SELECTIVE BRAIN COOLING IN INFANT PIGLETS AFTER CARDIAC-ARREST AND RESUSCITATION

Objectives: To test the hypothesis that selective brain cooling could be performed in an infant model of cardiac arrest and resuscitation wi thout changing core temperature and to study Its acute effects on regi onal organ blood flow, cerebral metabolism, and systemic hemodynamics. Design: Prospective, randomized, controlled study. Setting: Research laboratory at a university medical center. Subjects: Fourteen healthy infant piglets, weighing 3.5 to 6.0 kg. Interventions: Piglets were an esthetized and mechanically ventilated, and had vascular catheters pla ced, Parietal cortex (superficial brain), caudate nucleus (deep brain) , esophageal, and rectal temperatures were monitored. All animals unde rwent 6 mins of cardiac arrest induced by ventricular fibrillation, 6 mins of external cardiopulmonary resuscitation (CPR), defibrillation, and 2 hrs of reperfusion. Normal core temperature (rectal) was regulat ed in all animals, In seven control animals (group 1), brain temperatu re was not manipulated. In seven experimental animals (group 2), selec tive brain cooling was begun during CPR, using a cooling cap filled wi th -30 degrees C solution. Selective brain cooling was continued for 4 5 mins of reperfusion, after which passive rewarming was allowed, Regi onal blood flow (microspheres) and arterial and sagittal sinus blood g ases were measured prearrest, during CPR, and at 10 mins, 45 mins, and 2 hrs of reperfusion. Measurements and Main Results: Rectal temperatu re did not change over time in either group, In group 1, brain tempera ture remained constant except for a decrease of 0.6 degrees C at 10 mi ns of reperfusion. In group 2, superficial and deep brain temperatures were lowered to 32.8 +/- 0.7 (SEM) degrees C and 34.9 +/- 0.4 degrees C, respectively, by 15 mins of reperfusion. Superficial and deep brai n temperatures were further lowered to 27.8 +/- 0.8 degrees C and 31.1 +/- 0.3 degrees C, respectively, at 45 mins of reperfusion. Both temp eratures returned to baseline by 120 mins. Cerebral blood flow was not different between groups at any time point, although there was a tren d for higher flow in group 2 at 10 mins of reperfusion (314% of baseli ne) compared with group 1 (230% of baseline), Cerebral oxygen uptake w as lower in group 2 than in group 1 (69% vs, 44% of baseline, p = .02) at 45 mins of reperfusion, During CPR, aortic diastolic pressure was lower in group 2 than in group 1 (27 +/- 1 vs. 23 +/- 1 mm Hg, p = .00 7), Myocardial blood flow during CPR was also lower in group 2 (80 +/- 7 vs, 43 +/- 7 mL/min/100 g, p = .002), Kidney and intestinal blood f lows were reduced during CPR in both groups; however, group 2 animals also had lower intestinal flow vs. group 1 at 45 and 120 mins of reper fusion. Conclusions: Selective brain cooling by surface cooling can be achieved rapidly in an infant animal model of cardiac arrest and resu scitation without changing core temperature. Brain temperatures known to improve neurologic outcome can be achieved by this technique with m inimal adverse effects, Because of its ease of application, selective brain cooling may prove to be an effective, inexpensive method of cere bral resuscitation during pediatric CPR.