Semin cardiothorac vasc anesth

CPB Circuit Design: Augmented 

Venous Drainage

Minimally invasive cardiac procedures often require 

smaller-caliber venous cannulas that have a higher resis-

tance and render gravity venous drainage insufficient to 

allow for adequate CPB flow. For this reason augmenta-

tion of venous drainage is often required to achieve ade-

quate CPB flow. Augmentation of venous flow can be 

achieved by utilizing either vacuum assisted-venous 

drainage (VAVD) or centrifugal-assisted venous drainage 

(CAVD). Figure 1 illustrates the CPB circuit configura-

tions for VAVD and CAVD.

VAVD has been used in clinical practice for more than 

15 years,

13

 but clinical teams must be familiar with its 

inherent risks to utilize VAVD safely and effectively.

14

 

VAVD is performed via the application of external negative 

pressure (with an approved vacuum regulator, eg, the 

Boehringer model 3930) to a nonvented hard-shell venous 

reservoir. This negative pressure is ultimately imparted to 

the venous system of the patient and increases venous 

blood flow. The negative pressure is equal to the sum of 

gravity (−20 to −30 mm Hg depending on the height of the 

reservoir) combined with applied negative pressure (up to 

−70 mm Hg). The minimum amount of applied negative 

pressure should be used to achieve the required flow. To 

avoid blood trauma, the net negative pressure should not 

exceed −100 mm Hg.

15

 Below −120 mm Hg, the relation-

ship between blood trauma and negative pressure is linear.

The nonvented reservoir also creates an opportunity for 

positive pressurization (generated through sucker and vent 

lines) and paradoxical venous air embolism.

16

 For this rea-

son, reservoir pressure should be monitored (positive and 

negative), and an audible and visual alarm should be 

included to detect if the pressure in the reservoir becomes 

positive or too negative.

17

 In addition, most venous reser-

voirs incorporate a positive and negative pressure relief 

valve that will open if the pressure in the reservoir exceeds 

approximately 5 mm Hg or less than −150 mm Hg.