Background and Goal of Study: A previous study has already reported measurement values of some anatomical positions using MRI, and discussed the sniffing position is not useful for tracheal intubation (R-1). Our purpose was to investigate the relationship between the sniffing position and three axis theory in Japanese using MRI when tracheal intubation was performed.
Materials and Methods: Using MRI apparatus (Siemens, Germany), two T1 weighted images (i.e., in neutral (N) and sniffing (S) positions) were obtained in each volunteer. The sniffing position was obtained by placing a 5-cm pillow underneath the head. Four lines were drawn on the MRI films, and then three angles were measured by following the method described in R-1. Shortly, (1) the axis of the mouth (MA); (2) the pharyngeal axis (PA); (3) the laryngeal axis (LA); and (4) the line of vision were drawn on each film. Alpha angle (A) was defined as the one obtained between MA and PA; beta angle (B) between PA and LA, and delta angles (D) between line of vision and LA. When the intersection of the axes was located under the Th-2 level, B was regarded to be unmeasurable in the present study although all the images could show above Th-2 level in R-1. Data were expressed as mean (SD) and statistical analysis were performed using parried t-test.
Results and Discussions: Six male volunteers with no history of diseases in their upper airways were enrolled. The age was 38.4 years (10, 20-49). Height was 165 cm (8, 160-175). Body Materials Index (BMI) was 23.2 (2, 22-25). B in four volunteers could not be measured since the intersection of the axes was under the Th-2 level. A was 71.5 degrees in N, 51 degrees in S, respectively (P = 0.03). D was 43.5 in N and 35 in P (P = 0.02). Our results indicated the sniffing position provided smaller D values, which suggested the better vision for tracheal intubation.
Conclusions: One of the reasons for the discrepancy between our study result and R-1 result might be the racial difference. Further studies would be necessary to determine an influence of the sniffing position on the tracheal intubation.
Adnet F et al. Study of the sniffing position by Magnetic Resonance Imaging. Anesthesiology 2001; 94: 83-6.