Stroke; a journal of cerebral circulation
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Hyperventilation to extremely low arterial carbon dioxide tension (PaCO2) has been used in the management of persistent pulmonary hypertension in newborn infants. With progressive hypocarbia, cerebral vasoconstriction occurs, raising the concern that extreme hypocarbia may result in cerebral oxygen deprivation. Therefore, I evaluated regulation of the cerebral circulation during acute hypocarbia in 10 newborn lambs. ⋯ Cerebral venous lactate concentration increased significantly (3.49 +/- 0.23 vs. 2.01 +/- 0.22 mM, p less than 0.001) during severe hypocarbia (PaCO2 of less than 22 mm Hg), and the arterial-venous lactate concentration difference became negative. These results demonstrate uniform responses of whole-brain and regional blood flows and stable cerebral oxygen consumption during moderate and severe hypocarbia. Although there is evidence for cerebral lactate production during severe hypocarbia, this is not likely to indicate cerebral hypoxia as oxygen consumption does not change.