High-Flow Nasal Cannula and Desaturation Episodes in the Morbidly Obese Patients

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.

Many morbidly obese subjects present to our institution for GI procedures under deep sedation. 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. There are no prospective, randomized studies that compare the use of a high flow humidified nasal cannula system and standard nasal cannula in morbidly obese patients presenting for colonoscopy under anesthesia.

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 (9). 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. In the current narrative review, Sotello et al. summarized factors explained the improvement in respiratory parameters by using HFNC. (1) Washout of the nasopharyngeal dead space; (2) Reduction in inspiratory resistance associated with gas flow through the nasopharynx; (3) Improvement in respiratory mechanical parameters associated with gas temperature and state of humidification; (4) Reduction in metabolic work associated with gas conditioning; (5) Provision of mild distending pressure.

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.

We are hypothesizing that the HFNC will help maintain a patent airway and improve gaseous exchange in the morbidly obese patients undergoing deep sedation for colonoscopies and will result in a significant decrease in intraoperative desaturation events, thus improving morbidity and overall safety for this subgroup.