Toward quantification of loop diuretic responsiveness for congestive heart failure

Diuretics, such as furosemide, are routinely administered to dogs with congestive heart failure (CHF). Traditionally, dose and determination of efficacy primarily are based on clinical signs rather than quantitative measures of drug action. Treatment of human CHF patients increasingly is guided by quantification of urine sodium concentration (uNa) and urine volume after diuretic administration. Use of these and other measures of diuretic responsiveness is associated with decreased duration of hospitalization, complication rates, future rehospitalization, and mortality. At their core, loop diuretics act through natriuresis, and attention to body sodium (Na) stores and handling offers insight into the pathophysiology of CHF and pharmacology of diuretics beyond what is achievable from clinical signs alone. Human patients with low diuretic responsiveness or diuretic resistance are at risk for difficult or incomplete decongestion that requires diuretic intensification or other remedial strategies. Identification of the specific etiology of resistance in a patient can help tailor personalized interventions. In this review, we advance the concept of loop diuretic responsiveness by highlighting Na and natriuresis. Specifically, we review body water homeostasis and congestion in light of the increasingly recognized role of interstitial Na, propose definitions for diuretic responsiveness and resistance in veterinary subjects, review relevant findings of recent studies, explain how the particular cause of resistance can guide treatment, and identify current knowledge gaps. We believe that a quantitative approach to loop diuretic usage primarily involving natriuresis will advance our understanding and care of dogs with CHF.