Nephrology - Acute Kidney Injury (Aki)

Front 1

• What does AKI stand for?

Back 1

o Acute kidney injury

Front 2

• What is the difference between acute renal failure and acute kidney injury?

Back 2

o These terms are synonymous, though AKI is the technically correct term now used in the literature.

Front 3

• What is the definition of acute renal failure?

Back 3

o Abrupt decline in GFR

o As GFR is difficult to measure, we rely on increases in serum creatinine levels to indicate a fall in GFR

Front 4

• When using serum creatinine levels to estimate GFR, what important fact must be kept in mind?

Back 4

o Changes in serum creatinine concentrations always lag behind and underestimate the decline in GFR.

o In other words, by the time the serum creatinine levels rise, the GFR has already fallen significantly.

Front 5

• What is the definition of oliguria?

Back 5

o Less than 400 mL of urine output in 24 hours

Front 6

• What is the definition of anuria?

Back 6

o Less than 50 mL of urine output in 24 hours

Front 7

• What is the definition of uremia?

Back 7

o Nonspecific symptoms attributable to the retention of waste products in renal failure

o Uremia is diagnosed based on symptoms, not on BUN level, as symptoms do not always correlate with the BUN level. For example, a patient may have a modestly elevated BUN but be highly uremic. Conversely, a patient may have a highly elevated BUN but not be uremic.

Front 8

• What are the symptoms of uremia?

Back 8

o Fatigue, weakness, nausea, early morning vomiting, itchiness, peridcarditis, coma

Front 9

• What is the definition of azotemia?

Back 9

o Elevated BUN without symptoms

Front 10

• What, then, is the difference between uremia and azotemia?

Back 10

o Uremia depends on symptoms and may or may not correlate with BUN levels. Azotemia depends on BUN level and may or may not say something about symptoms.

Front 11

• What are the three basic pathophysiologic mechanisms leading to acute renal failure?

Back 11

o Prerenal failure

o Intrinsic renal failure

o Postrenal failure

Front 12

• What is the proximate cause of prerenal failure?

Back 12

o Diminished renal perfusion

Front 13

• How might a person with apparent hyervolemia develop pre-renal failure?

Back 13

o Renal hypoperfusion can occur even in the context of increased total ECF volume (hypervolemia).


This occurs in patients with an overall excess of total body water but a deficint of effective intravascular volume.

o Nephrotic syndrome provides an example, with massive peripheral edema but low effective arterial blood volume due to hypoalbuminemia.

Front 14

• Broadly speaking, causes of renal hypoperfusion leading to prerenal failure can be divided into 4 categories.

What are these 4 categories?

Back 14

o True volume depletion

o Reduced effective intravascular volume

o Decreased cardiac output

o Medications

Front 15

• Name 2 classes of medications that may reduce renal perfusion and lead to renal failure.

Back 15

o NSAIDs

o ACE inhibitors

Front 16

• What is the mechanism by which NSAIDs cause acute renal failure?

Back 16

o NSAIDs are a cause of prerenal failure, which means they must result in renal hypoperfusion in some way.

o NSAIDs block the synthesis of renal dilator prostaglandins, leading to renal vasoconstriction and hypoperfusion in susceptible patients.

Front 17

• Name 3 causes of true volume depletion.

Back 17

Hemorrhage

GI loss

Renal loss (diuretics)

Front 18

• Name 4 causes of reduced effective intravascular volume.

Back 18

Nephrotic syndrome

Cirrhosis with portal hypertension (hepatorenal syndrome)

Severe burns

Sepsis

Front 19

• Major causes of intrinsic renal failure can be divided into which three categories?

Back 19

Glomerular: glomerulonephritis

Tubular: acute tubular necrosis (ATN)

Interstitial: tubulointerstitial nephritis

Front 20

• What is ATN?

Back 20

o Acute tubular necrosis

Front 21

• Causes of acute tubular necrosis can be divided in which two broad categories?

