During deep hypothermic circulatory arrest (DHCA), what happens to CO2 levels as temperature decreases?

During deep hypothermic circulatory arrest (DHCA), as the temperature decreases, the behavior of carbon dioxide (CO2) in the blood is influenced by its solubility and the principles of gas behavior. At lower temperatures, gases like CO2 become more soluble in blood due to a decrease in the kinetic energy of molecules. Consequently, when the temperature drops, CO2 tends to dissolve more readily in the blood plasma, leading to higher levels of CO2 in solution.

As a result, even though metabolic activity decreases significantly during cooling, the increased solubility of CO2 means that the concentration of CO2 in blood can actually increase as temperatures decline. This causes a paradoxical increase in CO2 despite reduced production from decreased metabolism. Therefore, as temperature decreases, CO2 levels go into solution rather than remaining constant or reducing, ultimately leading to an increase in dissolved CO2 in the blood as it cools.

Understanding this principle is essential for managing patients during DHCA, as changes in CO2 levels can affect acid-base balance and dictate the perfusion strategy during cardiac surgery.