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Definition

Not necessarily considered a complication in its own right but one that might influence management of standing sedation and anesthesia is the notable increase in urine production following administration of alpha‐2 agonist medications to horses.

Risk factors

Use of alpha‐2 adrenergic agonists

Pathogenesis

Xylazine and detomidine have both been shown to increase urine production multi‐fold over normal in standing horses [127–129]. The mechanism by which alpha‐2 agonists increase urine production is primarily related to inhibition of anti‐diuretic hormone [37]. General anesthesia tends to reduce production [130] but it still remains above normal values of approximately 0.5 ml/kg/hour, even in water deprived animals [127].

Monitoring

Urine production can be assessed via the placement of a urinary catheter and measurement of urine output over the anesthetic period.

Treatment

There is no specific treatment, but diuresis of this magnitude may contribute to dehydration and should be considered when calculating intravenous fluid administration rates during sedation and anesthesia. In addition, horses sedated for standing procedures with alpha‐2 adrenergic agonist drugs will often shift body position or attempt to posture to void. Therefore, catheterization of the urinary bladder can be helpful for longer procedures and is especially recommended in female horses when procedures involve rectal or vaginal manipulation or when constant rate infusions of alpha‐2 agonists are used.