Acute Kidney Injury

Question 1

What is Acute kidney injury ?

Answer 1

• a problem resulting in an acute decrease in kidney function (rapid decreased GFR) within hours/days
• frequently accompanied by a decreased in the urine output -> oliguria, rarely anuria

Question 2

Diagnostic criteria of acute kidney injury:

Answer 2

• increased se creatinine > 0.3 mg/dL within 48 hours, or
• increased se creatinine > 1.5 times the baseline (0.6 to 1.2 mg/dL) in 7 days
  and
• urine volume < 0.5 ml/kg/h for 6 hours

Question 3

AKI mortality:

Answer 3

• 20-50%

Question 4

AKI risk factors:

Answer 4

• older age
• previous cardiac or renal insufficiency
• medications
• DM
  etc. ..

Question 5

Symptoms of acute renal failure:

Answer 5

• edema,
• periorbital edema
• fatigue
• dyspnea: due to pulmonary edema from hypervolemia
• anuria/oliguria
• nausea if uremia
• if metabolic acidosis is present, the patient may have Kussmaul breathing (a deep and difficulty breathing), hyperventilation

Question 6

Immediate complications of AKI:

Answer 6

• accumulation of uremic toxins
• electrolyte and fluid disturbance
• acid-base disturbance -> metabolic acidosis (although more related to chronic renal failure)
• complications: GI, endocrine, etc..

Question 7

Clinical consequences of AKI:

Answer 7

• increased risk of mortality

- increased risk for developing Chronic kidney disease

Question 8

Classification of AKI:

Answer 8

Based on the origin of the problem

• prerenal
• renal
• postrenal

Question 9

Prerenal AKI: different etiologies

Answer 9

Anything causing hemodynamic changes leading to a decrease in GFR.

• excessive fluid loss -> bleeding, diarrhea
• cardiogenic or septic shock -> leading to a decreased effective circulating volume and vasodilation
• vasoconstriction of afferent arteriole
• vasodilation of efferent arteriole -> ex: with ACEi use

Question 10

Prerenal AKI: clinical features

Answer 10

• oliguria
• low BP
• reflex tachycardia

Question 11

Renal: different etiologies

Answer 11

• Glomerular disease: GN
• tubular injury: Acute tubular necrosis (the most common cause of AKI)
• acute tubular interstitial nephritis: due to drugs or infections
• vascular disease: vasculitis, cholesterol, emboli, thrombosis, etc…

Question 12

Post-renal: different etiologies

Answer 12

Mainly due to obstruction

• tumor (inside the ureter or outside, compressing it)
• kidney stone
• blood clot
• BPH
• tumor causing obstruction of bladder

Question 13

Acute tubular necrosis: def

Answer 13

• most common cause of AKI
• characterized by damaged to the tubular epithelial cells, which are sensitive to hypoxia and toxins
• PCT and TAL -> most sensitive parts

Question 14

Acute tubular necrosis: different types

Answer 14

• ischemic ATN: cariogenic shock, or anything causing a decreased blood flow to the kidneys
• nephrotoxic ATN: poisons -> heavy metals, drugs
• pigment ATN: crush syndrome
• others: sepsis, iodinated contrast material, uric acid, tumor lysis syndrome

Question 15

Acute tubular necrosis: lab shows

Answer 15

• sediment in urine: brown granules

- ANT casts

Question 16

Phases of Acute kidney injury

Answer 16

1. Introductory phase: signs and symptoms of the underlying disease
2. Oliguric-anuric, uremic phase: 1-2 weeks
   - volume and electrolyte disturbances
   - uremia, and encephalopathy
   - complications: anemia, infections, vomiting, pericarditis, HF
3. Polyuric phase: 2-6 weeks
   - may lead to 4-6L/day of urine output with electrolyte disturbances

Question 17

Diagnostical approach: 1. Identify the underlying cause

Answer 17

• medical history: previous kidney disease, systemic diseases etc…
• physical examination: BP, HR, Skin, Lungs, signs of systemic illness like hepatosplenomegaly, percussion of bladder

Question 18

Diagnostical approach: 2. labs

Answer 18

• BUN (blood urea nitrogen), creatinine ratio:
  .Normal: between 10:1 and 20:1
  .Increased ratio: condition that causes a decrease in the flow of blood to the kidneys -> congestive heart failure or dehydration
  .decreased ratio: liver disease (due to decrease in the formation of urea) and malnutrition.
• CBC, electrolytes (Na, K, P, Ca), pH, HCO3, Uric acid
• immunulogy
• Urine output, protein, blood, Na in urine, osmolarity, specific gravity

- Urinary sediment:
.dysmorphic RBC -> glomerular origin
.Hyaline cast -> prerenal
.ANT cast -> renal
.WBC casts -> interstitial nephritis
.RBC casts -> glomerulonephritis
.Crystals -> uric acid

Question 19

Diagnostical approach: 3. radiology

Answer 19

• US

- CXR

Question 20

Diagnostical approach: 4. renal biopsy

Answer 20

Performed only if signs and symptoms of intrinsic renal cause, not in case of acute tubular necrosis.
Perform in case of acute tubular necrosis, if it doesn’t resolve after 2 weeks

Question 21

Treatment: prerenal and post renal AKI

Answer 21

Prerenal:

• treat volume depletion by replacing volume, stop ACEi/ARB, or diuretic use
• if HF: optimize cardiac function

Postrenal:
- treat the underlying cause

Question 22

Treatment: renal AKI

Answer 22

Supportive therapy:

• acidosis: Na-HCO3
• hyperkalemia: insulin + glucose
• hypervolemia: diuretic + dialysis
• hyperphosphatemia: give Ca-carbonate orally

Indications of renal replacement therapy (dialysis):

• resistant hypervolemia, resistant hyperkalemia, resistant acidosis
• uremic encephalopathy, pericarditis
• very high BUN,creatinine

Methods of dialysis can be continuous (24h in ICU) or intermittent