L27 Acute Kidney Injury

Question 1

What is the definition of AKI?

Answer 1

Rapid reduction in kidney function. It occurs over hours to days.

Question 2

How is AKI categorised?

Answer 2

Stage 1-3. It is based upon serum creatinine increase and urine output. Stage 3 being the more critical. As the stage increases, the risk of mortality increases. This is why it is important to diagnose people at stage 1.

Question 3

Give examples of intrinsic AKI causes.

Answer 3

• Acute Tubular injury due to sepsis, hypertension, drugs such as NSAIDs, contract, rhabdomyolysis, myeloma and snake bites.
• Vasculitis
• Glomerulonephritis
• Tubulointetstital injury

If the blood pressure remains low, you get cellular injury (intrinsic AKI). The cells suffer damage, through necrosis, they release intracellular leading to injury around the cells. Causes include nephrotoxins and prolong pre-renal (e.g. the prolonged low blood pressure).

Question 4

Give examples of post-renal AKI causes.

Answer 4

• Kidney stones

- Prostatic hypertrophy

Question 5

Give examples of pre-renal AKI causes.

Answer 5

• Sepsis
• Hypotension
• Hypovolemia
• Myocardial infraction
• Reduced effective circulating volume due to cardiac failure or liber cirrhosis
• Drugs

In pre-renal AKI, there is a drop in blood flow to the kidney. There is no cellular damage but the kidneys cannot remove the creatinine and the creatinine rises up. The most common cause is infection. If you remove it quickly, this is great and will not have long term effect.

Question 6

What is the pathophysiology of AKI?

Answer 6

The pathophysiology of the most common form of AKI, ischemia reperfusion, the blood pressure drops and the kidneys become stressed. The blood flow reduced. Once you send the blood supply back in:
- The kidneys want to preserve blood to the cortex as they do not regenerate - 80% of the glomeruli lie here in the cortex
Outer medulla contain the straight proximal tubule. There is an intense network of blood vessels. There is a lot of blood flow and exchange. Normally the outer medulla, the blood supply and oxygen potential is very low. When blood pressure low, the kidneys divert blood supply to the cortex, but this means the outer medulla will become injured. After injury, the outer medulla can recover. Dialysis can be used to bridge the gap between AKI and recovery of medulla.

Question 7

Give risk factors for AKI.

Answer 7

• Being hospitalized, especially for a serious condition that requires intensive care.
• Advanced age.
• Blockages in the blood vessels in your arms or legs (peripheral artery disease)
• Diabetes.
• High blood pressure.
• Heart failure.
• Kidney diseases.

Question 8

What is the clinical presentation of AKI?

Answer 8

• acutely ill/post-major surgery
	• hypovolaemia/hypotensive - due to long time under anaesthetic 
	• sepsis (infection)
• poor fluid intake
	• nausea, vomiting
	• ↓urine output - may be obstructed 
• excessive fluid losses
	• Fever 
	• Diuretics - due to an inappropriately high dose 
	• diarrhoea
	• high stoma output
	• haemorrhage
		○ trauma, GI 
burns

Question 9

What are complications of AKI?

Answer 9

Complications
• Hyperkalaemia
	• Cardiac arrest
• Acidaemia
	• Vascular instability
• Pulmonary oedema - usually iatrogenic as we usually give too much fluid to replace the fluids in a patient 
	• Respiratory arrest 
• Uraemia
	• Pericarditis - it can plead and lead to tamponade 
	• Encephalopathy - confusion 
• Gastrointestinal
	• Nausea/vomiting
	• gastritis
	• malnutrition
• Haematological
	• Anaemia - lack of erythropoietin 
Bleeding - uraemia has an effect on VBF leading to bleeding. They can bleed form their gastritis

Question 10

What investigations are done in suspected AKI?

Answer 10

• Full Blood Count (FBC)
• U&Es and bicarbonate (previous renal function)
• C-reactive protein (CRP) - produced by the liver in response to inflammation
• Liver Function Tests
• Calcium and phosphate
• Immunological screen
  
  • rarer forms of AKI
• Creatine kinase
  
  • (rhabdomyolysis) - released by muscle in muscle breakdown in trauma
• Urinalysis (prior to urinary catheter)

Question 11

What is the kidney functional reserve?

Answer 11

The kidneys have great functional reserve. 50% of function can be lost before serum creatinine level rises above the upper limit of normal. You can therefore lose a kidney if you have two functional kidneys. In AKI 50% of function is lost before serum creatinine level rises, and so it is not a good marker of injury that is on going

Question 12

What are rarer causes of AKI?

Answer 12

• Post-renal AKI
  
  • Obstruction
• Intrinsic AKI
  
  • ANCA associated vasculitis
  • Lupus nephritis
  • Interstitial nephritis
  • Myeloma

Question 13

Why is hyperkalaemia a medical emergency?

Answer 13

Risk of cardiac arrest

Question 14

Give the two types of RRT?

Answer 14

• intermittent RRT
  indicated for patients who are haemodynamically stable
  
  • haemodialysis
  • peritoneal dialysis
• continuous RRT
  indicated for patients who are haemodynamically unstable
  -CVVHD (continuous veno-venous haemodialysis)