Effectiveness of enhanced pulse oximetry sonifications for conveying oxygen saturation ranges: a laboratory comparison of five auditory displays.

Background: Anaesthetists monitor auditory information about a patient's vital signs in an environment that can be noisy and while performing other cognitively demanding tasks. It can be difficult to identify oxygen saturation (SpO2) values using existing pulse oximeter auditory displays (sonifications). Methods: In a laboratory setting, we compared the ability of non-clinician participants to detect transitions into and out of an SpO2 target range using five different sonifications while they performed a secondary distractor arithmetic task in the presence of background noise. The control sonification was based on the auditory display of current pulse oximeters and comprised a variable pitch with an alarm. The four experimental conditions included an Alarm Only condition, a Variable pitch only condition, and two conditions using sonifications enhanced with additional sound dimensions. Accuracy to detect SpO2 target transitions was the primary outcome. Results: We found that participants using the two sonifications enhanced with the additional sound dimensions of tremolo and brightness were significantly more accurate (83 and 96%, respectively) at detecting transitions to and from a target SpO2 range than participants using a pitch only sonification plus alarms (57%) as implemented in current pulse oximeters. Conclusions: Enhanced sonifications are more informative than conventional sonification. The implication is that they might allow anaesthetists to judge better when desaturation decreases below, or returns to, a target range.

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

UNLABELLED: Our study examined the effectiveness of pulse oximetry sonification enhanced with acoustic tremolo and brightness to help listeners differentiate clinically relevant oxygen saturation ranges. In a series of trials lasting 30 s each, 76 undergraduate participants identified final oxygen saturation range ( TARGET: 100% to 97%; Low: 96% to 90%; Critical: 89% and below), and detected threshold transitions into and out of the target range using conventional sonification (n = 38) or enhanced sonification (n = 38). Median (IQR [range]) accuracy for range identification with the conventional sonification was 80 (70-85 [45-95])%, whereas with the enhanced sonification it was 100 (99-100 [80-100])%; p < 0.001. Accuracy for detecting threshold transitions with the conventional sonification was 60 (50-75 [30-95])%, but with the enhanced sonification it was 100 (95-100 [75-100]%; p < 0.001. Participants can identify clinically meaningful oxygen saturation ranges and detect threshold transitions more accurately with enhanced sonification than with conventional sonification.

Use of the virtual instrumentation laboratory for the assessment of human factors in surgery and anesthesia.

There is a growing consensus that human factors issues for anesthesiologists, surgeons, and other operating room personnel require serious attention. We have established a program of collaboration between the University of California Davis Medical Center Departments of Anesthesiology and Surgery and the California State University Sacramento Biomedical Engineering Program to address ergonomic problems in anesthesiology and surgery using a Virtual Instrumentation Laboratory. A 17-workstation Virtual Instrument Laboratory using LabVIEW software on Power Macintosh platforms permits rapid prototyping of medical monitor displays as well as rapid development of data acquisition and processing circuits for physiologic data collection. The Virtual Instrument Lab has been used for three Master's thesis projects and a BME course titled Human Factors in the Design of Medical and Assistive Technology. Course projects have included: 1) The design of novel physiologic data displays for potential use in anesthesia workstations, and 2) The measurement of surface electromyographic signals and heart rate variability to investigate the physical and mental workload of performing laparoscopic surgery. The Virtual Instrument Lab allows BME students to investigate relatively complex human factors issues in anesthesiology and surgery in a short time span.

Manual record keeping is not necessary for anesthesia vigilance.

OBJECTIVE: The goal of this study was to determine whether the intraoperative vigilance of anesthesia residents is different when they keep a manual record than when an assistant performs the charting. METHODS: A total of 9 anesthesia residents were studied during 36 general anesthesia cases on ASA class 1 or 2 patients. In half of the cases, the resident performed all record keeping. In the other half, the anesthesia record was kept by a human assistant. Vigilance was measured as detection rate and response time for the resident to detect a simulated abnormal value displayed on the physiologic monitor. For analysis, anesthesia cases were divided into stages of induction, maintenance, and emergence. RESULTS: Response times and detection rates were not different when record keeping was performed by an assistant, rather than by the clinician. Shorter cases were associated with longer median response times (i.e., lower vigilance) during the maintenance phase, but only when record keeping was done manually. CONCLUSIONS: The results demonstrate that anesthesia residents are equally attentive to an experimental signal displayed on an electronic monitor while manually charting as they are when an assistant keeps the record. This brings into question the contention that eliminating the record-keeping task will result in a reduced level of vigilance.

