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Flashcards in Renal Deck (91)
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1

What is special about blood flow through the kidney?

afferent arteriole--> glomerulus--> efferent arteriole

2

What is GFR?

  • Considered the best indicator of renal function
  • based on pt size/gender/weigth/age
  • GFR can be calculated from timed urine volume measurements
  • multiple different formulas exist to calculate
  • ranges
    • normal 90-120mL/min
    • Troubling 60-89mL/min
      • decreases with age
      • maybe normal in elderly
    • abnormal <50 mL/min
      • where we start altering our anesthetics
    • Failure <15 mL/min

3

What is creatinine clearance?

  • Specific test for GFR- most reliable assessment tool for renal function (24 hour urine collection)
  • measures ability of glomeruli to excrete creatinine
  • Normal 95-150 mL/min
  • Mild dysfunction 50-80 mL/min
  • moderate dysfunction <25 mL/min
  • anephric <10mL/min

4

What does a UA measure?

  • Specific gravity
    • measures solutes in urine
    • kidneys ability to excrete concentrate/dilute urine
    • normal 1.003-1.008 (>1.018 indicates reasonable function)
  • Proteinuria
    • >150 mg/day- Can be seent with incrase exercise, HTN, DM
    • >750 mg/day indicates severe glomerular damage
      • more likely to develop AKI
  • Microscope
    • RBC (Bleeding), WBC (infection), casts (disease of nephron) or crystals (metabolism)

5

What is BUN?

Blood urea nitrogen

  • Primary source is liver (protein catabolism)
  • not a reliable indicator of GFR
    • 40-50% passively reabsorbed by renal tubule
    • hypovolemia increases this
    • normal 10-20 mg/dL
    • 20-40 mg/dL: dehydration, high catabolism, decreased GFR
    • >50 mg/dL indicates impairment of renal function
  • increased BUN with normal serum creatinine suggests non renal cause

6

What is serum creatinine?

  • Cretinine is a metabolite of cretine (muscle constitue)
    • generally reliable in healthy patients
  • prodcution and elminiation is relatively constant
  • inversely related to GFR
  • Normal 0.6-1.2 mg/dL
    • lower in elderly/females
  • creatinine levels double for every 50% reduciton in GFR
    • delayed lab

7

What is BUN: Cr ratio? Normal? Elevater? Low?

  • Normal 10:1
    • low tubular flow rates enhanve urea reabsorption but do not affect creatinine handling
  • >15:1 
    • volume depletion, CHF, cirrhosis, and nephrotic syndrome
      • increase in nitrogen, decrease in blood flow, decrease in BP (specifically CHF, cirrhosis)
  • <10:1
    • decreased urea input, increased creatinine produciton and volume expansion

8

What is fractional excretion of sodium?

  • Useful in differentiating between prerenal and renal causes of failure
  • >2% or >40 mEq/L
    • ATN/kidney damage
    • inability to conserve sodium- because proximal/distal tubule isn't reabsorbing Na
    • intrarenal
  • <1 or <20mEq/L
    • increased sodium reabsorption- water follows sodium, less Na in urine because it is reabsorbed
    • normal funcitoning tubules
    • prerenal- hypoperfusion

9

How can anesthesia effect renal function?

  • Effects are complicated and difficult to evaluate
    • type/depht of anesthesia, choice of agent, fluid regimen
  • Indirect or direct effects
    • most are indirect (hypoperfusion)
  • occur with both general and regional anesthesia
    • less pronounced with regional
      • more localized effect
    • with spinals, big sympathomimectomy,  vasodilation, drop in BP

10

Cardiovascular indirect effects on renal system with anesthesia?

  • Dose dependent decrease in CO and SVR
  • Decreased sympathetic tone (epidural/spinal)
    • fluid boluses and vasoconstrictors to increase BP
    • DO NOT use dopamine, no changes in outcome

11

Pulmonary indirect effects on renal with anesthesia?

  • Positive pressure ventilation
    • the higher hte PIP and PEEP, the greater decrease in RBF and GFR
      • increase intrathoracic pressure, decrease return SVR, decrease in RA and RVEDP, increase in SNS--> increase NE/Epi--> vasoconstriction--> decrease blood flow to kidneys
    • Increase in SNS activation, RAAS activation, and vasopressin release
    • ensure adequate hydration

12

Neuro indirect effect on renal system with anesthesia?

  • Increased sympathetic tone
    • anxiety, pain, light anesthesia, surgical stimuli

13

Endocrine indirect effects on renal system around anesthesia?

  • Epi, NE, ADH, angiotensin II
    • reduce renal blood flow through vasoconstriction
  • Aldosterone
    • enhances Na reabsorption and water retention
  • Prostaglandins (PGE2)
    • To blanace vasoconstriction and stress
      • in Litchfields online questions, he states prostaglandins vasodilate at kidneys
    • pathway includes phospholipase A2 and cyclooxygenase
      • avoid
        • celebrex, tylenol, toradol

14

Thiopental renal implications?

  • Reduced plasma protein binding 
  • increased volume of distribution
  • may undergo some metabolism in kidney
  • decrease initial dose
  • increased sensitivity
  • (not 1st choice of drugs) (BLUE ON PPT)

15

Etomidate renal implications?

  • Highly metabolized to pharmacologically inactive compounds
  • <3% of administered dose found unchanged in urine
  • shorter elimination half life than thipental
  • inhibits 11-b-hydroxylase--> last conversion to cortisl
  • NO change in dosing for renal disease
  • Green on ppt

16

Ketamine renal implications?

