Renal Failure

Question 1

What is acute renal failure?

Answer 1

• fall in GFR occurs over days
• reversible
• anuria (rarely) or oliguria <500mL/day
  
  • can occur w/o oliguria in rare cases
• can be asymptomatic

Question 2

What is chronic renal failure?

Answer 2

• fall in GFR onset over 6 months +, usually several years
• irreversible
• GFR < 50mL/min (<72 L/day)

Question 3

Why is CRF invariably associated with anaemia?

Answer 3

decresed EPO production by kidney

Question 4

What endocrine impairments occur in CRF?

Answer 4

• excessive RAS activation causing malignant hypertension
• reduced vitamin D activation leading to osteodystrophy, renal rickets, hypocalcaeimia
• decreased EPO production causing anaemia

Question 5

Normal plasma concentration of creatinine is

Answer 5

20-120uM/L

Question 6

Causes of ARF are

Answer 6

• pre-renal
• renal
• post-renal

Question 7

What causes pre-renal ARF?

Answer 7

• systemic perfusion pressure <70mmHg
• glomerular hydrostatic pressure <45mmHg
• caused by:
  
  • shock
  • sepsis
  • haemolysis (producing toxic haemoglobin)
  • rhabdomyolysis (breakdown of skeletal muscle producing toxic myoglobin)
  • nephrotoxic drugs - cause TI nephritis (renal)

Question 8

What causes intrinsic/renal ARF?

Answer 8

• glomerular disease (GN)
• TI nephritis
  
  • often drug-related
• tubular damage:
  
  • ischaemia causing ATN and eventual vascular obstruction
  • toxins like aminoglycoside antibiotics (gentamycin, tobramycin), contrast media, myoglobin

Question 9

What is the most comon renal cause of ARF?

Answer 9

• ATN
• oliguria (<400mL/day)
• +/- acidosis and increased K+
  
  • retention of H+ and K+ early on - can be fatal
• either recover or develop CRF due to cortical necrosis

Question 10

What are the causes of post-renal ARF?

Answer 10

• outlet obstruction
  
  • ureteric, cystic, or urethral
  • stones, clots, fibrosis, tumours
  • enlarged prostate, especially malignant

Question 11

How do remaining glomeruli compensate in CRF?

Answer 11

• hypertrophy
• increase GFR
• may look like tubular disease because nephron loses ability to regulate filtrate (overwhelmed with filtrate flow)

Question 12

How does uremia/CRF present?

Answer 12

accumulation of uremic toxins in blood, mostly urea

• symptomatic at <30% renal function
• fatigue
• loss of appetite
• nausea
• vomiting
• yellow powdery skin, pruritis
• thrombocytopaenia and brusing
• peeing 2-3L day (hyperfiltration of remaining nephrons)
  
  • specific gravity will equal that of plasma (1.0)
• if GFR <5L/day, severe oedema
  
  • fluid retention can cause malignant hypertension

Question 13

What are the common causes of CRF?

Answer 13

• diabetes
• hypertension
• chronic GN
• cystic disease

Question 14

What happens to sodium in water of CRF that is predominantly glomerular disease?

Answer 14

Na retention and hypertension

Question 15

What happens to salt and water in CRF caused by tubular disease?

Answer 15

• Na loss and decreased BP
• impaired concentrating ability
• polyuria (increased frequency of urination)

Question 16

What happens to potassium in CRF?

Answer 16

• [K+] tends to rise, especially in late-stage because it isn’t secreted
• higher in diabetes

Question 17

What happens to pH in CRF?

Answer 17

• pH decreases due to accumulation of H+ that cannot be excreted
  
  • volatile acids produced at high rates from normal metabolism
• excretion of H+ requires a high GFR
• reduced ammonia production by the kidney impacts the buffer system and H+ cannot be excreted as much
• bicarbonate concentration is reduced
• leads to acidosis

Question 18

What happens to calcium and phosphate in CRF?

Answer 18

• reduced filtration leads to PO₄ accumulation in blood
• PO₄ binds serum Ca²⁺, decreasing its concentration
  
  • ^_​parathyroid releases PTH –> Ca²⁺ resorption from bone
  • CaPO₄ can deposit in blood vessels and promote stenosis