8. What happens when the kidneys stop working?

Question 1

What effect does lethargy and anorexia have on the kidneys?

Answer 1

• Accumulation of nitrogenous waste products, hormones, peptides and other ‘middle-sized’ molecules
• Acidosis
• Hyponatraemia
• Volume depletion - low BP
• Anaemia

Question 2

What effect does a salt + water imbalance have on the kidneys?

Answer 2

• Inability to increase sodium reabsorption when sodium depleted
• Osmotic diuresis - caused by increase in waste substances e.g. urea
• High loss of salt and water - volume depletion - low BP
• Usually found in patients with tubulointerstitial disorders - damaged concentrating mechanisms
• Renal dysfunction - more usual to have difficulty excreting salt and water
• Retained sodium - hypertension, oedema, pulmonary oedema

Question 3

What are the implications of acidosis?

Answer 3

• Retention of H+
• To buffer, H+ swaps into cell with K+ - tendency to hyperkalaemia
• Kussmahl respiration (air hunger) - due to increased CO2 loss as compensation

Question 4

What are the implications of hyperkalaemia?

Answer 4

• Failure of distal tubule to secrete potassium
• Exacerbated by acidosis
• Cardiac arrhythmias and arrest

Question 5

What are the implications of renal failure on metabolism?

Answer 5

• Decreased erythropoietin - anaemia
• Low 1-25 Vit D levels - poor calcium absorption, hypocalcaemia (short term) and hyperparathyroidism (longer term)
• Increased CV risk

Question 6

Give some examples of acute and chronic loss of function due to renal failure?

Answer 6

Acute
• Anaemia
• Acidosis
• Renal size unchanged
• Overloaded volume
• Previously normal creatinine
• Acute metabolic complications
Chronic
• Anaemia
• Acidosis
• Renal size often reduced
• Overloaded volume
• Previously abnormal creatinine
• Chronic uraemic symptoms

Question 7

How can renal failure be managed initially?

Answer 7

• IV saline - correct fluid depletion
• IV sodium bicarbonate - correct acidosis
• IV insulin and dextrose - lower plasma K+ (drives K+ back into cells)
• Dialysis

Question 8

How can you assess GFR?

Answer 8

• Urea - poor indicator, confounded by diet, liver function etc.
• Creatinine - affected by muscle mass, age, race, sex etc. (need to look at patient when interpreting results)
• Creatinine clearance - difficult from elderly patients
• Estimated GFR - equations using age, ethnicity, (weight, albumin etc.) - generally unreliable for well preserved GFR
• Inulin clearance - research purposes only
• Radionuclide studies - EDTA clearance etc., reliable but expensive

Question 9

How can renal failure be managed in the long term?

Answer 9

• GFR measure
• Regular haemodialysis
• Low potassium diet and fluid restriction
• Erythropoietin injections
• 1-25 Vit D supplements - prevent hyperparathyroid bone disease