Preoxygenation With a High-flow Nasal Cannula or a Simple Mask Before General Anesthesia in Head and Neck Surgery

Rationale & background information:

Pre-oxygenation before general anesthesia is usually achieved using oxygen delivered via a facemask before induction of anesthesia; this potentially extends the time available for securing the airway before hypoxemia to 6 min. The lungs are commonly ventilated with a bag/facemask technique after induction, and this can be repeated if attempts at intubating the trachea are prolonged. However, facemask ventilation has traditionally been avoided in the circumstance which has the risk of gastric insufflation of gas, leading to increased intragastric pressure and raised risk of pulmonary aspiration of stomach contents. In addition, if difficult ventilation is anticipated, facemask ventilation may not be possible at all, and 6 minutes with hypoxemia may be insufficient for intubation.

An ideal preoxygenation to extend apnea tolerance during anesthesia induction is essential to avoid live threatening airway incidents. The high-flow nasal cannula, the OptiFlow System (Thrive, Fisher & Paykel®, Aukland New Zealand), has the ability to deliver warmed and humidified oxygen through specially designed nasal cannula and enable oxygen to be comfortably delivered at rates of > 70 liter/min. Several study showed that nasal delivery of humidified oxygen to paralyzed and anesthetized patients at these rates maintains oxygenation and achieves acceptable carbon dioxide concentration. The investigators hypothesized that an extended apneic period without facemask ventilation could be particularly beneficial to patients undergoing general anaesthesia.

Study goals and objectives:

To assess arterial oxygen partial pressure (PaO2) at defined time points during the preoxygenation and to compare between high flow heated humidified nasal oxygen versus standard preoxygenation with oxygen insufflation via face mask over at least 5 minutes