S10C91 - Acute Renal Failure

Question 1

Renal Failure: Approach

Answer 1

Prerenal – Intrinsic – Postrenal

Prerenal : decreased perfusion

Intrinsic: pathology in the kidney

Postrenal: obstructive

Community-acquired tends to be prerenal
Hospital-acquired tends to be intrinsic (ATN)

Question 2

GFR

Answer 2

• 120ml/min/1.73m2 in early adulthood

- decreases by 8 every decade after

Question 3

ATN

Answer 3

• form of intrinsic kidney injury

- decreased renal perfusion causes ischemic injury to the parenchyma

Question 4

Postrenal failure

Answer 4

• obstruction initially causes a rise in tubular pressure and thus a decreased driving force for filtration, however the pressure equalizes and after that it is vasoconstrictor properties that continue to depress the GFR
• relief of obstruction decreases the vasoconstriction

Question 5

ARF - recovery

Answer 5

• once insult to kidney has been removed, whatever remaining surviving nephrons will hypertrophy to try to boost the GFR, how much the GFR recovers depends on how many nephrons remain
• if not enough nephrons remain, the hyperfiltration results in sclerosis and actual worsening of function

Question 6

ARF: Sx

Answer 6

• symptoms are a late finding and are caused by the increased uremia
• n/v, drowsy, fatigue, confusion, coma

Question 7

Pre-renal: symptoms and causes

Answer 7

• -pre-renal: thirst, orthostatic light-headedness, decreased u/o
• causes: n/v/d, excessive urination, hemorrhage, fever, excessive sweating (reduced circulating volume)
• third spacing causes: sepsis, pancreatitis, burns, heaptic failure
• overdiuresis: CHF
• decreased fluid intake

Question 8

Intrinsic renal failure: symptoms and causes

Answer 8

• flank pain and hematuria: crystal-induced nephropathy, nephrolithiasis, papillary necrosis
• ischemic AKI: cardiac arrest, severe sepsis, hypotension
• pigment-induced ARF: rhabdomyolysis, hemolysis (recent TFN) (rhabdo from coma, seizures, intoxication, exercise)
• myalgias, dark urine, edema, malaise, fever think: glomerulonephritis from previous pharyngitis infxn or skin infxn
• fever, arthralgia, rash: interstitial nephritis
• acute renal arterial occlusion: flank pain
• cough, dyspnea, hemoptysis: pulmonary-renal syndrome (good pasture syndrome, wegener granulomatosis)

Question 9

Post-renal: symptoms and causes:

Answer 9

• previous prostat dz
• indwelling bladder catheters are a risk
• anuria
• alternating oliguria and polyuria are pathognomonic of obsruction

Question 10

Pre-renal: DDx

Answer 10

Hypovolemia:

• GI: decreased intake, vomiting, diarrhea
• diuretics
• third spacing
• skin loss: fever, burn
• other: hypoaldosteronsim, salt-losing nephropathy, post-obstructive diuresis

Hypotension:

• septic vasodilation
• hemorrhage
• decreased CO: ischemic/infarct, valvulopathy, cardiomyopathy, tamponade
• drugs: BB, CCB
• high-output failure: thyrotoxicosis, thiamine deficiency, paget dz, AV fistula

Renal artery and small vessel dz:

• ebolism
• thrombosis: atherosclerosis, vasculitis, SCD
• dissection
• drugs: NSAID, ACEi, ARB, cyclosporine, tacrolimus
• microvascular thrombosis: preeclampsia, HUS, DIC, vasculitis, SCD
• hypercalcemia

Question 11

Postrenal ARF: DDx

Answer 11

• malignancy
• nephrolithiasis
• reteroperitoneal dz
• GU surgery
• indwelling catheters

Infants/Children:

• urethra and bladder outlet: anatomic malformations (urethral atresia, meatal stenosis, urethral valves in boys)
• ureter: anatomic malformations: vesicoureteral reflux (females), ureterovesical jxn obstruction, ureterocele, megaureter (prune belly) syndrome, retrocaval ureter
• retroperitoneal tumor

All ages:

