement for perioperative anesthesia/analgesia was 1 event per 22,189 placements to 1 event per 4330 placements. Risk was significantly lower in obstetric epidurals.

Evaluating enhanced pulse oximetry auditory displays for neonatal oxygen targeting: A randomized laboratory trial with clinicians and non-clinicians.

Standard pulse oximeter auditory tones do not clearly indicate departures from the target range of oxygen saturation (SpO2) of 90%-95% in preterm neonates. We tested whether acoustically enhanced tones would improve participants' ability to identify SpO2 range. Twenty-one clinicians and 23 non-clinicians used (1) standard pulse oximetry variable-pitch tones plus alarms; (2) beacon-enhanced tones without alarms in which reference tones were inserted before standard pulse tones when SpO2 was outside target range; and (3) tremolo-enhanced tones without alarms in which pulse tones were modified with tremolo when SpO2 was outside target range. For clinicians, range identification accuracies (mean (SD)) in the standard, beacon, and tremolo conditions were 52% (16%), 73% (14%) and 76% (13%) respectively, and for non-clinicians 49% (16%), 76% (13%) and 72% (14%) respectively, with enhanced conditions always significantly more accurate than standard. Acoustic enhancements to pulse oximetry clearly indicate departures from preterm neonates' target SpO2 range.

Effects of multitasking on interpreting a spearcon sequence display for monitoring multiple patients.

Spearcons are time-compressed speech phrases. When arranged in a sequence representing vital signs of multiple patients, spearcons may be more informative than conventional auditory alarms. However, multiple resource theory suggests that certain timeshared tasks might interfere with listeners' ability to understand spearcons. We tested the relative interference with spearcon identification from the following ongoing tasks: (1) manual tracking, (2) linguistic detection of spoken target words, (3) arithmetic true-false judgments, or (4) an ignored background speech control. Participants were 80 non-clinicians. The linguistic task worsened spearcon identification more than the tracking task, p < .001, and more than ignored background speech, p = .012. The arithmetic task worsened spearcon identification more than the tracking task, p < .001. The linguistic task and arithmetic task both worsened performance, p = .674. However, no ongoing task affected participants' ability to detect which patient(s) in a sequence had abnormal vital signs. Future research could investigate whether timeshared tasks affect non-speech auditory alerts.

Measurement of dead space in subjects under general anesthesia using standard anesthesia equipment.

BACKGROUND: Pulmonary dead space is the volume of gas that is delivered to the lungs but does not participate in gas exchange. Knowing pulmonary dead space in patients under general anesthesia is clinically useful because it can aid in detecting disease processes such as pulmonary emboli or low cardiac output states. Dead space can be simply calculated by using the Bohr equation; however, it is difficult to measure mixed exhaled carbon dioxide (PECO(2)) with a standard anesthesia machine. Previously, a study at our institution demonstrated the carbon dioxide (CO(2)) concentration in the bellows of a standard anesthesia machine is an accurate approximation of PECO(2). In this study, we used the bellows PECO(2) measurement and arterial CO(2) (PaCO(2)) to calculate pulmonary dead space. We verified the technique by adding known apparatus dead space volumes during anesthesia. METHODS: Subjects were under general endotracheal anesthesia. A sampling line was positioned inside the ventilator bellows and connected to a capnometer. Measurements of PECO(2) and PaCO(2) from an arterial catheter were taken at baseline and after adding 100 mL and 200 mL of dead space to the endotracheal tube. Dead space was calculated using the Bohr equation (alveolar dead space/tidal volume = [PaCO(2) - PECO(2)]/PaCO(2)) at baseline and after adding 100 mL and 200 mL of apparatus dead space. RESULTS: The dead space at baseline was 265 ± 47 mL (mean ± SD) in 10 study subjects. After adding 100 mL of dead space to the endotracheal tube, the measured dead space increased by 110 ± 46 mL. The measured dead space increased by 158 ± 39 mL after adding 200 mL. CONCLUSIONS: Our baseline dead space measurements were in the expected range under general anesthesia. When dead space was added, we were able to calculate that an increase in dead space occurred. Our calculation was more accurate after adding a 100-mL volume than after adding 200 mL. We present a simple way to detect trends in dead space in ventilated patients using a Narkomed GS anesthesia machine (Dräger Medical, Lübeck, Germany).

Spearcon compression levels influence the gap in comprehension between untrained and trained listeners.

Auditory alarms in hospitals are ambiguous and do not provide enough information to support doctors and nurses' awareness of patient events. A potential alternative is the use of short segments of time-compressed speech, or spearcons. However, sometimes it might be desirable for patients to understand spearcons and sometimes not. We used reverse hierarchy theory to hypothesize that there will be a degree of compression where spearcons are intelligible for trained listeners but not for untrained listeners. In Experiment 1, spearcons were compressed to either 20% or 25% of their original duration. Their intelligibility was very high for trained participants, but also quite high for untrained participants. In Experiment 2 each word within each spearcon was compressed to a different degree based on the results of Experiment 1. This technique was effective in creating the desired difference in spearcon intelligibility between trained and untrained listeners. An implication of these results is that manipulating the degree of compression of spearcons "by word" can increase the effect of training so that untrained listeners reliably do not understand the content of the spearcons. (PsycInfo Database Record (c) 2021 APA, all rights reserved).