Today's Veterinary Practice

MAR-APR 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 34 CE: CARDIOVASCULAR AND RENAL DISEASE Systemic Hypertension in Dogs and Cats High blood pressure is important to identify, manage, and monitor for patients with both cardiovascular and renal disease. Systolic blood pressure >160 mm Hg is considered abnormal, and pressure >180 mm Hg increases risk for damage to the eyes, brain, kidneys, and cardiovascular system. 18,19 In one study, systemic hypertension at initial CKD diagnosis was documented for ≈20% of cats. 20 Among cats with systemic hypertension, azotemia has been reported for 62% and left ventricular hypertrophy for 59%. 21,22 Persistently elevated systemic blood pressure and evidence of target organ damage warrant vasodilator therapy, typically with amlodipine, a dihydropyridine calcium-channel blocker. ACE inhibition results in dilation of the renal efferent arterioles, but the effects are generally insufficient for ACE inhibitors to serve as sole therapy for systemic hypertension. However, evidence supports the routine addition of an ACE inhibitor for all patients receiving long-term amlodipine therapy to counter the anticipated activation of the RAAS. 23 The combined use of amlodipine and an ACE inhibitor is certainly appropriate when blood pressure remains >160 mmHg or the urine creatinine:protein ratio indicates proteinuria; however, these 2 drugs should not be started simultaneously because severe azotemia can arise. QUESTIONS TO GUIDE MANAGEMENT DECISIONS AND RECOMMENDATIONS ■ Is heart disease or kidney disease causing the clinical signs? Prioritize the disease causing the most severe clinical signs. ■ Are both biochemistry analysis and thoracic radiography needed? Usually yes, because the information they provide is often complementary. For example, when azotemia is present, radiographs will help indicate concurrent presence of active CHF (eg, pulmonary venous congestion, pulmonary edema, pleural effusion) and therefore will help guide decisions about diuretic dose reductions. If radiographs demonstrate evidence of CHF, information regarding current renal and electrolyte values can help guide decisions about increasing the diuretic dose, optimizing positive inotropic therapy, and reducing sodium intake. ■ What does urine specific gravity indicate in a patient receiving diuretics? Although this measure can help identify renal disease, it will be low in patients receiving diuretics and cannot be used to differentiate prerenal and renal azotemia. For patients receiving diuretics, use surrogate markers of hydration status (body weight, total protein, albumin) instead. ■ Is blood pressure accurate and repeatable (a serious challenge in some cats)? Are the blood pressure readings abnormally high or low? If too high, consider further workup and evaluation for systemic hypertension. If too low, determine whether the patient is clinically weak and the cardiac output low or whether the current medications are driving the blood pressure too low. ■ Which medications interact and what are the potential adverse effects? ■ Many medications used to manage cardiac disease are vasodilators that can have an effect on blood pressure (eg, ACE inhibitors [eg, enalapril, benazepril], inodilators [eg, pimobendan], dihydropyridine calcium- channel blockers [eg, amlodipine], ß-blockers, and some antiarrhythmics [eg, procainamide]). High doses of a diuretic can lower blood pressure by reducing intravascular blood volume and further stimulating the RAAS. ■ Risk for azotemia and electrolyte abnormalities increases with combined use of ACE inhibitors and diuretics. ■ Administration of a nonsteroidal anti- inflammatory drug in patients with cardiovascular or renal disease may cause acute azotemia. Efferent arteriole vasodilation induced by an ACE inhibitor combined with afferent arteriole vasoconstriction induced by nonsteroidal anti-inflammatory drug– induced cyclooxygenase inhibition can result in reduced GFR and subsequent azotemia. ■ Changes in renal function can affect medication clearance, resulting in drug toxicity. ■ Is azotemia mild or severe? ■ Mild azotemia, in the absence of clinical signs, may be well tolerated. ■ If azotemia worsens or is no longer mild, ACE inhibitors should be used at lower doses or discontinued. If a high diuretic dose is resulting in dehydration or worsening azotemia, consider whether it can be reduced. ■ Is fluid therapy carefully considered and appropriate? Fluid therapy for CKD can easily overload a diseased cardiovascular

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