Effect of intraoperative ketorolac on postanesthesia care unit comfort.

The efficacy of intraoperatively administered ketorolac for the prophylactic treatment of pain in the postanesthesia care unit (PACU) was examined in a prospective, double-blinded study. Thirty patients undergoing general anesthesia for orthopedic or lower abdominal surgery were randomized into two groups. Both groups received equivalent doses of opioids intraoperatively. Upon surgical closure, one group received intramuscular (IM) ketorolac 60 mg (2 mL) and the other group received normal saline 2 mL, IM. The saline control group more frequently required opioid-analgesic supplementation in the PACU than did the ketorolac group (P < 0.05). Time to first-required opioid dose in the PACU was 22 +/- 8 versus 76 +/- 11 min for the control group and ketorolac group, respectively (P < 0.001). The ketorolac group reported significantly lower pain scores 1 hr after PACU admission (P < 0.01). Time to PACU discharge was not different between groups. Intraoperatively administered ketorolac is an effective adjunct in the management of postoperative pain.

Monitor surveillance and vigilance of anesthesia residents.

BACKGROUND: Anesthesia residents take longer to detect changes in electronically monitored data during the induction phase of anesthesia during the maintenance phase. This study was performed to investigate the reasons for this delay and to validate a method of measuring vigilance. METHODS: The activity of ten residents was studied during 73 surgical procedures. Data were collected during three 15-min periods from each case: induction, starting with application of the electrocardiograph; maintenance, an arbitrary period between induction and emergence; and emergence, ending with detachment of the electrocardiograph. Vigilance was measured as the time taken to detect a change, from normal to abnormal, of an artificial parameter displayed on the physiologic monitor (response time). An observer simultaneously recorded each time that the resident looked toward the monitors. RESULTS: Vigilance to the monitor display was less during induction and emergence than during maintenance (P < 0.005). Residents spent less total time watching monitors during induction than during maintenance (P < 0.005), and the duration of each monitor observation was shorter (P < 0.0005). Anesthesia residents usually looked at the monitors several times before detecting the abnormal value. The measure of anesthesia vigilance correlated with independent measures of monitor watching time and frequency. CONCLUSIONS: The results suggest that during induction of anesthesia, which is a period of high anesthesiologist workload, residents glance toward monitors to gather data rather than scan displays. The results help to validate the method for measuring anesthesia vigilance.

A measure of intraoperative attention to monitor displays.

Vigilance is an important but difficult to measure attribute in anesthesia practitioners. We present a modified standard method to assess intraoperative vigilance toward electronic data displays. The response time to detect a simulated abnormal value on the physiologic monitor was measured. Eight anesthesia residents were studied during 60 surgical procedures. Responses to 439 abnormal values were analyzed. The average response time was 61 +/- 61 s (mean +/- SD), and 56% of the detections were made within 60 s. However, 16% of the abnormal values were undetected during the 5 min that they were displayed. Response times and the rate of missed events were greater during induction of anesthesia (a time of high workload) than during the maintenance or emergence phases of anesthesia. Response times were shorter during procedures on ASA 1 patients than on ASA 3 patients. The results suggest that anesthesiologists usually quickly detect abnormal values on physiologic monitors and that less attention is devoted to monitors during periods of high workload.

Recognition accuracy of current operating room alarms.

This prospective study was performed to determine whether anesthesia clinicians (i.e., both anesthesiologists and nurse anesthetists) can identify operating room alarms by their distinctive sounds and to identify factors related to alarm recognition accuracy. Nineteen alarms from 15 commonly used devices were recorded. These sounds were played, in a quiet room, to 44 anesthesia clinicians. The clinicians were asked to choose from a list the device that produced the alarm. After this recognition test, the clinicians rated the importance of each alarm and the frequency with which they heard it in the clinical situation. Clinicians correctly identified the alarm source 34% of the time. The recognition rate was higher for alarms rated as heard more frequently; however, alarms that were rated as more important were less likely to be correctly identified. Complexity of the sound did not influence accuracy of recognition. Most errors were attributed to similarities in sound or function, or both, among alarms. We conclude that anesthetists cannot reliably identify current operating room alarms by their distinctive sounds.

