Regional Cerebral Blood Flow and Glucose Utilization during Hypothermia in Newborn Dogs

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Abstract
To ascertain the effect of profound hypothermia on brain function and metabolism, newborn dogs were subjected to surface cooling during which regional cerebral blood flow (rCBF) and glucose unilization (rCGU) were measured with iodo-[14C]-antipyrine and 2-deoxy-[14C]-glucose, respectively. Puppies were anesthetized with nitrous oxide, paralyzed, and their lungs artificially ventilated to maintain arterial normoxia (PaO2 > 60 mmHg) and normal acid-base balance (PaCO2 = 35-41 mmHg; pHa = 7.34-7.42). When rectal temperature was decreased from 37 to 20.degree. C, mean arterial blood pressure (MABP) decreased from 75 to 47 mmHg (P < 0.001) and heart rate from 238 to 64 beats/min (P < 0.001). Arterial PCO2 was reduced from 38 to 31 mmHg (P < 0.001) (corrected to 37.degree. C), whereas pHa was unchanged from control (7.40). The electroencephalogram slowed progressively and became isoelectric at 22-25.degree. C. During normothermia (n = 6) blood flow to 16 component structures of brain varied from 17 (occipital white matter) to 65 (medulla) ml .cntdot. 100 g-1 .cntdot. min-1, whereas during hypothermia (n = 6) blood flow was lower in all regions (P < 0.001) at remarkably uniform levels (8.3-10.3 ml .cntdot. 100 g-1 .cntdot. min-1). Thus, the greatest reductions (range, 16-48% of control) in CBF occurred in those structures with the highest intrinsic flows during normothermia and were proportionately less in low flow structures. Regional CGU also decreased in all brain regions analyzed (P < 0.001). Normothermic CGU (n = 5) varied from 9 (occipital white matter) to 24 (cerebellum) .mu.mol .cntdot. 100 g-1 .cntdot. min-1, whereas during hypothermia rCGU (n = 5), like rCBF, was within a narrow range (0.47-0.57 .mu.mol .cntdot. 100 g-1 .cntdot. min-1). The percent reductions in rCGU (range, 2.0-6.5% of control) were always greater than corresponding reductions in rCBF. The findings indicate that cerebral glucose utilization is globally depressed during profound hypothermia but that CBF remains more than adequate to support the energy needs of the immature brain.