We greatly appreciate the interest expressed by Drs. Chou and Wu regarding our article. 1As reported previously, 2some subjects in whom the trachea is difficult to intubate are at increased risk of obstructive sleep apnea (OSA). Moreover, patients who have difficult intubation (DI) and OSA may share upper airway anatomical abnormalities with a difficult mask ventilation (DMV) situation. In our study, we identified five independent factors (age > 55 yr, body mass index > 26 kg/m2, beard, lack of teeth, and history of snoring) associated significantly with DMV. Some of these risk factors for DMV (age > 55 yr, body mass index > 26 kg/m2, and history of snoring) are related to malproportion of overall body size or malproportion between the oropharyngeal free space and internal structures of the oropharynx, as in OSA. Our first comment in response to Drs. Chou and Wu is that the purpose of our study was to identify factors predicting DMV and not to correlate DMV to OSA. Second, Drs. Chou and Wu reported that a longer mandible and hyoid distance (MHD) indicated an increased tongue mass in the hypopharynx, compromising the posterior airway space. 3Unfortunately, measurement of MHD may be difficult because of its wide variation among the adult population and the need for experience as mentioned in their letter. Moreover in their previous study, 3MHD was obtained from lateral cervical spine radiograph measurements and not from clinical findings. Last, in a more recent study, 2MHD was not significantly different in DI and non-DI patients and was not related to OSA. Nevertheless, we are convinced that MHD could be valuable information in predicting an OSA–DMV–DI situation if it could be validated in a clinical setting without performing measurements from radiographs. Therefore, further studies are required to determine if MHD could be a reliable clinical predictor of OSA–DMV–DI cases.
We thank Dr. Takenaka et al. for the interest in our work and their valuable comments. We fully agree that the jaw-thrust maneuver can reopen the obstructed airway by lifting up the base of the tongue and the epiglottis in anesthetized patients. Moreover, Calder et al. 4reported that impaired mandibular protrusion was associated with a more difficult laryngoscopy in patients with cervical spine disease. Indeed, in patients with an occipito-atlanto-axial disease as in the study of Calder et al. , 4a poor mandibular protrusion is recognized. Consequently, we may assume that decreased mandibular protrusion in an awake patient is a good predictor of a reduced cervical spine mobility associated with impaired laryngoscopy. In addition, this test may not assess reliably a potential decreased airway patency in the anesthetized patient without spine disease. Therefore, we cannot extrapolate information related to difficult laryngoscopy and difficult intubation to those with DMV requiring specific investigation. In our opinion, the relation between a reduced mandibular protrusion in the awake state and DMV remains to be shown.
We thank Dr. Gentili for his interest in our work and the comments. The purpose of our study was to identify factors predicting DMV per se and not to determine the influence of the degree of clinical experience of the anesthesiologist in a DMV situation. Consequently, as mentioned in the article, this study involved staff anesthesiologists. Nevertheless, we agree with Dr. Gentili that the annual clinical case loads for an individual anesthesiologist may influence his or her clinical practice. However, this is true for any daily clinical activity for a physician and was not the purpose of our study. Last, incidence of DMV has been assessed rarely in previous studies related to airway management, and no specific investigation has been performed to study DMV. This point may explain largely the discrepancy for the DMV incidence in our study in comparison with other studies.