The performance of neck circumference and other airway assessment tests for the prediction of difficult intubation in obese parturients undergoing cesarean delivery

Abstract

Background: Pregnancy and obesity each increase the chance of difficult tracheal intubation. This study assessed the performance of the neck circumference and other bedside tests in predicting difficult intubation, and aimed to identify the optimal cutoff point of the test(s) with the highest performance.

Methods: Parturients with a body mass index ≥30kg/m², undergoing a cesarean delivery employing conventional tracheal intubation, were enrolled. Preoperative neck circumference, sternomental distance and modified Mallampati test were examined. Difficult intubation was defined as intubation difficulty scale score ≥5.

Results: Five hundred and seventy parturients of mean body mass index 34.1 (±SD 3.8) kg/m² were recruited. The incidence of difficult intubation was 3.5%. The performance of the neck circumference test, conducted with the patient sitting or supine, and using the area under the receiver operating characteristic (ROC) curves, was 0.6 (95% CI 0.5 to 0.7) and 0.6 (95% CI 0.4 to 0.7) respectively. The area under the ROC for the modified Mallampati test was 0.6 (95% CI 0.5 to 0.7) and for the sternomental distance test was 0.7 (95% CI 0.6 to 0.8). A sternomental distance less than 14.5cm, and a ratio of neck circumference in the sitting position to sternomental distance of greater than or equal to 2.7, were optimal cutoff points to identify difficult intubation.

Conclusion: The neck circumference, the sternomental distance, the modified Mallampati test and the ratio of neck circumference to the sternomental distance show limited performance as screening tests to predict difficult intubation among obese parturients.

Keywords: Clinical prediction; Difficult intubation; Obese parturients.