Dehydration
Basic Information 
Definition
A state in which fluid losses (apparent losses as well as insensible losses combined) outpace fluid intake
Epidemiology
Species, Age, Sex
Foals are particularly at risk because of their high body water content and surface-to-volume ratio.
Contagion and Zoonosis
Dehydration is not contagious itself; however, some of the diseases that cause it may be communicable to others (eg, colitis caused by Salmonella spp. or rabid encephalitis).
Associated Conditions and Disorders
Diseases that increase fluid losses in excess of the horse’s ability to take in fluids, toxins that increase vascular leakage, disruption of the protective dermis by burn injury, as well as disorders that inhibit the horse’s ability to drink and swallow may cause dehydration.
Clinical Presentation
Physical Exam Findings
• Depression; lethargy; tachycardia; reduced pulse quality; increased duration of skin tent test; dry mucous membranes; increased capillary refill time (CRT); cool extremities; mucus-covered fecal balls; or dry, scant feces (Figures 1 and 2)
• Weight loss is the gold standard for determining the percent of body weight lost to dehydration.
• The approximate percent dehydration can be estimated from physical examination findings as follows:
FIGURE 1 Skin tent test for dehydration using the upper eyelid of the horse. This test may also be performed on the neck dorsal to the cervical vertebrae and cranial to the shoulder.
Etiology and Pathophysiology
• Pathophysiology: Dehydration results in a reduction of relative circulating volume. Decreased tissue perfusion reduces oxygen delivery to the tissues, increasing anaerobic metabolism and reducing tissue pH through acid accumulation and lactate production.
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