Q; During Cardiopulmonary bypass (CPB) heparinization is considered to be adequate if target heparin concentration is

 A) More than or equal to 4 units/mL 
 B) More than or equal to 40 units/mL 
C) Less than 4 units/mL 
D) Heparin levels can't be measured by any means
E) Measuring heparin level is not standard, so activated clotting time (ACT) should be used


Answer: A

Though activated whole blood clotting time (ACT) between 400 to 480 seconds is considered to be adequate for heparinization during CPB, but another reliable method is to keep heparin concentration  more than or equal to 4 units/mL.

D is not true (we just made it up :)


Reference:

Finley A, Greenberg C. Review article: heparin sensitivity and resistance: management during cardiopulmonary bypass. Anesth Analg 2013; 116:1210.