A new way to monitor and individualize your fluid therapy plan - Veterinary Medicine
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A new way to monitor and individualize your fluid therapy plan
Recent findings point to new ways to monitor fluid therapy perioperatively and to gear fluid therapy protocols to each individual animal.


Catecholamines. Catecholamines increase heart rate and cardiac contractility, and some are potent vasoconstrictors (e.g. dopamine, norepinephrine). Notably, catecholamines alter the intravascular volume-expanding effects of fluid therapy.44,45 Drugs that activate alpha receptors (e.g. dopamine, norepinephrine, and phenylephrine) and induce vasoconstriction reduce blood volume expansion, while those that activate beta receptors augment blood volume expansion.46 Since optimization of blood pressure and blood flow is the goal in a hypotensive anesthetized animal, the administration of a mixed alpha-beta agonist (e.g. dopamine) is the more rational therapeutic choice for maintaining arterial blood pressure.46

Final considerations. Finally, it should be emphasized that anesthetic-induced or -associated hypotension is best treated by decreasing or stopping the administration of anesthetic drugs. A potent analgesic (e.g. fentanyl) can be administered to reduce the requirement for inhalant or injectable anesthesia.47 A vasoconstrictor (e.g. dopamine, norepinephrine) or positive inotrope (e.g. dopamine, dobutamine) may be required to restore and maintain blood vessel tone or cardiac contractile function, blood flow, and arterial blood pressure, respectively, in animals that do not respond to fluid therapy due to vasodilatation or poor cardiac contractile function.48


Perioperative fluid therapy in animals is not innocuous and should be considered identical to drug therapy—individualized and goal-directed. Differences in the types of fluids (crystalloid or colloids) available determine their effects upon electrolyte and acid-base balance and their ability to restore or maintain arterial blood pressure and tissue perfusion.

Isotonic balanced crystalloids maintain water requirements, blood osmolality, tissue perfusion, and acid-base balance in otherwise normal healthy surgical candidates. Colloid solutions are more effective for treating low arterial blood pressure, poor tissue perfusion, and blood loss. Both crystalloids and colloids are dilutional to substances; they do not contain (e.g. hemoglobin) and should be dosed in order to prevent excessive hemodilution (hemoglobin < 7 g/dl) and avoid fluid overload. Thus, accurate assessment of fluid status (i.e. fluid responsiveness) and careful definition of targets at all stages of the perioperative period are needed to improve clinical outcomes.

Fluid administration is essential for optimizing tissue perfusion. The determination of PVI helps to predict fluid therapy responsiveness and to guide fluid replacement during anesthesia in dogs and cats.


The author thanks Dava Cazzolli, DVM, DACVECC; Jaime Chandler, DVM, DACVECC; Michelle Albino, LVT, CVT (Anesth); and Yukie Ueyama, DVM, for their assistance in abstracting data.

William Muir, DVM, MS, PhD, DACVA, DACVECC
338 W. 7th Ave.
Columbus, OH 43201

For references, see http://dvm360.com/FluidTherapy3Refs.


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