Introduction The purpose of inflations during cardiopulmonary resuscitation (CPR) is to deliver an adequate tidal volume (V_T) to facilitate gas exchange. However, no study has examined V_T delivery during chest compression (CC) in detail to understand the effect of CC on lung aeration. The aim of the study was to examine V_T changes during CC and their effect on lung aeration.

Methods Piglets were anaesthetised, instrumented and intubated with zero leak. They were then randomly assigned to CPR using either 3:1 compression:ventilation ratio (C:V) (n=6), continuous CC with asynchronous ventilations (CCaV) (90 CC/min with 30/min asynchronous ventilations) (n=6) or continuous CC superimposed with 30 s sustained inflations (CC+SI) with a CC rate of 120/min (n=5). A respiratory function monitor (NM3, Respironics, Philips, Andover, Massachusetts, USA) was used to continuously measure inspiration tidal volume (V_Ti) and expirational tidal volume (V_Te). ANOVA with Bonferroni post-test were used to compare variables of all three groups.

Results During the inflation in the 3:1 C:V group, the mean (SD) V_Ti and V_Te was 23.5 (5.3) mL/kg and 19.4 (2.7) mL/kg (p=0.16), respectively. During the CC, we observed a significant V_T loss in the 3:1 group with V_Ti and V_Te being 4.1 (1.2) mL/kg and 11.1 (3.3) mL/kg (p=0.007), respectively. In the CCaV group, V_Te was higher compared with V_Ti, but this was not significant. In the CC+SI group, a V_T gain during each CC with V_Ti and V_Te of 16.3 (3.2) mL/kg and 14 (3) mL/kg (p=0.21), respectively, was observed.

Conclusions V_T delivery is improved using CC+SI compared with 3:1 C:V. This improvement in V_T delivery may lead to better alveolar oxygen delivery and lung aeration.