Abstract
Background: Sufficient O<sub>2</sub> supply to the brain is necessary for adequate cerebral energy metabolism, function and growth. Objectives: To elucidate the relation between changes in cerebral arterial O<sub>2</sub> content and cerebral O<sub>2</sub> supply and changes in the oxygenation state of cerebral hemoglobin, and to determine whether concentration changes in oxyhemoglobin (ΔcO<sub>2</sub>Hb), deoxyhemoglobin (ΔcHHb), and cerebral arterial oxygenation (ΔcHbD; the difference between ΔcO<sub>2</sub>Hb and ΔcHHb), and cerebral blood volume (ΔCBV) can be used to assess the decline in brain cell function during hypoxemia in lambs born near term. Methods: 17 preterm lambs were delivered at a mean gestational age of 133 days. Decreases in cerebral arterial oxygen content were induced by a stepwise reduction in inspired oxygen concentration. Mean values of all continuous variables were calculated over the last 180 s of each hypoxemic level. Cerebral arterial blood gases were analyzed at the end of each level to calculate cerebral arterial O<sub>2</sub> content and cerebral O<sub>2</sub> supply. Results: Changes in cerebral arterial O<sub>2</sub> content and cerebral O<sub>2</sub> supply were positively linearly related with ΔcO<sub>2</sub>Hb and ΔcHbD, and negatively with ΔcHHb and the concentration changes in total hemoglobin. Electrocortical brain activity remained stable until the cO<sub>2</sub>Hb and cHbD decreased to >3.0 ± 0.9 and >8.1 ± 1.9 (mean ± SD) µmol/100 g, respectively, and cHHb and CBV increased to >4.3 ± 1.7 and 1.37 ± 0.48 ml/100 g, respectively, as compared to baseline. Conclusions: Changes in cerebral arterial O<sub>2</sub> content and cerebral O<sub>2</sub> supply are adequately reflected by changes in the oxygenation state of cerebral hemoglobin. Concentration changes in ΔcO<sub>2</sub>Hb, ΔcHHb, ΔcHbD and ΔCBV can be used to assess the decline in brain cell function during hypoxemia in lambs born near term.
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