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Hot times, hot dog


DVM360 MAGAZINE


Many of the severely affected dogs have protracted vomiting and diarrhea. The diarrhea may range from watery to hemorrhagic with mucosal sloughing. This may be secondary to disseminated intravascular coagulation or poor visceral perfusion. Gastric ulceration may occur as well, resulting in vomiting with or without blood. Disseminated intravascular coagulation is not an uncommon finding in dogs with heat-induced illness. The presence of petechiae and ecchymoses or blood in the urine, vomit or stool suggests that this may be occurring.

Management

Many owners recognize that their dogs are overheated and hose them down with cool water. This is very effective and often results in a normal body temperature at presentation if the dog is brought in immediately. Wetting the dog with water and blowing a fan over it is quite effective. Ice packs over the large superficial vessels in inguinal and axillary areas may help as well. Administering cool intravenous fluids is helpful and cooling measures are stopped when the rectal temperature reaches 103 F to avoid rebound hypothermia. Despite this, it is not unusual for these dogs to develop body temperatures between 95 F-100 F within the first few hours of hospitalization. If hypothermia occurs, warm water bottles or blankets may be necessary to maintain normothermia.

The severely affected dog often presents in hypovolemic shock. If cardiovascular disease is unlikely, then we administer cool balanced electrolyte fluids intravenously at 90 ml/kg/hr and continuously assess perfusion status and then titrate the rate and volume of fluids. Central venous pressure monitoring will help guide fluid therapy if massive volumes are required. If large doses of intravenous fluids do not improve tissue perfusion and blood pressure, then administration of colloids (i.e., hetastarch) should be considered and/or use of positive inotropes or pressure agents (such as dobutamine, dopamine or epinephrine). Dogs that cannot maintain an adequate blood pressure without them (for prolonged periods of time) carry a poor prognosis. Blood pressure and physical parameters of tissue perfusion should be continuously monitored in severely affected dogs.

Oxygen should be administered at presentation and should be continued until it has been determined that the dog can maintain arterial oxygenation. Serial physical assessment of the respiratory system, such as auscultation, respiratory rate and effort, and mucous membrane color is warranted in the dogs suffering from heat illness. More objective assessments such as arterial blood gas analysis and pulse oximetry may be required.

At presentation, neurologic examination should be performed to establish a baseline for future reference during the animal's hospital stay. The more severely affected dogs may present stuporous or comatose.

Serum electrolytes, PCV, total solids and blood glucose measurements should be performed and abnormalities corrected as warranted. Hypoglycemia is not unusual in the severely compromised dog with heat illness. An intravenous bolus of to gram per kilogram body weight of 25 percent dextrose should be administered and dextrose added to the intravenous fluids to a 2.5-percent to 5-percent concentration if hypoglycemia is present. Poor tissue perfusion should be corrected and mentation re-evaluated after perfusion is improved. If mentation continues to be abnormal after correcting these abnormalities, then cerebral edema may be present. Mannitol (0.5 grams/kg body weight slow IV) and/or anti-inflammatory doses of dexamethasone should be considered. The head should be slightly elevated (approximately 30 degrees above horizontal) to avoid occluding the jugular veins. Progression of neurologic abnormalities despite therapy carries a poor prognosis.

At presentation, a urinary catheter should be placed for monitoring urine output in the more severely affected dog. A complete urinalysis should be performed initially and serially as treatment progresses to detect early signs of renal damage, such as urinary casts. Urine output should be maintained at 2 ml/kg body weight or greater depending upon the amount of fluid being administered. Mean arterial pressure should ideally be at least 80 mmHg. If urine output remains insufficient despite adequate fluid replacement, then a combination of dopamine (3 micrograms/kg/min) and furosemide (2 mg/kg IV bolus followed by 1 mg/kg/hr infusion) should be considered, although the efficacy of dopamine in treating anuric/oliguric renal failure is questionable. Some veterinarians prefer to try 0.5 grams/kg IV of mannitol to induce diuresis. Serum sodium, potassium, total solids, BUN and creatinine should be monitored.


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