Diuretics

Question 1

Thiazide diuretics

Prototype

site of action

action

precaution

Answer 1

• Prototype: hydrochlorothiazide
• site of action: distal convoluted tubule
• action: impairs Na and Cl reabsorption
• precautions: K depleting
  
  • because there is more Na in the tubule when it gets to the end, more K is excreted

Question 2

When are thiazides (Hctz) often used?

Anesthesia concerns?

Answer 2

• Antihypertensive
  
  • Initially from decreased fluid volume
  • sustained effect is caused by peripheral vasodilation
• Anesthesia concerns:
  
  • hypokalemia
  • hypochloremia
  • hypomagnesemia
    
    • muscle weakness potentiates muscle relaxants
  • nephropathy
  • increased risk of digoxin toxicity
  • fluid volume status

Question 3

Furosimide

location of action

timing of effect

dose

PB

excretion

Answer 3

• Loop diuretic- blocks the Na/K/Cl channel
• Diuresis begins 2-10 minutes following IV injection
• dose: 0.1-1.0 mg/kg
  
  • ​start with 5 mg in the OR
• Extensive protein binding
• Excreted by glomerular filtration and renal tubule secretion

Question 4

What is furosemide used for?

Answer 4

• Uses:
  
  • mobilization of edema fluid
  • peripheral vasodilation precedes onset of diuresis, but furosemide only decreased BP by loss of fluid
  • reduction of ICP
  • decrease venous return
  • treat hypercalcemia
    
    • they inhibit absorption of Ca++
  • differential diagnosis of oliguria
    
    • small dose of 0.1 mg/kg will stimulate diuresis in presence of excessive ADH

Question 5

What are the side effects of loop diuretics?

Answer 5

• hypokalemia, hypochloremia
• presynaptic inhibition of cAMP and subsequent release of ACh potentiates nondepolarizing muscle relaxants (d/t hypokalemia??)
• enhances possibility of nephrotoxicity when administered with aminoglycosides and cephalosporins
  
  • don’t mix if they already have nephrotoxicity
• decreased renal clearance of lithium
• possible cross reactivity of sulfonamide allergy

Question 6

What kind of diuretic is Mannitol?

Structure? function?

administration?

clearance?

Answer 6

• Mannitol is an osmotic diuretic
• 6 carbon sugar- Hexose
  
  • Cleared from plasma through glomerular filtration, once in tubule fluid, it increases osmolarity and water, Na, Cl, and HCO3 is excreted
• Must give IV- it does not ever enter cells
• Clearance 100% by glomerular filtration, none of it is reabsorbed

Question 7

Uses of Mannitol

Answer 7

• Differential diagnosis of oliguria-
  
  • uop will increase if the cause of low UOP is low intravascular fluid volume
  • UOP will not increase if cause of the problem is glomerular or renal tubule function
• prophylaxis in acute renal failure
  
  • easier to manage fluid status, but no evidence of renal protective effect
  • it is seen to be effective after renal transplant
• reduction of ICP
• reduction of IOP

Question 8

What are the two ways mannitol can decrease ICP?

Answer 8

• increased plasma osmolarity draws water from tissues, including the brain
• decreases Cerebral spinal fluid by decreasing the rate of production of if

Question 9

What is the dose of mannitol?

onset, DOA

Anesthesia concerns?

Answer 9

• 0.25-1.00 g/kg IV
  
  • usually dose on higher end unless patient had cardiac problems/wont be able to tolerate significant increase in intravascular fluid
• Exerts effect in 10-15 min and lasts 2 hours
• Anesthesia concerns:
  
  • pulmonary edema
  • hypovolemia
  • electrolyte changes

Question 10

What are some potassium sparing diuretics?

Answer 10

• Epitheleal sodium channel blockers
  
  • Triamterene
• Aldosterone antagonists
  
  • spironolactone

Question 11

Triamterene:

site of action

action

precaution

Answer 11

• Site of action: collecting duct
• Action: Na channel blockade and inhibits K secretion into tubule; non-competative antagonism of aldosterone
• Precautions: can cause hyperkalemia
• Often used in combo with HCTZ

Question 12

Spironolactone

type of diuretic

structure

use

Answer 12

• Aldosterone antagonist (competitive); K sparing
• Structure: synthetic 17 lactone drug
• Use: primarily to treat heart failure, ascites, low-renin hypertension, hypokalemia, and Conn’s syndrome
• Spironolactone is a weak diuretic, and is usually combined with other diuretics; Not often used in the perioperative arena

Question 13

What is the Carbonic Anhydrase inhibitor?

use?

how does it work?

Answer 13

• Acetazolamide (Diamox)
  
  • used to treat Gloucoma, altitude sickness, ICP
• Carbonic anhydrase catalyzes H+ and HCO3 released from CO2 and H2O. H+ is then excreted in exchange for Na on the renal luminal membrane and HCO3 is reabsorbed with Na
  
  • because this enzyme is inhibited, excretion of H+ ions is diminished and loss of HCO3 is increased
  • Cl- is retained by kidney to offset loss of HCO3
  • Less H+ ions in distal tubules results in excretion of K in exchange for Na

Question 14

Dopaminergic agents

dose

Renal protection

Answer 14

• Low dose Dopamine 1-3 mcg/kg/min
• Renal protection
  
  • vasodilation
  • inhibition of Na-K-AtPase pump decreases renal O2 consumtion
  • effect diminished after 48 hours d/t downregulation of dopaminergic receptors