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Perf tech III > test 5 part 2 > Flashcards

test 5 part 2 Flashcards

1
Q

Primary function of the kidneys

A
  • Primary function: preserve internal homeostasis
  • Regulates body fluid composition
  • Regulates intravascular blood volume
  • Excretion of metabolic byproducts
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2
Q

Endocrine functions of kideny

A
  • Produces EPO
  • Synthesizes 1,25-dihydroxycholecalciferol
    * Vitamin D – regulates calcium and phosphorus homeostasis
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3
Q

Nephron

A

• Functional unit is the nephron – each kidney has more than
1 million
• Nephron has two main parts
• Glomerulus
• Specialized capillary network
• Allows filtration of fluid from plasma (no cellular components or proteins)
• Membrane is 100 x more permeable than normal capillaries
• Tubular system
• Collects filtered fluid
• Alters composition converting plasma filtrate to urine

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4
Q

Kidney Blood Flow

A 
• Receives 20% of CO
• Cortex receives more than 90% of
renal blood flow
        • Oxygen tension ~50mmHg
• Medulla oxygen tension ~8-10mmHg
        • Medulla is vulnerable to hypoperfusion and ischemia
• Prevent ischemia/acute kidney injury (AKI)
        • Increase oxygen delivery
        • Decrease oxygen demand
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5
Q

GFR

A
  • Glomerular filtration rate (GFR): quantity of glomerular filtrate formed in all nephrons of both kidneys per minute
  • Used as a test to measure kidney function and determine stages of kidney disease
  • 125 ml/min (180 L/day) in normal adult
  • (70-80 mmHg) to (160-180 mmHg)
  • On pump, perfusion pressure is often below autoregulatory threshold
    * Resulting in diminished urine output
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6
Q

Urine Formation

A
  • Decrease in urine output does not mean a decline in GFR
    * Does not imply AKI
  • Kidneys responds to decreased blood flow/ volume
    * Endocrine
  • Post-op pain, anxiety, and/or nausea may stimulate release of ADH independent of blood volume
    * Resulting in a decrease of urine volume despite normal renal function
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7
Q

Preoperative Renal Risk Factors

A
  • Preoperative renal dysfunction is the most significant risk factor
    * Elevated serum creatinine levels
  • Other risk factors include:
    * Age
    * DM
    * Reoperations
    * Exposure to radiocontrast and nephrotoxic drugs
    * Operation type
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8
Q

Tests to Measure Kidney Function

A
  • Blood creatinine level
    * Measures amount of creatinine in blood
    * Creatinine levels can vary depending on muscle mass
  • Creatinine clearance
    * Measures how well creatinine is removed from blood and kidneys
    * Better than just serum creatinine level
    * Performed on blood and urine sample collected over 24 hours
  • Blood urea nitrogen-to-creatinine ratio (BUN:creatinine)
    * Measures amount of urea in blood
    * Ratio can help identify kidney problems
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9
Q

Factors that Effect Serum Creatinine Levels

A 
Aging = decreased
female = decreased
Ethnicity =
       - African American = increased
        - Asian = decreased
Body habitus
        - Muscular = increased
        - Obesity = no change
Diet
        - meat = increased
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10
Q

Measuring GFR

A
  • Direct GFR measurement is most accurate to detect changes in kidney status
    * Complicated
    * Time consuming and expensive
    * Requires experienced personnel
    * Performed only in research settings or transplant centers
  • Estimated GFR (eGFR) is usually used
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11
Q

Estimated Glomerular Filtration Rate (eGFR)

A
  • Calculation based on serum creatinine test
  • Decreased kidney function
    * Decreased creatinine excretion in urine (decreased clearance)
    * Increased creatinine concentration in the blood
  • Different equations used to calculate eGFR
  • Claimed to be better predictor of renal outcome
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12
Q

Operative Renal Risk Factors

A
  • Overall, little conclusive evidence that cardiopulmonary bypass in-and-of itself causes renal dysfunction
  • But there are some things that could affect the possibility
  • Low flow
  • Need for IABP (low CO)
  • Prolonged bypass times
    * > 180 minutes
    * SIRS development
  • Inappropriate hemodilution
  • Embolic events
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13
Q

Hemodilution Effects on Renal Function

A
  • Increased risk of AKI when hct <21%
    * Suggests decrease in oxygen carrying capacity
  • Reduces viscosity
    * Enhanced microcirculatory flow
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14
Q

Embolic Events and Renal Function

A
  • Ascending aortic atherosclerosis
    * Independent risk factor
  • Increase postoperative renal dysfunction by 9.0 -17 % in patients with severe disease
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15
Q

Most patients who develop post operative renal failure:

A
  • SUFFER FROM PREEXISTING RENAL DISEASE
  • Have compromised renal perfusion secondary to low cardiac output during perioperative period
    * Low renal perfusion pressure while on bypass
    * Low renal perfusion pressure off pump caused by renal vasoconstriction during low cardiac output states
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16
Q

Pharmacological Intervention

A
  • Goal of any intervention is to prevent acute renal failure that requires dialysis
  • No studies have conclusively shown that any pharmacological agent was effective in preventing acute renal failure requiring dialysis
17
Q

Pharmacological Intervention: Dopamine

A
  • Low dose dopamine
    * Stimulate renal vasodilation
    * Inhibits sodium reabsorption
    * Meta-analysis of 3000pts showed no benefit of LDD
    * Currently has been phased out
18
Q

Pharmacological Interventions: Loop Diuretics

A
  • Furosemide
    * Attempt to prevent or treat ARF
    * Inhibits chloride and sodium transport
    * Decreases oxygen demand because of decrease in active transport
    * May lead to worse outcomes
    * Forced diuresis
    * **Just makes urine appear
19
Q

Pharmacological Interventions: Osmotic Diuretics

A
  • Mannitol
    * Thought to decrease renal injury when given before ischemic insult (i.e. CPB, XC)
    * Thought to flush out necrotic tubular debris
    * Scavenge oxygen free-radicals
    * Improve medullary blood flow
    * Reduce endothelial edema
    * Studies show no proven renal protection
20
Q

Operative Assessment of Renal Function

A
  • Decreased output is used as an indication of renal hypoperfusion
  • Oliguria: Urine output less than 0.25 to 0.33 ml/kg/hour
    * No other point-of-care assessment methods available
  • Studies have found no correlation between intraoperative urine volume and postoperative renal dysfunction (Alpert et al. and Knos et al)
  • Decreased urine output could be result of kinked or obstructed catheter or stress-induced ADH secretion
  • Maintaining adequate perfusion pressure may be most important to prevent renal hypoperfusion
21
Q

Main message

A
  • Perioperative low urine output does not predict postoperative AKI
    * Adequate urine flow does not exclude the possibility of impending AKI
    * Low urine output may be an indication of renal hypoperfusion
    * Initial treatment should ensure adequate blood volume and cardiac output before renal protective therapy is initiated

Perf tech III (55 decks)

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