What is being discussed here is ventilating a patient, and this is the most important skill to learn in your medical anesthesia rotation. At the outset of every case in the OR in which there is endotracheal intubation, the patient is first anesthetized to the point of apnea, and then the anesthesia team checks to ensure supported ventilation is possible, before the patient is paralyzed for the intubation.
Most intravenous medications used in anesthesia for oral surgery can suppress respiration and cause apnea, so it is imperative that the operator/anesthetist be able to support the patient’s respiration instantaneously via a bag/mask system.
Personally, I am not comfortable with the term “bagging the patient”, because you can have the mask on the face and be squeezing the bag, but you may not be ventilating the patient. This lack of ventilation, or lack of respiratory exchange, can be due to the things listed by SuxDrugs&Roc…large tongue, beard, high BMI, edentulous, and laryngospam. It is important to have lots of experience in mask ventilation.