Incidence and Predictors of a Difficult Airway in Lean vs. Obese Surgical Patients: A Large Prospective Cohort Study

BACKGROUND: With the high incidence of obesity rates, the determination of whether obese individuals are more difficult to intubate is of the utmost importance. This study aimed to determine the incidence of difficult intubation in obese vs lean patients in the general surgery population at a large tertiary, teaching hospital and assess obesity as a risk factor for difficult intubation. In addition, this study examined additional patient characteristics and anthropometric factors as independent predictors of difficult intubation. I hypothesize that obesity will not be a significant risk factor for difficult intubation. Instead factors such as age, higher Mallampati score, and male sex will be better predictors of difficult intubation. METHODS: This prospective cohort observational study enrolled 4,003 patients undergoing general endotracheal anesthesia. Emergent cases, patients with a known or suspected difficult airway, and patients not expected to initially undergo direct laryngoscopy were excluded. Patients were stratified into two cohorts based on body mass index (BMI): a non-obese group (BMI <30 kg m-2) and an obese group (BMI ≥30 kg m-2). Intubation difficulty was determined using the Intubation Difficulty Scale (IDS). RESULTS: The incidence of severely difficult intubation (IDS ≥ 5) was 5.9% in the obese cohort compared to 4.6% in the non-obese cohort which was not significant (p= 0.061). Controlling for other factors, obese patients were more likely to be difficult to intubate (odds ratio (OR), 1.438; 95% confidence interval (95% CI), [1.064, 1.943], p=0.001). In the analysis of additional patient characteristics and anthropometric values, age > 45 years (OR, 1.586; 95% CI, [1.064, 1.943], p<0.001), male sex (OR, 2.034; 95% CI, [1.532, 2.702], p<0.001), Mallampati score of 3-4 (OR, 2.441; 95% CI, [1.820, 3.273], p<0.001), neck circumference (OR, 1.096 per cm increase; 95% CI, [1.066, 1.128], p<0.001), thyromental distance (OR, 0.757 per cm increase; 95% CI, [0.691,0.830], p<0.001) and sternomental distance (OR, 0.923 per cm increase; 95% CI, [0.770, 0.874], p<0.001) were also significant. However, inter-incisor distance and waist circumference were not. CONCLUSIONS: Obese patients are more likely to be difficult to intubate. However, male sex, age > 45 years, and a high Mallampati score are stronger predictors of difficult intubation compared to BMI. Therefore, while BMI still provides relevant information, BMI alone should not be used as a sole predictor of difficult intubation.