• trauma
• blood clot
• urethra/bladder outlet: phimosis, urethral stricture, neurogenic bladder (DM, SC dz, MS, parkinson’s), stone, meds (anticholinergics, alpha-adrenergic antagonists, opiates)

Adults:

• urethra/bladder outlet: BPH, obstructed catheters, cancer (prostate, bladder, Cx, colon)
• ureter: stones, papillary necrosis (SCD, DM, pyelonephritis), tumor (carcinoma of ureter, uterus, prostate, bladder, colon, rectum, retro-peritoneal lymphoma, uterine leiomyomata), retroperitoneal fibrosis (TB, sarcoid, methylsergie, propranolol, idiopathic), stricutre (TB, radiation, schestosomiasis, NSAIDs), miscellaneous (aortic aneurysm, pregnant uterus, IBD, clot, trauma, surgical accident)

Question 12

Intrinsic renal failure: Ddx

Answer 12

Tubular dz:

• ischemic ATN
• nephrotoxins: aminoglycosides, contrast, cisplatin, amphotericin B, heme pigments (rhabdo, hemolysis)
• obstruction: uric acid, calcium oxalate, myeloma light chains, amyloid
• obstructive meds: sulfonamide, triamterene, acyclovir, indinavir

Interstitial dz:

• acute interstitial nephritis: drug rxn (NSAID, Abx, diuretics, phenytoin allopurinol, rifampin)
• infxn: b/l pyelonephritis, legionnaire dz, hantavirus infxn
• infiltrative dz: sarcoidosis, lyphoma
• autoimmune dz: SLE
• toxins: aristolochic acid (used for wt loss)

Glomerular dz:
-rapidly progressive glomerulonephritis: goodpasture syndrome, wegener granulomatosis, HSP, SLE, membranoproliferative glomerulonephritis, postinfectious glomerulonephritis

Small-vessel dz:

• microvascular thrombosis: preeclampsia, HUS, DIC, thrombotic thrombocytopenic purpura, vasculitis (polyarteritis nodosa, SCD, atheroembolism)
• malignant HTN
• scleroderma
• renal vein thrombosis

Question 13

Creatinine

Answer 13

• a pt with a low baseline Cr can lose 1/2 of their functioning nephrons before the develop an elevated Cr level
• Cr is a breakdown product of muscle protein creatine, therefore the level is linked to muscle mass

Question 14

urinalysis

Answer 14

• RBC enter filtrate in glomerulonephritis and form casts
• in ATN, tubular epithelium breaks down and allows pretein to leak into the filtrate and tubular epithelial cells in the sediment
• hyaline casts are commin in prerenal failure
• pigmented granular casts are common in ischemic or toxic tubular injury
• brown granular casts are common in pigment nephropathy (myoglobinuria/hemoglobinuria)

Question 15

Imaging in ARF

Answer 15

• osbtruction below bladder should be investigate with u/s
• renal u/s has 90% sensitivity and specificity for identifying hydronephrosis d/t mechanical obstruction
• noncontrast CT has same sensitivity for hydronephrosis as u/s and can identify the sit and cause of obstruction

Question 16

Post-obstructive diuresis

Answer 16

• occurs after prolonged obstruction causing renal failure or significant volume overload
• can lead to significant volume loss and even death
• admit if pt has persistent diuresis of >250cc/h for >2h with otherwise uncomplicated urethral obstruction

Question 17

Contrast-Induced Nephropathy

Answer 17

-becomes an issue once GFR

Question 18

Indications for emergent dialysis:

Answer 18

• uncontrolled hyperkalemia (K>6.5)
• intractible fluid overload in association with persistent hypoxia, lack of response to conservative measures
• uremic pericarditis
• progressive uremic/metabolic encephalopathy, asterixis, Sz
• serum sodium level 165
• severe metabolic acidosis resistant to sodium bicarbonate
• life-threatening poisoning iwth dialyzable drug (lithium, ASA, methanol, ethylene glylcol, theophylline)
• bleeding dyscrasia secondary to uremia
• excessive BUN and creatinine levels (should be kept