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Flashcards in Week 3: acute kidney injury Deck (14):
1

Define Acute Kidney Injury (AKI)

-syndrome characterized by rapid deterioration of renal function tha treads to accumulation of nitrogenous wastes in the body (azotemia).
-plasma Cr and BUN used as surrogate markers of azotemia
-bilateral process
-may or may not be associated with uremic symptoms
-may or may not be associated with drop in urine output

2

what is the criteria for diagnosing acute kidney injury?

One of the following occurring within 48 hrs (based on 2 creatinine elevations within 48 hrs)
1. absolute increase in serum Cr concentration of greater than 0.3 mg/dL from baseline
2. relative increase in serum Cr concentration of greater than 50%
3. urine output < 0.5mL/kg/hr for more than 6 hours

3

How is acute kidney injury staged?

I. increase of Cr 1.5 x baseline, or > 0.3 mg/dL
II: increased Cr 2x baseline
III: increase Cr 3x baseline or >4 mg/dl or on dialysis
There's also urine output criteria

4

What are circumstances that Cr is elevated but GRF is normal?

1. medications that block tubular secretion of cr
-trimethoprim
-cimetidine
-procainamide
2. substances that interfere with Cr assay
-1st gen cephalosporins
-ketotic states by acetoacetate

5

What are circumstances that Bun is elevated without changes in GFR?

-GI bleeding (endogenous protein load)
-high protein diet (protein metabolized to urea)
-catabolic steroids such as glucocorticoids (results in increase protein catabolism)

6

What are manifestations of AKI?

Main: azotemia- increase in BUN and creatinine
-hyperkalemia
-metabolic acidosis -problem with ammoniagenesis
-volume overload
-hyperphosphatemia

7

Distinguish between AKI and chronic kidney disease.

-chronic: kidney damage> 3 mos.
-hx: duration of symptoms of pruritus, nausea, loss of appetite, etc, usually means chronic
-renal size: small in CKD, except in DM, amyloid, polycystic kidney disease, and HIV nephropathy
-CDK: hyperparathyroidism, bone disease, anemia, half and half nails

8

What are causes of pre-renal AKI?

syndrome of renal hypo perfusion
1. intravascular volume depletion
-diarrhea, vomiting, diuretics, hemorrhage, dehydration
2. Decrease effective intravascular volume
-Heart failure, cirrhosis, sepsis
3. renal hypoperfusion
-renovascular disease, NSAIDS, ACEI, hepatorenal syndrome

9

Clinical presentation of pre renal AKI.

-orthostatic symptoms
-volume loss
-intraoperative hypotension
-heart failure
-liver disease
-thirst
FINDINGS ON PE
-hypotension, orthostatic changes in bp, tachycardia, dry mucous membranes, poor skin turgor, flat neck veins
-signs of CHF or liver disease: edema, JVD, acites

10

laboratory findings in pre-renal AKI

1. BUN: Cr ratio> 20:1
-due to depleted intravascular volume and response. BUN is first thing that goes up because kidney reabsorbs urea.
2. Urine indices
-oliguria: 1.020, Uosm>500mmol/L
-high renal sodium avidity: Una<20 mmol/L, Fractional excretion of Na is less than 1%
-inactive urine sediment

11

What are causes of post-renal AKI?

1. upper tract obstruction(ureteric)
-Intrinsic: kidney stone, transitional cell CA
-Extrinsic: Retroperitoneal adenopathy, abdominal aortic aneurysm
2. lower tract obstruction (bladder neck)
-BPH
-prostate CA
-urethral stricture
-neurogenic bladder

12

Clinical presentation of post-renal AKI

-flank pain, hematuria, pelvic malignancy
-symptoms of bladder outlet obstruction: nocturne, urinary frequency, urgency, decrease urinary stream, incomplete voiding
-PE: distended bladder, enlarged prostate, abdominal/pelvic mass

13

What are intra-renal causes of AKI?

1. vascular: atheroemboli, malignant HTN, HUS-TTP
2. glomerular: glomerulonephritis
3. tubular: acute tubular injury
4. interstitial: acute interstitial nephritis

14

Distinguish between pre-renal AKI from ATN

Pre-renal
-bland, hyaline casts
-BUN:Cr ratio >20:1
-oliguric
-improvement in renal function to volume challenge
-U[Na]1%
ATN
-muddy brown or granular casts
BUN to Cr 10:1
-may or may not be oliguric
-no improvement in renal fxn to volume challenge
-Uosm about 300
-U[Na}>40
-FE[Na]>2%