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Project - USMLE Step 3 > Symptom To Diagnosis - Acute Renal Failure > Flashcards

Symptom To Diagnosis - Acute Renal Failure Flashcards

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USMLE® Step 1 flashcards
1
Q

Time frame of ARF?

A

Occurs over hours or days and can occur in the presence of previously normal kidney function or in patients with CKD.

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2
Q

Is there a standard definition of ARF?

A

No. Criteria include:

  1. Increase in serum Cr >0.5.
  2. Increase of more than 20% above baseline Cr.
  3. Decrease of GFR of at least 50%.
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3
Q

Prerenal causes of ARF - 3 general categories:

A
  1. Hypovolemia.
  2. Hypotension.
  3. Changes in renal hemodynamics.
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4
Q

Prerenal ARF - Hypovolemia:

A
  1. GI fluid loss.
  2. Renal loss.
  3. Hemorrhage.
  4. 3rd spacing.
  5. Decrease in effective circulating volume: HF, Cirrhosis.
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5
Q

Prerenal ARF - Hypotension:

A
  1. Sepsis.
  2. Cardiogenic shock.
  3. Anaphylaxis.
  4. Anesthesia- and medication-induced.
  5. Relative hypotension below patient’s autoregulatory level.
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6
Q

Prerenal ARF - Changes in renal hemodynamics:

A
  1. NSAIDs/ COX2.
  2. ACEIs/ARBs.
  3. Renal artery thrombosis or embolism.
  4. AAA.
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7
Q

Intrarenal ARF - 4 general etiologies:

A
  1. Vascular.
  2. Glomerular.
  3. Tubular.
  4. Interstitial.
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8
Q

Intrarenal ARF - Vascular etiology:

A
  1. Vasculitis.
  2. Malignant HTN.
  3. Cholesterol emboli.
  4. Thrombotic microangiopathies –> TTP, HUS, DIC.
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9
Q

Intrarenal ARF - Glomerular etiologies:

A 
Inflammatory:
1. Post infectious GN.
2. Cryoglobulinemia.
3. Henoch-Schönlein purpura.
4. SLE.
5. ANCA GN.
6. Anti-BM disease.
\+ Thrombotic microangiopathies.
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10
Q

Intrarenal ARF - Tubular etiologies:

A
  1. Ischemic due to prolonged renal hypoperfusion.
  2. Toxin induced:
    a. Medications (aminoglycosides).
    b. Radiocontrast media.
    c. Heavy metals (cisplatinum).
    d. Intratubular pigments (myoglobin, Hb).
    e. Crystals (uric acid, oxalate) or proteins (myeloma).
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11
Q

Intrarenal ARF - Interstitial etiologies:

A
  1. Acute interstitial nephritis.
  2. Bilateral nephritis.
  3. Infiltration (lymphoma, sarcoidosis).
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12
Q

Postrenal ARF - mechanical causes from ureter:

A

Must be BILATERAL to cause ARF.

  1. Stones.
  2. Tumors.
  3. Hematoma.
  4. Retroperitoneal adenopathy or fibrosis.
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13
Q

Postrenal ARF - Mechanical causes from the bladder neck:

A
  1. BPH/Prostate cancer.
  2. Tumors.
  3. Stones.
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14
Q

Postrenal ARF - Mechanical causes from the urethra:

A
  1. Strictures.
  2. Tumors.
  3. Obstructed indwelling catheters.
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15
Q

A neurogenic cause of Postrenal ARF:

A

Neurogenic bladder.

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16
Q

Best overall measure of kidney function:

A

GFR (difficult to accurately measure in clinical practice).

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17
Q

Relationship between GFR and creatinine:

A

Varies inversely and exponentially, so that relatively small changes changes in serum serum creatinine may reflect significant decreases in GFR.

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18
Q

Creatinine clearance is lower or higher than GFR?

A

Higher because creatinine is also secreted in the urine.

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19
Q

Cystatin C as a measure of kidney function:

A
  1. Freely filtered by glomerulus.
  2. Less variable than creatinine.
  3. Not yet in widespread use.
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20
Q

Estimating GFR using the … formula?

A

Cockcroft-Gault.

[(140-age)x weight in kg]/ 72x creatinine in mg/dL.

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21
Q

Must not miss diagnoses in ARF:

A

Hypovolemia and obstruction.

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22
Q

The evaluation of ARF always begins with?

A
  1. Urine electrolytes.

2. Urinalysis.

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23
Q

ATN - Textbook presentation:

A

Presentation ranges from ASYMPTOMATIC (with discovery of an increased creatinine on routine laboratory testing) to symptoms of uremia (eg lethargy, nausea, delirium, seizures, edema, and dyspnea).

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24
Q

Inability to DECREASE AFFERENT arteriolar resistance:

A
  1. Older age.
  2. Atherosclerosis.
  3. Chronic HTN.
  4. CKD.
  5. Malignant HTN.
  6. NSAIDs/COX2.
  7. Sepsis.
  8. Hypercalcemia.
  9. Cyclosporine/Tacrolimus.
  10. Renal artery stenosis.
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25
Q

Inability to INCREASE EFFERENT arteriolar resistance:

A
  1. ACEIs.

