Well to de-code the medical jargon....acute desaturation....sudden onset of low levels of oxygen in his blood.....which would be the result of the causative factor....blood in his lungs. Reintubation would have been necessary to provide oxygen. Bilateral infiltrate....having pneumonia in both lungs....as the lungs heal from this type of thing, the little sacs at the end of the breathing tubes or alveoli, and in fact the smallest breathing tubes leading to the alveoli, re-expand or re-inflate....yes, this can cause pain, usually referred to pleuritic pain. Best advice I can give you, is to take him back to the doctor, explain his symptoms and make sure that everything is ok.