If we add nasal cannula to nonrebreather face mask or BVM with air leak, we will improve pre-oxygenation phase. This study that just published in Annals of EM enrolled 6o Healthy volunteers ,30 nonrebreather face mask and 30 bag-valve-mask. There will be an argument that Healthy lungs will be different from patients with restrictive or or obstructive lung diseases! But this support our routine practice using Nasal cannual with NRB or BVM.