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The management of hypovolemic shock focuses on restoration of intravascular volume for improvement in cardiovascular function, rather than normalization of hydration. Dehydration is a reflection of interstitial fluid balance, and while imperative to assess, treat, and monitor for improvement, treating hypovolemic shock must take priority. Interstitial fluid losses are generally gradual and are therefore corrected over time. Prolonged or severe dehydration can lead to hypovolemic shock. The percentage of dehydration (5–12%) is estimate based on physical exam (skin turgor, sunken eyes, urine output) and objective criteria, such as PCV/TS, loss of body weight, and urine specific gravity. The fluid deficit is determined using the percentage of dehydration and the patient's lean body weight. Estimation of lean body weight is imperative when determining the fluid prescription for obese patients, especially cats, as significant overhydration can result if overweight or obese body weight is used. The deficit is then corrected over a period of 12–48 hours depending on chronicity, patient's tolerance to fluid therapy, maintenance fluid needs, and any continuing fluid losses (Box 1.2). In small animal patients, maintenance fluid rates are generally 2–3 ml/kg/hour in dogs and 1–2 ml/kg/hour in cats [75].

Table 1.1 Commonly used vasopressors used in the emergency room and intensive care unit.

Source: Adapted from Simmons and Wohl [65]. CRI = constant rate infusion.

	CRI dose	Effect	Additional information
Dopamine	1–4 μg/kg/minute	Vasodilation (renal)	Mixed data for renal effects
	5–10 μg/kg/minute	Increased contractility, some vasoconstriction
	10–20 μg/kg/minute	Vasoconstriction, variable contractility effects
Dobutamine	2–20 μg/kg/minute (dogs)	Increased contractility, little vasoconstriction
	2–5 μg/kg/minute (cats)	Increased contractility, little vasoconstriction	Can cause seizures in cats
Norepinephrine	0.05–2 μg/kg/minute	Potent vasoconstriction
Vasopressin	0.5–2 mU/kg/minute (dogs)	Potent vasoconstriction (even in acidosis)	Limited clinical experience in dogs, no dose established for cats