Best practice & research. Clinical anaesthesiology
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Best Pract Res Clin Anaesthesiol · Sep 2014
ReviewDirect markers of organ perfusion to guide fluid therapy: when to start, when to stop.
Up until now, the discussion in the literature as to the choice of fluids is almost completely restricted to the composition, with little to no attention paid to the importance of hemodynamic end points to achieve a desired optimal volume. The determination of fluid volume is left to the discretion of the attending physician with only surrogate markers as guidance the initiation and cessation of fluid therapy. In this article, we aim to discuss the available literature on existing clinical and experimental criteria for the initiation and cessation of fluid therapy. Furthermore, we present recent data that have become available after the introduction of direct in vivo microscopy of the microcirculation at the bedside, and discuss its potential influence on the existing paradigms and controversies in fluid therapy.
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Best Pract Res Clin Anaesthesiol · Sep 2014
ReviewBalanced versus unbalanced salt solutions: what difference does it make?
The infusion of crystalloid solutions is a fundamental part of the management of critically ill patients. These solutions are used to maintain the balance of water and essential electrolytes and replace losses when patients have limited gastrointestinal intake. They also act as carriers for intravenous infusion of medication and red cells. The most commonly used solution, 0.9% saline, has equal concentrations of Na(+) and Cl(-) even though the plasma concentration of Na(+) normally is 40 meq/L higher than that of Cl(-). The use of this fluid thus can produce a hyperchloremic acidosis in a dose-dependent manner, but it is not known whether this has clinical significance. ⋯ There are strong observational data that support the notion that avoiding an elevated Cl(-) concentration or using fluids that reduce the rise in Cl(-) reduces renal dysfunction, infections, and possibly even mortality. However, observational studies only can indicate an association and cannot indicate causality. Unfortunately, randomized trials to date are far too limited to address this crucial issue. What is clear is that appropriate randomized trials will require very large populations. It also is not known whether the important variable is the concentration of Cl(-), the difference in concentrations of Na(+) and Cl(-), or the total body mass of Cl(-).
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Fluid therapy is a core concept in the management of perioperative and critically ill patients for maintenance of intravascular volume and organ perfusion. Recent evidence regarding the vascular barrier and its role in terms of vascular leakage has led to a new concept for fluid administration. ⋯ In daily practice, the assessment of individual thresholds in order to optimize cardiac preload and avoid hypovolaemia or deleterious fluid overload remains a challenge. Liberal versus restrictive fluid management has been challenged by recent evidence, and the ideal approach appears to be goal-directed fluid therapy.
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Best Pract Res Clin Anaesthesiol · Sep 2014
ReviewRole of the glycocalyx in fluid management: Small things matter.
Intravenous fluid therapy and perception of volume effects are often misunderstood. The pharmacokinetical difference between colloids and crystalloids depends on the condition of the vascular permeability barrier. Its functioning is still largely based on Starling's principle from 1896, realising that transport of fluid to and from the interstitial space follows the balance between opposing oncotic and hydrostatic pressures. ⋯ While crystalloids can freely pass through the glycocalyx, colloids are held back in the vasculature by this structure. This is reflected by a markedly higher intravascular persistence of isooncotic colloids (80-100%) versus crystalloids (around 20%), at least as long as the glycocalyx is intact. Protecting this structure in surgical practice means limiting the surgical trauma and avoiding intravascular hypervolemia.