Foreign body. Atelectasis is common in children who have inhaled an object, such as a peanut or small toy part, into their lungs. Narrowing of major airways from disease. Chronic infections, including fungal infections, tuberculosis and other diseases, can scar and constrict major airways. Tumor in a major airway.
He'll be placed on blood thinners to break up the clots...which can take from days to weeks. This is also a very dangerous time for him, as a clot could travel and lodge in a coronary artery on his heart, causing a heart attack, or it could travel and lodge in an artery in his brain causing a stroke.
If someone could answer how long it takes for the blood to replace, that would be great as I do not know the answer to that question myself. I do, however, know that blood does regenerate. The fluid component of the blood (plasma) is replaced in approximately 24 hours provided you remember to drink enough water. The red blood cells are replaced in a few weeks - one study performed recorded an average of 36 days, with a range from 20 to 56 days in the volunteers.