Acute Kidney Injury

Question 1

What is the definition of acute kidney injury?

Answer 1

Decline of renal excretory function over hours/days

Recognised by the rise in serum urea and creatinine

Question 2

What is the RIFLE criteria?

Answer 2

Risk
- serum creatinine by 1.5 or GFR decrease of 25%
Injury
- increased SCr by 2 or GFR decrease of over 50%
Failure
- increased SCr by 3 or greater than 353
- or GFR decrease of 75%
Loss
- persistent ARF (complete loss of kidney function for more than 4 weeks)
ESKD
- end stage kidney disease

Question 3

What are the diagnostic criteria of acute kidney injury?

Answer 3

Pre-renal
- circulatory failure
- shock (lack of blood to the kidney)
Renal 
- injury to the cells of the kidney
Post-renal
- obstruction

Question 4

Name some of the causes pre-renal failure.

Answer 4

Hypovolaemia and hypotension
- Diarrhoea/vomiting
- Inadequate fluid intake
- Blood loss through trauma 
Reduced effective circulating volume
- cardiac volume 
- septic shock (vasodilation) 
- cirrhosis 
Drugs 
- ACEI
- NSAIDs
Renal artery stenosis

Question 5

Name some causes of intrinsic renal disease.

Answer 5

Glomerulonephritis 
Tubular 
- ischaemic ATN
- nephrotoxic ATN
- myeloma cast nephropathy 
- rhabdomyolysis
Tubulointerstitial
- drugs (gentamicin) 
- myeloma
- sarcoid
Vasculitis 
- small and large vessels

Question 6

Name some causes of post-renal failure.

Answer 6

Renal papillary necrosis
Kidney stones
Reteroperitoneal fibrosis
Carcinoma of the cervix
Prostatic hypertrophy/malignancyt
Urethral stricture

Question 7

What is the cause of acute tubular necrosis?

Answer 7

Underperfusion of the tubules and/or direct toxicity
- hypotension
- sepsis
- toxins
Can be all three

Question 8

Which toxins can cause acute tubular necrosis?

Answer 8

Exogenous
- drugs (NSAIDs, gentamicin, ACEI)
- contrast 
- poisons (e.g. metals and antifreeze)
Endogenous
- myoglobin (rhabdo)
- haemoglobin (sickle cell)
- immunoglobulins
- calcium
- urate

Question 9

What happens to glomerular filtration as pressure falls?

Answer 9

Prostaglandins dilate the afferent arteriole to increase flow as the MAP falls towards 80mmHg

Question 10

How do NSAIDs affect renal perfusion?

Answer 10

NSAIDs inhibit prostaglandins (which naturally dilate the afferent arteriole), so the flow of blood into the glomeruli of the kidneys keeps falling

• affernet arteriole remains constricted
• should be taken off it in renal failure

Question 11

How do ACEI affect renal perfusion?

Answer 11

Systemic vasodilation

Efferent arteriole extra-vasodilated, which decreases the pressure within the glomerulus when a person is on ACEI

Question 12

What do you need to know to manage acute kidney injuries?

Answer 12

Bloods
- urea and creatinine
- potassium increased 
Urine output less than 400ml/day
Clinical assessment of fluid status 
- BP, JVP, oedema and heart sounds
Underlying diagnosis (history, exam and medication)

Question 13

What do you need to treat with acute kidney injuries?

Answer 13

Airway and breathing 
Circulation (shock) to restore renal perfusion 
- hyperkalaemia 
- pulmonary oedema 
Causes
- drugs
- sepsis

Question 14

Describe the diagnostic procedure behind acute kidney injuries.

Answer 14

History and exam (septic, rashes, haemoptysis, rhabdomyolysis)
Drugs (prescribed, OTC, supplements, radio-contrast and abuse)
Urinalysis
Renal ultrasound (small kidney indicates chronic condition)
GN screen - ANCA, ANA, Igs, EP, complement, aGBM, urine bence jones protien
Blood films - LDH, CK

Question 15

How would you exclude obstruction in AKIs?

Answer 15

Renal ultrasound
- hydronephrosis
CKD 
- small size
- loss of cortico-medullary differentiation

Question 16

Describe ECG changes seen in hyperkalaemia.

Answer 16

Suppression of impulse generation by the SA node
- prlonged PR interval
Decreased conduction by the AV node
- prolonged QRS
- junctional and ventricular escape rhythms
Peaked T waves
Progression to VF and VT possible

Question 17

What are the immediate problems associated with hyperkalemia?

Answer 17

<6 - no immediate concern
6-6.4 - risk of arrhythmia (needs treatment)
>6.5 - medical emergency

Question 18

How is hyperkalemia treated?

Answer 18

Reduced absorption from the gut used to stablise the patient 
- calcium resonium
Movement of potassium into cells
- insulin and 50% dextrose
Cardiac membrane stabiliser 
- calcium gluconate

Question 19

How is acidosis associated with hyperkalemia treated?

Answer 19

(Raised potassium and bicarbonate below 16)

- IV sodium-bicarbonate 1.26%

Question 20

Name the absolute indicators for dialysis.

Answer 20

Refractory potassium at 6.5mmol/l or above

Refractory pulmonary oedema (and not passing urine)

Question 21

Name the relative indicators for dialysis.

Answer 21

Acidosis (pH <7.1)
Uraemia (especially if urea is >40)
- risk of pericarditis and encephalopathy
Toxins (lithium, ethylene glycol etc.)