Case 90 - kidney system

Question 1

what is the definition of AKI?

Answer 1

• suddent development of renal insuffiency that results in retention of urea and other nitrogenous waste products

acute kidney injury network (AKIN) staging system for AKI (< 48 hours)

Stage 1

• increase SCr > 0.3 mg/dL
• UOP < 0.5 ml/kg/hr for > 6 hours

Stage 2

• baseline increase > 2 to 3 fold
• UOP < 0.5 ml/kg/hr for > 12 hrs

Stage 3

• baseline increase > 3 fold or inititation of RRT
• UOP < 0.3 ml/kg/hr > 24 hours or anuria > 12 hours

Question 2

What are the three etiologies of renal failure, and what is the pathophysio mechanism behind them?

Answer 2

3 etiologies of renal failure: pre-renal, renal, postrenal

anatomy - renal artery –> afferent arteriole –> glomerulus for filtration into renal rubules –> efferent arteriole

1) Pre-renal AKI
* pathophysiology - decreased blood flow to kidneys
a) decreased renal artery perfusion

• hypovolemia (poor intake or diuretics) - fluids
• low CO states (CHF) - inotropes
• hypotension (dec SVR) - vasopressors
• impair renal artery dilation (NSAIDs - inhibit cyclooxyngease)

b) afferent arteriole constriction
* Norepi, angiotensin, prostaglandins
c) efferent arteriole vasodilation
* ACE-i and ARBs
2) post renal azotemia

• pathophys - obstruction to urine flow beyond the kidney
• ureteral obstruction by stones, constriction, hydronephrosis

3) intrarenal renal failure

• intrinsic kidney disease
• most common is ATN = renal ischemia 2/2 renal hypoperfusion. tubular cell injury
  
  • could be due to nephrotoxins, hemoglobinuria, myoglobinuria (tx with fluid bolus, maintain renal perfusion, alkalinzation)

Question 3

What lab tests can you order to look at pre renal vs renal AKI?

Answer 3

assessment of AKI and oliguria

• foley catheter - trend hourly UOP
• hemodynamics and volume status
  
  • is preload optimized?
• Echo - look at ventricular function
  
  • low CO?
• nephrotoxic drugs given recently?
  
  • aminiglycosides, PCN, vanco

Labs:

• order BUN, SCr, elecrolytes, osmolality

Pre - Renal:

• BUN/Cr = > 20:1
• urine osmolality = > 500 (concentrated)
• Urine specific gravity = > 1.016 (concentratd)
• urine Na+ = < 20
• FENa = < 1%

Renal

• BUN/Cr = < 20:1
• urine osmolality = < 400 (not concentrated)
• Urine specific gravity = < 1.010 (not concentrated)
• urine Na+ = > 40
• FENa = > 2%

Question 4

What is the pathogenesis of contrast-induced nephropathy?

Answer 4

contrast induced nephropathy

• causes renal vasoconstrictoin and direct tubular injury (cytotoxic effects of tubular cells 2/2 oygen free radical formation)

Question 5

how can you reduce the risk of contrast induced nephropathy?

Answer 5

• radiocontrast media
  
  • non-ionized, low-osmolar or isoosmolar contrast + limit volume
• discontinue nephrotoxic drugs (NSAIDs, metformin)
• Volume expansion
  
  • 0.9% NaCl 1 mL/kg/hr for 24 hours
• Sodium Bicarb
  
  • administer prior to procedure, and continue for 6 hours after the procedure
• Acetylcysteine
  
  • 1200mg BID
  • antioxidant and vasodilatory properities

Question 6

What are indications for dialysis?

Answer 6

AEIOU

Acidosis

• impaired renal function leads to loss of bicarb and accumulation of acids
• can try to tx with Sodium bicarb
  
  • be aware of use of NaCo3 with hypernatremic, volume overload, respiratory acidosis pts

Electrolytes (hyperkalemia)

• exogenous source (potassium supplement, IVF, ACE-I
• tumor lysis syndrome, hematoma reabsorption, rhabdomyolysis

Intoxication

Overload (fluid)

• CHF patients
• dialysis used if refractory to diuretics and inotopric agents

Uremia

• urgent dialysis with encephalopathy, pericarditis, or hemorrhage

Question 7

why would you want to use continous renal replacement therapy (CRRT) as opposed to intermintent hemodilaysis?

Answer 7

Intermittent hemodialysis

• Pro - rapid decrease in plasma solute concentration
• Cons - can cause hypotension (HD instability)

CRRT

• Pro - well tolerated in hemodynamically unstable patients
• clears solute, but at slower rates than IHD

Slow continous ultrafiltration

• form of CRRT
• removes fluid, not solutes (used with heart failure pts)

Question 8

what are complications encoutered with RRT?

Answer 8

1) Hypotension
* fluid reomved at a rapid rate in a patient with poor oncotic pressure (sepsis, heart failure)
2) electrolyte derangements
* solute clearance also leads to electrolyte depletion –> arrythmias (hypokalemia, hypocalcemia)
3) large bore CVC

• depending on site, you have its complications (infection, pneumo)
• dialysis lines in subclavian vein can lead to scarring –> unable to use AV fistula in ipsilateral hand if needed in the future

4) Anticoagulation
* CRRT requires a/c –> slow flow rate leads to activation of clotting factors –> can clot filter

Question 9

what is better, IHD or CRRT?

Answer 9

neither is superior

• HD unstable pts, like ICU pts, will benefit from CRRT (b/c solute and water removed over a longer period of time at a slower rate)
• consider IHD for life-threatening hyperkalemia or ingested toxins