ETCO2 To Differentiate Cause of Arrest

Here is a fascinating 2003 study about the differences in initial ETCO2 readings between respiratory cardiac arrest versus vfib/vt arrests.

Difference in end-tidal CO2 between asphyxia cardiac arrest and ventricular fibrillation/pulseless ventricular tachycardia cardiac arrest in the prehospital setting.

The researchers analyzed 44 patients with respiratory cardiac arrest (asthma, hanging, obstructed airway, aspiration, etc.) and 141 with primary cardiac arrest, measuring their ETCO2 at intubation and then every minute.

They discovered that patients in respiratory induced cardiac arrest had a significantly higher initial ETCO2 than patients in primary cardiac arrest, but that the high initial reading was not prognostic for ROSC.

But after a minute, during which the respiratory numbers invariably came down, the minute numbers were prognostic for ROSC.

In the vfib/vt group initial, 1 minute and subsequent ETCO2 were prognostic for ROSC.

In all patients who achieved ROSC, no patient had an initial ETCO2 lower than 10 mmHg.

The authors write “during the period of asphyxia, continued cardiac output prior to cardiac arrest permits continued delivery of CO2 to the lungs, which (in the absence of exhalation) results in higher alveolar C02 when ventilation is resumed.”

The bottom line then is that initial ETCO2 readings can help provide clues into the causes of cardiac arrest, and help direct treatment. For instance, a patient with an extremely high initial reading likely had a hypoxic cause of arrest, and positive pressure ventilation will be a priority.

Here are numbers from the study:

Asphyxia Arrest Initial readings

ROSC = 70.1 Without ROSC = 62.8

VFIB/VT Initial Readings

ROSC = 20.3 Without = 8.2

Asphyxia Arrest After 1 minute

ROSC = 35.8 Without 19.4

VFIB/VT After 1 minute

ROSC = 30.2 Without = 14.2

Asphyxia Final

ROSC = 31.2 Without = 7.2

VFIB/VT Final

ROSC = 28.1 Without = 6.2