Im not sure where you heard the story about the xray tech. If her oxygen saturation was 80% she has something else going on, the mask would not cause that. I have been a respiratory therapist for 30 years. Yes, wearing a N95 will cause headaches because the thing straps so tightly to your face, after a few hours it gets unbearable. But this whole idea of masks causing oxygen desaturation is not ture, same with the idea of it causing a build up of carbon dioxide, not true. For this to happen you need a large volume of mechanical deadspace. When ventilating a patient using a ventilator, you have a inspiratory limb and a expiratory limb of the ventilator circuit. Where the patients endotracheal tube connects to the ventilator circuit is called the Y. The distance between the Y and the endotube is mechanical deadspace. Essentially, an area where exhaled gasses will collect and be delivered back to the patient. When we start adding CO2 and flow sensors at the Y, the deadspace can become gr  6fe5  eater than the volume being delivered to the patient especially if we are talking about premature babies. We try to deliver 6-10cc's of volume per KG of body weight. If the mechanical deadspace is greater than the volume being delivered to the patient, you are not delivering fresh air to the patient, you are only delivering the patients exhaled gases back to them. The space between the mask and your face would be the mechanical deadspace. There is not enough deadspace under the mask to cause a rise in CO2. The rise in CO2 is what would drive down the oxygen concentration being inhaled, there is not enough deadspace to have this effect.