Correlation Between Pre-Operative Airway Assessment Tests, Anthropometric Measurements And The Video-Laryngoscopic Modified Cormack-Lehane Visualization and Their Predictive Values for Difficult Intubation in Obesity Class-III Patients

Study Design This prospective observational clinical study was conducted in patients with a BMI ≥ 45 kg/m2 undergoing elective bariatric surgery between January 2018 and January 2019, in the Anesthesiology and Reanimation Clinic of the Health Sciences University, Bagcilar Training and Research Center, after obtaining approval from the Ethics Board of Health Sciences University Istanbul Bagcilar Training and Research Hospital (17.08.2017-2017/599).

Patient population The number of participants in this study was calculated based upon a previous study. A sample size calculator showed that 116 participants would be required to predict difficult intubation in obese patients (with 80% power, α=0,05 and, β=0,2). After obtaining the patients written informed consent, as a result of the power analysis, one hundred and twenty-one patients, aged 16-68 years, with a BMI ≥ 45 kg/m2, who were undergoing elective bariatric surgery were included in this study. Patients with a history of difficult airway, limited neck movements, oral-pharyngeal cancer or reconstructive surgery, cervical spinal injury and facial anomaly or scar, patients who required quick and awake endotracheal intubation, and patients who were not oriented-cooperative, were excluded from the study.

Study Protocol Age, sex, height, body weight, BMI, airway assessments and anthropometric measurements, including the MMS, thyromental distance TMD), sternomental distance (SMD), interincisor distance (IID), and neck, waist and chest circumference measurements of all patients were evaluated and recorded preoperatively. The MMS was assessed by Samsoon and Young Modifications and scores were assessed 1 to 4. The TMD and SMD were measured with the neck fully extended. The TMD was measured between the upper border of the thyroid cartilage and the bony point of the mentum, and the SMD was measured between the upper border of the manubrium sterni and the bony point of the mentum. The IID was measured when the patient opened their mouth, and the distance between upper and lower incisors was obtained. Neck circumference was measured at the level of the thyroid cartilage when the head was in a neutral position. The chest and waist circumference was measured around the widest circumference.

After patients were admitted to the operating room, all patients were positioned with the gel placed under their head. The intravenous route was inserted in the dorsum of the hand using a 20 G (Gauge) venous cannula, and a 2-4 mL/kg balanced crystalloid was infused. All patients were premedicated with 1-2mg midazolam (Zolamid 15mg/3ml, Defarma, Turkey). Each patient was routinely monitored with the standard monitorization, including three-lead electrocardiography (ECG), non-invasive arterial pressure, peripheral oxygen saturation (SpO2), and neuromuscular monitorization with the TOF-Watch SX (Organon, Ireland) device. All patients were pre-oxygenated using a face mask, with 100% oxygen for 3 to 5 minutes prior to induction of the anesthesia. Induction is made with 2 mg/kg propofol (Propofol 1%, Fresenius kabi, Germany) and 1 µgr/kg fentanyl (Talinat, VEM, Turkey) based on a lean body weight, and 0.6 mg /kg rocuronium bromide (Esmeron Organon, Holland) based on an ideal body weight. Following the adequate paralysis (loss of responsiveness to train of four stimulations with TOF), all patients were routinely intubated using C-MAC D-blade VL (Storz 8402 ZX C- MAC Karl Storz, Germany). Anesthesia was maintained with inhalation of 50% oxygen-medical air mixture and 2% minimum alveolar concentration (MAC) of sevoflurane (Sevoflurane, Abbott, England).

The time of the tracheal intubation was defined from insertion of the VL in the mouth until the endotracheal tube was placed through the vocal cords and expired carbon dioxide at capnography was observed. In the case of a peripheral oxygen saturation decrease (< 90%), performing of intubation was interrupted, and mask ventilation was resumed.