Neuropathologic aspects of hypothermic circulatory arrest in newborn dogs

A model of hypothermic circulatory arrest with recovery has been developed in the newborn dog. Eleven puppies were anesthetized with halothane, paralyzed and artificially ventilated with 70% nitrous oxide -30% oxygen to paO₂>60 mm Hg, paCO₂=33-42 mm Hg and pHa=7.35-7.42. Animals were surface cooled to 20°C, following which cardiac arrest was effected with i.v. KCl. Dogs remained asystolic without ventilation for 1.0, 1.5 or 1.75. Resuscitation was accomplished with closed-chest compression, mechanical ventilation, i.v. epinephrine and NaHCO₃, and rewarming to 37°C. Thereafter, the puppies were allowed to recover from anesthesia and maintained for either 18-22 h (n=9) or 72 h (n=2), at which time they underwent perfusion-fixation of their brains for pathologic analysis. Of the total, four out of four puppies arrested for 1.0 h exhibited no brain damage, including one recovered for 72 h; whereas one out of three and four out of four puppies arrested for 1.5 and 1.75 h, respectively, showed brain damage predominantly of the cerebral cortex but also of the basal ganglia and amygdaloid nucleus. The hippocampus was spared, even in a 1.75-h-arrested animal which was maintained for 72 h. No differences in pre- or post-arrest systemic blood pressure, heart rate, or acid-base balance were observed between the brain damaged and undamaged animals except for the single damaged animal arrested for 1.5 h, for which the blood pressure prior to cardiac arrest and during recovery was the lowest of all survivors. We conclude that newborn dogs undergoing hypothermic circulatory arrest for 1.0-1.5 h and which are fully recoverable without systemic hypotension exhibit no brain damage, whereas puppies arrested for 1.75 h exhibit brain damage entirely on the basis of global cerebral ischemia arising during the cardiac arrest. The experimental model has relevance to newborn human infants undergoing hypothermic circulatory arrest for the operative correction of congenital heart defects and should be useful for studying mechanisms of cellular injury in brain and other organs during prolonged ischemia.