O1037: Should We Wait to Initiate Chest Compressions When a Newborn Is Born with No Heart Rate? An Animal Study in an Ovine Model of Cardiac Arrest

Background: When neonates are born without a heart rate, they are at higher risk of mortality and morbidity despite effective resuscitation. Current practice to provide effective positive pressure ventilation (PPV) before starting chest compressions (CC) is important when the heart rate (HR) is < 60 bpm due to birth asphyxia. But when the HR is '0', starting CC after 30s of effective PPV through a secured endotracheal tube (ETT) or laryngeal mask airway (LMA), which could take at least 2 min may be detrimental. With recent recommendations to continue resuscitation for 20 min, initiating early CC with PPV could reduce the time to achieve the return of spontaneous circulation (ROSC).To evaluate the effect of immediate CC and face mask PPV on I) timing and rates of ROSC, II) gas exchange and hemodynamics, compared to delayed initiation of CC (after 2 min) in an ovine neonatal model of asphyxia.

Methods: Near-term lambs (139-140d) after instrumentation & post cord occlusion induced cardiac arrest (2 min after HR - 0 bpm) were randomized to
i) controls - initiate resuscitation with facemask (FM) PPV (21%O2 for 30s, then 100%O2), intubate at 2 min, followed by CC&PPV in the ratio of 3:1 until ROSC or up to 20 min, ii) Study - Start CC& FacemaskPPV (21%O2 for 30s, then FM100%O2) in the ratio of 3:1 and intubate at 2 min if ROSC is not achieved or up to 20 min. IV epinephrine was administered after 5 min and subsequently every 3 min for a total of 4 doses If lambs achieve ROSC, they are ventilated for 1 hour and euthanized. Time and rates of ROSC, blood gas, continuous peak carotid (CBF) & pulmonary blood flows (PBF) were recorded.

Results: Eleven lambs were randomized to controls (N-6) and study (N-5)(Fig 1a). Compared to controls (Fig 1a & 1b), the time to achieve ROSC was significantly shorter in the study group (Fig 1a & 1c). The pH and arterial carbon dioxide levels (Fig2 a & b) were non-significantly lower in the study group signifying gas exchange from the beginning of resuscitation. The arterial oxygenation was not different (Fig 2c). Peak CBF was significantly higher during resuscitation in the study compared to controls (Fig 3a), while the PBF was not different (Fig 3b).

Conclusion: Initiation of resuscitation with CC and FM PPV reduced the time to achieve ROSC while preparing and placing an ETT at 2 min in a complete cardiac arrest model. Clinical studies are needed to validate our findings in terms of mortality and neurodevelopmental outcomes.