Acute Renal Failure

Question 1

Define ARF

Answer 1

Urine flow <500mL/day occuring suddenly

Question 2

Why is plasma urea a poor indication of GFR?

Answer 2

Variable and diet dependent (decreased in malnutrition and liver disease, increased with GI protein load and catabolic start)

Question 3

How is GFR assessed?

Answer 3

Creatinine clearance = UV/P

where U = urinary [creatinine], V = urine vol/day, and P = plasma [creatinine]

Question 4

What is normal plasma [creatinine]?

Answer 4

50-120uM/L

Question 5

What is the daily production of creatinine proportional to?

Answer 5

Muscle mass

Question 6

What is GFR inversely proportional to?

Answer 6

Plasma [creatinine]

Question 7

What are the 3 classifications of ARF (related to underlying cause)?

Answer 7

Pre-renal
Renal
Post-renal

Question 8

List 5 pre-renal causes of ARF

Answer 8

Shock
Sepsis
Haemolysis
Rhabdomyolysis
Nephrotoxic drugs
N.B. Most of these cause ARF by leading to ATN (a renal cause of ARF) or to tubulo-interstitial nephritis in the case of nephrotoxic drugs

Question 9

When does ARF occur?

Answer 9

When SBP <45mmHg (no driving force)

Question 10

List 4 renal causes of ARF

Answer 10

Tubular damage due to ischaemia, e.g. ATN (most common), vascular obstruction
Glomerular disease (acute glomerulonephritis)
Tubulo-interstitial nephritis
Tubular damage due to toxins

Question 11

What kinds of toxins can cause tubular damage?

Answer 11

Antibiotics e.g. gentamicin
X-ray contrast media
Myoglobin

Question 12

What causes ATN?

Answer 12

Severe and/or prolonged pre-renal causes (e.g. shock)

Question 13

What defines ATN?

Answer 13

Oliguria <400mL/day +/- acidosis and increased K+

Question 14

What are some possible sequelae of ATN (besides ARF)?

Answer 14

VF and death due to increased K+
Recovery and diuresis
CRF

Question 15

What is the major post-renal cause of ARF?

Answer 15

Outlet obstruction (ureteric, cystic or urethral due to stones, clots, fibrosis, tumours, etc)

Question 16

What is the most accurate measure of daily fluid balance?

Answer 16

Daily body weight measurement

Question 17

List 6 specific pre-renal causes of renal failure

Answer 17

Haemorrhage
Hypoalbuminaemia
Renal artery stenosis
NSAIDs
ACEIs
Cardiac failure (due to decreased renal perfusion)

Question 18

What are the main ionic imbalances in ARF?

Answer 18

Na+ and water retention
Acidosis (due to H+ retention)
High [K+]

Question 19

What is the most common renal cause of ARF?

Answer 19

ATN