Does neck circumference help to predict difficult intubation in obstetric patients? A prospective observational study.

Background: Failed intubation in obstetrics remains the most common cause of death directly related to anesthesia. Neck circumference has been shown to be a predictor for difficult intubation in morbidly obese patients. The aim of this study was to determine an optimal cutoff point of neck circumference for prediction of difficult intubation in obstetric patients.

Methods: Ninety-four parturients scheduled for cesarean section under general anesthesia were included in the study. Preoperative airway assessment and neck circumference were measured. Difficult intubation was the primary outcome according to the intubation difficulty scale (IDS), intubation reported difficult if the IDS score was ≥5.

Results: Univariate analysis showed that Mallampati score and neck circumference were positive predictors for difficult intubation ( P = 0.005 and P = 0.011, respectively). Mouth opening, thyromental distance, sternomental distance, and the hyomental distance ratio were not useful predictors ( P = 0.68, P = 0.87, P = 0.48, and P = 0.27, respectively). Logistic regression for the Mallampati score and neck circumference negative results as independent predictors of difficult intubation in obstetric ( P = 0.53). Sensitivity analysis showed that neck circumference of 33.5 cm is the cutoff point to detect difficult intubation with 100% sensitivity (95% confidence interval [CI]: 69.2-100) and 50% specificity (95% CI: 38.9-61.1). The area under the curve for neck circumference was 0.746 (95% CI: 0.646-0.830) with a positive predictive value of 19.2 (95% CI: 9.6-32.5), a negative predicative value of 100 (95% CI: 91.6-100), and a P < 0.0001.

Conclusions: In obstetric patients, a neck circumference ≥33.5 cm is a sensitive predictor for difficult intubation.