Study of the "sniffing position" by magnetic resonance imaging

Background: The "sniffing position" is widely considered essential to the performance of orotracheal intubation and has become the cornerstone of training in anesthesiology. However, the anatomic superiority of this patient head position has not been established. Methods: Eight healthy young adult volunteers underwent magnetic resonance imaging scanning in three anatomic positions: head in neutral position, in simple extension, and in the "sniffing position" (neck flexed and head extended by means of a pillow). The following measurements were made on each scan: (1) the axis of the mouth (MA); (2) the pharyngeal axis (PA); (3) the laryngeal axis (LA); and (4) the Line of vision. The various angles between these axes were defined: alpha angle between the MA and PA, beta angle between PA and LA, and delta angle between line of vision and LA. Results: Both simple extension and sniffing positions significantly improved (P < 0.05) the <delta> angle associated with best laryngoscopic view. Our results show that the beta value increases significantly (P < 0.05) when the head position is shifted from the neutral position (<beta> = 7 +/- 6 degrees) to the sniffing position (beta = 13 +/- 6 degrees), and the alpha value slightly (but significantly) decreases (from 87 +/- 10 degrees to 63 +/- 11 degrees ;P < 0.05). Anatomic alignment of the LA, PA, and MA axes is impossible to achieve in any of the three positions tested. There were no significant differences between angles observed in simple extension and sniffing positions. Conclusions: The sniffing position does not achieve alignment of the three important axes (MA, PA, and LA) in awake patients with normal airway anatomy.