Critical Care Medicine-Renal, Electrolyte and Acid Base Disorders>>>>>Acute Renal Failure
Question 5#

Which of the following statements is MOST ACCURATE regarding the pathophysiology behind bilateral obstructive nephropathy?

A. Glomerular filtration rate (GFR) is increased by increasing renal blood flow and decrease in tubular hydrostatic pressure
B. Sodium excretion is partially stimulated after relief of obstruction due to upregulation of atrial natriuretic peptide
C. Arterial blood gas will demonstrate a hypokalemic, metabolic alkalosis
D. Renal ultrasound is NOT a useful screening tool for obstructive uropathy due to low specificity

Correct Answer is B


Correct Answer: B

Often renal sodium excretion increases after relief of the obstruction. Two mechanisms that could potentially contribute to this include the downregulation of the apical membrane transporters and an upregulation of atrial natriuretic peptide. In patients with obstructive uropathy, reduction in GFR occurs due to an increase in tubular hydrostatic pressure, which alters the balance between the glomerular capillaries and the renal tubules. The hyperkalemia and metabolic acidosis in these patients are most likely a reflection of a reduced GFR and renal function. Ultrasound is utilized as a good screening tool for patients with new-onset or unexplained AKI to rule out urinary tract obstruction as a potential etiology.


  1. Montford J, Teitelbaum I, Liebman S. Urinary tract obstruction. In: Vincent JL, Abraham E, Moore FA, Kochanek PM, Fink MP, eds. Chapter 110: Textbook of Critical Care. 7th ed. 790-793.
  2. Mourmouris P, Chiras T. Obstructive uropathy: from etiopathology to therapy. World J Nephrol Urol. 2014;3(1):1-6.