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Acute Renal Failure

Classification and Major Causes of Acute Renal Failure (ARF) (Ref. Hari. 18th ed., pg – 2300, Table 279-1)
    1. Hypovolemia, Severe burns
    2. Low cardiac output - CHF
    3. Altered renal systemic vascular resistance ratio
      1. Systemic vasodilatation: sepsis
      2. Renal vasoconstriction: hypercalcemia, norepinephrine, epinephrine, cyclosporine, amphotericin B
      3. Cirrhosis with ascites (hepatorenal syndrome)
    4. Renal hypoperfusion with impairment of renal auto regulatory responses NSAID, ACEI
    5. Hyperviscosity syndrome (rare) Multiple myeloma, macroglobulinemia, polycythemia
  2. INTRISIC RENAL ARF - The urine osmolality is usually isotonic (< 350 mosm/L), the urine sodium concentration is > 40 meq/L, and the FENa+ and renal failure indices are both >1% and frequently > 2 – 3%.The main causes are- Q
Renovascular obstruction
  1. Disease of glomeruli or renal microvasculature
    1. Glomerulonephritis and vasculitis
    2. HUS, TTP, DIC, toxemia of pregnancy, accelerated HT, radiation nephritis, SLE, scleroderma
  2. Acute tubular necrosis
    1. i. Ischemia: as for prerenal ARF
    2. ii. Toxins
      1. Exogenous: radiocontrast, cyclosporine, antibiotic (e.g., aminoglycosidesQ), chemotherapy (e.g., cisplatin), organic solvents (e.g., ethylene glycol), acetaminophen, illegal abortifacients
      2. Endogenous: rhabdomyolysis, hemolysis, uric acid, oxalate, plasma cell dyscrasia (e.g., myeloma)
  3. Interstitial nephritis – Drugs like rifampicin, methicillin, NSAIDs, Diuretics.
  4. Intratubular deposition and obstruction
    Myeloma proteins, uric acid, oxalate, acyclovir, methotrexate, sulphonamides
  5. Renal allograft rejection
  1. Ureteric
  2. Bladder neck
  3. Urethra
Extra Edge (Ref. Hari. 18th ed., Pg - 338)
  1. A reduction in urine output (oliguria, defined as <400 mL/24 h) usually denotes more significant AKI
  2. Amphotericin B causes AKI mainly by prerenal mechanism. PNQ


Important Points

ARF: (≅ AKI – Acute Kidney Injury) (Ref. Hari. 18th ed., pg - 1752)

Acute renal failure is defined as a sudden decrease in renal function resulting in the retention of urea nitrogen and creatinine in the blood.



The RIFLE criteria, for the staging of patients with AKI:

  1. Risk: serum creatinine increased 1.5 times or urine production of <0.5 ml/kg for 6 hours
  2. Injury: doubling of creatinine or urine production <0.5 ml/kg for 12 hours
  3. Failure: tripling of creatinine or creatinine (>4 mg/dl) OR urine output below 0.3 ml/kg for 24 hours
  4. Loss: persistent AKI or complete loss of kidney function for more than 4 weeks
  5. End-stage renal disease: complete loss of kidney function for more than 3 months.



Note: RIFLE criteria is given in 17th edition but it is not there in 18th edition !!!.

