Here is detailed information I received from the March of Dimes today that better explains Sawyer's congenital heart defect and why it was too much on his little body.
Truncus arteriosis is a congenital heart defect (CHD) that includes a large septal defect under a single great artery. It happens when the two large arteries that normally transport blood away from the heart (oxygen-poor blood to the lungs, oxygen-rich blood to the rest of the body) don’t develop as they should. Instead, only one large artery exists. This single artery (the truncus) carries blood both to the lungs and to the body. It is positioned over a large hole,called a ventricular septal defect, between the lower chambers of the heart. This defect can cause the blood to circulate improperly, combining oxygen-poor blood with oxygen-rich blood. This causes the heart to work extraordinarily hard to carry oxygen throughout the body. The lungs become overtaxed from all the extra blood flowing through them resulting in pulmonary hypertension. Sadly, this overburdened system is too much for babies, especially a preemature baby, to handle.