Effect of acute hypovolemic hypotension on cerebral metabolism in newborn piglets

To evaluate the temporal changes in cerebral energy metabolism in shock during the perinatal period, we studied cerebral blood flow (CBF) and other metabolic variables in newborn piglets subjected an acute hypovolemic hypotension (HVH). By 30 minutes following HVH, the cardiac output dropped 64%, but the CBF was maintained. Serum glucose rose 110% baseline, resulting in an increase in brain glucose delivery. Cerebral metabolic rate of glucose also increased 246%, while that of oxygen remained unaffected. Further, at 30 minutes of HVH, systemic arterial lactate levels increased 250%, but cerebrospinal fluid (CSF) lactate levels remained in the normal range. By contrast, at 60 minutes following HVH, the CBF dropped 60%, the cerebral metabolic rate for glucose dropped 45%, and that of oxygen 43% of the respective baseline values. A profound systemic lactatemia was noted (500% baseline value), with a concomitant rise in the CSF lactate levels to 190% baseline value. These findings suggest that post-hemorrhagic hypovolemia can be divided into two arbitrary, but distinct phases: 1) An initial phase of relative compensation lasting approximately 30 minutes, during which time the brain utilization of metabolic substrates is well preserved. 2) A later phase of decompensation by 60 minutes of HVH, during which time the CBF as well as brain utilization of metabolic substrates drop significantly. By this time a loss of blood-CSF or brain-CSF barrier for lactate can be seen. The findings of this study may have important implications in the treatment of hemorrhagic shock in the perinatal period.