NEONATAL ISCHEMIC NEUROPROTECTION BY MODEST HYPOTHERMIA IS ASSOCIATEDWITH ATTENUATED BRAIN ACIDOSIS

Background and Purpose A 2.9 degrees C reduction in the intraischemic rectal temperature of neonatal piglets is associated with less brain d amage compared with animals with normothermic rectal temperatures. Thi s investigation studied one potential mechanism for this observation: better maintenance of energy stores and less brain acidosis secondary to reduced metabolic activity associated with modest hypothermia. Meth ods P-31 MII spectroscopy was used to study piglets before, during, an d after 15 minutes of partial brain ischemia with intraischemic rectal temperatures of either 38.3 +/- 0.4 degrees C (n=10, normothermic) or 35.4 +/- 0.5 degrees C (n=10, hypothermic). Animals were followed up for up to 72 hours after ischemia and were evaluated clinically and by brain histology. Results Values for pH(i) remained 0.15 to 0.20 pH un its greater in modestly hypothermic than in normothermic piglets durin g ischemia and the initial 30 minutes after ischemia (P=.049, group ef fect). Phosphocreatine, beta-ATP, and inorganic phosphorus were simila r between groups. The relationship between the intraischemic energy st ate and subsequent clinical evidence of brain damage (irrespective of group assignment) revealed lower pH(i) over the last 7 minutes of isch emia for abnormal compared with normal piglets (5.98 +/- 0.22 versus 6 .39 +/- 0.24, respectively; P=.OD2). In contrast, intraischemic beta-A TP (41 +/- 19% versus 57 +/- 21% of control) and inorganic phosphorus (273 +/- 31% versus 224 +/- 92% of control) for abnormal and normal pi glets, respectively, did not differ between groups. Conclusions Intrai schemic modest hypothermia attenuates the severity of brain acidosis d uring and 30 minutes after ischemia compared with normothermic animals and supports the concept that attenuated brain acidosis is a potentia l mechanism by which hypothermia may reduce ischemic brain damage.