12.2: Acute renal failure Flashcards
What are the two hallmark s/sx of acute renal failure?
Azotemia with oliguria
What are the three major divisions of acute renal failure?
- Prerenal
- Intrarenal
- Post renal
How do you diagnose azotemia?
Increase in BUN and Cr
What is the cause of prerenal azotemia?
Decreased blood flow to the kidneys
What are the s/sx of prerenal azotemia?
- Decreased GFR
- Azotemia
- Oliguria
What is the BUN:Cr ratio with prerenal azotemia? Why does this occur?
- more than 15
- Cr is not reabsorbed, but BUN is. When there is an increase in renin, there is increased Na and BUN reuptake from the tubule, but not Cr. Thus the ratio increases
What are the two measures that indicate good tubule function? What happens to these with prerenal azotemia?
- FENa (fractional excretion of Na) = less than 1%
- urine osm more than 500
-These are normal (above) with prerenal azotemia
What are the signs of postrenal azotemia?
Decreased GFR, azotemia and oliguria
What causes the early rise in BUN:Cr ratio with POSTrenal azotemia? Why does it decrease later on?
Back pressure from blocked outflow increases hydro static pressure in the tubule, and increased BUN reabsorption
Tubular damage ensures and decreases BUN resorption
What happens to FENa and Urine osm with postrenal azotemia? Early Post Renal? Late posternal?
Early= Both remain intact (FEN less than 1% and urine osm more than 500
Late post-renal = tubular damage, leading to higher FENa, and lower urine osmolality
What is the most common cause of acute renal failure?
Acute tubular necrosis
What is acute tubular necrosis? What happens to GFR? Why? What appears in the urine?
Injury and necrosis of the tubular epithelium. Necrotic cells plug tubules to decrease GFR.
Brown, granular casts appear in the urine
Brown, granular casts in the urine = ?
Acute tubular necrosis
What are the major histological findings of acute tubular necrosis?
Loss of tubular epithelial nuclei and lumen, detachment of epithelial cells from BM
What happens to the following with acute tubular necrosis:
- BUN:Cr
- FENa
- Urine [c]
- Decreased BUN:Cr (less than 15)
- Increase FENa (more than 2%)
- osm less than 500
What are the two major etiologies of acute tubular necrosis?
Ischemic
Nephrotoxic
What parts of the nephron are particularly susceptible to ischemia?
Proximal tubule and medullary segment of the thick ascending limb
What causes nephrotoxic ATN? Which part of nephron is particularly susceptible?
Toxic agents cause necrosis of tubules
Proximal tubule
What are the toxic agents that can cause toxic ATN? (abx, environmental toxin, crush injury, automobile fluid type, radiology things?
- Aminoglycosides
- Heavy metals
- Myoglobinuria
- Ethylene glycol
- Radiocontrast dye
Oxalate crystals in the urine is suspicious for what type of poisoning?
Ethylene glycol
What produces urate to cause ATN?
Tumor lysis syndrome
What are the two measures to ensure that chemo does not induce ATN via tumor lysis syndrome?
- IVF to dilute urate
- Allopurinol
What are the urinary findings of ATN? (2)
- Oliguria
- Brown, granular casts
What happens to BUN and Cr with ATN?
Increases
What metabolic disturbance is seen with ATN? What causes this?
Hyperkalemia with metabolic acidosis
- Hyperkalemia from decreased K excretion
- Acidosis from decreased excretion of organic acids
What is the calculation for anion gap?
Na - (Cl + HCO3)
What is the treatment for hyperkalemia and acidosis 2/2 ATN? Will the necrotic tissues heal?
Dialysis
Yes
How long does it take for the necrotic tissue in ATN to regenerate? Why? What sign signifies healing?
2-3 weeks, since tubular cells are stable cells, and need time to reenter the cycle
Increasing urine output
What is acute interstitial nephritis?
Drug-induced HSR of the interstitium and tubules, resulting in intrarenal ARF
What are the drugs that classically cause acute interstitial nephritis? (3)
- NSAIDs
- PCN
- Diuretics
What are the histologic characteristics of interstitial nephritis?
Inflammation between the tubules, but relatively normal looking tubules
What are the three major s/sx of interstitial nephritis?
- Oliguria
- Fever
- Rash
What WBC can be seen in the urine with interstitial nephritis?
Eosinophils
What is the treatment for interstitial nephritis?
Remove offending drug
What can interstitial nephritis progress to?
Renal papillary necrosis
Eosinophils in the urine = ?
Acute interstitial nephritis
What are the s/sx of renal papillary necrosis?
Gross hematuria and flank pain
What are the 4 major causes of renal papillary necrosis?
- Chronic analgesic use
- DM
- Sickle cell dz
- Acute pyelonephritis
