Semin cardiothorac vasc anesth

CPB Circuit Design: Hemodilution, 

Transfusion, and Oxygen Delivery

Many studies on CPB circuit size in conventional sternot-

omy procedures can be expanded and applied to strategies 

for minimally invasive procedures. Body size and gender 

are associated with low nadir hematocrit (HCT) and 

increased rates of transfusion during CPB, with women 

and smaller patients at greatest risk.

26

 In addition, it was 

recently reported that even 1 or 2 units of red cell transfu-

sions are associated with morbidity and mortality.

27

 

Reduction of the CPB circuit prime volume and autolo-

gous priming have been recommended to minimize the 

incidence of low nadir HCT and subsequent allogeneic 

blood transfusions.

28,29

 Several reports have illustrated that 

a reduction in surface area priming volume and matching 

the CPB circuit to the size of the patient reduces the fre-

quency of low HCT values and subsequently reduces the 

incidence of allogeneic blood transfusions.

30-33

In addition to efforts to maintain HCT, it is important to 

appreciate the concept of oxygen delivery (DO

2

) during 

CPB for minimally invasive procedures. DO

2

 is dependent 

on the combination of HCT and CPB flow rates. DO

2

 can 

be calculated using the following formula:

      

DO

 CPB flow indexed  1   Hemoglobin

1 36 Sat

paO

 

2

2

=

+

× 

×

×

×

0

0 0

(

.

)

. 003

(

)

.

 (1)

DO

2

 levels below 262 mL/min/m

2

 during CPB with mod-

erate hypothermia have been associated with acute kidney 

injury.

34

 This concept can be particularly useful in the set-

ting of minimally invasive procedures with peripheral can-

nulation where higher CPB flows may be more challenging 

than conventional sternotomy procedures. Just as in con-

ventional procedures, efforts to provide adequate CPB 

flow to maintain DO

2

 levels 

≥262 mL/min/m

2

 may mini-

mize the incidence of acute kidney injury.

In summary, we recommend the following strategies to 

minimize hemodilution and transfusion and maintain ade-

quate DO

2

 during minimally invasive procedures:

•

• Match the size of the circuit to the size of the patient

•

• 3/8″ venous line with VAVD

•

• lower prime oxygenators and filters

•

• minimized tubing length

•

• Calculate and maintain DO

2

 

≥262mL/min/m

2

.