Symptoms and Signs:
Patient may have features of uremia (Nausea, Vomiting, Diarrhea, Dyspnea & Oliguria)
Urinalysis shows an active urinary sediment, with renal tubular epithelial cells, cellular debris, pigmented granular casts, renal tubular cell casts, and “muddy brown”Q coarse granular casts.
Controversy about Definition of Oliguria & anuria
  1. Oliguria has been defined in different ways in Harrison 17th ed./ 18th ed. / Baily & Love (25th ed., Pg- 1279)
  2. In Harrison 17th edition oliguria has been defined as urine output less 500 ml /day (Page 271), in 17th ed itself it is defined as urine output less than 400ml/day (Page 1752) but in 18th edition oliguria defined in urine output 400 ml/day. (Harrison-18th ed., Pg – 338)!!!
  3. In (Hari. 18th ed., Pg - 265) oliguria i.e. urine output less than 500 ml/day & anuria is complete absence of urine formation.
  4. In (Hari. 18th ed., Pg - 273, 1146) oliguria is urine output less than 400 ml/day and anuria is complete absence of urine formation.
  5. In (Baily & Love 25th ed., Pg - 1279) oliguria has been defined as urine output less than 300 ml/day!!!.
  6. In (Harrison 17th edition) anuria has been defined as urine output less than 50ml/day (Pg 271)
  7. In (Harrison 18th edition) anuria has been defined as urine output less than 100ml/day (Pg 338)
  8. In (Baily & Love 25th ed., Pg - 1279) anuria has been defined as complete absence of urine formation !!!.
Table - Laboratory Findings in Acute Renal Failure (Ref. Hari. 18th ed., pg - 337, Table 44-2)
Index Prerenal Azotemia Acute Renal Failure
BUN/PCr Ratio >20:1 10–15:1
Urine sodium (UNa), meq/L <20 >40
Urine osmolality, mosmol/L >500 <350
Fractional excretion of sodium <1% >2%
Urine/plasma creatinine (UCr/PCr) >40 <20
Renal failure index < 1 >1


Important Points


Extra Edge
AKI from ATN due to ischemic injury, sepsis, or certain nephrotoxins has characteristic urine sediment findings: pigmented "muddy brown" granular casts and tubular epithelial cell casts.


Recent Advances
In pre renal failure, FENa is < 1% but the FENa may be >1.0% in some cases of prerenal ARF under following situations.
  1. If patients are receiving diuretics
  2. With preexisting chronic kidney disease
  3. Salt-wasting syndromes
  4. Adrenal insufficiency
Marker of Acute Kidney Injury. (Ref. Hari. 18th ed., pg - 2304)
  1. Kidney injury molecule-1 (KIM-1)
  2. Neutrophil gelatinase associated lipocalin (NGAL)


Phases of ARF
a. Oliguria
b. Polyuria
  1. Oliguria Phase
    Clinical feature of oliguria phase & its treatment: (Ref. Hari. 18th ed., pg - 2300, Table 279-1)
Clinical feature Treatment
1. Intravascular volume overload: a. Salt and water restriction
b. Diuretics
c. Dialysis
2. Hyponatremia a. Restriction of free water intake
3. Hyperkalemia a. Restriction of dietary K intake
b. Eliminate K supplements and K – sparing diuretics
c. Potassium – binding ion – exchange resins
d. Glucose (50 mL of 50% dextrose) and insulin (10 units regular)
e. Calcium gluconate (10mL of 10% solution over 5min)
f. Dialysis
4. Metabolic acidosis a. Sodium bicarbonate
b. Dialysis
5. Hyperphosphatemia a. Restriction of dietary phosphate intake
b. Phosphate binding agents (calcium carbonate, aluminum hydroxide)
6. Hypocalcemia Calcium carbonate
7. Hypermagnesemia Discontinue Mg – containing antacids
8. Hyperuricemia Allopurinol
9. Nutrition a. Restriction of dietary protein ~0.6 g/kg per day)
b. Carbohydrate (~ 100g/d)
  1. Polyuria phase
    During the recovery phase of ARF, polyuria occurs and there is loss of all electrolytes.
Indication for Urgent Dialysis 
  1. Potassium persistently high
  2. Acidosis (pH < 7.2)
  3. Daily rise in level of blood urea more than 30 mg/dL or a total rise of BUN more than 300 mg/dL
  4. Serum creatinine > 7 mg/dL
  5. Pulmonary oedema not responding to diuresis
  6. Pericarditis
  7. High catabolic state with rapidly progressive renal failure.

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