Final answer:
The cardinal sign of aortic dissection is severe chest or back pain, which is not obvious while a patient is on bypass due to anesthesia and lack of heart function.
Step-by-step explanation:
It is described as tearing or ripping and can radiate to the neck or down the back. During aortic dissection, blood enters the media layer of the aortic wall through an intimal tear, creating a false lumen and separating the layers of the aorta. This can lead to reduced blood flow to organs, rupture, or other severe complications.
While a patient is on cardiopulmonary bypass during surgery, the cardinal signs of aortic dissection are not obvious because the heart is not beating and blood is being circulated through the bypass machine. As such, pain, which is a significant clinical indicator, is not experienced by the patient under anesthesia. The diagnosis of aortic dissection in this scenario is usually dependent on imaging studies undertaken prior to surgery.