TITLE: PREDICTING PERCEPTIONS OF RESTFULNESS AFTER ANESTHESIA: IS THE EEG USEFUL?

AUTHORS: Alfred W. Doenicke, MD¹, M. F. Roizen, MD², A. Tung, MD², J. Soukoup, MD¹, R. Hoerncke, MD¹
AFFILIATION: ¹Ludwig Maximilians-University of Munich, Munich, Germany; ²University of Chicago, Chicago, IL.

INTRODUCTION: Patients emerging from ketamine ane- sthesia do not describe the anesthetic period as restful (1). This perception may be due to the increase in theta (4-8 Hz) activity in the EEG characteristic of ketamine administration (2). We hypothesized that addition of etomidate or propofol to ketamine would improve the perception of restfulness during the anesthetic period by reducing theta activity.
METHODS: After IRB and volunteer approval, each of 8 subjects received 3 total i.v. anesthetics lasting 50 min each and separated by 14 days. Ten minutes after premedication with i.v. droperidol 1.25 mg, midazolam 2 mg, and atropine 0.5 mg, anesthesia was induced with a bolus injection of ketamine 1 mg/ kg; ketamine 0.5 mg/kg and propofol 2 mg/kg; or ketamine 0.5 mg/kg and etomidate-Lipuro 0.3 mg/kg. Anesthesia induced with ketamine was maintained with ketamine 0.5 mg/kg/hr. Anesthesia induced with ketamine and propofol was maintained with ketamine 5 µ/g/kg/min and propofol 0.2 mg/kg/min for the first 30 min, 0.13 mg/kg/min for the next 10 min, and 0.1 mg/kg/ min for the last 10 min. Anesthesia induced with ketamine and etomidate was maintained with ketamine 5 µ/g/kg/min and etomidate 20 µ/g/kg/min for the first 30 min, 13 µ/g/kg/min for the next 10 min, and 10 µ/g/kg/min for the last 10 min. Upon emergence, patients were questioned at 3 and 10 min and at 8 hr about the restfulness of the anesthetic period. EEG data were recorded digitally using both the Aspect 1050 EEG monitor (Aspect Medical Systems, Natick, MA) and on paper (Nihon Kohiden, Kyoto Japan). All spectral analyses were performed using the Aspect 1050 EEG monitor.
RESULTS: Relative theta activity (Rtheta) in subjects ane- sthetized with ketamine alone averaged 23.5% of total EEG power over the 50 min. Average Rtheta in subjects given both ketamine and etomidate was 15.3%, and in subjects given ketamine and propofol was 10.1%. All 8 volunteers rated restfulness as shown in the Table.

DISCUSSION: Despite equivalent depth of anesthesia, different intravenous anesthetics may produce differing perceptions of the anesthetic experience. Theta activity did not correlate with perception of restfulness.
REFERENCES:

1. J Pharmacol Exp Ther 1966;152:32.

2. Anesth Analg 1969; 48:141.