Delayed onset of cardiac compressions in cardiopulmonary resuscitation of newborn pigs with asphyctic cardiac arrest

Background: When 30 s of initial positive pressure ventilation fails to stabilize the heart rate (HR) of newborns in the delivery room, the International Liaison Committee on Resuscitation guidelines recommend initiation of cardiac compressions. However, it may take longer than 30 s to establish effective pulmonary gas exchange. Whether a longer period of initial ventilation to reverse asphyxia would result in less need for cardiac compressions is unknown. Objectives: Our purpose was to investigate the effect of three different initial ventilation intervals prior to initiation of cardiac compressions on hemodynamic parameters, arterial blood gases, oxygen saturations and markers of inflammation and hypoxic damage in a piglet model of asystole due to asphyxia. Methods: Noroc piglets were anesthetized and mechanically ventilated. Progressive asphyxia was induced until asystole occurred. Randomization was made to ventilation with 21% O₂ for (1) 30 s (n = 16), (2) 1 min (n = 16), or (3) 1.5 min (n = 8) before initiation of cardiac compressions. Return of spontaneous circulation (ROSC) was defined as HR ≥100 min^-1. Results: Piglets initially ventilated for 30 s and 1 and 1.5 min achieved ROSC in a median of 150 (interquartile range 115-180),163 (124-177) and 282 (199-364) s, respectively. p value for group 1 versus group 2 was 0.51 and <0.001 for group 1 versus group 3. There were no differences in temporal changes in oxygen saturations, mean arterial blood pressure, HR, pH, pCO ₂, interleukin-1β or lactate/pyruvate ratios between groups. Conclusion: Although an additional 30 s to ensure effective ventilation does not impair the speed or success in achieving ROSC, delaying circulatory support for as long as 1.5 min of initial ventilation may be harmful.