SummaryLaryngoscopy is sometimes easier with the patient's head and neck in the extension-extension position (head extension with the neck extended by the head section of the table bent down at 30°) rather than the classical 'sniffing the morning air' position. We therefore tested the hypothesis that the axial force required for laryngoscopy is less in the extension-extension than the sniffing position. We measured the force axial to the handle of a Macintosh 3 laryngoscope in 20 subjects under general anaesthesia who had been given neuromuscular blocking drugs. Measurement of force was made in the sniffing position and the extension-extension position. The mean (SD) axial force required in the extension-extension position was lower than in the sniffing position (19.6 (7.8) N versus 23.6 (8.6) N, p = 0.04). In the setting of routine tracheal intubation, less force is required when the patient is in the extension-extension position than in the sniffing position. The 'sniffing the morning air' position has been recommended for oral tracheal intubation by direct laryngoscopy [1]. The sniffing position can be achieved using a small pillow behind the patient's head, resulting in atlanto-occipital extension and cervical vertebral flexion. However, intubation is sometimes easier with cervical extension, e.g. by extending the head section of the operating table (Fig. 1), or by removing the pillow from beneath the patient's head and placing it behind the shoulders. These manoeuvres result in atlanto-occipital extension and extension of the cervical vertebrae -'extension-extension'. There are few scientific data comparing the extension-extension position (as opposed to simple head extension on a flat table) to the sniffing position in laryngoscopy and intubation. A published study [2] that used an otorhinolaryngological laryngoscope to visualise the anterior vocal cords showed that less force was required in the extension-extension position than in the sniffing position. It is uncertain how relevant this is to anaesthetic practice.The force that is applied to the laryngoscope is one of the factors that relates to the ease of intubation, as the laryngoscopist needs to visualise at least the corniculate cartilages of the larynx in order to intubate the trachea safely. We therefore tested the hypothesis that the laryngoscopy force required to view the corniculate cartilages is less with the patient's head in the extensionextension position than in the sniffing position. MethodsWith Local Research Ethics Committee approval and written, informed consent, we recruited male and female patients aged between 18 and 80 years presenting for elective surgery under general anaesthesia with neuromuscular blockade at the Sir Charles Gairdner Hospital. Exclusion criteria included predicted or actual difficult laryngoscopy, previous neck injury, neck surgery or any anatomical deficiency of the neck, and any patients in whom cricoid pressure was to be used at induction and laryngoscopy.In order to estimate the sample size required, we con...
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