You should probably consider establishing upper and lower limits and making the area of concern flash (possibly a red or yellow background with a black line flashing back to the normal waveform) if values go above or below those limits. For example:
- ETCO2 values above or below baseline (35-45mmHg)
- HR below 60 (considered bradycardic) or above 120 (tachycardic).
- SPO2 below 90%
If you look at a modern EKG monitor that's exactly what happens - if a patient's heart rate becomes tachycardic the EKG that's being displayed in real time will begin to flash, alerting a paramedic / nurse / doctor / janitor that there's an issue with the EKG (as opposed to pulse rate, blocked ET tube, IV pump spilling out all over the floor, etc.)
Nurses, Paramedics, doctors, etc. are trained to be able to see and identify specific waveforms and shapes - an ETCO2 wave should have a characteristic "plateau" shape, an EKG rhythym should have a regular, narrow wave when the ventricles fire, etc. To do this the display has to be clear enough and have a high enough contrast that it can be made out from across the room. The "coloured lines on a black background" is an absolutely necessary part of the display - for example, variations in the P wave on an EKG may indicate abnormal atrial activity, and extremely shallow ETCO2 waves indicate the patient isn't releasing enough CO2 (it may be getting trapped in the lungs or may not be returning from the periphery).
In addition, there's typically a large number in the top corner (usually top right but it's not important as long as it's consistent) that aids in "immediate" recognition. In this case the number isn't just a redundancy but another way to quickly identify what's going on. A patient with a heart rate of "100" technically falls in the normal range, unless they're in a non-perfusing rhythm (like v-tach, which requires immediate defibrillation).
If you start radically changing display methods you're not going to get a lot of buy-in from the intended users; we all learned EKG recognition more or less the same way, so if I were to wheel a patient into a hospital in Turkey or Moldavia and hand then the EKG strip from my monitor the doctor should be able to identify the electrical activity from the tracing.
You may want to take a look at what's already out there - the Physio and Zoll field monitors and some of the Philips unit telemetry displays are really, really good at displaying this kind of activity.
BTW, "colored lines on black background" arose from the old style EKG monitors that used a light that physically bounced up and down on the end of a needle that swung behind a metered glass window. Nowadays we can change the color (I usually set different colors for ETCO2, SPO2 and EKG leads so I can easily differentiate between 7 different colored lines) but it means that a display will last longer (only has to light up the small line instead of the entire screen) and is easier to read at night / over long periods of time (there have been studies on observer fatigue but I can't find them just now).