A priori power analysis of the previous published data [9] showed that the investigators will need to study 14 pairs to detect a 10% difference in the cervical spine extension (occiput-C5) values (25.9 degrees) with a SD of 2.8 degrees, after intubation with of Macintosh laryngoscope, a type-I error of 0.05 and a power of 90%. The investigators will add 10% more patients for a final sample size of 32 patients to account for patients dropping out during the study.