Ultrasound for predicting difficult airway in obstetric anesthesia Protocol and methods for a prospective observational clinical study

Background: Failed intubation and ventilation during cesarean deliveries are important causes of anesthetic-related maternal mortality. Due to the physiological changes in airway anatomy, parturient had higher incidences of difficult airway than non-obstetric population. Accurate airway assessment is the first step and the most important in airway management. However, the common clinical screening tests, shown low sensitivity and specificity with a limited predictive value. Ultrasound is a quick, noninvasive, inexpensive tool, with the advancement of ultrasound technology, modern ultrasound machine is more portable with better resolution and enhanced tissue penetration, provide better imaging in tissues like epiglottis, vocal cords, ring-shaped membrane, and can be used in airway assessment. Here, the aim of the current study was to find whether preoperative ultrasound assessment of neck anatomy can predict difficult airway in parturient, and provide new ideas and a theoretical basis in the airway management of obstetric anesthesia. Methods: This is a prospective, observational single-blinded study in a single-center. Subjects will be recruited from patients aged from 18 to 60 years, gestational age >= 36 weeks, scheduled for cesarean section under general anesthesia and tracheal intubation. Ultrasound measurement will be performed to detect anterior cervical soft tissue thickness at five anatomical levels (hyoid bone, epiglottis, cricothyroid membrane, thyroid isthmus and suprasternal notch) in the upper airway. The thickness of the soft tissue in the front of the neck and clinical airway measurements will be compared between the "easy intubation" and "difficult intubation" group divided by Cormack-Lehane grade. Receiver-operating characteristic curves were used to determine the sensitivity and specificity of "difficulty prediction capability" of each sonographic and physical measurements. Clinical factors associated with difficult intubation will be determined by univariate analyses. Multiple logistic regression analysis performed to determine independent predictors of difficult intubation. Conclusions: The study outlined in this protocol will explore the possibility of ultrasound for predicting difficult airway in obstetric anesthesia. This may provide new insight into the practice of airway management.