A capnogram clinicians can actually read

mmHg or kPa, depending on where you train

In the English version of the app EtCO2 reads in mmHg, next to blood pressure in the same unit. Switch the app to Swedish, Danish, Norwegian or Finnish and it reads in kPa instead, because that is what a monitor on a Nordic ward shows, even though blood pressure on the same screen stays in mmHg. Only the display changes. The underlying value is the same, so a scenario behaves identically in either unit.

The two angles that carry the diagnosis

A capnogram has four phases, but it's really two angles that a clinician reads. The alpha angle sits between the rising edge and the plateau: it opens up as airway obstruction worsens, and in a severe bronchospasm it can erase the plateau entirely into what's often called a shark-fin shape. The beta angle sits between the plateau and the downstroke, and it opens with rebreathing. The Patient Simulator draws a normal capnogram with both angles where they belong, so trainees learn what a healthy trace looks like before they have to spot one that isn't. For a deeper walkthrough of both angles and the abnormal shapes they produce, see reading a capnogram.

A plateau that slopes, on purpose

The plateau itself rises gently across a breath rather than sitting dead flat, because alveoli empty at slightly different rates in a real lung. A perfectly horizontal plateau isn't a cleaner signal, it's a less realistic one.

Rounded corners, for a reason

Building the waveform's transitions as sharp mathematical corners was an early mistake we corrected after a doctor pointed out that no real capnograph produces one. Gas takes time to travel through the sampling line and spreads out on the way, and the sensor itself has a response time. The Patient Simulator runs the ideal waveform through a response-time filter that rounds each transition by an amount proportional to how sharp it is, which is exactly what preserves the alpha and beta angles instead of flattening them the way a generic smoothing pass would.

Apnea reads as no reading, not zero

In any cardiac-arrest rhythm the trace goes completely flat at zero: a capnograph measures real exhaled gas, so there's nothing left to add texture to. The number itself shows as "no reading" rather than 0, because end-tidal specifically means the value at the end of an exhaled breath, and an apneic patient has none.

Locked in phase with the breath, always

One breathing engine drives both this waveform and the respiration trace, so the two can never show a patient inhaling on one screen and exhaling on the other.

Normal values, and what a low or high EtCO2 usually means, are in EtCO2: what it means and normal values.