Acute Kidney Injury (AKI)

Question 1

What is acute kidney injury (AKI)?

Answer 1

Acute kidney injury can be defined (as per KDIGO and RIFLE criteria) as any of the following:

• ≥50% rise in serum creatinine from baseline within last 7 days
• Increase in serum creatinine by ≥26.5mmol/l within 48 hours
• Urine output <0.5mls/kg/hour (oliguria) for more than 6 hours

Question 2

How can the severity of AKI be assessed?

Answer 2

The severity of AKI can be classified by creatinine level, relative to baseline:

• Stage 1 = 1.5-1.9 times the baseline
• Stage 2 = 2-2.9 times the baseline
• Stage 3 = >3 times the baseline

Question 3

Give examples of pre-renal causes of AKI

Answer 3

• Sepsis
• Dehydration (including pre-operative NBM or bowel preparation)
• Haemorrhage
• Cardiac failure
• Liver failure (causing a hepatorenal syndrome)
• Renal artery stenosis

Question 4

Give examples of renal causes of AKI

Answer 4

• Nephrotoxins, such as NSAIDs, ACEi (or ARBs), antibiotics (such as aminoglycosides), or chemotherapy (such as cisplatin)
• Parenchymal Disease, such as glomerulonephritides, acute tubulointerstitial nephritis, rhabdomyolysis, Haemolytic Uraemic Syndrome (HUS) or multiple myeloma

Question 5

Give examples of post-renal causes of AKI

Answer 5

• Ureteric
  
  • Retroperitoneal fibrosis
  • Bilateral renal stones
  • Tumours (either mural or extra-mural)
• Bladder
  
  • Acute urinary retention
  • Blocked catheter
• Urethral
  
  • Prostatic enlargement (BPH or malignancy)
  • Renal stones

Question 6

What investigations should be ordered for AKI?

Note: laboratory

Answer 6

Examine the patient and assess their fluid status, alongside a bladder scan for any evidence of retention, before reviewing the drug chart for any nephrotoxins that could be causing or confounding the condition.

A urine dip will help in identifying a potential underlying cause. Initial bloods should be taken alongside U&Es, including FBC, CRP, LFTs, and Ca²⁺. A blood gas if useful in severe cases to ensure no significant acid-base disturbance secondary to renal dysfunction has occurred.

Question 7

What investigations should be ordered for AKI?

Note: imaging

Answer 7

An ultrasound scan of the kidneys, ureters and bladder is required in severe cases of AKI, especially if there is no response to initial management, in order to evaluate for any obstructive causes.

Any hydronephrosis present can indicate a potential obstructive pathology in the urinary tract that can be addressed accordingly if the underlying cause of the AKI.

Question 8

What is the role of urine dipstick in determing cause of AKI?

Answer 8

A urine dip can aid in differentiating between pre-renal and intrinsic causes of AKI.

Urine specific gravity and osmolality values will be higher in pre-renal causes, whilst urine Na excretion will be lower, due to the kidney actively conserving Na and water in pre-renal cases, compared to intrinsic causes.

Any glomerulonephritis will show high levels of blood and protein.

Question 9

What is hydronephrosis?

Answer 9

Hydronephrosis is the swelling of a kidney due to a build-up of urine.

Question 10

What is shown in the image?

Answer 10

Ultrasound scan of the kidney, showing marked hydronephrosis caused by a left ureteral stone.

Question 11

How is fluid status managed in AKI?

Answer 11

Assess the patient’s hydration status, looking predominantly for signs of dehydration, such as dry mucous membranes, increased capillary refill time, reduced skin turgor, tachycardia or (in severe cases) hypotension.

If suspected of pre-renal AKI, give a fluid bolus (between 250-500mL, depending on the patient) and re-assess their fluid status after 10-15 minutes, monitoring the urine output after the bolus. Give repeat fluid boluses until the patient is euvolaemic, before prescribing maintenance fluids if required.

Question 12

How is fluid status monitored in AKI?

Answer 12

Re-assess the patient clinically on a regular basis and ensure they have regular observations.

Start monitoring urine output, starting a fluid balance chart and consider catheterising the patient to permit more accurate assessment. Regular blood tests (especially U&Es) are required to monitor the progression of serum creatinine.

In those that do not respond to fluid therapy, consider intrinsic or post-renal aetiology as the underlying cause for the condition and manage accordingly.

Question 13

What drugs need to be stopped in a patient with an AKI?

Answer 13

Drugs to be potentially stopped:

• ACEi and ARBs
• NSAIDs
• Aminoglycoside antibiotics
• Potassium-sparing diuretics (due to increased risk of hyperkalaemia)

Question 14

What drugs need to be altered or reduced in patient with an AKI?

Answer 14

Drugs to be altered or reduced:

• Metformin (risk of lactic acidosis)
• Diuretics (in cases of intra-vascular fluid depletion)
• Low-molecular weight heparin