A new paradigm for the design of audible alarms that convey urgency information

OBJECTIVE

The current international standard (IEC 60601-1-8) stipulates that medical device audible alarms should be priority-encoded and validated for efficacy. Evidence suggests that the melodic alarms described in the standard are not functioning as originally intended. We present a multi-disciplinary, human factors paradigm for audible alarm development whereby urgency information is encoded via modulation of the physical characteristics of sounds. We also test the feasibility of this approach using information measures.

METHODS

We designed series of experimental sounds that varied along controlled physical and acoustical dimensions. Subjects rated these sound series for perceived urgency. Based on these ratings, selected sounds from each series were assigned a priority category from 'low' to 'high' - we call these resulting sets of sounds 'urgency-codecs'. The method of categorical judgments (based on information theory) was used to compare each urgency-codec for ability to convey urgency information.

RESULTS

Subjects were consistent in their ratings of the three series of experimental sounds for perceived urgency. The urgency data pertaining to one of the series (harmonic interval) was successfully fit to a psychophysical empirical law. The urgency-codec derived from another sound series (melodic interval) was found to have the highest signal (correct interpretation of urgency level by subjects) transmission rate.

CONCLUSIONS

The proposed paradigm is feasible, and it offers an evidence-based strategy for alarm sound design and testing. This approach would be performed before implementation of new alarm sounds in clinical settings, and should result in development of alarm sounds that satisfy the requirements of priority-encoding and validation.

The right picture is worth a thousand numbers: data displays in anesthesia

OBJECTIVE

To review the literature on data displays in anesthesia identifying issues and developing design recommendations.

BACKGROUND

Unexpected incidents are common in critical care medicine. Adverse outcomes are frequently the catastrophic endpoints of an "evolving" chain of subtle incidents. One strategy to reduce the likelihood of an adverse patient outcome during anesthesia is to improve the anesthesiologist's ability to detect, diagnose, and treat critical incidents.

METHOD

A literature review and analysis of data displays.

RESULTS

Current numerical and waveform displays do not support anesthesiologists optimally. An alternative is graphical displays that functionally integrate variables into objects. In a well-designed graphic object, deviations from normal are shown by distortions in the object's symmetry. The emerging patterns that result from distorted symmetry facilitate the correct diagnosis. When treatment is effective, an object's shape is restored to normal. Graphical displays can be an effective tool in supporting anesthesiologists' situation awareness.

CONCLUSION

Problems related to graphical displays have delayed their use in anesthesia, including the lack of conclusive clinical evidence of their value. However, currently more evidence is accumulating that graphical displays have the potential to improve clinical performance. The successful development of these graphical displays takes into account task requirements, a user's perceptual processes, and task-specific cognition.

APPLICATION

This paper provides suggestions for the development of more effective displays in anesthesiology. Graphical displays can increase the anesthesiologist's situation awareness and improve clinical performance. Clinical use of these displays has the potential to significantly improve patient safety.

The graphical presentation of decision support information in an intelligent anaesthesia monitor

This contribution examines the graphical presentation of decision support information generated by an intelligent monitor, named SENTINEL, developed for use during anaesthesia. Clinicians make diagnoses in real-time during operations by examining clinically significant trends in multiple signals. SENTINEL attempts to mimic this decision process by using a system of fuzzy trend templates. SENTINEL's implementation of fuzzy trend templates is capable of providing the dual fuzzy measures of belief and plausibility, which are derived from the theory of evidence. It is thus capable of generating fairly rich diagnostic decision support information. However, for SENTINEL to be effective, the visual presentation of this information must be intuitive to the anaesthetist, who may not be familiar with the theory of evidence. This paper discusses techniques that are being evaluated to meet the requirements of the SENTINEL anaesthesia monitor. Specifically, the paper presents methods for highlighting clinically significant trends in physiological (or derived) signals by superimposing a coloured band on the signal that reflects fuzzy output from the intelligent monitor. This paper also discusses the intuitive graphical presentation of binary diagnostic fuzzy measures, including their further interpretation and presentation as crisp "alarm" and "warning" conditions.

Computer simulation of sensorless fuzzy control of a rotary blood pump to assure normal physiology

Rotary blood pumps have been considered effective permanently implantable devices. However, control of such pumps is quite complicated. Sensorless control of pump flow is required because no invasive flow or pressure sensors are wanted. Whereas insufficient pump output can cause underperfusion and should be avoided, overpumping may cause ventricular collapse and must be prevented. An intelligent physiologic control algorithm is highly desirable to reach optimal pump output based on physiologic requirements. We present an intelligent physiologic control mechanism for the blood pump allowing it to achieve normal physiology. Sensorless control of pump flow is gained by analysis of the electric motor current and speed. The required pump output flow is chosen based on heart rate, and an intelligent fuzzy logic based control mechanism is developed to adjust the motor input so that the pump output can reach required flow while also preventing the occurrence of ventricular suction or cannular collapse. Computer simulation was carried out, and the results indicate that the proposed algorithms can achieve required pump flow to obtain normal physiology, whereas overpumping can be prevented to provide safe operation.

Design and validation of an intelligent patient monitoring and alarm system based on a fuzzy logic process model

The process of patient care performed by an anaesthesiologist during high invasive surgery requires fundamental knowledge of the physiologic processes and a long standing experience in patient management to cope with the inter-individual variability of the patients. Biomedical engineering research improves the patient monitoring task by providing technical devices to measure a large number of a patient's vital parameters. These measurements improve the safety of the patient during the surgical procedure, because pathological states can be recognised earlier, but may also lead to an increased cognitive load of the physician. In order to reduce cognitive strain and to support intra-operative monitoring for the anaesthesiologist an intelligent patient monitoring and alarm system has been proposed and implemented which evaluates a patient's haemodynamic state on the basis of a current vital parameter constellation with a knowledge-based approach. In this paper general design aspects and evaluation of the intelligent patient monitoring and alarm system in the operating theatre are described. The validation of the inference engine of the intelligent patient monitoring and alarm system was performed in two steps. Firstly, the knowledge base was validated with real patient data which was acquired online in the operating theatre. Secondly, a research prototype of the whole system was implemented in the operating theatre. In the first step, the anaesthetists were asked to enter a state variable evaluation before a drug application or any other intervention on the patient into a recording system. These state variable evaluations were compared to those generated by the intelligent alarm system on the same vital parameter constellations. Altogether 641 state variable evaluations were entered by six different physicians. In total, the sensitivity of alarm recognition is 99.3%, the specificity is 66% and the predictability is 45%. The second step was performed using a research prototype of the system in anaesthesiological routine. The evaluation of 684 events yielded a sensitivity, specificity and predictability of the alarm recognition of more than 99%.

Fuzzy control concept for a total artificial heart

The development of an electromechanically driven total artificial heart (Helmholtz-TAH) was initiated in 1990. Anatomical fitting, biocompatibility, and automatic physiologic adaptation of pump output are the basic requirements that characterize the overall TAH concept. For evaluation of these features, a TAH labtype was developed. It provides most features of the conceptual artificial heart and supports in vitro testing of energy conversion, pump behavior, structural parts, sensors, and control concepts. A fuzzy controller has been implemented for adaptation of the pump rate to body perfusion demand by left pump chamber filling detection. This controller will be an important element of a future extensive TAH control system. The implementation is supported by a professional fuzzy control development tool that allows on-line and real time optimization of control strategies for dynamic processes. The first experiments proved the feasibility and the advantages of this fuzzy control concept. The first in vitro test results are presented.