Anesthetic induction agents cause a number of physiological changes within the respiratory system. Almost every induction agent causes apnoea. There is a reduction of FRC and an increase in airway resistance. Combined with preoxygenation with a high fraction of oxygen there is a significant risk of pulmonary atelectasis. Adding a continuous positive pressure during ventilation of the apnoeic patient improves many of the respiratory effects caused by induction agents. However the added continuous pressure will increase the total inspiratory pressure and a high inspiratory pressure is associated with an increased risk of gastric insufflation during mask ventilation. On the other hand there are data suggesting that continuous positive pressure is beneficial in treatment of GERD-symptoms.