2. ARBs.

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26
Q

ATN accounts for …-…% of ARF in hospitalized patients and for …% in outpatients.

A

55-60%.

11%.

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27
Q

MCC of ATN:

A

Post operative ATN and contrast-induced nephropathy (CIN).

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28
Q

Mortality in HOSPITALIZED patients with ATN is about …%.

In ICU patients, mortality is about …%.

A

37%.

78%.

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29
Q

Risk factors for increased mortality in ARF:

A
  1. Male sex.
  2. Advanced age.
  3. Comorbid illness.
  4. Malignancy.
  5. Oliguria.
  6. Sepsis.
  7. Mechanical ventilation.
  8. Multiorgan failure.
  9. Severity of illness.
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30
Q

ATN - Full recovery occurs?

A

Over 1-2 weeks in about 60% of survivors.

A post ATN diuresis, during which urinary output transiently increases, may be seen.

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31
Q

Overall, …-…% of patients with ATN require long-term dialysis.

A

5-10%.

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32
Q

…% of patients in whom ATN develops in the ICU and who survive require dialysis.

A

33%.

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33
Q

Which tests are used to distinguish ATN from PRERENAL states?

A
  1. Urine electrolytes.
  2. Urinalysis.
  3. Serum BUN.
  4. Creatinine.
34
Q

What is used to distinguish ATN from OBSTRUCTION?

A

Ultrasound.

35
Q

When are the urine sodium and FENa misleading???

A
  1. Will be HIGH if the patient is taking diuretics or has received IV saline prior to collection of the urine sample, even if the patient is PRErenal.
  2. Can be LOW in ATN due to rhabdomyolysis, myoglobinuria, hemolysis, sepsis, cirrhosis, HF, and CIN.
36
Q

FENa or urine sodium?

A

FENa is better for distinguishing prerenal states from ATN.

37
Q

In well-hydrated individuals FEurea is?

A

50-65%.

38
Q

Prerenal ARF - FEurea is?

A

<35%.

39
Q

ATN - FEurea is?

A

> 50%.

40
Q

Major advantage of FEurea:

A

IT IS NOT AFFECTED BY DIURETIC USE.

41
Q

BUN/Cr can be elevated in?

A
  1. Classically in Prerenal ARF.
  2. GI bleeding.
  3. Steroids.
  4. High-protein intake.
  5. Increased catabolism.
42
Q

BUN/Cr can be low in?

A

With ARF 2o to Rhabdomyolysis, or with decreased production due to malnutrition or liver disease.

43
Q

Ability of the physical exam to diagnose hypovolemia?

A

NOT WELL STUDIED.

44
Q

Catheterization can be a … test in ARF.

A

Diagnostic.

45
Q

Urinary tract obstruction - Textbook presentation:

A

Symptoms vary with site, degree, and rapidity of onset of the obstruction, ranging from severe pain with acute obstruction to mild or no pain.
Incontinence and dribbling are common.

46
Q

Anuria is defined as?

A

<100mL of urine per day.

47
Q

In PARTIAL urinary tract obstruction, can the urinary output be increased?

A

Yes - Due to tubular injury that impairs concentrating ability and sodium reabsorption.

48
Q

Obstruction accounts for …% of outpatient ARFs.

A

17%. (2-5% of inpatient ARFs)

49
Q

Urine electrolytes - Helpful in UT obstruction?

A

Not very helpful.

50
Q

Post void residual is normally?

A

<100mL - Increased if obstruction is distal to the ureters.

51
Q

There are 4 settings in which obstruction can occur without dilatation of the complete collecting system.

A
  1. Within the first 1-3d, due to relative lack of compliance of collecting system.
  2. When the patient is also volume depleted.
  3. Retroperitoneal fibrosis - Hydronephrosis without ureteral dilatation - Hydronephrosis and fibrosis are better seen on CT scan.
  4. With obstruction so mild that there is no impairment in renal function.
52
Q

Medications that commonly induce urinary retention in susceptible patients:

A
  1. Antihistamines.
  2. Anticholinergics.
  3. Antispasmodics.
  4. TCAs.
  5. Antidepressants.
  6. Opioids.
  7. Alpha-agonists.
53
Q

Symptoms of BPH can be categorized as:

A
  1. Storage symptoms - Urinary frequency, Nocturia, urge/stress incontinence.
  2. Voiding symptoms - Hesitancy, poor flow, straining, dysuria.
  3. Postmicturition symptoms - Dribbling, incomplete emptying.
54
Q

EBD of BPH - Guidelines recommend that ALL patients have?

A
  1. DRE.
  2. Urinalysis.
  3. Serum creatinine.
    Other testing (urodynamics, imaging) is optional.
55
Q

EBD of BPH - DRE:

A
  1. Cannot ascertain anterior or posterior extension or feel entire posterior surface.
  2. Prostate size is underestimated by 25-55% compared with transrectal US. Underestimation increases the larger the prostate volume.
56
Q

Bottom-line about DRE in BPH:

A

Prostate is even bigger than you think it is on DRE.

