P1.221: High Frequency Ventilation with Continuous Chest Compressions Reduces Brain Lactic Acid in Preterm Lambs

Background: Gas exchange is severely impaired during cardiopulmonary resuscitation (CPR) in the cardiac arrested lamb model despite ventilation with 100% O2. A study in extremely preterm (~125d gestation, equivalent to ~ 25 weeks) asphyxiated cardiac arrested lambs comparing 3:1 compression to ventilation to continuous chest compressions with high frequency percussive ventilation (HFPV) showed improved cerebral oxygen delivery during resuscitation, as well as reduction in FiO2 requirement and PaCO2 following return of spontaneous circulation (ROSC) in the HFPV+CCC Group. We sought to analyze brain and plasma for lactic acid, as well as oxidative stress markers between groups.

Methods: Time-dated pregnant ewes at 124-126d gestation (term ~ 147d) underwent C-section. Fetal lambs were instrumented to analyze blood gases and carotid flow and asphyxiated by umbilical cord occlusion to cardiac arrest. Resuscitation was carried out by (a) standard 3:1 compression to ventilation (3:1 CV), (b) continuous chest compressions asynchronous with ventilation via a T-piece resuscitator (CCCaV) or (c) continuous chest compressions with HFPV (CCC+HFPV). Blood gases as well as plasma for oxidative stress markers were collected at in utero baseline, 2 minutes in resuscitation, at time of ROSC, and 15 minutes post-ROSC. Left frontal brain was collected for lactic acid levels.

Results: Twenty-one lambs were analyzed across three groups. All lambs achieved ROSC after 1 to 2 doses of epinephrine. There was no difference in baseline characteristics and time to ROSC between groups: mean (standard deviation) across all groups was 4.5 (1.22) minutes. PaCO2 during CPR, at time of ROSC, and 15 minutes post-ROSC was lower in the HFPV+CCC group compared to the groups (Figure 1b). PaO2 was higher during CPR and at time of ROSC in the HFPV+CCC group compared to the other groups (Figure 1a). Cerebral oxygen delivery during CPR was higher in the HFPV+CCC group – 0.18 (0.11) mL O2/kg/min compared to the groups: 3:1 C:V of 0.3 (0.03) and CCCaV of 0.05 (0.04). PaO2 was the same 15 minutes post-ROSC (Figure 1a), but the HFPV+CCC group had a lower FiO2 – median (IQR) of 0.40 (0.40-0.50) compared to the 3:1 C:V Group of 1.0 (0.6-1.0) and CCCaV group of 1.0 (1.0-1.0).

Plasma oxidative stress ([sulfone methionine + sulfoxide methionine] to methionine ratio) changed over time, but there was no difference between groups (Figure 2a). Brain tissue lactic acid was lower in the HFPV+CCC group compared to the groups (Figure 2b).

Conclusion: Resuscitation using continuous chest compression during high frequency percussive ventilation is feasible with similar success of ROSC and improved gas exchange, cerebral oxygen delivery, and reduced brain lactic acid without increasing oxidative stress in asphyxiated preterm neonatal lambs in cardiac arrest. Clinical studies evaluating the use of HFPV (small instrument similar to a T-piece device) during neonatal resuscitation are needed.