Monitoring end-tidal carbon dioxide (EtCO2) is suggested as an indicator of cardiopulmonary resuscitation (CPR) quality since it reflects blood flow to the lungs. However, the relationship between EtCO2 and CPR quality parameters is poorly understood. In this study, we analyzed the EtCO2 linear relation with chest compression depth, chest compression rate, and ventilation rate. Six resuscitation episodes with the capnogram and the compression depth signal were selected to identify intervals with a stable EtCO2 value. The corresponding ventilation rate, compression depth and compression rate were annotated. Multiple linear regression was used to correlate EtCO2 changes with variations of CPR parameters, intra and inter-patient. Median (P25, P75) coefficient of determination R2 per patient was 0.86 (0.78, 0.89), decreasing to 0.64 when values were considered jointly. An increase of 1 ventilation per minute caused a decrease of 1.1 mmHg in EtCO2. An increase of 1 mm in depth caused an increase of 0.26 mmHg. Compression rate did not significantly influence the results. EtCO2 reflected CPR quality during resuscitation attempts, although the relationship between EtCO2 and CPR quality parameters varied between patients. The main explanatory variable was ventilation rate.