The Effects Of Intravenous Ketamine And Propofol On The BIS And Aepex  

H. Kang*, N. Scott#, N. Sutcliffe# and G.N.C. Kenny*
*Glasgow University Department of Anaesthesia, Royal Infirmary, 8-16, Alexandra Parade, Glasgow G31 2ER, UK
#HCI International Medical Centre, Beardmore Street, Clyde bank, Glasgow G81 4HX, UK

Background and Goal of Study:

Inhalational anaesthetics have been reported to cause graded changes in AEP. However ketamine does not appear to alter AEP compared with the awake state¹, implying the preservation of primary processing of auditory stimuli in the primary auditory cortex by ketamine. That study was performed using induction doses of ketamine, thus the study on the effect of more prolonged exposure to ketamine might be necessary to clarify time-dependent effects. By contrast, in a study accomplished under propofol and fentanyl anaesthesia, ketamine was shown to increase BIS.² The effects of ketamine on the BIS and AEPex were investigated during anaesthetic maintenance (ketamine phase) and compared with intravenous maintenance using propofol (propofol phase) in the same patients.

Materials and Methods:

After obtaining Ethics Committee approval and written informed consent, nine patients, aged 17 to 70 years (ASA II and III) and ejection fraction > 35%, scheduled for elective coronary artery bypass surgery or valve replacement were recruited in this study. Anaesthesia was induced and maintained with ketamine. The initial target blood ketamine concentration was set at 3 µg ml^-1 for induction and increased by 0.5mcg/ml every 30 seconds until loss of consciousness. In all patients remifentanil TCI was commenced at the same time with the blood target of 6 ng ml^-1. After loss of consciousness, the patient’s lungs were artificially ventilated with 100% oxygen. Neuromuscular blockade was provided with vecuronium 10mg administered iv, the trachea intubated 2 minutes later and controlled ventilation with 50 % oxygen commenced. After maintenance with ketamine for 30 minutes, surgery was started and ketamine replaced by propofol which was maintained at 3-3.5 µg ml^-1 during the surgery. BIS and AEPex were recorded every 10 minutes during anaesthetic maintenance with both intravenous anaesthetics.

Results:

From nine patients investigated for ketamine, seven patients were exposed to propofol. Surgical incision did not increase BIS, AEPex and cardiovascular variables. Mean BIS value during anaesthetic maintenance with ketamine significantly decreased from 72.2 to 61.3, 59.5, 54.6, 50.5, 47.4 and 46.3, at 10, 20, 30, 40, 50 and 60 minutes, respectively, during the administration of propofol (Table 1). BIS values after switching to propofol from ketamine also showed time-dependent decrease. Mean BIS value at 10 minutes of propofol exposure significantly decreased from 61.3 to 47.4 and 46.3, respectively, at 50 and 60 minutes. However mean AEPex value(s) during the infusion of ketamine were not significantly different from those values at most time points during the exposure to propofol except 50 and 60 minutes.

Table 1 Changes of AEPex and BIS in ketamine and propofol phases during anaesthesia

Data are mean (SD)

^$ represents mean values of three values at 10, 20 and 30 minutes after induction in ketamine phase

ANOVA with multiple comparison using post hoc Tukey test

^*P<0.05 vs mean values (72.2 for BIS and 43.0 for AEPex) of ketamine phase

^# P<0.0001 vs mean values (72.2 for BIS and 43.0 for AEPex) of ketamine phase

^† P<0.001 vs mean value (72.2) of ketamine phase

^‡ P<0.05 vs 10 minutes of propofol phase

Conclusions:

BIS during anaesthesia with ketamine was maintained much higher than during anaesthesia with propofol, suggesting dependence of BIS on both anaesthetics. This contrasted with AEPex which showed consistent values regardless of anaesthetic agents used at the same period.

References

1. Schwender D, Klasing S, Madler C, Poppel E, Peter K. Br J Anaesth 1993; 71:629-632

2. Hirota K, Kubota T, Ishihara H, Matsuki A. Eur J Anaesthesiol 1999; 16:779-83