AKI

Question 1

Define AKI

Answer 1

A sudden decline in renal function (GFR) significant enough to produce uraemia, and also often oliguria – a urine output of <400ml/day.
It normally occurs over hours/days or week
- often reversible. Diagnosis is usually based on serum urea and/or creatinine levels.

Severe Acute Kidney Injury is defined as a creatinine level of >500umol/L

Question 2

Appropriate investigations of AKI and what should results be?

Answer 2

Urine dipstick
Urine microscopy – look particularly for the presence of red cell casts and red cells.
Blood tests – U+E’s (particularly Cr and K+, FBC, free haemoglobin and myoglobin.
Kidney function is monitored through urine output analysis and creatinine clearance monitoring – creatinine clearance monitoring is the ideal, i.e. it is a more precise indication of GFR than serum urea monitoring alone!
Check if the patient is on any nephrotoxic drugs.

Question 3

What are the defining criteria of AKI?

Answer 3

• Increase in serum urea > 26 μmol/L within 48 hrs
• Increase in serum creatinine to > 1.5 times baseline within preceding 7 days
• Urine volume < 0.5 ml/kg/hr for 6 hours

Question 4

Broadly speaking what how can the causes of AKI be classified?

Answer 4

Pre-renal
Renal
Post-renal

Question 5

Aetiology of AKI

Answer 5

• Usually occurs in context of catastrophic illness
o Hypotension, sepsis, orthopaedic surgery
o Common in critical illness
o 45% are ATN
o 21% are pre-renal
• 48% are hospital acquired

Question 6

Describe what causes a pre-renal AKI

Answer 6

Inadequate perfusion of kidneys

1. Hypovolaemia due to diuretics (renal loss), NSAIDS, ACEi, diarrhoea, DKA, vomiting (dehydration - extrarenal loss)
2. Systemic vasodilation due to sepsis
3. Decreased CO due to HF/MI
4. Intrarenal vasoconstriction (cardiorenal syndrome)

Question 7

Describe what causes a renal AKI

Answer 7

Intrinsic kidney damage

eg. acute tubular necrosis, glomerulonephritis, small vessel vasculitis/thrombosed renal artery

Question 8

Describe what causes a post-renal AKI

Answer 8

Obstruction of urine flow

Most commonly stones, clots, blocked catheters, malignancies (bladder, prostate etc), fibrosis

Question 9

Which type of AKI is most common in hospital?

Answer 9

Pre-renal

Question 10

RF for AKI

Answer 10

• Advanced age*
• Underlying renal disease* eg CKD
• Malignant hypertension
• DM*
• Sodium retaining states
• Radiocontrast
• Nephrotoxin* exposure: NSAIDs, chemotherapy, aminoglycosides
• Trauma, haemorrhage
• Sepsis*
• Surgery
• Cardiac arrest
• Fluid loss

Question 11

Epidemiology of AKI

Answer 11

Greater incidence in ICU (20-50%) – mainly caused by sepsis

Question 12

Presenting symptoms of AKI

Answer 12

•	Symptoms of uraemia
o	Nausea, vomiting, anorexia, confusion
•	Features of underlying disease
o	Pre-renal
	Hypovolaemia: thirst, dizziness, vomiting, confusion
o	Intrinsic
	Glomerular: nephritic syndrome (haematuria, proteinuria, hypertension)
	Tubular: hypovolaemia
o	Post-renal
	Flank pain, haematuria
	Urgency, frequency and hesitancy
•	Oliguria/anuria - decreased urine output
•	Complications
o	Salt and water retention
	Orthopnoea
	Pulmonary oedema

Question 13

Presenting symptoms of acute interstitial nephritis

Answer 13

Oliguria + triad (of drug side effect): rash, fever, eosinophilia +/- painful joints

Question 14

Signs of AKI

Answer 14

Asterixis

Question 15

Signs of pre-renal AKI

Answer 15

 AF
 Hypotension + tachycardia, dry mucous membranes
 CCF -> JVP, ascites

Question 16

Signs of intrinsic AKI

Answer 16

 Butterfly rash (SLE?)
 Nephrotic syndrome -> pulmonary + peripheral oedema, raised JVP
 Vascular obstruction -> petechiae/purpura/bruising + pallor + tiredness

Question 17

Signs of post-renal AKI

Answer 17

 Costovertebral angle tenderness
 Prostatic hypertrophy
 Bladder enlargement

Question 18

What investigations would you do for AKI

Answer 18

Urinalysis
Bloods
Renal US
AXR
CXR
ECG
Venous blood gas

Question 19

What might you find in urinalysis indicative of AKI

Answer 19

o RBCS, WBCs, cellular casts, proteinuria, bacteria, nitrites, leucocyte esterase, glucose, urine osmolality

Question 20

What might you find in bloods indicative of AKI

Answer 20

In a metabolic profile:
	Acutely elevated serum creatinine
	Hyperkalaemia
	Metabolic acidosis
o	Serum urea:creatinine ratio >20:1 = pre-renal

FBC
 Anaemia, thrombocytopenia -> intrinsic AKI
 Infection -> pre-renal + intrinsic AKI

Blood film - could look for schistocytes = small vessel disease = intrinsic AKI

Serology
 Auto-antibodies – Anti-GBM, ANA (SLE), anti-streptolysin-O
 Immunoglobulins - IgA
 Protein electrophoresis (multiple myeloma)

Question 21

What might you see on renal US?

Answer 21

o Dilated renal calyces (hydronephrosis) – post renal

Question 22

What might you see on AXR

Answer 22

renal stones

Question 23

What might you see on CXR

Answer 23

Pulmonary oedema

Cardiomegaly

Question 24

What might you see on ECG

Answer 24

Severe hyperkalaemia
Peaked T waves
Widened QRS
Increased PR interval

Question 25

What might you see on venous blood gas

Answer 25

metabolic acidosis

Question 26

Management of pre-renal AKI

Answer 26

o Volume expansion +/- blood transfusion o Vasopressor o Treat infection

Question 27

Management of renal AKI

Answer 27

o Treat underlying condition o Stop nephrotoxic agents o Treat infection

Question 28

Management of post-renal AKI

Answer 28

o Bladder catheterisation | o Relief of obstruction above bladder neck

Question 29

What things should you monitor in all AKI patients?

Answer 29

``` Creatinine K+ Na+ Phos Ca glucose ```

Question 30

What do you give to a patient who's volume overloaded

Answer 30

Loop diuretic

Question 31

What do you give to a patient who is hyperkalaemic and why?

Answer 31

Calcium gluconate - reduces ventricular fibrillation Insulin and glucose - insulin drives K+ into cells via the sodium potassium ATP pump Salbutamol nebuliser

Question 32

In what cases would you use renal replacement therapy?

Answer 32

* Hyperphosphataemia - asymptomatic * Uraemia -> affects all systems -> buzzword = pericarditis, pruritis, skin colour changes, peripheral weakness (loads of others, refer to 1st page) * Volume overload -> HTN, pulmonary oedema, peripheral oedema * Hyperkalaemia -> muscle weakness, tingling/numbness, n&v, chest pain, palpitations, arrhythmias * Metabolic acidosis -> tachypnoea * CKD * ESRD (end stage renal failure)

Question 33

Prognosis of AKI

Answer 33

• Recovery depends on cause, severity and duration o Increased mortality • 6% of ICU patients need RRT • Irreversible in >5%