Reduction in mouth opening with semi-rigid cervical collars.

BACKGROUND Reduced mouth opening may be a major contributing factor to the deterioration in the view obtained at laryngoscopy when a semi-rigid cervical collar is in place. We set out to assess the degree to which mouth opening is restricted by a cervical collar. METHODS We measured maximal inter-incisor distance in 52 volunteers. It was measured again after application of each of three appropriately sized semi-rigid cervical collars (Stifneck, Miami J, and Philadelphia). RESULTS Inter-incisor distance was significantly reduced by the application of a cervical collar [No collar 41 (7) mm-mean (SD); Stifneck 26 (8) P<0.0001; Miami J 29 (9) P<0.0001; Philadelphia 29 (9) P<0.0001]. There was a wide and unpredictable variation between subjects in the reduction in mouth opening and a significant proportion had an inter-incisor distance of 20 mm or less (Stifneck, 25%; Miami J, 21%; Philadelphia, 21%). CONCLUSIONS Application of a semi-rigid cervical collar can significantly reduce mouth opening. This could hinder definitive airway placement. Our results support removing the anterior portion of the collar before attempts at tracheal intubation.