  • Biotransformed in the liver
  • Norketamine is active metabolite (1/5 to 1/3 as potent)
    • may contribute to prolonged effects
  • <4% unchanged in urine
  • NO change in intiial dosing
  • May need to reduce subsequent dosing and infusion rate
    • good renal overall!
  • Green on ppt- good to give

17

Propofol renal implications?

  • Clearance exceeds hepatic blood flow (extra hepatic sites)
  • metabolites excreted in urine
  • renal dysfunction does not alter clearance
  • NO change in dosing
    • however, vasodilator so need to watch BP
  • Green on ppt

18

Dexmedetomidine renal implications?

  • Sedation and anxiolysis
  • extensive hepatic metabolism (methyl and glucuronide)
  • extensive renal excretion of metabolites
    • active metabolites
  • reduce dosage in patients with renal insufficiency
    • d/t sedation
    • Blue on ppt!

19

Midazolam renal implications?

  • Eliminiation 1/2 time, Vd, and clearance not altered
  • NOchange in bolus dosing; may need to decrease infusion
  • metabolite 1-hydroxymidazolam is about 1/2 as potent as midazolam
  • rapidly conjugated to 1-hydroxymidazolam glucuronide and cleared by kidney
    • may accumulate in kidney failure
  • Blue on ppt!

20

Diazepam renal implications?

  • Highly lipid soluble and extensively protein bound-  altered PB, more free drug in renal)
  • renal insufficiency is associated with increased plasma concentrations
  • multiple active metabolites
  • use with caution in renal failure patients
  • prolonged respiratory depression
  • RED ON PPT!! DO NOT GIVE

21

Methoxyflurane renal implications?

  • extensive metabolism- 70% to inorganic fluroid
  • avoid in renal failure patients
  • fluoride-induced nephrotoxicity
    • polyuria, hypernatremia, hyperosmolarity, increased plasma cretine, and inability to concentrate urine
  • <40 umol/L- below toxicity
  • 50-80 umol/L- subclinical toxicity
  • >80umol/L- clinical toxicity
  • >50 umol/L as indicator of toxicity
    • peak values alone not enough for dx of renal problems
  • RED ON PPT!

22

 

Halothane renal implications?

  • Decreased RBF, GFR, UOP r/t decrease in BP
  • 20% metabolized with metabolites renally excreted
    • trifluroacetic acid and bromide
  • RED ON PPT!

23

Enflurane renal implications?

  • Decreased RBF, GFR, and UOP r/t decrease in BP
  • 2-5% metabolized with metabolites renally excreted
    • fluoride ions
    • renal failure following enflurane has been reported
    • genetics?
  • RED ON PPT!

24

Isoflurane renal implications?

  • Decrease RBF, GFR, UOP
  • Metabolized to trifluoroacetic acid
  • prolonged sedation >24 hours have fluoride ions 15-50 umol/L
  • no renal impairment!
    • GREEN ON PPT

25

Desflurane renal implications?

  • Decreases RBF, GFR, and UOP
  • minimal metabolism
  • no evidence of nephrotoxic effects
  • no renal impairment
    • ​GREEN ON PPT!

26

Sevoflurane renal implications?

  • 3-5% biodegradation
  • inorganic fluroide ions
    • F ions the same or higher than enflurane
    • can be >50 umol/L
  • increased NAG (B-N-acetylglucosaminidase)
    • indicator of acute proximal renal tubular injury
    • BUN and plasma creatinine did not change
      • humans have much more NAG than rats, no damage from sevo in humans
  • CO2 absorbers
    • base -catalyzed degradation
    • vinyl ether compound called compound A
      • renal PCT injury in rates
    • barium hydroxide>soda lime
  • No renal failure notes in low flow or clsoed circuit anesthesia
    • most still practice >2 L flow
  • GREEN ON PPT!

27

Morphine renal implications?

  • RED DO NOT GIVE
  • Renal metabolism makes significant contributions morphine metabolism
    • no differencein clearance rates even in pt with cirrhosis
  • M6G (active/75-85%) and M3G (inactive 5-10%)
  • 1-2 % unchanged in urine
  • about 90% excreted by kidneys with the rest via biliary excretion
  • accumulation of metabolites may occur in patients with renal failure
    • prolonged respiratory depression > 7 days reported

28

Meperidine renal implications?

  • RED ON PPT!
  • Hepatic metabolism to normeperidine
  • urinary excretion is principal eliminiation route
  • is pH dependent
    • acidification of urine may speed eliminiation
  • 1/2 life is about 15 hours, up to 35 hours in patients with renal failure
  • normeperidine produces CNS stimulation and toxicity can manifest as myoclonus and seizures
  • in patients receiving meperidine for >3 days- delirium may be observed
    • espeically in the elderly

29

Fentanyl renal implications?

Sufentanil?

all safe renal!!-- GREEN ON PPT!

​Fentanyl:

  • metabolized to norfentanyl (minimally active)
  • <10% excreted unchanged in urine
    • detected for 72 hours
  • prolonged respiratory depression in chronic renal failure patients

Sufentail:

  • <1% unchanged
    • n-dealkylation metabolites are considered active
  • maximal renal tubular reabsorption of free drug(why?)
  • metabolites excreted equally between renal/biliary
  • prolonged respiratory depression in chronic renal failure patients

 

30

Alfentanil? Remifentanil renal implications?

Alfentanil

  • Eliminations 1/2 time and plasma clearance not altered
  • protein binding is reduced and free drug increases
  • <1% excreted unchange

Remifentanil

  • with renal failure
    • no changes in PK and PD
  • In patients on HD
    • reduced clearance and prolonged elimination 1/2l life
    • lower infusion rate required

BOTH GREEN ON PPT!