Monitor Displays: Non-Moving Waveforms May Be Superior to Moving Waveforms

Jonathan V. Roth, MD

Optimizing At-A-Glance Monitoring

Ford et al. reported that anesthesiologists frequently look at monitors for very short periods of times and have called for designs that take this behavior into consideration.1 In this spirit, monitors that display traces that do not move (i.e., the static waveforms that are over-written with each new sweep), as opposed to waveforms that move across the screen, may have advantages that should be considered in future designs.

As an example, the Datascope “Expert” (Datascope Corporation, Paramus, NJ) has waveforms that do not move across the screen; the static waveforms get replaced as each new sweep comes by. It takes about 6 seconds for each sweep across the screen of the ECG, pulse oximeter, and pressure waveforms. It takes about 15 seconds for the sweep of the capnograph. If one quickly counts the ECG, pressure, or pulse oximeter displayed waveforms and multiplies that number by 10, or multiplies the number of capnograph waveforms by 4, one can closely estimate the rate per minute. Sometimes there are artifacts that cause the numerical display to be incorrect. Knowledge of these monitor specific relationships allows one to quickly determine the actual state of affairs.

As examples, the ECG and pulse oximeter rates displayed may either be unobtainable or in error as a result of a double count or artifact. If this is not recognized, it has the potential to lead to wrong treatment. This author has witnessed a situation where the actual heart rate was 55 beats per minute, both the pulse ox and ECG were double counting and displaying a rate of 110, and a beta blocker was administered. With moving waveforms, it would seem that it would more difficult for practitioners to learn that a given distance between moving complexes equates to a given rate over a range of rates. The respiratory rate displayed on the ventilator system may be falsely elevated if the ventilatory system is recognizing cardiac oscillations as breaths. This author has witnessed a patient with an actual respiratory rate of 12 breaths per minute, the ventilator displaying a rate of 34 because it was counting cardiac oscillations, and an opioid narcotic was administered.

Another advantage is that if one needs a display to be static in order to closely examine some feature of a waveform, it may be easier and faster to look at a nonmoving display than one that is moving. Monitors with a moving display require at least one extra step in order to freeze the moving display. Whether or not a practitioner is more likely to recognize an abnormality on a static display than on a moving waveform is a question that will require further study.

In summary, it seems possible or likely that it is easier and faster with a static waveform system to recognize an abnormal waveform, or that the numerical display is incorrect, and obtain a more accurate rate. As with the Expert system, sweep speeds should be set so that a minute rate can be obtained by a whole number multiple of the number of waveforms displayed. Future studies will be required to support the above opinion.


Reference

  1. Ford S, Birmingham E, King A, Lim J, Anesermino M. At-a-glance monitoring: covert observations of anesthesiologists in the operating room. Anesth Analg 2010;111:653-8.

Jonathan V. Roth, MD
Associate Professor of Anesthesiology
Department of Anesthesiology
Albert Einstein Medical Center
Thomas Jefferson School of Medicine
Philadelphia, PA