Core cooling is generally started as soon as the arterial and venous cannulae are placed and secured. Rapid cooling is avoided, with a goal of achieving core temperatures of 18 - 20 C over 20 minutes. A temperature gradient between 5 and 8 C between the core and perfusate temperatures is maintained throughout the cooling period. If the nasopharyngeal probe is in proper position, then additional vasodilatation may be required. The cardioplegia is delivered over a period of 3 - 4 minutes at a measured pressure below 200 mm Hg.
Cardiopulmonary bypass is next discontinued and the arterial cannula is clamped and removed.
The patient is exsanguinated into the venous reservoir aided by gentle compression on the abdomen and inflation of the lungs. In most cases the venous cannula is also clamped and removed. Circulatory Arrest Period . At the end of the circulatory arrest period, the heart is filled with saline to exclude any retained air, and attention is paid to displacing air from all systemic chambers. The arterial and venous cannulae are replaced and secured.