Topic 2: Renal Response to CPB

Question 1

Incidence of renal failure (i.e. requiring dialysis) %

Answer 1

(1%) - may be up to 13%

better patient preparation
improved perfusion techniques
better management cardiac performance postop

Question 2

If renal dysfunction occurs during/after CPB: ?% mortality rate

Answer 2

> 50%

Question 3

Nephron two main parts?

Answer 3

1. glomerulus
   specialized capillary network
   allows filtration of fluid from plasma (no cellular components or proteins)
   membrane is 100 x more permeable than normal capillaries
2. tubular system
   collects filtered fluid
   alters composition converting plasma filtrate to urine

Question 4

Glomerular Filtration Rate (GFR) mL/min in normal adult?

Answer 4

100 to 200 mL/min in normal adult

Question 5

Other risks for Acute Renal Failure include? (4)

Answer 5

impaired cardiac function
complexity of procedure
advanced age - greater than 63
genetics - inflammatory response

Question 6

GFR - % vol filtered that is reabsorbed by diffusion?

what is actively reabsorbed?

Answer 6

99% of volume filtered is reabsorbed (osmotic
diffusion)
glucose and amino acids actively reabsorbed

Question 7

what happens to U.O. when there is an increase pressure 100 to 200 mmHg ?

Answer 7

urine output — increases by factor of 7

Question 8

Common Emboli

Answer 8

aortic atheroma

Question 9

decrease blood pressure below 50 mmHg does what to U.O.?

Answer 9

output to stop

Question 10

Patients undergoing valve surgery twice the risk compared to what patients?

Answer 10

to CABG patients

Question 11

Preoperative renal dysfunction most significant risk factor?

Answer 11

Elevated serum creatinine

Decreased creatinine clearance

Question 12

ARF-D develops in what % of patients post

CPB

Answer 12

1.2 to 13%

little conclusive evidence that modern cardiopulmonary bypass in-and-of itself causes renal dysfunction

Question 13

Intraoperative Renal Risk Factors? (9)

Answer 13

Low flow
Decreased blood volume
IABP
Prolonged CPB times with SIRS
Inappropriate
hemodilution
Emboli
Avoiding hypothermia
Pulsatility

Question 14

High hematocrit

Answer 14

Decrease in microcirculatory blood flow

Question 15

Low hematocrit

Answer 15

Decrease in renal oxygen-carrying capacity

Question 16

Warm heart surgery –Is renal dysfunction
increased?
Strokes/ RF?
plasma renin activity/vasopressin concentration?
Renal clearance?

Answer 16

◦strokes & renal failure occurred more frequently at 37oC than at 34oC–Difference not statistically significant (Arom et. al.)
◦no difference plasma renin activity or concentration of vasopressin (Lehot et. al)
◦transient increase in renal clearance and other indices of renal function while on bypass
–returned to normal after bypass
–Temperature has no lasting effect (Regragui et. al.)

Question 17

Incidence of emboli and their associated

clinical problems greatly reduced when? (2)

Answer 17

stopped using bubble oxygenators

started using arterial / cardiotomy filter

Question 18

Most patients who develop post operative

renal failure have what two things?

Answer 18

Suffer from preexisting renal disease

Have compromised renal perfusion secondary to low cardiac output during perioperative period

Question 19

Have compromised renal perfusion secondary to low cardiac output during perioperative period caused by what two states?

Answer 19

• -low renal perfusion pressure while on bypass

- -low renal perfusion pressure off pump caused by renal vasoconstriction during low CO states

Question 20

Goal of any pharmacological intervention is to prevent acute renal failure that requires dialysis – does it work???

Answer 20

No studies have conclusively shown that any
pharmacological agent was effective in
preventing acute renal failure requiring
dialysis or death during or after cardiac
surgery

Question 21

decreased urine output is usually an indication of what?

Answer 21

renal hypoperfusion

Maintaining adequate perfusion pressure may be most important counter to renal hypoperfusion

Question 22

Oliguria:

Answer 22

Urine output less than 0.25 to 0.33

ml/kg/hour

Question 23

Assessment of Renal Function

Answer 23

Monitor U.O.
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)

Question 24

Decreased urine output could be result of what?

Answer 24

kinked or obstructed catheter or stress -induced ADH secretion