PATHOPHYSIOLOGY

CHRONIC RENAL FAILURE
Pathophysiology
• GFR remains the same initially due to hyperfiltration and nephron hypertrophy
• It is only after total GFR has dropped below 50% that urea and creatinine levels in the blood become to increase due to poor clearance  plasma creatinine value will roughly double in a 50% reduction in GFR
• Hyperfiltration and hypertrophy, while initially beneficial, are thought to be a major cause of progressive renal dysfunction
 increased glomerular capillary pressure  damaged capillaries  segmental glomerulosclerosis  global glomerulosclerosis
• Increased potassium, urea and creatinine in both chronic and acute renal failure
• Chronic can be differentiated as it also associated with
o Anaemia  inadequate EPO
o Bone deficiency low calcium, increased phosphate and overactive PTH
o Key finding in ultrasonography is small kidneys due to atrophy and fibrosis
Disease Processes seen in CRF
o Anaemia – inadequate EPO produced in kidneys
o Vascular disease – this is the major cause of death in chronic renal failure.
o Hypertension – results from hypervolaemia from sodium and water retention. May be associated with excess renin retention
o Dehydration – some patients preserve fluid but loose tubular function so a very dilute urine is excreted which can lead to dehydration
o Skin –
 Uremic frost – high levels of urea see crystals deposited on skin
 Itch – often arises with secondary or tertiary hyperthyroidism
 Pallor (anaemia) or skin pigmentation can occur
o Gastrointestinal – nausea, vomiting, anorexia and heartburn are common
o Endocrine
 Men – loss of libido, impotence, decreased sperm count
 Women – loss of libido, reduced ovulation and infertility
o Neurological and Psychiatric – untreated, renal failure can cause fatigue, diminished consciousness and even coma. Tremor, increased muscle tone and agitation often accompany this. Glove and stocking sensory loss and distal muscle weakness is common.
o Immunological – uremia suppresses the function of immune cells and dialysis can inappropriately activate immune effectors, such as complement.
o Hyperlipidemia – this is common due to decreased catabolism of triglycerides.
o Cardiac disease – pericarditis is more likely if urea or phosphate levels are high, or if there is severe secondary hyperparathyroidism.