The impact of ventilation rate on end-tidal carbon dioxide level during manual cardiopulmonary resuscitation.

AIM

Ventilation rate is a confounding factor for interpretation of end-tidal carbon dioxide (ETCO) during cardiopulmonary resuscitation (CPR). The aim of our study was to model the effect of ventilation rate on ETCO during manual CPR in adult out-of-hospital cardiac arrest (OHCA).

METHODS

We conducted a retrospective analysis of OHCA monitor-defibrillator files with concurrent capnogram, compression depth, transthoracic impedance and ECG. We annotated pairs of capnogram segments presenting differences in average ventilation rate and average ETCO value but with other influencing factors (e.g. compression rate and depth) presenting similar values within the pair. ETCO variation as a function of ventilation rate was adjusted through curve fitting using non-linear least squares as a measure of goodness of fit.

RESULTS

A total of 141 pairs of segments from 102 patients were annotated. Each pair provided a single data point for curve fitting. The best goodness of fit yielded a coefficient of determination R of 0.93. Our model described that ETCO decays exponentially with increasing ventilation rate. The model showed no differences attributable to the airway type (endotracheal tube or supraglottic King-LT-D).

CONCLUSION

Capnogram interpretation during CPR is challenging since many factors influence ETCO. For adequate interpretation, we need to know the effect of each factor on ETCO. Our model allows quantifying the effect of ventilation rate on ETCO variation. Our findings could contribute to better interpretation of ETCO during CPR.