Background and Goal of Study	
Intubation difficulty is an important issue in daily clinical practice for anesthesiologists.1 Intubation difficulty scale (IDS) was introduced in 1997 to capture 7 major factors comprehensively,2 but there has been no estimation on relative impacts of time for each one of them. Otherwise, predict power of IDS has been questioned on video tracheal intubation system.3 This study aims to quantify the time required to tackle every factor. 
Materials and Methods
After approval from the IRB (institutional review board), we collected written informed consent from each patient (CYCH IRB: 097028). Preoperatively, a complete medical history related to tracheal intubation (TI) was obtained from every adult patient that would receive an operation and TI under direct laryngoscopy with a #3 Macintosh blade. After induction, the anesthetists recorded the direct view score according to the 7 IDS factors.. With a stop watch, a research assistant independently recorded the duration of each attempt until a successful intubation. We construct multiple linear regression and mixed effects models to determine the relative time impact of each factor.
Results
A total of 1095 patients were collected. The IDS score ranged from 0 to 10. There were 37.1% and 1.8% of them with IDS=0 and >5, respectively, which were lower than those reported by Adnet,2 or, 5.3%. (Figure 1) The mean duration of intubation was 23.9±21.8 seconds. The final linear regression equation was as follows: Duration of intubation time in seconds = 15.2 + 31.1 (no. additional attempts) + 26.2 (no. additional operators) + 11.4 (no. alternative techniques) + 7.9 (intubation with increased lift force) + 4.9 (intubation with external laryngeal pressure) + 3.5 (Cormack grade - 1). (Table 1) After adjustment for repeated intubations by the same anesthesiologists with mixed effects model, we found the regression coefficients were largely the same, indicating the robustness of this model. 
Conclusion
All factors included in the IDS contribute to the time required for intubation except vocal cord adduction. After more corroboration in different settings, the equation would be useful to predict the required time as a feedback on training sessions of tracheal intubation.


01 / Intubation difficulty scale and time in clinical practice