Abstract 100: Neuroprotection Provided by Transnasal Airflow-Induced Brain Cooling in a Model of Pediatric Cardiac Arrest

Abstract

Introduction: High transnasal airflow at ambient temperature increases evaporative cooling of the nasal passages and drives a countercurrent heat exchange between cooled venous blood draining the nasal turbinates with cephalic arterial blood. Hypothesis: High transnasal airflow is not inferior to standard surface cooling in protecting the brain in an infant swine model of asphyxic cardiac arrest. Methods: Arterial O2 saturation was decreased to ~35% for 45 min followed by 7 min airway occlusion to produce asphyxic cardiac arrest in 2-week-old anesthetized piglets (4 kg). Viable neuronal counts were assessed at 6 days of recovery in 6 groups (n=5-9): 1) sham surgery, 2) normothermic recovery, 3) surface cooling to decrease rectal temperature from 38.5 to 34C between 10-120 min 4) transnasal cooling with airflow of 32 L/min from 10-120 min, 5) surface cooling onset delayed until 120 min ROSC, and 6) transnasal cooling delayed by 120 min ROSC. In all 4 cooling groups, hypothermia was sustained at 34C with surface cooling until 20 h ROSC followed by 6-8 h of rewarming. Results: Nasal airflow of 32 L/min decreased brain temperature from 38.3±0.3°C to 33.8±0.6 within 60 min without spatial temperature gradients in these 45-g brains. Surface cooling and transnasal airflow rescued the number of viable neurons in putamen from 38±23% (% of sham viable neurons; ±SD) in the normothermic group to 67±33% and 76±36%, respectively, when initiated at 10 min ROSC, and to 72±30% and 61±25%, respectively, when initiated at 120 min. In sensorimotor cortex, surface cooling and transnasal airflow rescued neurons from 56±36% in the normothermic group to 89±37% and 89±29%, respectively, when initiated at 10 min ROSC, and to 84±19% and 81±28%, respectively, when initiated at 120 min. Conclusions: The use of a high transnasal airflow is as effective as standard surface cooling when initiated at 10 or 120 min after ROSC in protecting vulnerable putamen and sensorimotor cortex from asphyxic cardiac arrest in infant piglets. Because of its simplicity, portability, and low cost, we postulate that transnasal cooling potentially could be deployed in the field by first responders for early initiation of brain cooling prior to maintenance with standard surface cooling after pediatric cardiac arrest.