Pathology - Acute Renal Failure
Prerenal causes include reduced effective arterial volume (e.g., congestive heart failure, hypovolemia, systemic vasodilation such as in sepsis) or renal vasoconstriction due to medications like NSAIDs, ACE inhibitors, or the renin-angiotensin system. Intrarenal causes include acute tubular necrosis, acute interstitial nephritis, glomerulonephritis, and thrombotic microangiopathy. Postrenal causes include kidney stones, benign prostatic hyperplasia (BPH), neurogenic bladder, and neoplasia. Prerenal conditions occur when there is reduced blood flow to the kidneys, leading to a decrease in glomerular filtration rate (GFR) and causing the retention of salt and water. Intrarenal: Defined by patchy tubular necrosis causing tubule blockage, fluid backflow through the necrotic tubule, and subsequent reduction in GFR. Postrenal conditions occur only when there is bilateral outflow blockage, leading to increased ureteral pressure that affects nephrotubules and reduces glomerular filtration rate (GFR). Oliguria, azotemia, and hyperkalemia. Lab results: (1) Prerenal: low urinary Na+ (< 10), high urine osmolality (> 500), fractional excretion of Na+ (Fe Na+) < 1%, BUN/Cr ratio > 20; (2) Intrarenal: low urine osmolality (< 350), Fe Na+ > 2%, presence of urinary epithelial/granular casts; (3) Postrenal: high urinary Na+ (> 40), Fe Na+ > 4%, BUN/Cr ratio > 20. Pre- and intrarenal: Manage fluid and electrolyte levels; address underlying cause; consider dialysis if needed. Postrenal: Managing blockage.
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