Determination of the appropriate sizes of oropharyngeal airways in adults: correlation with external facial measurements: A randomised crossover study

BACKGROUND: Two external facial measurements have been recommended as reference criteria for estimating appropriate oropharyngeal airway sizes: the distances between the maxillary incisors to the angle of the mandible, and that from the corner of the mouth to the angle of the mandible. OBJECTIVE: To compare the two guidelines and to determine the optimal external facial measurements for the selection of an appropriately sized airway in adults. DESIGN: Randomised crossover study. SETTING: Operating theatres in a university hospital. PATIENTS: A total of 113 patients requiring tracheal intubation for general anaesthesia. INTERVENTIONS: Two oropharyngeal airway sizes were selected on the basis of two external facial measurements (tip of the upper central maxillary incisors to the angle of the mandible and corner of the mouth to the angle of the mandible). After assessing manual and pressure-controlled ventilation without an airway, the adequacy of ventilation with each oropharyngeal airway was assessed in a similar manner. Before changing the oropharyngeal airway, the view at the distal end of each airway was evaluated using endoscopy via a fibreoptic bronchoscope. MAIN OUTCOME MEASURES: Ventilation parameters and the endoscopic views at the distal ends of the airways were assessed. RESULTS: In the maxillary incisors to the angle of the mandible group, there was clear manual ventilation through the oropharyngeal airway in all patients, whereas partially obstructed ventilation was observed in 6% of patients in the corner of the mouth to the angle of the mandible group. In the maxillary incisors to the angle of the mandible group, mechanical ventilation through the oropharyngeal airway was adequate in all patients but in the corner of the mouth to the angle of the mandible group, inadequate ventilation was observed in 7% patients. In the maxillary incisors to the angle of the mandible group, the endoscopy did not identify any patient with complete obstruction of the airway by the tongue but in the corner of the mouth to the angle of the mandible group, 40% of patients had complete obstruction by the tongue. In the maxillary incisors to the angle of the mandible group, the tip of the airway passed beyond the tip of the epiglottis in 22% of patients, in contrast, none of the airways in the corner of the mouth to the angle of the mandible group passed beyond the tip of the epiglottis. CONCLUSION: With regard to adequate ventilation in conjunction with an acceptable endoscopic view, an oropharyngeal airway whose size is based upon the distance from the maxillary incisors to the angle of the mandible is more advantageous than if based upon the distance from the corner of the mouth to the angle of the mandible. TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT01945411. The clinical trial was registered before patient enrolment.restrictio