Renal ARF
Etiologies:
Can be due to:
- Glomerular damage
- Tubular damage (Commonest cause)
- Interstitial damage
(Glomerular diseases to be discussed in other lectures)
A- Tubular Damage Causing ARF:
Etiologies:
- Prolonged ischemia (decreased blood flow)
- i.v. contrast agents
- Drugs (medicines)
- Uric acid
- Pigments (e.g., hemoglobin, myoglobin; any pathologies on muscle structure; gym)
What Happens After Tubule Damage?
In tubular damage, tubules cannot absorb water & sodium, so water & sodium are lost in the urine, so: Dilute urine, High urine Na (FeNa is high) and output is not reduced (may be even high)
Causes of Tubular Damage (Acute Tubular Necrosis ⇒ ATN):
-
Ischemia to the tubules:
- Due to prolonged hypovolemia or hypotension
- In most cases, recovery in a few weeks, if managed properly in the hospital.
-
i.v. contrast: Can precipitate in the tubules
- More chances in DM & dehydrated patients
- i.v. fluids before the X-ray procedure reduce the risk.
-
Drugs: Aminoglycosides, NSAIDs, antibiotics
-
Pigment nephropathy: Certain pigments can filter through the glomerulus in abnormal situations.
- Hb: In hemolysis; hematuria
- Myoglobin: In rhabdomyolysis (myoglobin is a pigment in skeletal muscle) urine is “tea-colored” & tests dipstick positive for blood, just like hematuria, but there are no RBCs.
-
Tubule damage by uric acid:
- Occurs when blood uric acid is very high ⇒ uric acid filters through the glomerulus ⇒ can damage the tubules.
- Happens in cancers when chemotherapy is started & there is too much breakdown of cancer cells, which releases uric acid.
- This is called TUMOR LYSIS SYNDROME. It can cause acute renal failure due to tubule damage by uric acid.
Gout, chemotherapy;Malignancy, allupirinol treatment for high uric acid - given before prior to chemotherapy and gout
B- Interstitial Damage Causing Renal Failure:
Also called “interstitial nephritis” Commonest cause: Antibiotics (PCN, Cephalosporins), Infections, NSAIDs Urine:
- WBC casts & eosinophils in urine
C- Glomerular Causes of ARF:
Various glomerulonephritis can cause ARF. Urine shows:
- “Deformed” RBCs
- RBC casts
- Proteinuria
Investigations in Renal Type of ARF:
-
Blood:
- High BUN & Creatinine
-
Urine:
- Output may be normal or high
- Low osmolality/specific gravity (dilute urine)
- Na lost in the urine, so fractional excretion of Na is high (FeNa)
| Feature | Pre-Renal ARF | Renal ARF |
|---|---|---|
| Urine output | Low | Normal or high |
| Specific gravity | High (concentrated) | Low (dilute) |
| FENa | Low | High |
Other Urinalysis Features:Z
- Tubular damage: Granular/muddy casts
- Hyperuricemia: Uric acid crystals
- Interstitial nephritis: WBC casts
- Glomerulonephritis: RBC casts
Management of ARFy
- Treat the underlying cause
- Fluid & electrolyte management
- Strict intake/output charting
- If oliguria, give Lasix
Treatment of Hyperkalemia (of any etiology)
Calcium gluconate + ventolin + insulin + glucose + diuretics
- i.v. calcium gluconate - coats myocardium - protective (immediate treatment, if K is very high or ECG changes present)
- Ventolin nebulization lower K+ (pushes serum K into the cells)
- i.v. insulin + i.v. glucose (insulin pushes K from blood into the cells)
- Diuretics like Lasix or thiazides
- Dialysis (if the above treatment is not helpful)
- Stop K containing foods
- Oral KAY-EXALATE (it’s a K binding resin)
Prognosis of ARF
- Depends on the cause
- In most patients, renal function recovers in 3-4 weeks if treated properly in the hospital.
- In others, renal damage becomes irreversible ⇒ leads to CRF (chronic renal failure)