Study of the "sniffing position" by magnetic resonance imaging

Background: The "sniffing position" is widely considered essential to the p erformance of orotracheal intubation and has become the cornerstone of trai ning in anesthesiology. However, the anatomic superiority of this patient h ead 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 exte nded by means of a pillow). The following measurements were made on each sc an: (1) the axis of the mouth (MA); (2) the pharyngeal axis (PA); (3) the l aryngeal 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 betw een PA and LA, and delta angle between line of vision and LA. Results: Both simple extension and sniffing positions significantly improve d (P < 0.05) the <delta> angle associated with best laryngoscopic view. Our results show that the beta value increases significantly (P < 0.05) when t he head position is shifted from the neutral position (<beta> = 7 +/- 6 deg rees) to the sniffing position (beta = 13 +/- 6 degrees), and the alpha val ue 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 im possible to achieve in any of the three positions tested. There were no sig nificant differences between angles observed in simple extension and sniffi ng positions. Conclusions: The sniffing position does not achieve alignment of the three important axes (MA, PA, and LA) in awake patients with normal airway anatom y.