Assessment of Different Indices as Predictors of Difficult Airway in Obese Patients

Introduction Difficulties with tracheal intubation contribute to the morbidity and mortality associated with anesthesia. Suggested predictors for difficult airway include, history of obstructive sleep apnea, high Mallampati score, elderly, male, short neck, and high Wilson score. However, none of these has high diagnostic accuracy particularly in obese population. Parameters used to quantify obesity such as Body Mass Index(BMI), mid arm circumference, skin fold thickness, etc. have not been used as independent predictors of difficult airway. This study has been designed to evaluate the accuracy of commonly used tools to assess difficult airway and to test other obesity markers as scale for assessing difficult airway i.e. Bag mask ventilation grade ≥3 or Cormack-Lehane Grade≥3 on Direct Laryngoscopy or number of intubation attempts ≥3. Aim To assess BMI, Mallampati grading, Neck circumference and Thyromental distance as predictors of difficult airway in obese patients and to validate neck circumference to thyromental distance ratio and skin fold thickness as a tool for assessment of difficult airway (Bag mask ventilation grade ≥3 or Cormack-Lehane Grade≥3 on Direct Laryngoscopy or number of intubation attempts ≥3.) in obese patients. Methods This prospective observational study was carried out on 51 obese patients (as per BMI) of ASA grade II, either sex, aged 23 to 57 years posted for elective surgery under general anesthesia with endotracheal intubation. After subjective assessment of difficult airway following data sets and variables were obtained - sex, weight, height, body mass index (BMI), Modified Mallampati class (MPG), Cormack-Lehane (CL) grade, adequacy of bag mask ventilation (BMV), number of endotracheal intubation attempts, patient's neck circumference (NC), thyromental distance (TMD), waist-hip ratio (WHR) and Skin fold thickness. The observations made during the study were statistically analyzed and correlated as predictors for difficult airway. Result Correlation of MPG to CL-grade (r-0.41, p-0.003), BMV (r-0.31, p-0.028) & No. of intubation attempts (r-0.37, p-0.007) was mild & statistically significant. Correlation of Neck Circumference with CL-grade (r-0.57, p-0.000), & No. of intubation attempts (r-0.62, p-0.000), found moderate & statistically significant, & with BMV was mild and statistically significant (r-0.48, p-0.000). Correlation of Thyromental Distance to CL-grade (r-0.65, p-0.000), BMV (r-0.70, p-0.000) & No. of intubation attempts (r-0.61, p-0.000) was moderate & statistically significant. Correlation of BMI to CL-grade (r-0.11, p-0.428), BMV (r-0.04, p-0.757) & No. of intubation attempts (r-0.16, p-0.257) was weak & not significant. Skin Fold Thickness showed no significant association with Difficult airway i.e., CL Grade (p-0.478), BMV (p-0.101), and No. of intubation attempts (p-0.143). Correlation of NC/TMD ratio with BMV (r-0.74, p-0.000), CL-grade (r-0.76, p-0.000), & No. of intubation attempts (r-0.77, p-0.000) was moderate & statistically significant. Conclusion NC, TMD and NC/TMD Ratio depicted a close association with airway difficulty in obese patients. Obesity grade is a risk factor for difficult airway but predictors of obesity including Skin Fold Thickness, individually did not show association with difficult airway (small sample size may be a limiting factor). None of the commonly performed tests alone has proven to be adequate in predicting difficult intubation in the obese population.