Abstract
Fluid selection and administration during shock is typically guided by consideration of macrovascular abnormalities and resuscitative targets (perfusion parameters, heart rate, blood pressure, cardiac output). However, the microcirculatory unit (comprised of arterioles, true capillaries, and venules) is vital for the effective delivery of oxygen and nutrients to cells and removal of waste products from the tissue beds. Given that the microcirculation is subject to both systemic and local control, there is potential for functional changes and impacts on tissue perfusion that are not reflected by macrocirculatory parameters. This chapter will present an overview of the structure, function and regulation of the microcirculation and endothelial surface layer in health and shock states such as trauma, hemorrhage and sepsis. This will set the stage for consideration of how these microcirculatory characteristics, and the potential disconnect between micro- and macrovascular perfusion, may affect decisions related to acute fluid therapy (fluid type, amount, and rate) and monitoring of resuscitative efforts. Available evidence for the impact of various fluids and resuscitative strategies on the microcirculation will also be reviewed.
Highlights
Given the complex and multi-faceted nature of emergent and critical disease processes, determination of optimal approaches to fluid resuscitation continues to be a challenge for both human and veterinary medicine
In a human clinical study of patients with traumatic hemorrhagic shock, it was shown that the presence of microvascular derangement at the time of presentation that persisted after resuscitative efforts was more predictive of progression to multiple organ dysfunction syndrome than other more traditional parameters [78]
The hemodynamic coherence between the macroand microcirculation is often poor in shock states such as hemorrhage or sepsis
Summary
Given the complex and multi-faceted nature of emergent and critical disease processes, determination of optimal approaches to fluid resuscitation continues to be a challenge for both human and veterinary medicine. Independent regulation of flow based on local tissue needs results in selective capillary perfusion and the potential for microcirculatory shunting.
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