The output of four modern vaporizers in the presence of helium.

It has been previously demonstrated that the output of calibrated vaporizers is influenced by the concentration of nitrous oxide in the carrier gas. This study was performed to determine whether helium in the carrier gas affects the output of modern calibrated vaporizers. A factorial design was used to determine the influence of carrier-gas helium concentration, carrier-gas flow rate and vaporizer dial setting on the output of four vaporizers: Ohio Calibrated Enflurane, Ohio Calibrated Isoflurane, Ohmeda Isotec 4, and Dräger Vapor 19.1 Isoflurane. Three vaporizers of each model were tested. Output was converted to % of baseline so that different dial settings could be compared. For a given dial setting, baseline was defined as the output at a carrier-gas flow rate of 3 L.min-1 and helium concentration of zero. The data were analyzed using multiple linear regression. There was an effect of helium concentration on vaporizer output in all models. None of these changes was clinically important, since vaporizer output did not vary by more than +/- 10%, except at high flows and at high helium concentrations with the Ohmeda Isotec 4. It is concluded that these vaporizers can be used safely with helium.

Effects of epinephrine and ritodrine in dogs with acute hyperkalemia.

As plasma potassium concentrations, whether normal or elevated, can be reduced by intravenous administration of either epinephrine or ritodrine, the effects of these drugs were examined during acute hyperkalemia. Six anesthetized dogs were studied every 2 wk, on 18 separate occasions. Hyperkalemia was induced by intravenous infusion of potassium chloride, resulting in plasma potassium concentrations of 9.6 +/- 0.3 mEq/L (mean +/- SEM), bradycardia, and idioventricular rhythm. Dogs were then given slow intravenous injections every 30 min of either saline (controls), epinephrine, or ritodrine. Epinephrine doses were 0.01, 0.1, 1.0, 10, or 100 micrograms/kg; ritodrine doses were 0.1, 1.0, 10, 100, or 1000 micrograms/kg. At the highest does, both epinephrine and ritodrine caused clinically important decreases in plasma potassium, reducing concentrations to below 7.0 mEq/L. Ritodrine had a significantly greater effect than epinephrine. Side effects included hypertension and dysrhythmias with epinephrine, serious hypotension with ritodrine, and tachycardia with both drugs. For both drugs, the doses that caused a decrease in plasma potassium also caused an increase in heart rate and there was a correlation between plasma potassium levels and heart rate. Epinephrine and ritodrine may be useful in treating acute hyperkalemia, but cardiovascular side effects may occur. Increased heart rate could be used as an indicator of therapeutic effect and the magnitude of the increase in heart rate may be helpful in predicting the level of response.

The Utah anesthesia workstation.

A prototype anesthesia workstation has been developed to demonstrate the feasibility of a computer-assisted anesthesia workplace. The workstation provides a central display of information and aids the user in controlling and monitoring the anesthesia delivery system. The anesthesiologist interacts with the workstation through a Macintosh computer, which is easy for the clinician to understand and to use. Seventeen sensors and monitors transmit information from the anesthesia delivery system to the computer. The computer monitors this information using a set of rules, evaluated once each breath, to detect changes in the delivery system. If an event is detected, the computer alerts the anesthesiologist with a diagram, a text message, and an audible warning. A laboratory test of the monitoring system was performed to see if it properly identified 26 different critical events during simulated low flow and closed circuit anesthesia. Five hundred and eight-three of 660 simulated critical events (88%) were identified with the unique and correct message. On 35 occasions, multiple messages were displayed, including the correct one. Critical events were misidentified or not detected 42 times. Eight false positive alarms occurred during the 20 h of testing; all occurred as a result of baseline drift in a single transducer. These results demonstrate that a sophisticated monitoring system can reliably diagnose specific anesthesia machine failures.