To the Editor:—
Adnet et al. 1are to be congratulated for performing an important study comparing the efficacy of the sniffing versus simple head extension positions for tracheal intubation. However, since the end points for the sniffing position were not measured, I have three concerns as to whether a true sniffing position was achieved by the study protocol. First, the sniffing position consists, in part, of approximately 35° of flexion of the lower cervical spine on the chest. The 35° of neck flexion on the chest can be achieved by elevating the occiput by 7 cm. In the study protocol, the neck flexion on the chest was achieved by placing the patient's head on a 7-cm-high “cushion.” However, the compressibility of the “cushion” was unspecified. I placed the heads of normal-sized patients on 7-cm-high uncompressed pillows and foam supports that are used in my operating rooms for head support and found that the height of both the pillow and the foam supports decreased by 50%. Thus, compression of the “cushion” by the head significantly decreases the height of the “cushion” (and the flexion of the lower cervical spine on the chest) and results in only a partial sniffing position.
Second, simple elevation of the occiput by 7 cm will not result in the sniffing position in many obese patients because one must also reposition the abnormally contoured scapula, shoulders, and nape of the neck (i.e. , recontour the upper body and head and neck with a blanket and towel ramp) in order to achieve not only 35° flexion of the neck on the chest but also 85–90° extension of the head on the neck at the atlantooccipital joint. Thus, it is unknown exactly what position produced the significant improvement in the laryngoscopic view, compared to simple head extension, in the obese patients.
Third, for the laryngoscopies performed in the sniffing position, the authors did not affirmatively or positively state that the head was actually extended on the neck at the atlantooccipital joint at the time of laryngoscopy. Failure to do so would constitute failure to achieve the sniffing position.
Thus, for these three reasons, and given the fact that head extension from the neutral position causes flexion of the cervical spine on the chest to some degree, exactly what was studied and what was the difference between the two positions are unclear. The proper scientific end point for the two intubating positions would have been to externally measure the planes and axes of the chest, neck, and head. Because the end points for the two positions were not measured, I do not believe the authors are entitled to draw conclusions regarding the comparative efficacy of the “sniffing” and simple head extension position for laryngoscopy and tracheal intubation.