Can the Ratio of Chin-neck Circumference and Neck Circumference to Chin-neck Circumference Predict Difficult Intubation in Obese Patients?

Importance and Purpose of the Study: Proper management of the difficult airway is an important part of preventing anesthesia-related mortality and morbidity. Difficult airways, characterized by both difficult mask ventilation and difficult intubation, are common in obese patients. Many studies have shown an association between obesity or morbid obesity and difficult intubation. We thought that in obese patients, increased subcutaneous fat tissue in the nape of the neck may restrict the head extension and cause difficult intubation and difficult mask ventilation, and the increase in the chin-nape circumference may predict difficult intubation and difficult mask ventilation. We also predicted that the ratio of neck circumference to chin-nape circumference might predict difficult intubation and difficult mask ventilation.

Materials and Methods: After the approval of the ethics committee, obese patients who require tracheal intubation, undergo elective surgery, over the age of 18, with a body mass index (BMI) of more than 30 were evaluated. Patients with cervical spine anomaly, emergency procedures, known history of difficult intubation or upper respiratory tract disease, and planned awake intubation were excluded from the study. Mallampati score, mouth opening, upper lip bite test, distance between incisors, thyromental distance, sternomental distance and thyromental height were recorded. Using a tape measure, the neck circumference from the thyroid cartilage level and the chin-neck circumference from the mentum level were measured with the patient in a neutral position. The ratio of neck circumference to thyromental distance and the ratio of neck circumference to chin-nape circumference were calculated from these measurements. Mask ventilation was graded according to the method described by Han et al. After adequate muscle relaxation was achieved, tracheal intubation was performed with an appropriately sized Macintosh blade using direct laryngoscopy. Difficult intubation evaluation was performed using the Difficult Intubation Scale (IDS) based on seven variables.

Results: A statistically significant relationship was found between difficult intubation and the distance between incisors, neck circumference, neck circumference / thyromental distance, neck circumference / sternomental distance, and chin-nape circumference. In the multivariate regression analysis performed with these parameters, the distance between the incisors was <4.85 cm and the neck circumference> 41.5 cm was found to be independent risk factors for difficult intubation. A statistically significant relationship was found between difficult mask ventilation and age, male gender, OSAS, neck circumference, neck circumference / thyromental distance, neck circumference / sternomental distance, neck circumference / chin-nape circumference and chin-nape circumference. In the multivariate regression analysis performed with these parameters, it was determined that male gender and neck circumference thicker than 45.5 cm were independent risk factors for difficult mask ventilation.

Conclusion: The ratio of neck circumference to chin-nape circumference and chin-nape circumference are successful in predicting difficult mask ventilation in obese patients. While chin-nape circumference is successful in predicting difficult intubation in obese patients, neck circumference / chin-nape circumference is unsuccessful.