Once the fluid therapy plan is underway, ongoing assessment is critical. If adequate fluids have been administered and reasonable resuscitation endpoints have not been reached, several causes should be considered: inadequate volume administration, ongoing hemorrhage, third body fluid spacing, heart disease or pericardial fluid, severe vasodilation, vasoconstriction, organ ischemia, hypoglycemia, hypokalemia, arrhythmias, severe acidemia or alkalemia, decreased venous return, severe anemia, endocrine disease (hypoadrenocorticism or critical illness related to corticosteroid insufficiency), hypothermia, or brain pathology. These variables should be rapidly assessed and corrected. If a central venous pressure (CVP) line is available, it should be checked to see whether CVP is near the endpoints assigned (Table: Resuscitation Endpoints). If not, or if no CVP is available, a fluid challenge can be given. This typically consists of a bolus (10–15 mL/kg) of crystalloids and a bolus (5 mL/kg) of hetastarch. If the perfusion parameters improve with this challenge, then the likely cause of the nonresponsive shock is inadequate volume, and colloids are titrated to reach the desired endpoints. Ultrasound, with an experienced ultrasonographer, may be useful to assess cardiac function and/or volume status in select patients.
If fluid volume appears adequate and underlying etiologies have been addressed and treated and the animal is still hypotensive, vasopressors can be used. Oxyglobin® can be given at the dosages listed above if it has not yet been used. If stroma-free hemoglobin fails to increase the blood pressure, then dopamine is administered at 2–15 mg/kg/min as a constant-rate infusion; alternative vasopressors include norepinephrine, vasopressin, and phenylephrine. These medications are weaned once blood pressure has stabilized.
Last full review/revision November 2013 by Andrew Linklater, DVM, DACVECC