Moffitt Renal Report 3/11: Post-Obstructive Diuresis

Take-home: In post-obstructive decompression, watch out for hematuria, hypotension and electrolyte abnormalities

Post-obstructive diuresis

  • After obstruction, there will be an appropriate physiologic response which will help eliminate the excess volume and solutes, but even after homeostasis is achieved, there can be an inappropriate diuresis
  • Pathophysiology: multiple mechanisms described, but one component is a loss of response to ADH in the collecting ducts due to kidney injury resulting in a lost ability to concentrate urine.
  • The diuresis can last for weeks!
  • Complications (see this paper from Vincent for details)
    • Electrolyte abnormalities (K derangements, hypernatremia due to free water loss)
    • Hematuria
    • Hypotension
  • Fluid management: don’t replace the UOP 1:1 with fluids. While there is a component of an abnormal response due to kidney injury, patients often are hypervolemic and diuresis may be an appropriate physiologic response. Use clinical parameters such as blood pressure and electrolytes to know how much to replace and what fluids to use. You can use the serum sodium and urine osm as guides. Usually you will be giving fluids at a rate less than the UOP.
    • Also note that sometimes we are the cause of post-obstructive diuresis because we give too much fluid!

Rule of thumb for Cr rise: with complete anuria (GFR of 0), can expect the Cr to rise about 1mg/dL per day. This can help you figure out chronicity of the renal injury

Additional pearl – Dialysis Disequilibrium Syndrome (DDS): in someone with kidney failure with really high BUN and really high Cr due to a non-reversible cause (i.e. ESRD), hemodialysis can actually decrease the BUN and uremic toxins too quickly. This can cause “DDS” which leads to sxs like headache, nausea, astereixis and can progress to seizure, confusion, coma if severe. The pathogenesis is not entirely understood but is thought to be related to cerebral edema cause by rapid decrease of urea and osm shifts. These patients sometimes need CRRT to make a more gradual correction.

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