Marked reduction of brainstem blood flow in artificially ventilated newborn piglets during normoxia and normocapnic hypoxia.

OBJECTIVE: To estimate the effect of artificial ventilation on regional cerebral blood flow, cardiovascular regulation, and cerebral oxidative metabolism in newborns. DESIGN AND
SUBJECTS: Comparison of three randomized treatment groups of newborn piglets: Group 1 (artificially ventilated sham-operated group; n =7); group 2 (artificially ventilated group with normoxia and moderate normocapnic hypoxia; n =7); group 3 (spontaneously breathing group with normoxia and moderate normocapnic hypoxia; n =6). MEASUREMENTS AND
RESULTS: Animals were anesthetized with 0.5% isoflurane in 70% nitrous oxide and 30% oxygen. Groups 1 and 2 were artificially ventilated. Animals in group 3 breathed spontaneously. Moderate normocapnic hypoxia was induced in groups 2 and 3 for 1 h by lowering the inspiratory oxygen fraction from 0.35 to 0.11. Mode of ventilation induced at most marginal effects on global cerebrovascular response, cardiovascular regulation, and cerebral oxidative metabolism. However, under normoxic conditions, regional cerebral blood flow of the medulla oblongata, pons, mesencephalon, thalamus, and cerebellum were markedly reduced in artificially ventilated piglets ( P <0.05). Moderate normocapnic hypoxia led to a marked increase in regional cerebral blood flow, which was significantly lower in the medulla oblongata, pons, mesencephalon, thalamus, and cerebellum of artificially ventilated piglets ( P <0.05).
CONCLUSION: Artificial ventilation clearly induces reduced neuronal activity in the brain stem and cerebellum of newborn piglets. This is suggested by a considerably reduced blood flow in these regions under normoxia and moderate normocapnic hypoxia. However, there is no relevant detrimental effect on cardiovascular regulation and brain oxidative metabolism.