A prospective study of bispectral index scoring in mentally retarded patients receiving general anesthesia.

Study Objective: To determine whether degree of mental retardation (MR) affects bispectral index scale (BIS) scores during general anesthesia.

Design: Prospective clinical study.

Setting: University Hospital.

Patients: 80 ASA physical status I, II and III patients with varying degrees of MR, undergoing dental rehabilitation.

Interventions: Patients were grouped into mild, moderate, severe or profound degrees of MR, by an independent registered research nurse according to criteria by the American Psychiatric Association.

Measurements: All patients were given a standard sevoflurane in oxygen anesthetic with ASA standard monitoring. A research assistant who was blinded to study group assignment recorded the BIS scores continuously on a computer and compared the scores at the following time points: awake, induction of anesthesia, intravenous catheter placement, tracheal intubation, start of surgery, end of surgery, awakening to commands, and tracheal extubation.

Main Results: No significant differences in BIS scores existed among the study groups at any time point. No significant difference in slope of induction of anesthesia was noted among the study groups. However, the slope of emergence from anesthesia leading to tracheal extubation showed a significantly longer emergence time in the higher MR groups.

Conclusion: MR does not affect BIS values during general anesthesia.