Despite achievement and maintenance of global hemodynamic and oxygenation goals, patients may develop microcirculatory dysfunction with associated organ failure. A thorough understanding of the microcirculatory system under physiologic conditions will assist the clinician in early recognition of microcirculatory dysfunction in impending and actual disease states. Penelope S. Benedik and Shannan K. Hamlin Erythrocytes are not just oxygen delivery devices but play

an active metabolic role in modulating microvascular blood flow. Hemoglobin and red blood cell morphology change as local oxygen levels fall, eliciting the release of adenosine triphosphate and nitric oxide to initiate local vasodilation. Aged erythrocytes selleck screening library undergo physical and functional selleck changes such that some of the red cell’s most physiologically helpful attributes are diminished. This article reviews the functional anatomy and applied physiology of the erythrocyte and the microcirculation with

an emphasis on how erythrocytes modulate microvascular function. The effects of cell storage on the metabolic functions of the erythrocyte are also briefly discussed. Shannan K. Hamlin and Penelope S. Benedik Blood rheology, or hemorheology, involves the flow and deformation behavior of blood and its formed elements (ie, erythrocytes, leukocytes, the platelets). The adequacy of blood flow to meet metabolic demands through large circulatory vessels depends highly on vascular control mechanisms. However, the extent to which rheologic properties of blood contribute to vascular flow resistance,

particularly in the microcirculation, is becoming more appreciated. Current evidence suggests that microvascular blood flow is determined by local vessel resistance and hemorheologic factors such as blood viscosity, erythrocyte deformability, and erythrocyte aggregation. Such knowledge will aid clinicians caring for patients with hemodynamic alterations. Penelope S. Benedik This article describes promising emerging technologies developed for measuring tissue-level oxygenation or perfusion, each with its own inherent limitations. The end user must understand what the instrument measures and how to interpret the readings. Optical monitoring using near-infrared spectrometry, Doppler shift, and videomicroscopy are discussed in terms of their application at the tissue level. Assessment of the metabolic state of the extracellular space with existing technology and proxy indicators of metabolic status are discussed. Also addressed are potential sources of variation for each technique, and the role that the clinician plays in the proper interpretation of the data.