Acute kidney injury

Question 1

What is acute kidney injury?

Answer 1

AKI is a syndrome of decreased renal function measured by serum creatinine or urine output occurring over hours – days. There are stages based on creatinine levels.  

Question 2

What classification system is used to stage acute kidney injury?

Answer 2

KDIGO classification (look it up)

Stage 1:
SCr ≥ 27 umol/L or a urine output of <0.5mL/kg/h for 6-12 hrs

Stage 2:
creatinine increase 2-2.9 baseline or urine output of <0.5mL/kg/h for ≥ 12 hours

Stage 3:
creatinine increase > 3 x baseline/ Scr ≥ 354 umol/L/ initiation of RRT/ eGFR < 35 mL/min or a urine output of <0.3mL/kg/h for ≥ 24 hour

Question 3

What are the 3 types of acute kidney injury?

Answer 3

1. Pre-renal (decreased renal perfusion)
2. Real/ intrarenal (cellular damage)
3. Post-renal (obstruction)

Question 4

What are the causes of pre-renal AKI?

Answer 4

• Hypovolaemia (e.g., haemorrhage, severe vomiting) 
• Heart failure  
• Cirrhosis  
• Nephrotic syndrome  
• Hypotension (e.g. shock, sepsis, anaphylaxis) 
• Renal hypoperfusion (e.g. NSAIDs, ACE inhibitors, ARBs, renal artery stenosis) 

Question 5

What are the causes for renal AKI?

Answer 5

• Glomerular - glomerulonephritis, haemolytic uraemic syndrome 
• Tubular - acute tubular necrosis 
• Interstitial - acute interstitial nephritis (e.g. NSAIDs, autoimmune) 
• Vasculitides (e.g. Wegener’s granulomatosis)  
• Eclampsia 

Question 6

What are the causes for post-renal AKI?

Answer 6

• Calculi  
• Urethral stricture 
• Prostatic hypertrophy or malignancy  
• Bladder tumour  

Question 7

What are the risk factors for AKI?

Answer 7

• Pre-existing CKD  
• Age >75
• Male, comorbidity 
• Sepsis 
• Hypovolemia 
• Use of nephrotoxic medication 
• DM  

Question 8

What presenting symptoms of AKI can be found in the history?

Answer 8

(Depends on cause.)
- Malaise
- Anorexia
- Pruritus
- Drowsiness
- Convulsions
- coma (from uraemia) 
- Oliguria/anuria 
- Nausea/vomiting 
- Dehydration 
- Confusion 

Question 9

What signs of AKI can be found on physical examination?

Answer 9

• Decreased Urine Output → oliguria (reduced urine output) or anuria (complete absence of urine output)
• Signs of Volume Depletion (prerenal AKI) → hypotension, tachycardia, reduced skin turgor, orthostatic hypotension, thirsty
• Signs of Fluid Overload (Na+ and H2O retention) → peripheral or pulmonary oedema, hypertension, HF, SOB
• Signs of Uraemia (failure of kidneys to excrete) → anorexia, nausea, encephalopathy, asterixis, pericarditis
• Signs of Renal Obstruction (postrenal AKI) → distended bladder (suprapubic distension), incomplete voiding (LUTS), pain over bladder or flanks
• Arrhythmias → due to changes in electrolyte balance (eg. hyperkalaemia)
• Hyperkalaemia = muscle weakness and paraesthesia

Question 10

What investigations are used to diagnose/ monitor AKI?

Answer 10

U&E’s ⇒ sodium, potassium, urea, creatinine:
- Increase in Serum Creatinine
- Decrease in Urine Output
- Urine Dipstick → positive protein indicates intrinsic cause (rules out pre-renal and post-renal causes). AIN will cause +++ leukocytes. Glomerulonephritis would cause positive blood.
- Potassium → increased
*Severe ⇒ K>6.5 or if any ECG changes
*ECG Findings in Hyperkalaemia ⇒ peaked or ‘tall tented’ T waves, loss of P waves, broad QRS complexes
- If after initial assessment no obvious cause can be found → Renal Ultrasound (esp. post-renal to look for obstruction) should be done
- ABG

Question 11

How is AKI managed?

Answer 11

Stop Nephrotoxic Substances → ACEi’s, ARBs, NSAIDs, Diuretics, Metformin, Gentamicin (aminoglycosides), Tetracycline.

DAMN = diuretics, aminoglycosides (gentamicin) + ACEi’s, metformin, NSAIDs

Manage Volume Status → IV Fluids (0.9% Sodium Chloride) if hypovolaemia (pre-renal). IV Diuretics or Dialysis (or fluid restriction) if hypervolaemia.

Hyperkalaemia (Tx if ECG changes or K>6.5) → IV calcium gluconate 10% 30mL to stabilise cardiac membrane (doesn’t directly reduce potassium). Insulin (Actrapid) to drive K+ into cells, along with dextrose to prevent hypoglycaemia. (Calcium Resonium can remove potassium from body)

Post-Renal AKI → patient may need catheterisation

Haemodialysis (Renal Replacement Therapy) → if patient isn’t responding to medical treatment

Indications for Haemodialysis ⇒ acidosis, refractory hyperkalaemia, refractory pulmonary oedema, uraemic complications

Question 12

Identify possible complications of AKI

Answer 12

● Pulmonary oedema
● Acidaemia
● Uraemia
● Hyperkalaemia
● Bleeding

Question 13

Summarise the prognosis of AKI

Answer 13

● Inpatient mortality varies depending on cause and comorbidities, and early recognition
● Indicators of poor prognosis:
*Age
*Multiple organ failure
*Oliguria
*Hypotension
*CKD
● Patients who develop AKI are at increased risk of developing CKD