Introduction: We aim to compare the upper lip bite test with the modified Mallampati test as predictors of difficult laryngoscopy and/or difficult intubation among morbidly obese patients.
Methods: A total of 500 morbidly obese patients (body mass index > 40 kg/m2) undergoing general anaesthesia with tracheal intubation are included in this prospective single-blinded observational clinical study. The preoperative airway assessment is obtained by the modified Mallampati test and upper lip bite test. The difficulty of laryngoscopy is assessed by an experienced anaesthetist in patients adequately anaesthetised and fully relaxed. The view is classified according to Cormack and Lehane's classification. Modified Mallampati test III or IV and upper lip bite test III are considered positive tests. Difficult laryngoscopy is defined as Cormack and Lehane's classification III and IV, whereas difficult endotracheal intubation is defined as an intubation difficulty scale ⩾ 5.
Results: The incidences of Cormack and Lehane's classification III and IV and intubation difficulty scale ⩾ 5 are 9.4% and 11.8% respectively. The specificity, positive predictive value and accuracy are higher with the upper lip bite test. The combination of the upper lip bite test and the modified Mallampati test improved these measures. The likelihood ratio + was significantly higher for the upper lip bite test (6.35 and 9.47) than for the modified Mallampati test (3.21 and 3.16).
Conclusion: The upper lip bite test is a test with high sensitivity, specificity, negative predictive value and accuracy making it a favourable test for identifying easy and difficult intubations and laryngoscopies in morbidly obese patients.
Keywords: Difficult intubation; Difficult laryngoscopy; Modified Mallampati classification; Morbidly obese patients; Upper lip bite test.