Hi, Salli, what you need to be watching for, especially since he has asthma, is bronchospasm. If the cough seems too extreme to you, you might want to do the hypertonic saline, and then when that is finished, just dump in the GSH solution into the neb and let him continue nebbing the GSH. Everyone has a different tolerance for hypertonicity, and you kinda have to experiment to get the right degree but no more for your son. HTH!