Acute kidney injury

Question 1

Dx of AKI

Answer 1

increase in SCr by >26.5umol/L within 48 h
increase in SCr by 1.5x above baseline in 1 wk
urine volume < 0.5 ml/kg/hr for 6 hours
creatinine also secreted by tubules, slightly overestimates GFR

creatinine major marker for GFR, but slow to respond to AKI

Question 2

Relationship btw SCr and GFR

Answer 2

not linear
high GFR: large changes in GFR only show small change in SCr
low GFR: small changes in GFR will show large changes in SCr

Question 3

AKI classification

Answer 3

Prerenal
intrinsic renal
Postrenal

Question 4

Prerenal AKI causes

Answer 4

response to systemic hypoperfusion
intrarenal v/c
impairment of autoregulation
can lead to renal ischemia
afferent arteriole v/d able to compensate for hypoperfusion up to MAP of 80mmHg

Question 5

Intrinsic renal AKI causes

Answer 5

Large vessel disease
Microvascular, glomerular
Ischemic/nephrotoxic acute tubular necrosis
Tubulointerstitial disease (acute interstitial nephritis, intratubular obstruction)

Question 6

Postrenal AKI causes

Answer 6

calculi

Question 7

Pathophysiology of acute tubular necrosis

Answer 7

Ischemic/toxic damage to tubules –> sloughing of cells
occlusion of tubules with casts
loss of tubular integrity = backleak into interstitium
impaired renal autoregulation
inappropriate stimulation of tubuloglomerular feedback due to increased tubular Cl delivery
macula densa stimulated, afferent arteriole v/c
alterations in other vasoactive agents –> further impairment of renal autoregulation
Inflammation

Question 8

Incidence of AKI

Answer 8

complicates 1-5% hospital admissions, 30% ICU

high morbidity & mortality

Question 9

Risk factors for AKI

Answer 9

Pre-existing renal disease (GFR 75)
Volume depleted
Myeloma (light chain disease)
High osmolar ionic contrast
Nephrotoxin use

Question 10

Approach to AKI

Answer 10

Hx
PE:
- dry - reduced skin turgor, JVP low, postural hypotension (drop in SBP > 20, DBP > 10), shock
- wet - pitting edema, JVP high, hypertension, pulmonary crackles/S3
CV, peripheral vascular, MSK
Urinanalysis - prerenal: hyaline casts
intrinsic renal: pigment, “muddy brown” granular casts (dysmorphic RBCs with glomerulonephritis, RBC, WBC)

Lab: SCr, phos, Ca, electrolytes, CBC-D,
Imaging: CXR, US, CT KUB

Question 11

Fractional excretion of sodium

Answer 11

(Una/Pna) / (Ucr/Pcr)

Question 12

Tx of AKI

Answer 12

prerenal : deal with shock
Intrinsic renal:

Large vessel disease: stenting/angioplasty, thrombolysis/anticoag, immunosuppression
Microvascular: immunosuppression if inflammatory
Glomerular: primary GN: immunosuppression
Ischemic/nephrotoxic ATN: improve perfusion, Drugs, - detox/decontaminate
Tubulointerstitial disease: deal with infection, stop offending agent, give vol, tumor lysis syndrome

Question 13

Complications of acute renal failure

Answer 13

CV
Neurologic
GI
Metabolic - hyperkalemia, acidosis, hypocalcemia, hyperphosphatemia
hematologic
infection