Few data exist regarding resuscitation of hypovolemic shock in infants, and alternative strategies such as vasopressor therapy merit further evaluation. However, the effects of norepinephrine on cerebral perfusion and oxygenation during hemorrhagic shock in the pediatric population are still unclear. Eight anesthetized piglets were subjected to hypotension by blood withdrawal of 25 mL/kg. Norepinephrine was titrated to achieve baseline mean arterial blood pressure (MAP), and cerebral oxygenation was determined by brain tissue PO 2 (P ti O 2 ) and near-infrared spectroscopy-derived tissue oxygen index (TOI). Then, norepinephrine was stopped, MAP was allowed to decrease again below 30 mm Hg, and shed blood was retransfused. During hemorrhage, TOI dropped from 69 Ϯ 3 to 59 Ϯ 3%, and P ti O 2 from 29 Ϯ 6 to 13 Ϯ 1 mm Hg (mean Ϯ SEM; p Ͻ 0.001). Following norepinephrine, cerebral perfusion pressure (CPP) could be restored immediately, whereas TOI and P ti O 2 did not increase significantly. In contrast, following retransfusion, TOI and P ti O 2 increased to 68 Ϯ 3% and 27 Ϯ 7 mm Hg reaching baseline values, respectively. In conclusion, while norepinephrine increased CPP immediately, cerebral oxygenation as reflected by TOI and P ti O 2 could not be improved by norepinephrine, but only by retransfusion. H ypovolemia is the most common cause of circulatory failure in children (1). When inadequate tissue perfusion is not recognized and treated rapidly, critical tissue hypoxia may develop, leading to multiorgan failure and global cerebral ischemia followed by impaired brain function (2). With respect to hypovolemic and hemorrhagic shock, few clinical and experimental data exist in infants (3). In adults, there is growing evidence that conventionally aggressive fluid resuscitation does not increase the chance of survival in hemorrhagic shock (4). Accordingly, alternative strategies such as vasopressor therapy merit further evaluation. Administration of the widely used norepinephrine (NE) has been advocated to control hypotension, even in the acute phase of hemorrhage (5). Preliminary experimental data have suggested that early administration of NE may improve cerebral perfusion and oxygenation, at least in a model of brain-injury (6). However, the effects of NE on systemic hemodynamics and cerebral perfusion and oxygenation in a pediatric model of hemorrhagic shock are still unclear.NIRS is a relatively new technique with the capacity to detect changes in cerebral hemodynamics and oxygenation continuously and noninvasively at the bedside (7). In addition, impaired cerebral oxygenation has been found to correlate closely to experimental hypotension-induced alterations in cerebral blood flow (CBF) (8). Thus, we undertook this study to determine in a pediatric model of hemorrhagic shock 1) whether changes in cerebral perfusion and oxygenation accompanying hemorrhage could be detected by NIRS, and 2) whether the use of NE would improve cerebral perfusion and oxygenation.
MATERIALS AND METHODSThis is an experimental ...
