[Mouth opening in relation to the craniocervical position during induction of general anesthesia]

Decreased mouth opening and limited neck mobility sometimes make direct laryngoscopy or tracheal intubation difficult and compromise the safety in establishing the airway during induction of general anesthesia. Recent report indicated that mouth opening was related to the craniocervical position in awake subjects. The query about whether the neck position modulate the mouth opening during anesthetic induction under paralyzed condition is not clarified. We hypothesized that the neck extension and the flexion induce changes in inter-incisor distance (IID) during anesthetic induction.

Thirty relatively young patients for general anesthesia were (male; 20, female; 10) subjected. IID was measured with his/her neck positioned flexed, neutral and extended in the sagittal plane, each at preanesthetic awake period, and during anesthetic induction period. The effect of sniffing position on the mouth opening was also studied.

At preanesthetic period, IID (mean +/- SD in mm) at neck flexion (37.4 +/- 7.8) was significantly shorter than both at neutral (44.1 +/- 7.5) and at extension (47.4 +/- 7.0). During induction, significant increase in IID was observed as patients' neck position changed from flexed (31.8 +/- 5.4) to neutral (36.6 +/- 5.4), and extended, (41.7 +/- 8.3). Sniffing position did not affect the mouth opening both at preanesthetic and during anesthetic induction period.

Craniocervical extension may play a desirable role in the airway management with mouth opening widely during anesthetic induction under neuromuscular blockade.