Flashcards in Renal Response to CPB- Exam 1 Deck (56):
What does the kidney do?
Regulates fluid composition, intravascular volume and excretion of metabolic byproducts
What is the incidence of renal failure (i.e. requiring dialysis)
Why is the incidence of renal failure decreasing?
Better patient preparation
Improved perfusion techniques
better management cardiac performance post op
If renal dysfunction occurs, what is the mortality rate?
>50% mortality rate
What is the function unit of the kidney?
How many nephrons in each kidney?
More than 1 million
What are the two main parts of the nephron?
What is the glomerulus?
Specialized capillary network
Allows filtration of fluid from plasma (no cellular components or proteins)
Glomerular membrane vs. normal capillaries
100x more permeable than normal capillaries
Collects filtered fluid
alters composition converting plasma filtrate to urine
What is the normal Glomerular Filtration Rate
100-200 mL/min in normal adult; preserved over a broad range of blood pressures
What percent of the volume filtered is reabsorbed (osmotic diffusion)?
How is urine output related to arterial blood pressure?
Linear increase in output with increase in arterial blood pressure
If you increase pressure 100 to 200 mmHg urine output increases by factor of what?
Decrease blood pressure below 50 mmHg causes what?
Urine output to stop
What allows long term control of blood pressure?
What determines how concentrated or dilute the urine is?
ARF Risk in patients with valve surgery vs. CABG
Patients undergoing valve surgery twice the risk compared to CABG patients
What is the most significant risk factor for acute renal failure?
Preoperative renal dysfunction
How can you determine preoperative renal dysfunction?
Elevated serum creatinine
Decreased creatinine clearance
What are some other risk factors for acute renal failure?
Impaired cardiac function
Complexity of procedure
ARF-D develops in what percent of patients?
1.2 to 13% of patients post CPB
Intraoperative Renal Risk Factors
Decreased blood volume
Prolonged CPB times with SIRS
High Hematocrit results in
Decrease in microcirculatory blood flow
Low hematocrit results in
Decrease in renal oxygen-carrying capacity
What lowers organ metabolic requirements?
What is hte most important target in hypothermia?
Stroke & Renal failure at 37C vs 34C?
Strokes and renal failure occured more frequently at 37C than 34C; difference not statistically significant
What is the difference in plasma renin activity or concentration of vasopressin?
No difference in plasma renin activity or concentration of vasopressin 37C vs 34C
What happened to renal clearance and other indices of renal function while on bypass with warm heart surgery?
Transient increase in renal clearance returned to normal after bypass; temp had no lasting effect
Some studies say it is better
others show no idfference
no studies show it is harmful
Most cases not creating "true" pulse pressure
Adds significant degree of complexity
No significant advantage
Incidence of emboli and their associated clinical problems greatly reduced when...
Stopped using bubble oxygenators
Started using arterial/cardiotomy filter
Most patients who develop post op renal failure:
suffer form pre-existing renal disease
Have compromised renal perfusion secondary to low CO during perioperative period
What on bypass can cause post op renal failure ?
Low renal perfusion pressure while on bypass
Low renal perfusion pressure off pump caused by renal vasoconstriction during low cardiac output states
What is the goal of any pharmacological intervention?
Prevent acute renal failure that requires dialysis
Calcium Channel Antagonists
What is an indication of renal hypoperfusion?
Monitor urine output with decreased output
U/O less than 0.25-0.33 ml/kg/hr
What is the relationship between intraoperative urine volume and post op renal dysfunction?
Decreased urine output could be result of what?
Kinked or obstructed catheter or stress-induced ADH
What is the most important counter to renal hypoperfusion?
Maintaining adequate perfusion
MOA: Stimulate dopamine receptors in renal vasculature; vasodilation; inhibits sodium reabsorption in proximal tubule
Dose: 0.5 ug/kg/min
Problems: Post-Op A-fib, impairment of ventilatory drive in response to hypoxemia and hypercarbia, supress circulating levels of anterior pituitary-dependent hormones; renal effect is unpredictable
Current Research: No benefit, unpredictable
Type: Synthetic benzazepine derivation
MOA: Binds selectively to DA1 receptors, causes systemic and renal vasodilation; theoretically augments RBF during CPB
Dose: 0.1 ug/kg/min
Problems: Should not be used prophylactically, further research necessary
Current ResearcH: Improvement in creatinine clearance, less renal-replacement therapy, decreased time of mechanical ventilation and ICU stay; currently no difference in ARF-D incidence
Type: Synthetic sympathomimetic amine
MOA: stimulates B2 and dopaminergic DA1 receptors, exerting both systemic and renovasodilatory effect
Dose: 0.5 ug/kg/kim- 2.0 ug/kg/min
Problems: Only modest improvements in creatinine clearance; role is still speculative
Current Research: Potentially inhibits SIRS due to decrease in proinflammatory cytokines by B2 and DA1 receptor stimulation
Furosemide (Loop Diuretics)
MOA: inhibits active transcellular transport of Cl and Na, produce natriuresis
Problems: Higher rate of renal impairment compared to LDD; worsens outcome when treating oliguria
Current Research: reducing active transport decreases cellular oxygen demand and decreases damange to mTAL. May increase clearance of necrotic cellular debris diminishing tubular obstruction; improvement in urine flow rates but no change in overall dialysis-free survival
Mannitol (Osmotic Diuretic)
MOA: "Flushing" effect of necrotic tubular debris, oxygen-free radical scavenging and improevement in meduallary blood flow reducing endothelial edema
Dose: 0.25 - 1.0 g/kg before aortic XC
Problems: Unproven as a renal protectant
Current Studies: No greater renal protection
MOA: Dilates afferent arterioles, increases Pgc and GFR. Inibits the tubular reabsorption of chloride and sodium, redistributes medullary BF and bloods endothelin in renal vasculature
Problems: Worse in patients with nonoliguric ARF, due to hypotension from ANP; no role in perioperative renal dysfunction
Research: Increase in dialysis-free survival only in patients with oliguric ARF.
Calcium Channel Antagonists
Research: improved GFR, enhance vasodilating protraglandin E2, supress the vasoconstricting prostaglandin Thromboxane B2, modulate vascular sythesis of endothelin, improvements in postop renal function measured by creatinine clearance
Type: dihydropyridine calcium channel antagonist
MOA: preferential increase in regional blood flow to ischemic regions of hte kidneys
Research: in patients with baseline serum creatinine levels less than 1.3 mg% undergoing elective CABG with CPB. IV infusion of felodipine administered during the second half of hypothermic CPB nad discontinued before rewarming. GFR and active tubular transport improved
Reductions in urinary microenzyme excretion
Problems: Little protection against ARF
MOA: lowers blood pressure while possibly preserving renal function
Problem: Induced renal injury as evidenced by increase in urinary N-acetylglucosaminidase levels
Research: Suggests no benefit, potential harm due to the effects of hyperglycemia
Normally discontinued 7-10 days before open-heart surgery to minimize perioperative hemorrhage due to platelet dysfunction.
MOA: inhibition of thromboxane, a potent renovasoconstrictor
Dose: 100 mg until day of surgery
Potentially beneficial for preserving post op renal function.
Problems: increase in postop bleeding
Research: Significantly less postop renal insufficiency in aspirin-treated group