Sternomental distance as the sole predictor of difficult laryngoscopy in obstetric anaesthesia

Sternomental distance and view at laryngoscopy were documented in 523 parturients undergoing elective or emergency Caesarean section under general anaesthesia. Eighteen (3.5%) had a grade III or IV laryngoscopic view (Cormack and Lehane's classification) and were classified as potentially difficult tracheal intubations. There was a significant difference between sternomental distance in those patients with a grade III or IV laryngoscopic view compared with those with a grade I or II (13.17 (SD 1.54) cm vs 14.3 (1.49) cm; P = 0.0013). A sternomental distance of 13.5 cm or less with the head fully extended on the neck and the mouth closed provided, using discriminant analysis, the best cut-off point for predicting subsequent difficult laryngoscopy. A sternomental distance of 13.5 cm or less had a sensitivity, specificity, positive and negative predictive values of 66.7%, 71.1%, 7.6% and 98.4%, respectively. While there was no association between sternomental distance and age, weight, height or body mass index (BMI), there was a significant association between grade of laryngoscopy (III and IV) and older (P = 0.049) and heavier (P = 0.0495) mothers. The results suggest that while sternomental distance on its own may not be an adequate sole predictor of subsequent difficult laryngoscopy the measurement should be incorporated into a series of quick and simple preoperative tests.