The Use of High Flow Nasal Cannula, Standard Face Mask and Standard Nasal Cannula in Morbidly Obese Patients

Overview

It is standard practice in the United States and many parts of world to perform Gastrointestinal endoscopy with the patient under deep intravenous sedation. Obesity is accepted as a patient specific risk factor for hypoxic events during procedural sedation for GI endoscopic procedures. The obese population has a higher prevalence of obstructive sleep apnea (OSA), which is characterized by repeated obstruction of the upper airway, and leads to apnea and desaturation. This prospective, randomized study was designed to compare the effectiveness of the high flow nasal cannula, standard nasal cannula and standard face mask in morbidly obese patients with a high risk of sleep apnea, (BMI greater than 40, STOPBANG greater or equal to 5) receiving deep intravenous sedation during colonoscopies. This study will assess which method leads to a lower incidence of intraoperative desaturation events compared to the current standard of care.

The prevalence of morbid obesity is increasing worldwide. As the severity of obesity increases, the incidence of diagnosed obstructive sleep apnea also rises. Studies have shown an incidence of sleep apnea as high as 64% in patients with a body mass index (BMI) over 40 and 100% in patients with a BMI greater than 60. Patients with OSA have been shown to have significant desaturations under intravenous sedation due to airway narrowing and obstruction. Several studies have also shown that morbidly obese subjects, independent of a diagnosis of OSA, run a higher perioperative risk of adverse airway events, including hypoxia. Providing anesthesia for this patient population is challenging and requires careful titration of drugs and superb airway management skills. The current standard of care for oxygen delivery in this setting is a Salter nasal cannula. Humidified high flow nasal cannula (HFNC) oxygen therapy utilizes an air oxygen blend allowing from 21% to 100% FiO2 delivery and generates up to 60 L/min flow rates. The gas is heated (35 to 40 degree Celsius) and humidified through an active heated humidifier and delivered via a single limb heated inspiratory circuit (to avoid heat loss and condensation) to the subject through a large diameter nasal cannula. Theoretically, HFNC offers significant advantages in oxygenation and ventilation over conventional methods. Constant high flow oxygen delivery provides steady inspired oxygen fraction (FiO2) and decreases oxygen dilution. It also washes out physiologic dead space and generates positive end expiration pressure (PEEP) that augments ventilation. Some studies have demonstrated a positive effect of HFNC on the apnea-hypopnea index (AHI) showing that use of HFNC could decrease hypoxic episodes in subjects with repetitive upper airway obstruction such as obstructive sleep apnea. The STOP-BANG questionnaire (SB) has been used successfully to screen patients undergoing therapeutic endoscopic procedures at higher risk for sedation-related adverse events.