Case 13 - AKI Flashcards
What are the normal functions of the kidneys?
Excrete waste products via the production of urine Make hormones - activated vitamin D, EPO Regulate blood pressure Regulate salt and water Metabolise some drugs
What is an AKI?
When the kidney gets a sudden, severe decline in excretory function due to pre-renal, renal or post-renal cause
Kidneys usually regain function, but can lead to CKD or even ESRD and RRT being needed
What is the usual metabolism of creatinine?
Creatinine is a product of muscle metabolism - but is not representative of muscle breakdown (for this we would use creatine kinase)
It is freely filtered at the glomerulus into the urine
Therefore, serum concentration of creatinine can tell us how well the kidneys are working at filtering
Make roughly the same amount of creatinine every day
However muscle mass will vary with shape, size and ethnicity so should take these into account when GFR is estimated
What is the countercurrent multiplier?
Descending loop is impermeable to ions, and only permeable to water
Ascending loop is impermeable to water, and only permeable to ions
Salt is actively pumped out of the ascending loop into the medulla
Water from the descending loop follows the osmotic gradient
The longer the loop of Henle the more salt and water the loop pumps out and therefore the more water gets reabsorbed into the peritubular capillaries
What are pre-renal causes of AKI?
Most AKIs are due to this: Hypotension Sepsis Dehydration Shock Severe HF Compartment syndrome Liver failure - hepatorenal syndrome
What are renal causes of AKI?
NSAIDs ACE-i ARB Gentamicin Vasculitis Rhabdomyolysis Myeloma Contrast from a CT scan
What are post-renal causes of AKI?
Prostate enlargement
Renal stone
Pelvic cancer
RFs for AKI?
Older age Low fluid intake - neuro disability/impairment CKD History of AKI Chronic conditions
Signs and symptoms of AKI?
Dehydration - tachycardia, thirst, drowsy, fever Joint pain Rash Palpable bladder Abdo bruit
Investigations for AKI?
ECG - to look for signs of hyperkalaemia - tall tented T waves, absence of P waves, wide QRS
USS - to look for urinary tract obstruction/hydronephrosis
CXR - pulmonary oedema or pneumonia
Urine - dip for blood and protein, culture for infection
Treatment for AKI?
Sepsis and other causes shoudl be treated
ACE-i and other nephrotoxic drugs should be stopped
Labs - U and Es for creatinine
Fluids - monitor input, output and administer fluids
Obstruction? USS for stage 3 AKI in 24 hours, do they need a bladder scan?
Renal/critical care?
Dip urine for protein and blood
Give fluids - initially 500ml bolus and then a litre over 24 hours, reassses
Consider RRT if acidosis/hyperkalaemia/uraemia/overload is non-responsive to fluids
Treatment of hyperkalaemia?
Initially, re-check the lab result to ensure this is true hyperkalaemia and order ECG
If there’s ECG changes treat straight away
For hyperkalaemia over 6.5 treat straight away
Give calcium gluconate - this stabilises the cardiac membranes against the destabilising effects of potassium
Then give insulin/glucose solution - the glucose draws the potassium into beta cells with it, and the insulin prevents hyperglycaemia
Can also use salbutamol and bicarbonate
What is acute tubular necrosis?
Occurs when there are multiple factors working together to cause renal ischaemia
High mortality
Treatment is supportive
What are the 3 stages of ATN?
Oligouric - the tubules are not able to generate urine so little urine is passed by the body (<500ml/day)
Vulnerable to overload - so fluid restrict
Will have high creatinine
Maintenance - as the tubules recover their function, they are able to make urine again
Creatinine stabilises
Polyuric - lots of urine made as the tubules regain their function
At risk of electrolyte imbalance and washing
Encourage lots of fluids
Creatinine levels come down
How do you stage an AKI?
1= 1.5-1.9 BL Creatinine OR <0.5ml/kg/hr urine made for 6-12 hours
2=2-2.9 BL Creatinine OR <0.5ml/kg/hr urine made for 12+ hours
3=3+ BL creatinine OR <0.3 ml/kg/hr for 24+ hours or anuria for 12+ hours
