Nephrology and Urology Flashcards
What does RIFLE mean in classification of acute renal failure (ARF) or acute kidney injury (AKI)?
- Risk of renal dysfunction
- Injury to kidney
- Failure of kidney function
- Loss of kidney function (persistent ARF)
- End-stage kidney disease (ESKD) or end-stage renal disease (ESRD)
Risk of renal dysfunction
a. GFR criteria: increased serum creatinine 1.5-fold or GFR decrease more than 25%
b. Urine output (UO) criteria: UO less than 0.5 mL/kg/hr for 6 hours
Injury to kidney
a. GFR criteria: increased serum creatinine 2-fold or GFR decrease more than 50%
b. UO criteria: UO less than 0.5 mL/kg/hr for 12 hours
Failure of kidney function
a. GFR criteria: increased serum creatinine 3-fold or GFR decrease more than 75% or serum creatinine more than 4mg/dL (350 μmol/L) in setting of acute increase of at least 0.5 mg/dL (44 μmol/L)
b. UO criteria: UO less than 0.3 mL/kg/hr for 24 hours (oliguria) or anuria for 12 hours
Loss of kidney function (persistent ARF)
Complete loss of kidney function for more than 4 weeks
End-stage kidney disease (ESKD) or end-stage renal disease (ESRD)
Complete loss of kidney function for more than 3 months
Prerenal causes of ARF (60-70%)
- Hypovolemia
- Hypotension
- Ineffective circulating volume (CHF, cirrhosis, nephrotic syndrome, early sepsis)
- Aortic aneurysm
- Renal artery stenosis or embolic disease
Intrinsic renal causes (25-40%)
- Acute tubular necrosis
- Nephrotoxins (NSAIDs, aminoglycosides, radiologic contrast)
- Interstitial diseases (acute interstitial nephritis, SLE, infection)
- Glomerulonephritis
- Vascular diseases (polyarteritis nodosa, vasculitis)
Postrenal causes (5-10%)
- Tubular obstruction
- Obstructive uropathy (urolithiasis, BPH, bladder outlet obstruction)
Diagnostic Studies to order in ARF
- GFR
- Serum creatinine and BUN
- Urinalysis
- Serum cystatin C
- Urine biomarkers (IL-8 and kidney injury molecule-1 [KIM-1])
- Renal U/S
BUN in diagnosing ARF
- Provides an estimate of renal function, but is much more sensitive to dehydration, catabolism, diet, renal perfusion and liver disease
- Urea is reabsorbed in the nephron during stasis, which causes false elevations of BUN; therefore, this is not a reliable indicator of renal function
Urinalysis in diagnosing ARF
- It is essentially normal in prerenal and postrenal causes of ARF with only a few hyaline casts
- Granular casts, WBCs and casts, RBCs and casts, proteinuria, and tubular epithelial cells indicate intrinsic renal causes of ARF
Serum cystatin C and urine biomarkers in diagnosing ARF
-These are new biomarkers that shows promise for detecting AKI
Prerenal causes blood and urine studies
- Urine sodium <20 mEq/L
- Fractional excretion of sodium (FENa) less than 1%
- Urine osmolality greater than 500 mOsm/kg
- Elevated BUN-to-plasma Cr ratio (20:1)
- Urine specific gravity greater than 1.020
Intrinsic renal causes blood and urine studies
- Increased urine sodium greater than 40 mEq/L
- FENa greater than 1-2%
- Urine osmolality of 300-500 mOsm/kg
- Decreased BUN-to-plasma Cr ratio (<15:1)
- Urine specific gravity of 1.010 to 1.020
Postrenal causes blood and urine studies
Urine sodium, FENa osmolality, and BUN-to-Cr ratio can vary depending on how long the obstruction has been present
What on the renal U/S would indicate a chronic problem in ARF?
A kidney smaller than 10 cm
What are other laboratory findings associated with a loss of renal function?
- Azotemia
- Decreased creatinine clearance
- Metabolic acidosis
- Hyperkalemia
Treatment of ARF involves correction of the underlying problem. What are some examples of that?
- Achievement of normal hemodynamics in prerenal states (IV fluids, improving cardiac output)
- Adjustment and avoidance of medications and nephrotoxic agents in intrarenal states
- Relief of urinary tract obstruction (ureteral stents, urethral catheter) in postrenal states
- Consideration of early intervention under the supervision of a nephrologist or intensivist for management of potential renal replacement therapy
What are some indications for short-term dialysis?
- When serum creatinine exceeds 5-10 mg/dL
- Unresponsive acidosis
- Electrolyte disorders
- Fluid overload
- Uremic complications
What is chronic kidney disease (CKD)?
- Progression of ongoing loss of kidney function (GFR)
- National kidney foundation (NKF) defines CKD as GFR <60 mL/min/1.73 m2 or presence of kidney damage (proteinuria, glomerulonephritis or structural damage from polycystic kidney disease) for ≥3 months
Stages of CKD: Stage 1
Kidney damage with normal GFR greater than 90 mL/min/1.73 m2 body surface area (BSA) and persistent albuminuria
Stages of CKD: Stage 2
Kidney damage with mild decrease in GFR 60-89 mL/min/1.73 m2 BSA
Stages of CKD: Stage 3
Moderate decrease in GFR 30-59 mL/min/1.73 m2 BSA