Rethinking your approach to perioperative fluid therapy - Veterinary Medicine
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Rethinking your approach to perioperative fluid therapy
The traditional "recipe-based" approach to perioperative fluid therapy is outdated. Instead, we should think of perioperative fluid therapy as equivalent to intravenous drug therapy: Every anesthetic and surgical circumstance warrants its own unique fluid requirements.


Fluid balance basics: Then and now

An understanding of fluid balance is based on the distribution of water into various fluid compartments (intravascular, interstitial, intracellular) and the concentration of salts (electrolytes including sodium, chloride, and potassium) and protein within these fluid compartments. The complexities of neuroendocrine, renal, and interstitial fluid dynamics including lymph flow, although appreciated, are often underemphasized.15

For example, the classic Starling equation (Starling's law of the capillary), which emphasizes hydrostatic and osmotic forces, is generally used to explain fluid balance in the vascular system, Although instructive, this equation is quantitatively inconsistent with experimental and clinical observations of transvascular fluid flux and edema formation.16

New knowledge about this basic physiologic concept and the mechanisms responsible for intravenous fluid distribution and elimination continues to emerge and has helped to clarify and redefine best practices for perioperative fluid therapy.17,18

1. An endothelial surface layer (glycocalyx) is a key factor in determining vascular permeability. Fluid leaves the capillary throughout its entire length.
The outdated Starling's law of the capillary has been replaced by the double barrier concept, wherein fluids exit over the entire length of the capillary.17-19 An endothelial surface layer (ESL), the glycocalyx, is now known to control vascular permeability, thereby serving as the principal determinant of fluid flux from the vasculature and the development of interstitial edema (Figure 1).19

The ESL can be degraded by trauma, inflammation (sepsis), and fluid overload, all of which predispose the animal to interstitial fluid accumulation and edema.19 Importantly, albumin helps to maintain the ESL and vascular fluid homeostasis. Hypoalbuminemia is strongly associated with a poor outcome, implying that the serum albumin concentration should be maintained within normal limits (> 1.5 g/dl).20

2. Some of the many consequences of fluid overload.
Unfortunately, and as a result of decades of liberal and inadequately monitored fluid administration, the consequences of fluid overload are well-known (Figure 2).17,18,21,22 They include tissue edema, coagulopathy, pulmonary and renal failure, ileus, delayed wound healing, hypothermia, nosocomial infections, and abdominal compartment syndrome.


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