Modified volumetric capnography-derived parameter: A potentially stable indicator in monitoring cardiopulmonary resuscitation efficacy in a porcine model

Aim: We aimed to investigate whether the ability of the volumetric capnography-derived parameter, the volume of CO₂ eliminated per minute and per kg body weight (V'CO₂ kg^-1), in monitoring the quality of CPR and predicting the return of spontaneous circulation (ROSC) remains undisturbed by hyperventilation.

Methods: This randomised crossover study included 12 male domestic pigs. After 4 min of untreated ventricular fibrillation, mechanical CPR was administered. Following 5-min washout periods, each animal underwent two sessions of experiments; four 5-min ventilation trials followed by advanced life support, consecutively in the two sessions.

Results: Different ventilation types had no significant impact on V'CO₂ kg^-1 or haemodynamics. However, PETCO₂ was significantly affected by the ventilation type and coronary perfusion pressure (P < 0.05). The means ± standard deviations of PETCO₂ decreased linearly with an increase in the respiratory rate (RR) (P < 0.05). The PETCO₂ decreased from 20.42 ± 9.51 to 16.16 ± 5.07 (P < 0.05) as the tidal volume increased from 10 to 20 mL min^-1. No significant differences in V'CO₂ kg^-1 were observed between the three RR levels of ventilation types (P = 0.274). Post hoc analysis demonstrated a significant difference between the highest value of V'CO₂ kg^-1 in double tidal volume hyperventilation and normal ventilation and triple respiratory rate hyperventilation (P < 0.05). The AUC for V'CO₂ kg^-1 and PETCO₂ in discriminating between survivors and non-survivors was 0.80 and 0.71, respectively.

Conclusions: V'CO₂ kg^-1 performs better than PETCO₂ in monitoring the quality of CPR during hyperventilation. In predicting ROSC during variations in a ventilation state, V'CO₂ kg^-1 has good predictive ability.