Asphyxia, cardiac arrest and resuscitation in rats. I. Short term recovery

This study was conducted to investigate the degree of insult from asphyxia leading to total body circulatory arrest, as a model for brain resuscitation studies in rats. Of 78 male rats, 68 were anesthetized with halothane in O2/N2O, controlled ventilated, paralyzed with pancuronium and asphyxiated, 5, 7.5, 10, 12.5 and 15 min, respectively. Asphyxiation led to circulatory arrest in 244 +/- 22 s (mean +/- S.E.M.). Resuscitation was successful in 65% within 60 s using controlled ventilation with 100% O2, extrathoracic compressions and epinephrine intravenously. Subsequent intensive care to 6, 12 or 24 h was successful in 50% of resuscitated rats. At 6, 12 and 24 h of recovery, neurologic deficit scores and light microscopic neuropathology scores of the brain after in vivo fixation of the total body with intraventricular paraformaldehyde 3%, revealed a large scatter variability without a clear pattern. Lesions were located mostly in the frontal cortex and hippocampus (footplate) with ischemic neuronal change as the most frequent structural change. Brain cell necrosis was not seen after successful resuscitation. It seems that both scores were influenced by post-insult stress, as indicated by paroxysmal hypertension and motor activity, by complications, such as obstruction of the tracheotomy cannula by abundant sputum production, and by partial sedation with N2O and paralysis with pancuronium. This study indicates the feasibility of an asphyxial insult in rats for use in resuscitation studies of short duration. Although 24 h post-insult recovery is possible, up to 6 h seems most practical, with asphyxia of 7.5-10 min most successful and controllable. Questions are raised about the effects of irritation during the post-insult intensive care on both neurological deficit and neuropathology scores.