Treatment of severe parvoviral enteritis (Proceedings)
Without treatment, canine parvovirus (CPV) infection is often a fatal disease ending in severe dehydration, endotoxic or septic shock, and multiple organ failure. With aggressive therapy and supportive care, however, a survival rate of 85-95% has been achieved at our hospital. Following are recommendations which should be considered in the treatment of all dogs infected with CPV.
Fluid replacement for losses incurred through vomiting and diarrhea is the cornerstone of treatment for dogs with CPV enteritis and should be continued until oral intake is resumed.The initial fluid of choice is a balanced electrolyte solution. The route and rate of initial fluid therapy varies with the patient. If CPV infection has resulted in hypovolemic shock, a rapid intravenous fluid bolus of up to 90 ml/kg/hr may be necessary to restore perfusion. If circulatory collapse prevents venous access, fluids can be administered initially via a 20 g 1½" spinal needle placed in the intraosseous space in the shaft of the femur. Once circulation has improved with intraosseous fluids, an intravenous catheter can be placed for continued fluid therapy. It is important to note that subcutaneous fluids will not be absorbed by animals with severe dehydration or circulatory collapse because of peripheral vasoconstriction. In addition, hypertonic solutions should be avoided in dehydrated patients.
Animals that are dehydrated but not in shock should be rehydrated over 4 hours. The amount of fluid given is estimated by the following formula: % dehydration x body weight (kg) = # liters to replace deficit. Maintenance requirements (2-3 ml/kg/h), as well as continuing losses from vomiting and diarrhea, must also be taken into consideration during initial fluid therapy.
Once perfusion has been restored, the fluid rate can be decreased to 4 - 6 ml/kg/h in most patients. Urine output should approximate 1 - 2 ml/kg/h and urine specific gravity should range from 1.015 - 1.020. Fluid therapy must be adjusted to replace continuing losses through vomiting and diarrhea. As fluid losses subside, the fluid rate is gradually tapered.
Many puppies, particularly toy breeds or septic animals, are prone to hypoglycemia with CPV enteritis. Following rehydration, 2.5 - 5% dextrose can be added to the balanced electrolyte solution (100 ml of 50% dextrose added to 1 liter will make a 5% solution).
Puppies with anorexia, vomiting, and diarrhea are also prone to hypokalemia which can result in muscle weakness, gastrointestinal ileus, polyuria, cardiac arrhythmias, and general malaise. Serum potassium should be monitored daily in these patients. If it is low, potassium chloride should be added to the fluids according to recommendations in medical texts. If potassium is in the normal range, 14-20 mEq KCl should be added to each liter to prevent the levels from dropping.
Puppies with CPV enteritis often experience severe protein losing enteropathy because of destruction of the intestinal villi. If the albumin decreases below 1.5 g/dl, the total protein decreases below 3.5 g/dl, or the animal develops evidence of pitting edema, administration of a colloid fluid is indicated to maintain intravascular oncotic pressure. If the puppy is anemic through parasitism or gastrointestinal blood loss, a transfusion of whole blood (preferably from a recovered animal with a high CPV antibody titer) is indicated. A dosage of 10 - 20 ml/kg can safely be administered to most puppies over a 4 hour period. If the puppy is not anemic but is hypoproteinemic, a plasma transfusion (10 - 20 ml/kg IV) should be administered through an in-line filter over 2 - 4 hours. In addition to providing oncotic components, both whole blood and plasma contain antibodies and serum protease inhibitors which may be beneficial in neutralizing circulating virus and controlling the systemic inflammatory response associated with the disease. Plasma and blood products are available though commercial blood banks.
If natural colloids are not available, puppies with decreased total protein and edema should receive a synthetic colloid, such as hetastarch or dextran 70. To avoid potential volume overload, the dosage of 20 ml/kg/day should not be exceeded, but colloid infusions can be repeated after 24 hours if needed. Colloids can be given rapidly to patients in shock or as a continuous infusion over 24 hours to more stable patients. General guidelines are to supply one third of fluid needs as a colloid and two thirds as a crystalloid solution.