Correlation between modified LEMON score and intubation difficulty in adult trauma patients undergoing emergency surgery

After the approval of the institutional review board (approval number: 2016-11-014), electronic medical records of adult trauma patients who underwent emergency surgery under general anesthesia in an operating theater between March 2016 and August 2016 were reviewed retrospectively. Patients who were already intubated before anesthesia induction or underwent surgical procedures under regional anesthesia were excluded.

All patients’ airways were evaluated by the well-trained residents or attending members of staff of the anesthesia department before anesthesia induction. Patient’s airway assessment was performed according to the LEON method (Fig. 1, left) as follows: (1) Look, look at the patient externally for characteristics that are known to cause difficult laryngoscopy, intubation, or ventilation—in the LEON method, “Look” criteria assesses for presence of four features (facial trauma, large incisors, beard or mustaches, and large tongue); (2) evaluate the 3-3-2 rule—assess the alignment of the pharyngeal, laryngeal, and oral axes; (3) obstruction—presence of any conditions that can cause airway obstruction; and (4) neck mobility—assess for the presence of limited neck mobility or use of a hard neck collar immobilizer. General anesthesia was performed according to the institution’s routine clinical practice. Anesthesia was induced with propofol (1 to 2 mg/kg) and maintained with volatile anesthetics, such as sevoflurane or desflurane. Target-controlled infusions of propofol and remifentanil were used. A neuromuscular blocking agent (NMBA), rocuronium bromide (0.6 mg/kg), was administered to facilitate tracheal intubation. Initially, tracheal intubation was performed by using a direct laryngoscope or video laryngoscope based on the intubating doctor’s choice; however, a lightwand device or fiberoptic bronchoscopy was also used in cases of failed first attempt or difficult intubation. After tracheal intubation, the intubating doctor self-reported in the electronic medical records using the intubation difficulty scale (IDS; Fig. 1, right) as follows: N₁, the number of supplementary intubation attempts; N₂, the number of supplementary operators; N₃, the number of alternative intubation techniques used; N₄, glottic exposure as defined by the Cormack and Lehane grade (grade 1, N₄ = 0; grade 2, N₄ = 1; grade 3, N₄ = 2; grade 4, N₄ = 3); N₅, the lifting force applied during laryngoscopy (N₅ = 1 if a subjectively increased lifting force was required); N₆, external laryngeal pressure to improve glottic exposure (N₆ = 1 if external laryngeal pressure was required); and N₇, position of the vocal cords at intubation (N₇ = 0 if vocal cords in abduction or were not visualized; N₇ = 1 if vocal cords in adduction or blocking the tube passage). The IDS score is the sum of N₁ through N₇. An IDS score between 1 and 5 represents slight difficulty, and IDS score > 5 represents moderate to major difficulty. In the present study, patients were divided into the difficult intubation group (group D) and non-difficult intubation group (group ND) according to whether their IDS score was > 5 or ≤ 5.

All analyses were performed using MedCalc® 16.2 (MedCalc Software, Ostend, Belgium). Continuous variables were compared using the Student’s t test or Mann-Whitney U test. Categorical variables were analyzed using a chi-square test, and the Cochran-Armitage test was used for trend analysis. Correlation between the LEON score and IDS was calculated using the Spearman’s rank correlation. To determine the relationship between one dependent factor and one or more independent factors, a logistic regression analysis was performed. Data are expressed as means ± standard deviations, medians [interquartile ranges], or number (%). P < 0.05 was considered to be statistically significant.