The effects of reversal of
hypotension on the cerebral microcirculation, oxygenation, and metabolism in
septic shock remain unclear. In 12 sheep,
peritonitis was induced by injection of feces into the abdominal cavity. At the onset of
septic shock (mean arterial pressure (MAP) < 65 mmHg, unresponsive to fluid challenge), a
norepinephrine infusion was titrated in eight sheep to restore a MAP ≥ 75 mmHg; the other four sheep were kept hypotensive. The microcirculation of the cerebral cortex was evaluated using side-stream dark-field video-microscopy. Brain partial pressure of
oxygen (PbtO2) was measured, and cerebral metabolism was assessed using microdialysis. All animals developed
septic shock after a median of 15 (14−19) h. When MAP was raised using
norepinephrine, the PbtO2 increased significantly (from 41 ± 4 to 55 ± 5 mmHg), and the cerebral
lactate/
pyruvate ratio decreased (from 47 ± 13 to 28 ± 4) compared with values at
shock onset. Changes in the microcirculation were unchanged with restoration of MAP and the
glutamate increased further (from 17 ± 11 to 23 ± 16 μM), as it did in the untreated animals. In
septic shock, the correction of
hypotension with vasopressors may improve cerebral oxygenation but does not reverse the alterations in brain microcirculation or cerebral metabolism.