Back 21

o Nephrotoxic agents

o Ischemic causes

Front 22

• Name three common nephrotoxic agents.

Back 22

Aminoglycosides

Radiocontrast

Chemotherapy

Front 23

• Name two ischemic causes of ATN.

Back 23

o Hypotension

o Vascular catastrophe

Front 24

• What is the proximate cause of postrenal failure?

Back 24

o Blockage of urinary outflow

Front 25

• What are by far the two most common causes of postrenal failure?

Back 25

Prostatic obstruction (benign or malignant)

Ureteral obstruction due to malignancy

Front 26

• What is meant by obstructive nephropathy?

Back 26

o Postrenal failure

Front 27

• How is obstructive nephropathy typically diagnosed?

Back 27

o Hydronephrosis seen on ultrasound

Front 28

After history and physical, what tests might help you determine the etiology of renal failure?

Back 28

Urinalysis and measurement of urinary electrolytes

Front 29

o Name the likely cause of renal failure associated with each of the following findings on urinalysis:

o 1) High specific gravity, normal microscopy

Back 29

 Prerenal failure

Front 30

o 2) Isothenuria, red cells on microscopy

Back 30

o Postrenal obstruction due to crystals or stones

Front 31

o 3) Isothenuria, white cells on microscopy

Back 31

o Postrenal obstruction due to prostatic hypertrophy

Front 32

o 4) Isothenuria with normal microscopy

Back 32

o Postrenal obstruction due to compression from tumor

Front 33

o 5) Isothenuria, muddy brown casts on microscopy

Back 33

ATN

Front 34

o 6) Isothenuria, proteinuria, and RBC casts

Back 34

o Glomerulonephritis

Front 35

o 7) Isothenuria, mild proteinuria, white cell casts and leukocytes

Back 35

o Tubulointerstitial nephritis

Front 36

o What is the fractional excretion of sodium?

Back 36

o Percent of sodium filtered by kidneys that is not reabsorbed

Front 37

o What percentage of filtered Na+ is reabsorbed by a healthy kidney?

Back 37

o 99%

Front 38

o What is the normal fractional excretion of sodium?

Back 38

o <1%

Front 39

o What is the fractional excretion of sodium and measurement of urine sodium used for clinically?

Back 39

o The only thing these are useful for is to differentiate between oliguric prerenal failure from OLIGURIC ATN

o Non-oliguric ATN cannot be distinguished from other types of renal failure using fractional excretion of sodium or urine sodium levels.

Front 40

o What will the fractional excretion of sodium be in a patient with exclusively prerenal failure?

Back 40

<1 %

Front 41

o What will the fractional excretion of sodium be in a patient with oligurin ATN?

Back 41

>2%

Front 42

o What is the normal urine sodium?

Back 42

o Around 20 mmol/L

Front 43

o In a patient with prerenal failure due to true hypovolemia or effective intravascular volume depletion, what would you expect the urine sodium to be and why?

Back 43

o You would expect it to be low (<20 mmol/L).

o The reason is simple: the body regulates ECF volume through the RAAD system and sodium retention, with the idea being that the retained sodium will subsequently expand extracellular volume.

o If the kidney body is working to retain sodium, urine sodium levels will decrease as serum sodium levels increase.

Front 44

o In a patient with oliguric renal failure due to ATN, what would expect their urine sodium to be?

Back 44

o >20 mmol/L

Front 45

o What are the indications for dialysis in a patient with acute renal failure?

Back 45

o Fluid overload evidenced by pulmonary edema

o Metabolic acid/base disorders

o Hyperkalemia

o Severe hyperphosphatemia

o Uremic pericarditis

o Uremia

Front 46

o What is the major threat posed by hyperkalemia?

Back 46

o Fatal cardiac arrhythmias

Front 47

o What investigation do you order for a patient with suspected hyperkalemia?

Back 47

o STAT ECG!

