Predictive performance of a multivariable difficult intubation model for obese patients

Abstract

Background: A predictive model of scores of difficult intubation (DI) may help physicians screen for airway difficulty to reduce morbidity and mortality in obese patients. The present study aimed to set up and evaluate the predictive performance of a newly developed, practical, multivariate DI model for obese patients.

Methods: A prospective multi-center study was undertaken on adults with a body mass index (BMI) of 30 kg/m2 or more who were undergoing conventional endotracheal intubation. The BMI and 10 preoperative airway tests (namely, malformation of the teeth in the upper jaw, the modified Mallampati test [MMT], the upper lip bite test, neck mobility testing, the neck circumference [NC], the length of the neck, the interincisor gap, the hyomental distance, the thyromental distance [TM] and the sternomental distance) were examined. A DI was defined as one with an intubation difficulty scale (IDS) score ≥ 5.

Results: The 1,015 patients recruited for the study had a mean BMI of 34.2 (standard deviation: 4.3 kg/m2). The proportions for easy intubation, slight DI and DI were 81%, 15.8% and 3.2%, respectively. Drawing on the results of a multivariate analysis, clinically meaningful variables related to obesity (namely, BMI, MMT, and the ratio of NC to TM) were used to build a predictive model for DI. Nevertheless, the best model only had a fair predictive performance. The area under the receiver operating characteristic curve (AUC) was 0.71 (95% confidence interval 0.68-0.84).

Conclusions: The predictive performance of the selected model showed limited benefit for preoperative screening to predict DI among obese patients.

Fig 1. Seven components of the intubation difficulty scale (IDS).

N1 represents the number of intubation attempts; N2 the number of operators; N3 the number of alternative techniques; N4 the Cormack and Lehane laryngoscopic views; N5 the lifting force applied during laryngoscopy (score 0 if considerable; score 1 if considerable); N6 the necessity to apply external laryngeal pressure to optimize glottic exposure (score 0 if no external pressure or if only the Sellick maneuver was applied; and N7 the visibility of the laryngeal aperture (score 0 if abducted vocal cord; score 1 if adducted vocal cord or invisible).

Fig 2. The receiver operating characteristic (ROC) curve of the predictive model of difficult intubation among obese patients.

Fig 3. A comparison of the area under the receiver operating characteristic curve (AUC) of the three equations.