Head Elevation, Cerebral Venous System, and Intracranial Pressure: Review and Hypothesis

Abstract

BACKGROUND Facilitation of venous outflow from the brain is largely believed to be responsible for the beneficial effect of head elevation on intracranial pressure (ICP). However, the impact on cerebral perfusion pressure can be deleterious. Although the adverse effect of obstructing venous outflow in the setting of intracranial hypertension is well documented, the converse (improvement with augmented drainage) has not been demonstrated. Our hypothesis is that the effect of active augmentation of cerebral venous outflow on ICP, although unknown, could be potentially beneficial under conditions of intracranial hypertension. METHODS Published literature was perused to ascertain known relationships between head elevation, ICP, cerebral perfusion pressure, and the cerebral venous system. RESULTS Head elevation benefits ICP control in intracranial hypertension from improved venous outflow via various networks and craniospinal cerebrospinal fluid displacement; but patients on the severe spectrum have a high likelihood of experiencing cerebral perfusion pressure decline especially beyond 30°. In addition, the interaction between autoregulation, compliance, head elevation, ICP pulse amplitude, cerebral perfusion pressure, and ICP becomes increasingly dyssynchronous in the severely affected brain. Although the detrimental effects of obstructing venous drainage are well documented, the possibility of augmenting venous outflow by withdrawal of sagittal sinus blood has not been described previously. CONCLUSION There could exist a potential role for targeted sagittal sinus venous aspiration in favorably influencing control of increased ICP conditions, without significant risk to cerebral perfusion.