AIM Concept Integration
4th Year MBBS
Renal Module
4th Year MBBS
Renal Module
Topic 3 — Acute Kidney Injury and Renal Vascular Disorders: Tubular Injury, Electrolyte Emergencies and Acute Renal Care
A rapid revision step connecting the major pathological, clinical and acute-care relationships of the topic.
1. THE TOPIC IN ONE CONNECTED FLOW
Acute kidney injury develops when renal perfusion falls, kidney tissue is directly injured or urinary drainage is obstructed. These different starting points converge on reduced glomerular filtration, producing retention of waste products, water, potassium and acids. The same flow links pathology to presentation, investigation, acute management and the complications that determine urgency.
Cause
Hypoperfusion
Renal injury
Urinary obstruction
Renal injury
Urinary obstruction
→
Core Mechanism
Reduced renal filtration or direct tubular dysfunction
→
Functional Change
↓ GFR
Impaired excretion
Fluid/electrolyte disturbance
Impaired excretion
Fluid/electrolyte disturbance
→
Clinical Expression
Oliguria or anuria
Edema or dehydration
Uremic symptoms
Edema or dehydration
Uremic symptoms
→
Diagnostic Clues
Creatinine trend
Urine sediment
Electrolytes
Renal ultrasound
Urine sediment
Electrolytes
Renal ultrasound
→
Intervention
Correct reversible cause
Manage volume
Treat electrolyte danger
Manage volume
Treat electrolyte danger
→
Outcome
Recovery or progression
Hyperkalemia
Acidosis
Pulmonary edema
Uremia
Hyperkalemia
Acidosis
Pulmonary edema
Uremia
2. KEY CLINICAL CONNECTIONS
Acute Tubular Injury
Ischemia or nephrotoxin
→
tubular epithelial injury
→
cell shedding, casts and tubular obstruction
→
back-leak of filtrate
→
reduced GFR.
→
tubular epithelial injury
→
cell shedding, casts and tubular obstruction
→
back-leak of filtrate
→
reduced GFR.
Muddy-brown granular casts
→
support tubular rather than glomerular injury.
→
support tubular rather than glomerular injury.
Sodium and Brain Water
Hyponatremia
→
water enters brain cells
→
cerebral swelling
→
confusion or seizures.
→
water enters brain cells
→
cerebral swelling
→
confusion or seizures.
Hypernatremia
→
water leaves brain cells
→
neurological dysfunction; chronic abnormalities require controlled correction.
→
water leaves brain cells
→
neurological dysfunction; chronic abnormalities require controlled correction.
AKI, Potassium and Acute Care
Reduced renal potassium excretion
→
hyperkalemia
→
cardiac electrical instability
→
urgent treatment.
→
hyperkalemia
→
cardiac electrical instability
→
urgent treatment.
Persistent hyperkalemia, pulmonary edema, severe acidosis or uremic complications
→
urgent renal specialist assessment ± renal replacement therapy.
→
urgent renal specialist assessment ± renal replacement therapy.
3. AIM HIGH-YIELD INTEGRATION REVIEW
⭐ Prerenal hypoperfusion
→ intact tubules conserve sodium and water
→ relatively concentrated urine; persistent ischemia can progress to structural tubular injury.
→ intact tubules conserve sodium and water
→ relatively concentrated urine; persistent ischemia can progress to structural tubular injury.
Acute tubular injury
→ epithelial flattening, brush-border loss and cell shedding
→ tubular dysfunction and granular casts
→ reduced GFR.
→ epithelial flattening, brush-border loss and cell shedding
→ tubular dysfunction and granular casts
→ reduced GFR.
Postrenal obstruction
→ pressure rises proximal to the blockage
→ filtration falls
→ hydronephrosis may appear on ultrasound
→ obstruction should be relieved promptly.
→ pressure rises proximal to the blockage
→ filtration falls
→ hydronephrosis may appear on ultrasound
→ obstruction should be relieved promptly.
⭐ Longstanding hypertension
→ hyaline arteriolosclerosis
→ chronic renal ischemia
→ finely granular, contracted kidneys and progressive renal impairment.
→ hyaline arteriolosclerosis
→ chronic renal ischemia
→ finely granular, contracted kidneys and progressive renal impairment.
Severe malignant hypertension
→ fibrinoid necrosis and hyperplastic arteriolosclerosis
→ marked vascular narrowing
→ acute renal ischemia and rapidly worsening renal function.
→ fibrinoid necrosis and hyperplastic arteriolosclerosis
→ marked vascular narrowing
→ acute renal ischemia and rapidly worsening renal function.
Renal artery stenosis
→ reduced renal perfusion
→ renin–angiotensin–aldosterone activation
→ secondary hypertension and possible deterioration in renal function.
→ reduced renal perfusion
→ renin–angiotensin–aldosterone activation
→ secondary hypertension and possible deterioration in renal function.
⭐ Hyponatremia versus hypernatremia:
low sodium
→ cellular swelling; high sodium
→ cellular dehydration
→ neurological manifestations and the need for controlled correction.
low sodium
→ cellular swelling; high sodium
→ cellular dehydration
→ neurological manifestations and the need for controlled correction.
⭐ AKI with hyperkalemia, severe acidosis, pulmonary edema, uremic features or persistent anuria
→ high-risk renal failure
→ urgent specialist referral and consideration of renal replacement therapy.
→ high-risk renal failure
→ urgent specialist referral and consideration of renal replacement therapy.