Front 48

o What is the classic ECG finding associated with hyperkalemia?

Back 48

o Peaked T waves

Front 49

o What is the treatment for severe hyperkalemia?

Back 49

o Severe hyperkalemia is an emergency and best treated medically and not with dialysis

Front 50

o Describe the medical management of hyperkalemia.

Back 50

o Remember the acronym C BIG KD

o C – calcium

o B – bicarbonate, beta agonist (albuterol)

o I – insulin

o G – glucose

o K – kayexalate

o D – diuresis

Front 51

o What is the function of calcium in the treatment of hyperkalemia?

Back 51

o Oppose the membrane effects of high potassium concentration on the heart

Front 52

Which electrolyte disturbance is classically associated with AKI?

Back 52

Hyperkalemia

Front 53

Which acid base disorder is classically associated with AKI?

Back 53

Metabolic acidosis with respiratory compensation

Front 54

In which patients with AKI would you consider urgent hemodialysis?

Back 54

Remember the mnemonic AEIOU:

A – acidosis

E – electrolytes (hyperkalemia)

I – intoxication

O – volume overload

U – uremia (i.e. uremic pericarditis or a profound alteration in mental status)

Front 55

Describe the elements of a focused history for acute kidney injury.

Back 55

Timing – sudden anuria or gradual?

Associated symptoms – Light-headedness, fevers/chills, nausea/vomiting, diarrhea, flank pain, dysuria, hematuria, arthralgias, rashes

Review of recent medications, including OTC medications, especially NSAIDs and ACE inhibitors, as well as herbal medications, and recent CT scans with contrast

PMHx: heart failure, liver disease, underlying chronic kidney disease, SLE, multiple myeloma, BPH

Front 56

Name 5 classes of drugs notorious for causing AKI.

Back 56

NSAIDs

Aminoglycosides

Amphotericin B

ACE inhibitors

ARBs

Front 57

Name 5 common NSAIDs you want to ask your patient with AKI about.

Back 57

Advil (ibuprofen)

Motrin (ibuprofen)

Aleve (naproxen)

Celebrex (celecoxib)

Toradol (ketorolac)

Front 58

Describe the key elements of a physical exam for the patient with AKI.

Back 58

1) Volume status: vitals (including orthostatic vitals), mucous membranes, JVP, skin turgor, axillary sweat, edema

2) Cardiac exam: S3 of heart failure? Rub of uremic pericarditis?

3) Respiratory exam: crackles?

4) Abdominal exam: ascites/enlarged liver?

5) Kidney exam: CVA tenderness?

Front 59

What investigations would you order for the patient with AKI?

Back 59

CBC, lytes, BUN/creatinine, LFTs if not already ordered

Urine dipstick, urine microscopy, urine Na+, urine creatinine, urine specific gravity/osmolarity

Renal ultrasound

Front 60

Name 2 indices used to distinguish prerenal from other causes of renal failure.

Back 60

1) BUN to creatinine ratio

2) Fractional excretion of sodium

Front 61

What ratio of BUN to creatinine is suggestive of a prerenal etiology of acute kidney injury?

Back 61

20:1 or greater

Front 62

How does you calculate the fractional excretion of sodium?

Back 62

[(urine sodium x serum creatinine) / (serum sodium x urine creatinine)] x 100

Front 63

What tests must you therefore order to calculate the fractional excretion of sodium?

Back 63

Urine sodium, urine creatinine

Front 64

What does urine sediment testing mean?

Back 64

Urine microscopy

Front 65

What do red cell casts suggest?

Back 65

Glomerulonephritis?

Front 66

What do white cell casts suggest?

Back 66

Pyelonephritis or interstitial nephritis

Front 67

What do granular casts suggest?

Back 67

ATN

Front 68

What imaging studies should be ordered to investigate the causes of AKI?

Back 68

Renal ultrasound to rule out obstruction (post-renal)