Proportional Versus Fixed Chest Compression Depth for Guideline-Compliant Resuscitation of Infant Asphyxial Cardiac Arrest.

Objectives: Current guidelines for parameters of the delivery of chest compressions (CC) for infants and children are largely consensus based. Of the two recommended depth targets - 1.5 inches and 1/3 anterior-posterior chest diameter (APD) - it is unclear whether these have equal potential for injury. In previous experiments, our group showed in an animal model of pediatric asphyxial out-of-hospital cardiac arrest (OHCA; modeling ∼ 7 year-old children) that 1/3 APD resulted in significantly deeper CC and a higher likelihood of life-threatening injury. We sought to examine and compare injury characteristics of CC delivered at 1.5 inches or 1/3 APD in an infant model of asphyxial OHCA.

Methods: Swine were sedated, anesthetized, paralyzed, intubated through direct laryngoscopy, and then mechanically ventilated (10 ml/kg, FiO2:21%). APD was measured and confirmed by two investigators via a sliding T-square at the xiphoid. After instrumentation for vital signs monitoring, and while still anesthetized, the endotracheal tube was manually occluded to induce asphyxia, and occlusion was maintained for 9 min. Animals were then randomized to receive CC with a depth of 1.5 inches (Group 1) or 1/3 APD (Group 2), both with a rate of 100 per minute. Advanced life support drugs were administered at 13 min, and defibrillation at 14 min. Resuscitation continued until return of spontaneous circulation (ROSC) or 20 min of failed resuscitation. Survivors were sacrificed with KCl after 20 min of observation. Veterinary staff conducted necropsy to assay lung injury, rib fracture, hemothorax, airway bleeding, great vessel dissection, and heart/liver/spleen contusion. Injury characteristics were summarized and compared via Chi-Squared test or Mann-Whitney U-test using an alpha = 0.05.

Results: A total of 36 animals were included for analysis (Group 1: 18; Group 2: 18). Mean (SD) APD overall was 5.58 (0.23) inches, yielding a mean 1/3 APD depth of 1.86 inches. APD did not differ between groups. ROSC rates did not differ between groups. No injury characteristics differed significantly between groups.

Conclusions: In an swine model of infant asphyxial OHCA and resuscitation considering 1/3 APD or 1.5 inches, neither CC depth strategy was associated with increased injury.