20. Acute Kidney Injury Flashcards

1
Q

what does a small amount of highly concentrated urine with low Na mean?

A

warning that irreversible cell damage is imminent.
reason: water has been reabsorbed due to ADH, and salt has been reabsorbed due to aldosterone. Both were upreg’d due to sympathetic stimulation

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2
Q

definition of acute kidney injury?

A

reduction in GFR by 25% or more

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3
Q

how is GFR measured?

A

serum creatinine concentration. accumulates in serum if not cleared by kidneys

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4
Q

which artery supplies the tubular structures?

A

efferent. but decr blood flow in either will cause possible ischemia to the nephron blood supply

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5
Q

generally, a decrease in circulating blood (ECV) supply activates what?

What causes decr. in ECV?

A

sympathetics!
tachy, vasoconstriction, RAAS system, thirst, ADH
also aldo, AtII –> incr reabsorption of Na

causes: CHF, cirrhosis, sepsis, vasodilators, nephrotic syndrome, RAS, ACEi - anything that decreases GFR

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6
Q

define pre-renal azotemia

A

moderate decrease in renal perfusion (GFR decreases)

renal sympathetics activate, sodium is reabsorbed –> low urine Na concentration

water is reab –> concentrated urine

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7
Q

define acute tubular necrosis (ATN)

What do you see on labs?

A

severe/sustained fall in renal perfusion (sustained decr. ECV) –> cell death; tubular fluid is not processed, results in accumulation of toxins/electrolytes, may result in isothenuria (urine = plasma osmolarity)

incr. serum creatinine/BUN in the setting of decr ECV (incr. HR, decr. BP, cool skin, diaphoresis)

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8
Q

what marks the transition point between pre-renal azotemia and ATN?

A

urine osmolality approach PLASMA values (i.e., tubular fluid not altered much by action of tubular cells) = ISOTHENURIA

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9
Q

at the point of ATN, what is the significance clinically?

A

past the point of being able to restore renal function by restoring circulating volume

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10
Q

Pre-renal AKI treatment:

ATN treatment

A

pre-renal: restore ECV to maintain perfusion

ATN: decr. fluid intake, K, correct A/B balance, dialysis (basically maintain homeostasis until the tubules regenerate)

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11
Q

ATN: what will be seen on urine microscopy?

A

muddy brown casts

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12
Q

ATN clinical labs demonstrate:

A

FENa: if 2% (since tubules aren’t working properly and are unable to respond to aldosterone/AII and are excreting too much Na)

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13
Q

how should I monitor patients with Pre-renal AKI?

A

monitor serum creatinine, minimize blood loss, restore ECV

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14
Q

calculation for FENa?

What does FENa 1?

A

(USPC)/(UCPS) x 100

1 = tubules aren’t reabsorbing Na properly

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15
Q

What is intrinsic AKI? Where can it happen? 3

A

toxic or immunologic injury within the kidney compartment.

can be glomerular, tubulo-interstitial, or vascular

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16
Q

with a tubular injury, will I see proteinuria?

A

no, will see proteinuria with a glomerular injury

17
Q

What would you see with glomerular AKI?

A

oliguria with HTN
cola-colored urine
hematuria (dysmorphic RBC + casts)

18
Q

What is tubular-interstitial AKI caused by? 3 broad categories

A
Allergic Interstitial nephritis (AIN)
Endogenous toxins (myoglobin, light chains, uric acid)
Exogenous toxins (nsaids, contrast, Calcineurin inhibitors, Aminoglycosides, crystals, acetaminophen, ETOH, Lithium)
19
Q

What is allergic interstitial nephritis?

labs?
creatinine?
oliguric or non-oliguric?
urine findings?
bx findings?
systemic findings?

trmt:

A

hypersensitivity rxn to exogenous chemicals/meds that can act as haptens (penicillin, cephalosporin, PPIs, sulfur-based Rx, NSAIDs, etc)

Labs:
incr serum creatinine
non-oliguric (>0.5ml/kg/hr)
urine: sterile pyuria (+WBC)
bx: lymphocytes + eosinophils
systemic: rash

discontinue offending agent

20
Q

How does myoglobin cause AKI?

causes?
labs?
creatinine?
oliguric or non-oliguric?
urine findings?
bx findings?
systemic findings?

Trmt?
contraindications?

A

myoglobin released from muscle damage (crush injury, rhabdomyolysis, NMS) cause VASOCONSTRICTION of afferent arteriole and direct toxicity to RTE

labs:
incr. CPK
can be oliguric or non-oliguric
pink urine + pink plasma
systemic: edematous

trmt: hydration, alkalinazation, dialysis
contraindications: diuretics

21
Q

How does light chains cause AKI?

causes?
labs?
creatinine?
oliguric or non-oliguric?
urine findings?
bx findings?
systemic findings?

