"Bystander" chest compressions and assisted ventilation independently improve outcome from piglet asphyxial pulseless cardiac arrest

Introduction: "Bystander" CPR with chest compressions alone (CC) and chest compressions with assisted ventilation (CC+V) result in comparable survival from swine fibrillatory cardiac arrest. After piglet asphyxial cardiac arrest with loss of aortic pulsations (LOAP), CC+V improved outcome whereas CC or ventilation only (V) did not. We hypothesized different relative efficacy of these CPR techniques earlier in the asphyxial process. In piglets, systolic BP <50 mmHg ("pulseless") occurs 1-2 minutes prior to LOAP after endotracheal tube (ETT) clamping. In a piglet asphyxial pulseless cardiac arrest model, we compared 4 bystander CPR techniques: CC+V, CC, V, and none. Methods: Asphyxial cardiac arrest was produced by clamping the ETTs of piglets (12±1 kg) until SBP was <50 mmHg (7±1min). Animals were randomly assigned to 8 minutes of CC+V (ratio of 15:2 with 17% O₂ / 4% CO₂ by bag-valve-ETT), CC (100/min), V (20/min), or no "bystander" CPR. Standard "paramedic" advanced life support was then provided, followed by 1 hour of ICU care. ROSC (return of spontaneous circulation) was defined as SBP >60 mmHg for >1 min. Data (mean±SEM) were analyzed by ANOVA and Fisher's exact test. Results: CC+V CC V NONE S_aO₂(1′ CPR) 54±6%***34±14%** *72±6%***7±3% pH_a (1′ CPR) 7.20±.10**7.17±09**7.23±.08 **7.05±10 ROSC 10/10 6/10 6/10 4/10 ROSC (<3 min) 10/10***4/10 6/10**0/10 24-hr Survival 8/10***5/10*6/10**0/10 Differs from "NONE,"*p≤0.05,**p≤0.01,** *p<0.001 24-hr survival occurred in 18/20 piglets with ROSC in <3 min vs 1/20 without ROSC in ∼3 min (p∼0.0001). Conclusions: In this model, immediate provision of "bystander" CPR with CC+V, CC, or V improved 24-hr survival. Although CC and V independently improved outcome, CC+V tended to be more effective (p=0.20 vs CC). 24-hr survival was highly dependent on response to the first 3 minutes of "bystander" CPR.