Acute Kidney Diseases

How is acute kidney injury defined?

an abrupt decline in kidney function over 7 days or less that may represent injury, risk for damage, or actual damage to the kidney itself

KDIGO serum creatinine for stage 1 AKI

1.5-1.9 times baseline in 7 days OR >= 0.3 mg/dL increase in 48 hours

KDIGO urine output for stage 1 AKI

< 0.5 mL/kg/hr for 6-12 hours

KDIGO serum creatinine for stage 2 AKI

2.0-2.9 times baseline in 7 days

KDIGO urine output for stage 2 AKI

< 0.5 mL/kg/hour for >= 12 hours

KDIGO serum creatinine for stage 3 AKI

3.0 times baseline in 7 days OR increase in SCr to >= 4 mg/dL OR initiation of renal replacement therapy OR in patients < 18 years with a decrease in eGFR to < 35 mL/min per 1.72 m²

KDIGO urine output for stage 3 AKI

< 0.3 mL/kg/hour for >= 24 hours OR anuria for >= 12 hours

what are the three AKI classifications?

Pre-renal AKI, Intrinsic AKI, Post-renal AKI

examples of Pre-renal AKI

decreased kidney perfusion (severe dehydration) and decreased effective circulating volume (heart failure)

what occurs when there is decreased kidney perfusion and decreased effective circulating volume?

decreased renal blood flow which leads to hypoperfusion of kidneys (leads to decrease in GFR and increased Na/H2O reabsorption at the proximal tubule) - these lead to increased aldosterone and ADH secretion, increased Na/H2O reabsorption at the distal tubule, and AKI/oliguria

what causes intrinsic AKI?

glomerulonephritis, tubulointerstitial nephritis, acute tubular necrosis, vasculitis, and is often drug induced

if intrinsic AKI is left untreated most forms of kidney injury will result in ______________________

ATN (acute tubular necrosis)

what is the pathophysiology of ischemic ATN?

autoregulation of afferent arteriole constriction decreases oxygen demand in the medullary nephrons to prevent damage via macula densa cells and tubuloglomerular feedback

what happens to GFR when the kidneys work to protect medullary nephrons in ischemic ATN?

GFR decreases

T/F: if there is severe hypoxia or presence of multiple risk factors in ischemic ATN, they will overwhelm protective mechanisms and lead to AKI

true

what effects decrease the risk of ischemic ATN?

decreased tubular transport, decreased GFR, prostaglandin E2, adenosine, bradykinin, nitric oxide

what are some exacerbating effects of ischemic ATN?

nephrotoxic medications (aminoglycosides, amphotericin, IV iodinated contrast), NSAIDs, angiotensin II, calcium, myoglobin

exmaples of post-kidney AKI

nephrolithiasis, benign prostatic hyperplasia (BPH), and malignancy

How can kidney stones, BPH, and malignancies cause AKI?

there is an obstruction to urine outflow which leads to increased intraluminal pressures, release of inflammatory mediators, cellular and interstitial edema, renal vasoconstriction, medullary hypoxia, renal tubular injury - ultimately leading to decreased GFR

where can kidney stones obstruct?

in the renal pelvis or ureter

what can kidney stone obstruction cause?

hydronephrosis

functional changes that indicate AKI

increase in traditional biomarkers of kidney injury (SCr, BUN), change in glomerular and/or tubular function, and absence of true damage to the kidney

kidney damage that indicates AKI:

presence of glomerular and/or tubular injury, or is identified by novel biomarkers (NGAL-Marker, TIMP2 and IGFBP7 markers, and KIM1 markers)

what does the NGAL-marker indicate?

proximal tubule injury

what do the markers TIMP2 and IGFBP7 indicate?

cell cycle arrest

what does KIM1 indicate?

proximal tubule injury

what is the timeline definition for Acute kidney disease (AKD)

AKI for > 7 days but not yet CKD (occurs after 90 days)

what are the complications of AKI?

edema/flid overload, electrolyte imbalance, acid/base imbalance, uremia, risk of CKD, and risk of CVD

what is uremia?

Azotemia with symptoms

what is azotemia?

an elevation of BUN > 20 mg/dL

how is uremia diagnosed?

a constellation of clinical findings and laboratory abnormalities

symptoms of uremia?

decreased appetite, change in taste, anorexia, nausea/vomiting, pruritis, altered mental status/encephalopathy

what condition is an indication for emergent dialysis therapy (extracorporeal kidney replacement therapy)?

uremia