Regional peripheral circulation

When delivering critical care, one must understand the specific properties that characterize the various regional circulations because therapies that benefit one region may be detrimental to another. Vascular tone is influenced by (1) innervation and neural processes, (2) circulating endocrine and neuroendocrine mediators, (3) local metabolic products, (4) blood gas composition, (5) endothelial-derived factors, and (6) myogenic processes. The cerebral circulation is characterized by a blood-brain barrier. Regulation of myocardial perfusion is tailored to match regional myocardial oxygen supply to demand over the widest possible range of cardiac workload. Critically ill patients are at risk for impaired splanchnic blood flow that can impair the two chief functions of the gastrointestinal system: (1) digestion and absorption of nutrients and (2) maintenance of a barrier to the translocation of enteric antigens. Renal blood flow remains constant over a wide range of renal artery perfusion pressures, but urinary flow rate is a function of renal perfusion pressure..