Hypothermia    
 

During surgical procedures in which the heart or large vessel are involved it becomes necessary to stop heart  function and maintain circulation through artificial means.  Cardiopulmonary bypass (CPB) machines are then required for artificial heart function.  The cardiopulmonary bypass  machine collects blood from the right atrium and  returns it to the aorta through cannulas.  The purpose of this machine is not only to imitate the heart but to control blood gas content as well. This instrument has a tendency to damage formed elements of the blood through the action of its pump. This is where whole body hypothermia comes into play. Whole body hypothermia reduces the  tissue oxygen requirements necessary which in turn allows for less blood flow and ultimately less action by the  pump. Another of the effects of hypothermia is to reduce metabolic activity within the tissues. In the brain for  example this amounts to approximately 5% per degree of cooling. This accompanying reduction in tissue  requirements is most likely the reason for the observed preserving effects of hypothermia. Some form of  hypothermia is being used in 85% of the 275,000 cardiopulmonary bypass procedures performed every year.  .

 
 

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