If two identical twins are standing next to each other at a family reunion, and one chokes on a sandwich leading to cardiac arrest, and the second suffers a simultaneous VF arrest, and two medics arrive exactly 5 minutes later, and both patients are intubated at the same time, will their ETC02 numbers be the same or different?
Despite being identical twins, they will have different ETCO2 readings. The twin who went into VF arrest will likely have an ETCO2 in the 20s with CPR. The twin who choked on his sandwich will have an ETCO2 much higher –likely in the 70s or more. His heart continued to beat for awhile while he slowly died of hypoxia from an obstructed airway. The pumping heart pumped CO2 to the lungs where it built up. Cardiac arrests due to respiratory causes usually have much higher initial ETCO2s than those who suffered sudden cardiac arrest. (Patient who are hypercapnic as their norm are an exception.). Those who suffered respiratory causes of their arrest will see their initial high ETCO2 fall back to more normal levels after a minute of ventilation.
Use ETCO2 to help predict the cause of the arrest (cardiac versus respiratory) and then treat accordingly.