The changes of the sternomental distance under general anesthesia and with increasing age

ABSTRACT

BACKGROUND: Because the sternomental distance (SMD) is evaluated in conscience patients and in the sitting position, this could change under general anesthesia, which is a state that the patient is unconscious and fully relaxed in the supine position. Increasing age also affects the SMD. We investigated the change in the SMD with the patients under general anesthesia and we also investigated the effect of age on the SMD. METHODS: A total of 108 patients were allocated to Group Y (20-30 yr), Group M (31-50 yr) and Group O (51-70 yr). The SMD, as measured when the patients were awake and sitting, was defined as baseline. The SMD was measured in the supine position, the shoulder-suppressed supine position, at the time of loss of consciousness (LOC), 4 min after vecuronium administration and in the sniffing position. The percent change of the SMD (%) was defined as (the baseline SMD - the measured SMD)/the baseline SMD x 100. RESULTS: Compared with the baseline, the SMD decreased significantly in the supine position, the shoulder-suppressed supine position, at the time of LOC, during neuromuscular blockade and in the sniffing position in all the groups. Group O showed a shorter SMD than did Groups Y and M for all the measurements. There was no significant difference in the percent change of the SMD between the groups. CONCLUSIONS: This study demonstrated that the SMD was significantly reduced by the supine position, the sniffing position, at the time of loss of consciousness and during neuromuscular blockade with the patient under general anesthesia and also with the increasing age of the patient.