Objective: Develop a clinically relevant model of pediatric asphyxial cardiopulmonary arrest in rats.
Design: Prospective interventional study.
Setting: University research laboratory.
Subjects: Postnatal day 16-18 rats (n = 9/group).
Interventions: Anesthetized rats were endotracheally intubated and mechanically ventilated, and vascular catheters were inserted. Vecuronium was administered, and the ventilator was disconnected from the rats for 8 mins, whereupon rats were resuscitated with epinephrine, sodium bicarbonate, and chest compressions until spontaneous circulation returned. Shams underwent all procedures except asphyxia.
Measurements and main results: Asphyxial arrest typically occurred by 1 min after the ventilator was disconnected. Return of spontaneous circulation typically occurred <30 secs after resuscitation. An isoelectric electroencephalograph was observed for 30 mins after asphyxia, and rats remained comatose for 12-24 hrs. Overall survival rate was 85%. Motor function measured using beam balance and inclined plane tests was impaired on days 1 and 2, but recovered by day 3, in rats after asphyxia vs. sham injury (p <.05). Spatial memory acquisition measured using the Morris-water maze on days 7-14 and 28-35 was also impaired in rats after asphyxia vs. sham injury (total latency 379 +/- 28 vs. 501 +/- 40 secs, respectively, p <.05). DNA fragmentation was detected in CA1 hippocampal neurons bilaterally 3-7 days after asphyxia. Neurodegeneration detected using Fluorojade B was seen in bilateral CA1 hippocampi and layer V cortical neurons 3-7 days after asphyxia, with persistent neurodegeneration in CA1 hippocampus detected up to 5 wks after asphyxia. CA1 hippocampal neuron survival after asphyxia was 39-43% (p <.001 vs. sham). Evidence of DNA or cellular injury was not detected in sham rats.
Conclusions: This model of asphyxial cardiopulmonary arrest in postnatal day 17 rats produces many of the clinical manifestations of pediatric hypoxic-ischemic encephalopathy. This model may be useful for the preclinical testing of novel and currently available interventions aimed at improving neurologic outcome in infants and children after cardiopulmonary arrest.