MODEST HYPOTHERMIA PROVIDES PARTIAL NEUROPROTECTION WHEN USED FOR IMMEDIATE RESUSCITATION AFTER BRAIN ISCHEMIA

Intraischemic reduction in temperature of 2-3 degrees C (modest hypoth ermia) has been demonstrated to provide partial neuroprotection in neo natal animals. This investigation determined if modest hypothermia ini tiated immediately after brain ischemia provides neuroprotection. Pigl ets were studied with rectal temperature maintained during the Ist h a fter 15 min of brain ischemia at either 38.3 +/- 0.3 degrees C (normot hermia, n = 11) or at 35.8 +/- 0.5 degrees C (modest hypothermia, rt = 11). The severity of brain ischemia was similar between groups as ind icated by equivalent reduction in mean blood pressure (90 +/- 15 to 24 +/- 3 versus 92 +/- 13 to 26 +/- 3 mmHg), and changes in cerebral met abolites and intracellular pH (pH(i)) measured by magnetic resonance s pectroscopy (P-nucleoside triphosphate = 44 +/- 9 versus 42 +/- 18% of control, control = 100%, pH(i): 6.25 +/- .15 versus 6.24 +/- 0.22 for normothermic and modestly hypothermic groups, respectively). In the f irst 90 min after ischemia, there were no differences between groups i n the duration and extent of brain acidosis, and relative concentratio ns of phosphorylated metabolites. Categorical assessment of neurobehav ior was evaluated at 72 h postischemia (n = 16), or earlier if an anim al's condition deteriorated (n = 6). Postischemic hypothermia was asso ciated with less severe stages of encephalopathy compared with normoth ermia (p = 0.05). Histologic neuronal injury was assessed categoricall y in 16 brain regions, and postischemic hypothermia resulted in less n euronal injury in temporal (p = 0.024) and occipital (p = 0.044) corte x at 10 mm beneath the cortical surface, and in the basal ganglia (p = 0.038) compared with that in normothermia. Modest hypothermia for 1 h immediately after brain ischemia provides partial neuroprotection and may represent an adjunct to resuscitative strategies.