The Difficult Airway: Incidence and Predictors in Lean vs. Obese Patients

BACKGROUND: As the incidence of morbid obesity continues to rise, anesthesiologists are increasingly concerned with the possible association between morbid obesity and difficult intubation. Current literature exploring the association between the morbidly obese and difficult intubation is contradictory1-6. Moreover, "difficult intubation" lacks standardization with studies variably utilizing the Intubation Difficulty Scale2,3,5,7, the Cormack-Lehane grade8,9, or institutional or investigator preference1,4,6. Overall, results remain uncertain despite best attempts to aggregate past data10. METHODS: A cohort of 127 morbidly obese individuals (BMI≥40) and 739 non-morbidly obese individuals (BMI<40) consented to participate in the study. Individuals were preoperatively assessed for obstructive sleep apnea (OSA), neck range of motion (ROM), neck circumference (NC), thyromental distance (TM), sternomental distance (SM), interincisor distance (IID), upper lip bite test (ULBT), and Mallampati score. Following intubation, the laryngoscopist was asked to assess difficulty using the validated Intubation Difficulty Scale (IDS) (Adnet 1997). Difficult endotracheal intubation, difficult laryngoscopy, and difficult mask ventilation were defined as an IDS score ≥6, a Cormack-Lehane grade of 3 or 4, and by designation of the provider, respectively. RESULTS: The incidence of difficult endotracheal intubation, difficult laryngoscopy and difficult mask ventilation was determined to be 4.7%, 9.5% and 6.3% in the morbidly obese cohort as compared to 4.7%, 6.8% and, 2.4% in the non-morbidly obese cohort. BMI is not associated with difficult intubation (p-value=0.995); however, gender (p-value=0.037), OSA (p-value=0.006), NC (p-value=0.012), IID (p-value=0.034), ULBT (p-value=0.020), and Mallampati (p-value=0.006) are. BMI is also not associated with difficult laryngoscopy (p-value=0.279); however, gender (p-value=0.048), OSA (p-value=0.011), neck ROM (p-value=0.028), NC (p-value=0.002), TM (p-value=0.017), SM (p-value=0.001), ULBT (p-value=0.036) and Mallampati (p-value=0.014) are. BMI is associated with difficult mask ventilation (p-value=<0.001). CONCLUSIONS: BMI is not associated with difficult intubation or laryngoscopy, only difficult mask ventilation. Thus, a high BMI by itself does not predict difficult intubation. Other factors such as gender, Mallampati classification, and presence of OSA may be more suitable in predicting intubation difficulty.