DIFFERENCES IN QUANTITATED ELECTROENCEPHALOGRAPHIC VARIABLES DURING SURGICAL STIMULATION OF HORSES ANESTHETIZED WITH ISOFLURANE

The effects of noxious surgical stimulation on the electroencephalogra m (EEG) in 15 horses anesthetized with isoflurane were evaluated durin g orthopedic (group 1) and soft tissue (group 2) procedures. The quant itative EEG variables theta/delta ratio (T/D), alpha/delta ratio (A/D) , beta/delta ratio (B/D), median power frequency (MED), and 80% spectr al edge frequency (SEF 80) recorded during surgeries at 1.7% end-tidal concentration of isoflurane (ETISO) were compared with values from fi ve nonstimulated control horses anesthetized at 1.7% ETISO. The EEG va riables T/D, A/D, MED, and SEF 80 from surgically stimulated horses we re significantly higher compared with controls. These differences in m easured EEG variables were accompanied by a significantly lower relati ve power in the delta frequency band and a concomitant significantly h igher alpha activity. Because the A/D ratio, MED, and SEF 80 in surgic ally stimulated horses were significantly higher than in nonstimulated control horses these measured EEG variables may provide a valuable to ol for identification of nociceptive transmission in isoflurane anesth etized horses. (C)Copyright 1996 by The American College of Veterinary Surgeons