Clinical Case Scenario
A 72-year-old male with severe HFrEF (LVEF 25%) is admitted to the ICU with acute decompensated heart failure - pulmonary oedema with elevated JVP and marked peripheral congestion. His BP is 98/56 mmHg, lactate 1.8 mmol/L, warm extremities and no evidence of cardiogenic shock. He is started on Non-Invasive Ventilatory support.
He receives intravenous furosemide, with brisk diuresis, substantial natriuresis and rapid symptomatic improvement during the first 48 hours.
By day 4, however, he remains clinically congested. Despite progressively increasing the intravenous furosemide dose, urine output and urinary sodium excretion decrease markedly compared with the initial response. His BP remains stable, renal function has not significantly deteriorated, cardiac output is unchanged, and renal ultrasound shows no obstruction.
Which nephron adaptation best explains this progressive reduction in loop-diuretic response?
