Upper lip bite test for prediction of difficult airway: A systematic review

Upper lip bite test (ULBT) is one of the various bedside tests used for prediction of difficult laryngoscopic intubation. However, its usefulness is not still very clear, and there is controversy regarding its accuracy. The aim of this systematic review was to determine the accuracy of the ULBT for predicting difficult airway including difficult laryngoscopy or difficult tracheal intubation.

We searched the databases of PubMed, Scopus, and Google scholar for prospective studies published up until October 2016 assessing the accuracy of ULBT in comparison to Cormack-Lehane grading. The selected keywords were "upper lip bite test", "upper lip catch test", "prediction", "difficult airway", "difficult laryngoscopy", "difficult intubation". Inclusion criteria were studies assessing ULBT for prediction of difficult intubation, considering Cormack-Lehane grade III and IV as difficult airway, written in English, and reporting sensitivity, specificity, NPV, PPV, and accuracy. Exclusion criteria were studies not reporting accuracy or not having enough data for its calculation. Based on the mentioned criteria, 27 studies enrolling 18141 patients were included. This systematic review was performed based on the guidelines on conducting systematic reviews of diagnostic studies.

Prevalence of airway difficulties according to the direct laryngoscopic view varied from 2.8% to 27% and according to the ULBT was from 2% to 21%. In 11 of the 27 studies, sensitivity of ULBT in prediction of difficult airway was more than 70%. All of the studies except one showed a high specificity for ULBT (>85%). Moreover, these studies indicated a high NPV. Accuracy of ULBT was >85% in 24 out of 27 studies.

It appears that ULBT is a useful bedside test for evaluation of patient airway before the general anesthesia.