Safety Study of Positive Airway Pressure Via a Nasal Mask in Obese Patients

Upper airway obstruction (UAO) is an unpredictable and frequently occurring complication during induction of general anesthesia. Since obese patients ( BMI\>30 km/ m2) are more vulnerable to develop airway obstruction either during sleep or under anesthesia, and the segment of obese individuals in the entire population keep growing, difficult airway management under anesthesia becomes even more challenging than ever. The most serious event related to difficult airway management under anesthesia is "cannot intubate, cannot ventilate". Unfortunately, even with modern technologic advances, 16% of death and permanent brain damage related to anesthesia have been attributed to failure of difficult airway management 3. The American Society of Anesthesiologist (ASA) closed claim analysis of anesthesia complications indicate that a difficult airway is one of the most challenging scenarios continuously facing anesthesia providers. Indeed, it can be a fatal complication of general anesthesia. Therefore, measures used to reduce the incidence of difficult airways during anesthesia remain to be improved. The mechanism of UAO during anesthesia has not been well understood. Posterior displacement of soft palate, tongue and epiglottis are believed to be the primary contributing factors. Obesity is well known to be an essential characteristic which reflects propensity to UAO. Accordingly, obese patients are a high-risk group for perioperative airway catastrophe and prone to develop progressively narrower pharyngeal airways due to an increase of soft tissue volume surrounding the pharyngeal airway. More and more evidence indicates that the mechanism of UAO during anesthesia shares many similarities with the upper airway obstruction observed during obstructive sleep apnea (OSA). Nasal continuous positive airway pressure (nCPAP) via nasal mask (NM) can maintain the airway patent with near 100% success in patients with OSA, if they can tolerate it. Under anesthesia, tolerance should not be an issue as the patient is anesthetized. Obesity is a major risk factors for obstructive sleep apnea and obese patients have a higher prevalence of UAO during anesthesia. Therefore, the investigators hypotheses that nCPAP should eliminate airway obstruction in obese patients under anesthesia. The investigators propose to test this hypothesis and determine the efficacy of nCPAP on maintaining airway patency in obese patients who require general anesthesia.