Acute Kidney Injury (AKI) 

Definition: 
A sudden decline in kidney function resulting in impaired waste excretion, electrolyte imbalance, and fluid dysregulation. 

Stages of AKI:  
(reference: KDIGO)
 


AKI is classified into three main categories based on the location of the problem: 

Pre-renal (before the kidney) 

Intra-renal (intrinsic) (within the kidney) 

Post-renal (after the kidney) 

 

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1. Pre-Renal AKI (↓ Renal Perfusion) 
Most common cause of AKI 
Occurs when blood flow to the kidneys is reduced, but kidney tissue is initially intact.

Causes

A. Hypovolaemia 
Dehydration 
Haemorrhage 
Vomiting or diarrhoea 
Burns 
Excessive diuretic use

B. Reduced Cardiac Output 
Heart failure 
Myocardial infarction 
Cardiogenic shock 
Severe arrhythmias

C. Systemic Vasodilation / Hypotension 
Sepsis 
Anaphylaxis 
Septic shock 

D. Renal Vasoconstriction / Impaired Autoregulation 
NSAIDs (↓ prostaglandins) 
ACE inhibitors / ARBs (↓ efferent arteriolar tone) 
Hepatorenal syndrome 
 
Key Nursing/Clinical Point 
✔ Reversible if treated early 
✔ Prolonged pre-renal AKI → acute tubular necrosis (ATN) 
 
2. Intra-Renal (Intrinsic) AKI 
Damage occurs within the kidney structures (glomeruli, tubules, interstitium, or vessels). 
 
A. Acute Tubular Necrosis (ATN)  
– Most common intrinsic cause 
Causes 
Prolonged ischaemia (from untreated pre-renal AKI) 
Nephrotoxins: 
Aminoglycosides 
Contrast medium 
Cisplatin 
Myoglobin (rhabdomyolysis) 
Haemoglobin (massive haemolysis)

B. Acute Interstitial Nephritis (AIN) 
Inflammation of the interstitium 
Causes 
Drugs (most common): 
Antibiotics (penicillins, cephalosporins) 
NSAIDs 
Proton pump inhibitors 
Infections 
Autoimmune disease 
Classic triad (rare but testable): 
Fever 
Rash 
Eosinophilia 
 
C. Glomerulonephritis 
Inflammation of glomeruli 
Causes 
Post-streptococcal glomerulonephritis 
Lupus nephritis 
IgA nephropathy 
Vasculitis (e.g., ANCA-associated) 
Features 
Haematuria 
Proteinuria 
Hypertension

D. Vascular Causes (can also be considered pre renal) 
Renal artery thrombosis or embolism 
Renal vein thrombosis 
Malignant hypertension 
Thrombotic microangiopathies (HUS, TTP) 
 
3. Post-Renal AKI (Urinary Tract Obstruction) 
Occurs due to obstruction of urine outflow, leading to back pressure and kidney damage.

Causes 

A. Lower Urinary Tract 
Benign prostatic hyperplasia (BPH) 
Prostate cancer 
Urethral stricture 
Neurogenic bladder

B. Upper Urinary Tract 
Kidney stones (bilateral or solitary kidney) 
Tumours (bladder, pelvic) 
Retroperitoneal fibrosis

C. Other 
Blocked urinary catheter 
 
Key Nursing/Clinical Point 
✔ AKI may be reversible if obstruction is relieved promptly 
✔ Always check bladder volume (bladder scan) and catheter patency 
 
Summary Table 


 
Exam & Clinical Key Points: 
Pre-renal is most common 
ATN is the most common intrinsic cause 
Always consider post-renal causes in older adults 
Early recognition may prevent progression to chronic kidney disease 
NICE Topic and Guidance available: https://cks.nice.org.uk/topics/acute-kidney-injury/