Elimination of Gaseous Microemboli From Cardiopulmonary Bypass Using Hypobaric Oxygenation

BACKGROUND:

Numerous gaseous microemboli (GME) are delivered
into the arterial circulation during cardiopulmonary bypass (CPB).
These emboli damage end organs through multiple mechanisms that are
thought to contribute to neurocognitive deficits after cardiac surgery. Here, we use hypobaric oxygenation to reduce dissolved gases in blood and greatly reduce GME delivery during CPB.

METHODS:

Variable
subatmospheric pressures were applied to 100% oxygen sweep gas in
standard hollow fiber microporous membrane oxygenators to oxygenate and
denitrogenate blood. GME were quantified using ultrasound while air
embolism from the surgical field was simulated experimentally. We assessed end-organ tissues in swine postoperatively using light microscopy.

RESULTS:

Variable
sweep gas pressures allowed reliable oxygenation independent of carbon
dioxide removal while denitrogenating arterial blood. Hypobaric
oxygenation produced dose-dependent reductions of Doppler signals
produced by bolus and continuous GME loads in vitro. Swine were
maintained using hypobaric oxygenation for 4 hours on CPB with no
apparent adverse events. Compared with current practice standards of
oxygen/air sweep gas, hypobaric oxygenation reduced GME volumes exiting
the oxygenator (by 80%), exiting the arterial filter (95%), and arriving
at the aortic cannula (∼100%), indicating progressive reabsorption of
emboli throughout the CPB circuit in vivo. Analysis of brain tissue
suggested decreased microvascular injury under hypobaric conditions.

CONCLUSIONS:

Hypobaric
oxygenation is an effective, low-cost, common sense approach that
capitalizes on the simple physical makeup of GME to achieve their
near-total elimination during CPB. This technique holds great potential
for limiting end-organ damage and improving outcomes in a variety of
patients undergoing extracorporeal circulation.