Trmt?
contraindications?

A

Multiple myeloma, plasma cell dyscrasias produce light chains that accumulate in the PCT –> toxic

Insidious loss of GFR over days-months
Non-oliguric
May have RTA Type II
decr. AG (due to incr serum globulins, which are + charge)
incr. risk of AKI in response to minor changes in ECV
urine dipstick = NEGATIVE
Urine microscopy: no cells, casts, or crystals

Trmt:
Alkylating agents (melphalan) & Prednisone
Velcade/Bortezomib
Thalidomide and lenalidomide (Revlamid)
Autologous transplantation
22
Q

How does uric acid cause AKI?

causes?
labs?
oliguric or non-oliguric?
urine findings?

Trmt?
contraindications?

A

Tumor lysis syndrome or defects in purine metabolism (Lesch-Nyhan Syndrome); Uric acid accumulates in peri-tubular fluid and precipitate into uric acid crystals -> inflammatory response

Labs:
Hyperuricemia
Urine sediment: bland, urate crystals
Oliguric or non-oliguric
High FENa
phosphate & LDH (due to cell lysis)
Trmt:
Hydration
Alkalination 
Allopurinol + Febuxostat
Recombinant IV uricase
23
Q

Exogenous toxins that can cause AKI?

A
NSAIDs
Iodinated Contrast
Calcineurin Inhibitors
Aminoglycosides
Crystals
Acetaminophen
ETOH
Lithium
24
Q

How does NSAIDs cause AKI?

Lab findings?

A

Inhibit vasodilator prostaglandins -> afferent arteriole vasoconstriction -> medullary ischemia

low FENa (due to afferent arteriolar vasoconstriction)
high K + metabolic acidosis due to distal inhibition of K/H secretion
25
How does iodinated contrast cause AKI? | Lab findings?
afferent arteriole vasoconstriction Viscous –> impedes tubular flow Directly toxic to renal tubule cells incr. creatinine 24-48 hours after contrast administration non-oliguric low FENa (due to vasoconstriction) urine sediment: no casts, cells, crystals
26
How does calcineurin inhibitors cause AKI?
afferent arteriole vasoconstriction | Directly toxic to renal tubular cells
27
How does aminoglycosides cause AKI? | Lab findings?
Interferes with mitochondria function and IP3 signal transduction in proximal RTE and cochlear hair cells Ex: Gentamycin, Streptomyosin, tobramycin Non-oliguric Urine microscopy: no casts, cells, crystals Possible RTA Type I or Type II 3-5 days after dosing
28
How does lithium cause AKI?
block ADH mediated actions in DCT -> diuresis
29
How does acetaminophen cause AKI?
causes chronic interstitial nephritis, papillary necrosis, calcifications
30
How does ETOH cause AKI? | Lab findings?
blocks ADH release from pituitary -> diuresis
31
Hoes does RAS cause AKI? findings? Trmt?
Atherosclerotic renal artery stenosis - occlusion by thrombus or embolus Urine sediment: no cells, casts Unilateral: incr Serum Cr with rapid compensation by incr RBF and GFR in contralateral kidney; non-oliguric AKI Bilateral: Anuric AKI
32
Hoes does renal vein thrombosis cause AKI? findings? Trmt?
Renal vein thrombosis - due to hypercoagulable states: protein C/S deficiency, anti-heparin antibodies (HIT), antiphospholipid syndrome, malignancy, nephrotic syndrome, severe sepsis Bilateral Dull loin ache or no pain Oliguria with gross hematuria (due to damage from back pressure)
33
What is post-renal AKI? What causes it? How does it cause AKI? findings? trmt?
Obstruction to outflow of urine - Congenital (posterior urethral valves) - Acquired (prostatic hypertrophy, radiation damage to trigone, nephrolithiasis, single kidney) decr. flow in the medullary capillary bed -> decr. GFR via TG feedback - > ischemic flow at the distal tubule and CD - > decr. effectiveness of ADH action at the CD - > accumulation of toxins in the blood + urine composition = plasma composition results in Type IV RTA (Hyperkalemia, Non-AG acidosis) ``` Non-oliguric – urine is dilute and contains less K/H Hyperkalemia + Non-AG acidosis (Type IV RTA) distended bladder (dullness to percussion) ``` Process: 1. Urinary catheter 2. Ultrasound – most sensitive for detecting obstruction 3. CT w/o contrast – best for finding kidney stone
34
How do you relieve a post-obstructive AKI? What must you be careful of?
Catheter – relieves obstruction; be careful of - over-rapid decompression of chronically obstructed bladder, which may result in tearing of the venous plexus lining the bladder - restoration of GFR may produce large amounts of urine, which may result in decr. ECV, hypokalemia, and hypomagnesemia solution: match 1:1 urine output Cystoscopy – remove stones