Colors for ECG Tracings, SpO2 Pulse Oximetry on Patient Monitors in the OR and ICU

Ranga P. Venna, MD

Q

Dear Q&A,

Are there any established guidelines regarding the colors designated for ECG tracings, SpO2 pulse oximetry on patient monitors in the OR and the ICU?

A Dear Reader,

There are no agreed upon standards. Various groups from clinicians to industry have discussed this issue, without resolution. Many clinicians like to customize their screens and create specific configurations, including color, for each type of surgery, and the monitor manufacturers are quite accommodating. Clinical practice illustrates different color schemes are the norm not just between institutions but also within institutions.

The first issue is how to link numerics to waveforms, assuming the patient is treated based upon numerics and the waveform is used to validate the data. This is commonly done with color. The second issue is how to distinguish one set of numerics from another, since not all numerics are associated with waveforms, and this is where standardizing color may be helpful, but not practical. If heart rate is always green and arterial pressure is always red, pulse oximetry is always yellow, carbon dioxide is always white, and temperature is always cyan, then the most basic form of patient monitoring can be achieved unambiguously. An anesthesiologist supervising multiple rooms has the advantage of looking at the data they are interested in with only a glance, and in a crisis could gather the important physiologic data very quickly.

Problems arise when multiple measurements of a single parameter appear on the screen. For example, a patient has an arterial line and an automated blood pressure cuff. The arterial waveform and both sets of numerics will be in red. This raises the question as to which numerics are which; which ones will be used to treat the patient? Upon careful inspection the NIBP numerics contain information about the cycle time and the age of the data, which will not be found on the arterial line. Two ECG waveforms with ST segment depression from multiple leads along with one impedance plethysmography waveform with numerics for respiratory rate, all come from the ECG module. Are they all colored green?

Goggles worn during cases employing lasers present another problem by filtering out certain wavelengths or colors of light.

One significant problem concerning standardizing colors is that color is limited as a display feature for many people due to the prevalence of color blindness. Red green is much more common in men with an occurrence of approximately 10% in the population. If color becomes a standard as a visual indicator of important information, you will fail to convey the information intended with color to roughly 4,686 red green colorblind anesthesia providers (32,103 male anesthesiologists and 14,760 male CRNAs currently in practice). A more unusual form of color blindness is blue yellow, which occurs equally in men and women but is limited to 5% of the 10% of color blind individuals (0.5% of the population).

Most monitors that display 6 or 8 waveforms on a screen will undoubtedly require more colors than are presently available. The issue is not just waveforms but includes numerics as well, especially if they display respiratory gas information. The general consensus appears to be that standardization of colors would be useful, but most likely could not be fully implemented in many patient monitoring systems.

Discussion of these issues leads to the recognition that 1 factor, such as color, will probably not satisfy requirements for unique identification of physiologic parameters as discussed above.

In summary, the following points should be taken into account:

  1. Color may be adequate for the most simple configuration of patient monitoring, but remains a problem for the 4,700 red green colorblind anesthesia providers.
  2. Position of the waveform and numerics on the screen through a defined hierarchical mechanism may complement colors, but when a large number of numerics are displayed their absolute positions on the screen will change.
  3. Recognition of waveform morphology is helpful, but it doesn’t help link the waveform to the numerics without color.
  4. Recognition of the expected numeric values associated with the patient’s physiology comes into play. For example, a cvp of 9 (single digit pressure) will not be confused for heart rate once the ECG waveform is visualized. It will not be confused with arterial pressure because that display includes systolic, diastolic, and mean pressures. It will not be confused with SpO2 or temperature.

In reality all 4 of the factors mentioned above contribute in part to identification of a parameter of interest, which cannot be generally reduced to simply color.


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