What is the definition of AKI?
- Increase in Cr higher than 0.3 mg/dl (26.5 umol/L) in 48 hours
- A rise in Cr >1.5 times the baseline.
- A decrease of urine volume =/< than 0.5 mg/kg/hr
If one or more of the criteria are met, the patient can be diagnosed with AKI.
What occurs during AKI?
- When a patient is in AKI there is a rapid decrease in the glomerular filtration rate which allows a build up of waste: nitrogen, Cr and urea.
Why does pre-renal failure occur?
- Pre renal failure occurs due to poor nephron perfusion.
What conditions contribute to pre-renal failure?
- Shock
- hypotension
- sepsis
- over diuresis
- heart failure
- cirrhosis
- bilat renal artery stenosis
- solitary functioning kidney which is worsened by ACE and other drugs
NSAIDS, calcineurin inhibitors, diuretics
Acute kidney injury can be divided into vascular/interstitial/glomerular and tubular, of the aforementioned, which is the most common cause of AKI?
- Tubular necrosis
What causes acute tubular necrosis?
- Prolonged ischemia
What are some intrinsic causes of AKI?
- Underlying diseases such as lupus, wegner and good pasture syndrome. Rheumatological disease and systemic illnesses
With underlying disease that can cause AKI like lupus and RA what is the reason AKi occurs?
- AKI occurs due to inflammation of the renal vasculature and glomeruli
What occurs in the body when there is hypotension or poor systemic perfusion?
- Baroreceptors in the arteries and heart receptors respond to these changes by increasing sympathetic tone, the afferent arterioles sense the decrease in perfusion which leads to an increase in renin secretion and the antidiuretic hormone secretion.
How long can the afferent arteriole maintain adequate perfusion?
- The afferent arterioles can maintain adequate perfusion until the SBP drops below 80 mmhg
What is Renin?
- A protein enzyme released by the juxtaglomerular cells in the afferent arteriolar wall.
What exactly does Renin do?
- Renin converts Angiotensin 1 to angiotensin 2
What does Angiotensin 2 do?
Angiotensin 2 increases Aldosterone synthesis
When Angiotensin 2 increase Aldosterone synthesis, what happens next?
- Increased aldosterone synthesis causes vasoconstriction and sympathetic nervous system stimulation.
When there is a mild to moderate decrease in cardiac output what does angiotensin 2 do?
- Angiotensin 2 works on the efferent arteriole to maintain filtration fraction
What would cause Angiotensin 2 to constrict the afferent arteriole and further decease GFR?
- If there is a drop in cardiac output followed by another decrease, then Angiotensin 2 would cause further restriction by increasing vasocontraction of the afferent arteriole
In pre renal AKI what should the urine sodium level be?
- 20 mEq/L
What is a better predictor of AKI when evaluating U/A results?
- Fractional excretion of sodium, this is not affected by urine out and it measures on the percent of Na+ excreted. FENa is usually less than 1% in AKI and greater than 2% in ATN
What is the gold standard for differentiating pre-renal failure from other causes of AKI?
- Fluid administration, when volume is replenished the Cr should trend down toward the patients baseline within 24-72 hours.
How is volume replenished in AKI?
- with Isotonic saline
With ATN how does the Cr rise?
- By 0.3 to 0.5 mg/dl per day in pre renal the rate will be slower.
