Today's Veterinary Practice

MAY-JUN 2018

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PEER REVIEWED 28 CE: CONGESTIVE HEART FAILURE IN CANINES Historically, sodium nitroprusside was the treatment of choice. This drug was given as a CRI, and the dose was increased to reduce the blood pressure to the required level. It required close monitoring of the blood pressure and could only be used for 24 to 48 hours at the risk of developing cyanide toxicity. Unfortunately, it has now become prohibitively expensive. Topical nitroglycerine ointment has been used, but studies and clinical experience have questioned its effectiveness. Amlodipine can be given orally but is slower in onset of action. Injectable nitrate compounds have been used anecdotally. Hydralazine is a potent arterio dilator and has been used at 0.5 to 3 mg/kg IV bolus q12h or as a CRI at 1.5 to 5 mcg/kg/min IV. Reflex tachycardia and hypotension are the most serious side effects seen. For patients that are hypotensive (eg, dogs with dilated cardiomyopathy (DCM) and some dogs with DMVD), pressor agents may be required to increase blood pressure.3 Dopamine or, more commonly, dobutamine (which is less arrhythmogenic) have been used as CRIs, and, in my clinical experience, the beneficial effects seem to last for 4 to 6 weeks. Hospital Monitoring Clinical improvement can be seen with normalization of breathing rate and effort. It can be confirmed with thoracic radiographs, remembering that radiographic improvement often lags clinical improvement by 1 to 2 days ( FIGURE 2 ). In a small subset of patients that are equivocal for the diagnosis of CHF, repeating thoracic radiographs after 1 week on furosemide at 2 mg/kg q12h can be very helpful in confirming the diagnosis; this is usually accompanied by clinical improvement. It is also important to check electrolytes and renal parameters, as high-dose diuretics — especially in patients that are not eating — can rapidly result in electrolyte disturbances and renal insufficiency. Hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis can occur. When electrolytes and renal parameters are checked before the start of treatment, blood urea nitrogen and creatinine are often mildly elevated due to prerenal causes, as the heart does not supply sufficient pressure to make the kidneys work effectively. This finding should not discourage appropriate treatment of heart failure with diuretics, as the values will improve as the heart failure resolves. In some patients with severe CHF, the dose of diuretics necessary to resolve pulmonary edema can cause dehydration and azotemia with depression and poor appetite/anorexia. In these patients, the diuretic dose should be reduced as soon as the heart failure is controlled; allow for rehydration and resolution of azotemia while monitoring closely for recurrence of heart failure. It is difficult to imagine a situation where IV fluids are indicated at the same time as treating CHF with diuretics. FIGURE 2. (A) Lateral and (B) dorsoventral thoracic radiographs from the same dog as Figure 1. Note the resolution of the pulmonary edema after treatment for acute congestive heart failure with furosemide and pimobendan. The cardiac silhouette is still enlarged but is smaller (the vertebral heart score decreased from 11.6 to 11). A B

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