57
Q

NSAID-induced renal hypoperfusion - Textbook presentation:

A

ARF caused by NSAIDS is usually asymptomatic and is MC detected by finding an increased serum creatinine.

58
Q

NSAID-induced renal hypoperfusion is seen within?

A

3-7d starting therapy.

59
Q

5 patients that have impaired autoregulation of kidney function:

A
  1. CKD.
  2. HTN.
  3. Volume depletion.
  4. HF.
  5. Cirrhosis.
60
Q

Interstitial nephritis - Textbook presentation:

A 
Classic symptoms include:
1. Renal insufficiency.
2. Hematuria.
3. Pyuria.
4. WBCs casts.
5. Fever.
6. Eosinophilia.
The full syndrome is RARELY seen today since it occur primarily with methicillin-induced acute interstitial nephritis.
61
Q

Interstitial nephritis is found in …-…% of all renal biopsies and in up to …% of patients who had biopsy done for ARF.

A

2-3%.

15%.

62
Q

Etiology of interstitial nephritis:

A

10% –> Infections.
85% –> Medications.
4% –> Idiopathic.

63
Q

Important point about diagnosis of interstitial nephritis:

A

The ABSENCE of fever, rash, eosinophilia, or eosinophiluria does NOT rule out interstitial nephritis.

64
Q

EBD of interstitial nephritis - Urine eosinophils:

A

Sens is 67%.
Spec is 83%.
LR+= 3.9.
LR-= 0.39.

65
Q

EBD of interstitial nephritis - FENa:

A

Usually >1%.

66
Q

EBD of interstitial nephritis - Gold standard:

A

Renal biopsy.

67
Q

Vascular causes of ARF:

A

Rare, but serious - 3 mechanisms:

  1. Renal artery thrombosis.
  2. Thromboembolism of the renal arteries.
  3. Atheroembolism.
68
Q

Renal artery thrombosis - Textbook presentation:

A
  1. Severe flank pain.
  2. Hematuria.
  3. Nausea.
  4. Vomiting.
  5. Fever.
  6. HTN.
69
Q

MCC of renal artery thrombosis:

A

Blunt trauma.

70
Q

Non traumatic causes of renal artery thrombosis:

A
  1. Dissecting aortic or renal artery aneurysms.
  2. Vasculitis.
  3. Cocaine abuse.
  4. Antiphospholipid antibody syndrome.
71
Q

EBD of renal artery thrombosis:

A
  1. Angiogram is the gold standard.

2. Infused CT is often diagnostic.

72
Q

Thromboembolism of the renal arteries - Textbook presentation:

A

Most patients have flank pain, often with hematuria or anuria.

73
Q

Thromboembolism of the renal arteries - Sources of emboli?

A
  1. Cardiac: Afib, MI, rheumatic valvular disease, prosthetic valves, subacute bacterial endocarditis.
  2. Aortic or renal aneurysms.
  3. Intra-arterial catheterization.
74
Q

EBD of thromboembolism of the renal arteries - Diagnosis at onset:

A

Diagnosed at onset of symptoms in only 30% of patients.

75
Q

EBD of thromboembolism of the renal arteries - Lab results:

A
  1. Leukocytosis.
  2. UP LDH.
  3. UP transaminases (LDH increased more).
76
Q

Atheroembolism - Textbook presentation:

A

Classic presentation is a white man over age 60 with HTN, smoking, and vascular disease in whom Livedo reticularis and acute or subacute renal failure develop after an inciting event.

77
Q

Atheroembolism - 3 subsequent syndromes:

A
  1. Abrupt onset of renal failure after an inciting event (such as angiography).
  2. Subacute worsening of renal function a few weeks after the event.
  3. Chronic renal impairment.
78
Q

Incidence of Atheroembolism of the renal arteries:

A

Probably quite low (<1-2%), but may be as high as 5-6% in high-risk patients.

79
Q

Clinical manifestations of Atheroembolism of the renal arteries (from 5 case series):

A 
35-90% --> Skin lesions (livedo reticularis).
8-30% --> GI symptoms.
22-73% --> Eosinophilia.
4-23% --> CNS involvement.
28-61% --> Dialysis needed.
80
Q

Atheroembolism of the renal arteries - EBD:

A
  1. Renal or skin biopsy.

2. Can sometimes be diagnosed on fundoscopic exam.

81
Q

CKD - Textbook presentation:

A

Patients are often asymptomatic, or may have non specific symptoms such as fatigue.
Patients with kidney failure can present with fluid overload, uremic symptoms (fatigue, nausea, delirium), or manifestations of electrolyte abnormalities (such as Arrhythmias).

82
Q

ARF is defined as?

A

An abrupt decrease in GFR + increase in serum Cr, resulting in an inability to maintain fluid and electrolyte balance.

Project - USMLE Step 3 (82 decks)

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