Fluid therapy infusion rates/volumes

The volume to be infused and rate of delivery are only part of the therapeutic plan for fluid therapy, albeit the most important in acute resuscitation. The electrolyte and acid-base status of the horse should also be considered and fluids chosen to help to correct physiological imbalances. Unfortunately, it is not possible to predict electrolyte and acid-base disturbances accurately based on clinical signs. Seemingly similar clinical presentations may have a quite different pathophysiology (Brownlow Hutchins 1982, Svendsen et al 1979). The recent availability of relatively inexpensive, portable blood gas and electrolyte measuring equipment (Grosenbaugh et al 1998) has made determining the acid-base status possible in ambulatory equine practice and allows the field veterinarian to monitor and treat these disturbances. As stated earlier, in the absence of specific laboratory information, fluid therapy should probably be limited to isotonic polyionic crystalloid fluids, possibly with the addition of 10-20 mEq/1 potassium chloride in the maintenance phase. 

Some clinicians also advocate i.v. naloxone (an opioid antagonist) at 0.01-0.03 mg/kg for horses with life-threatening hemorrhages. The beneficial mechanisms of action of this therapy are not understood but it may act by increasing cardiac contractility. Aminocaproic acid, 20 g infused i.v. in 1 liter normal saline followed by 10 g in i.v. fluids every 6h, may be used to inhibit fibrinolysis. Blood transfusions may be indicated, especially in horses with extreme tachycardia or a packed cell volume <15%, which compromises the oxygenation of the myocardium. Following major and minor hemorrhage, cross-matched blood may be administered i.v. at a rate of 11/10 min. 

For those patients with normal to moderately impaired renal function, the cornerstone of initial treatment of hypercalcemia is volume expansion to increase urinary calcium excretion (see Table 49-6). Patients with severe renal insufficiency usually do not tolerate volume expansion they may be initiated on therapy with calcitonin. Patients with symptomatic hypercalcemia are often dehydrated secondary to vomiting and polyuria thus rehydration with saline-containing fluids is necessary to interrupt the stimulus for sodium and calcium reabsorption in the renal mbule. ° Rehydration can be accomplished by the infusion of normal saline at rates of 200 to 300 mL/h, depending on concomitant conditions (primarily cardiovascular and renal) and extent of hypercalcemia. Adequacy of hydration is assessed by measuring fluid intake and output or by central venous pressure monitoring. Loop diuretics such as furosemide (40 to 80 mg IV every 1 to 4 hours) or ethacrynic acid (for patients with sulfa allergies) may also be instiffited to increase urinary calcium excretion and to minimize the development of volume overload from the administration of saline (see Table 49-6). Loop diuretics such as furosemide... 

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