Purpose: Previous studies from our group demonstrated that chest compression (CCs) applied according to depth feedback produced potentially fatal intrathoracic damage in paediatric porcine models. The objective of this study is to assess if CPR feedback from an automated external defibrillator (AED) using the impedance cardiogram (ICG) can guide CC application to achieve high levels of end-tidal carbon dioxide (EtCO2), shock success (SS) and return of spontaneous circulation (ROSC) without significant intrathoracic damage.

Methods: Twelve piglets (10.5–25.0 kg) were studied under anaesthesia. Physiological variables; arterial blood pressure (BP) and EtCO2 (capnography) were recorded. After defibrillation pads were placed, ventricular fibrillation (VF) was electrically induced. After 30s of untreated VF, five two-minute episodes of CCs were applied targeting the ICG amplitude that provokes “Good Compressions” prompts by a HeartSine SAM 500P AED. CC depth was measured using a CPRmeter. During CPR, physiological variables and CC depth were recorded every 15s. After the final episode, approximately 12m:30s after VF induction, defibrillation was attempted. After a 5-minute rest period, surviving animals were euthanised and post-mortem examinations conducted.

Results: During CPR, mean EtCO2 was 18±0.19mmHg and 84.8% of observations of EtCO2 were >15mmHg with 95% CI = (81.3%, 87.9%). Median(IQR) systolic BP was 55mmHg(47,69). When defibrillated, 12/12 animals achieved first SS, and 11/12 achieved ROSC. Mean CC depth was 23.88±0.2mm. After the rest period, animals displayed a median (IQR) EtCO2 of 45mmHg (42,47), and a median (IQR) mean arterial BP of 78mmHg (54,79). Post-mortem examination displayed rib fractures in 9/12 piglets, however no additional or significant intrathoracic damage was observed.

Conclusions: The results of this study indicate ICG can direct CCs to achieve high levels EtCO2, SS and ROSC across the paediatric weight range in a porcine model without inducing the

6 - Impedance Cardiogram Directed Chest Compression Feedback in a Porcine Model of Paediatric Sudden Cardiac Arrest is Associated with High Levels of End-tidal Carbon Dioxide, Shock Success and ROSC