An intubation difficulty scale (IDS) is the most commonly used tool to pronounce difficult intubation among obese patients in research area. There have not been any studies on assessing the use of IDS. The objectives were to determine the performance of the IDS among obese patients to define difficult tracheal intubation (DI) according to the subjective assessment of the difficulty experienced and to identify their optimal cutoff points.

Cross-sectional study.

Tertiary care hospital.

Adult obese Thai patients who underwent conventional endotracheal intubation.

Data of subjective assessment of the difficulty experienced by category—easy, somewhat difficult, and difficult—were collected from experienced anesthetic personnel who performed endotracheal intubation. IDS scores were collected by research assistants.

There were 552 obese patients recruited. The incidence of somewhat DI was 14.3% and that of DI was 2.2%. The overall performance of the IDS using area under the receiver operating characteristic curves of somewhat DI is 0.99 with 95% confidence interval (CI) of 0.98 and 0.99 and that of DI is 1 (95% confidence interval, 1-1). For somewhat DI, the optimal cutoff point is 2; it provides sensitivity and specificity of 100% and 92%. The IDS scores of 5 indicate DI which had sensitivity and specificity of 100% and 100%.

The IDS remains a good tool to declare DI among obese patients. It is recommended that a score of 2 or higher is an optimal cutoff point to indicate somewhat DI and a score of 5 or higher is an optimal cutoff point to indicate DI.