SPR L16 Pathophysiology of Renal Failure Flashcards Preview

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Pathophysiology of Renal Failure

Learning Outcomes for general perusal

  • Assessment of renal function
  • Definitions and causes of renal failure
  • Pathophysiology and principles of management in acute renal failure


Assessment of renal function

basic assessment relied upon measurement of plasma [urea] and [creatinine], waste products of protein metabolism that accumulate when renal function is impaired. 

How are the following used?

  1. Serum creatinine and urea levels
  2. Urine output
  3. GFR
    1. What are normal GFR values for men?
    2. For women?
    3. Whay is the rate of creatinine production used?
    4. But only when do creatinine levels rise above normal?
    5. What is this a reflection of?

  1. Urea and creatinine most commonly measured, reflect excretion of nitrogenous waste products
  2. acute renal failure (at least 0.5 ml/kg/hr)

  3. Creatinine clearance = UV/P

U= urinary creatinine conc

V= urinary output in mL/min

P= Plasma [Creatinine])​

  1. 90-140 ml/min

  2. 80-125 ml/min

  3. Since the rate of creatinine production is relatively constant (unlike that of urea), plasma [creatinine] itself is an indicator of GFR. Most labs now provide an ‘Estimated GFR’, based on plasma [creatinine], age, sex and ethnicity.

  4. do not rise above normal until the glomerular filtration rate falls by 50%.

  5. the large safety margin built into normal renal function (live donors get by perfectly happily with one kidney, despite a halving of GFR). 


Definitions and causes of renal failure

  1. Give a definiton of renal failure
  2. What are the criteria for renal failure?
    1. What are the grades?

  1. Failure of renal function (Reduced glomerular filtration rate), can be Acute or chronic (or acute on chronic) 
  2. See picture

    1. Grades : Risk, Injury, Failure, Loss, End Stage of Kidney Disease (RIFLE)


Definitions and causes of renal failure

Outline the following gradings of renal failure

  1. R - Risk
  2. I - Injury
  3. F - Failure
  4. L - Loss 
  5. E - End Stage Kidney Disease

  1. [Creatinine] x 1.5 , <0.5ml/kg/hr x 6hr
  2. [Creatinine] x 2 , <0.5ml/kg/hr x 12hr
  3. [Creatinine] x 3 OR

    >350µmol/L with an acute rise >40µmol/L, <0.3ml/kg/hr x 24hr

  4. Persistant failure >4weeks

  5. Persistent Failure >3months


Acute Renal Failure

  1. Give the clinical features of acute renal failure (uraemia)
  2. What are the categories of causes of acute renal failure?

  1. Anorexia, nausea, vomiting, Pruritis, Confusion, reduced consciousness, fits, coma

  2. Pre-renal

    Renal (renal parenchymal disease)



 Acute Renal Failure (2)

  1. What are the responses to reduced perfusion?

  1. Activation of renin-angiotensin-aldosterone system

    Increased ADH secretion


Acute Renal Failure

  1. What is pre-renal failure?
  2. Give examples of why it happens

  1. Impaired renal perfusion

  2. Shock: Hypovolaemic, Cardiogenic, Anaphylaxis/speticaemia, Obstructive

    Obstruction of the renal vasculature


How is Pre-Renal Failure Treated?

  • Treat cause of hypoperfusion
    • Eg restore BP
  • Monitor carefully for fluid overload
    • Increased CVP/JVP
    • Signs of pulmonary oedema


Renal failure due to renal parenchymal disease: acute tubular necrosis

  1. What is it often caused by?
  2. What do the pathogenic features include?
  3. When does tubular regrowth occur?

  1. Often caused by ischaemic damage (pre-renal failure may lead to acute tubular necrosis)

  2. Tubular cell injury

    Constriction of renal microvessels

    Reduced glomerular filtration

  3. recovery in 7-21 days


See picture for an illustration of loss of normal


Acute Renal Failure

What are the features of Features of renal failure due to acute tubular necrosis


  • Reduced tubular Na+/H2O re-absorption (tubular damage)
    • Reduced urine osmolality (<350 mOsm/kg)
    • Reduced urine specific gravity (<1.010)
    • Increased urine [Na+] (>40 mmol/l)
    • Increased fractional excretion Na+ (FENa) (>1%)
    • Reduced plasma [Na+]
  • Reduced tubular K+ secretion

    • Increased plasma [K+]

  • Reduced tubular H+ secretion

    • Metabolic acidosis


  • Reduced glomerular filtration: risk of fluid overload 


Outline the management of acute tubular necrosis

  • Manage underlying condition/complications and allow recovery
  • Limit Na+/K+/fluid intake
  • Control protein intake
  • Limit if dialysis not option (<40g /day)
  • Maintain if dialysed (>70g/day)
  • Dialysis until renal function recovers


Acute Renal Failure

  1. What are the causes of Postrenal Failure?
  2. Outline the management of this condition

  1. Urinary tract obstruction: Withinn lumen, Within wall, Outside wall

  2. Relieving the obstruction, eg using a urinary catheter

    Treating any underlying cause

    Preventing/treating infections, which are a frequent complication of urinary tract obstruction with stasis

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