|Year : 2008 | Volume
| Issue : 2 | Page : 175-178
Comparative Evaluation of Spectral Entropy and Bispectral Index during Propofol/Thiopentone Anaesthesia in Patients with Supratentorial Tumours - A Preliminary Study
Manish Jagia1, Hemanshu Prabhakar2, HH Dash3
1 Senior Resident, Department of Neuroanesthesiology, All India Institute of Medical Sciences, New Delhi- - 110029, India
2 Asst.Prof, Department of Neuroanesthesiology, All India Institute of Medical Sciences, New Delhi- - 110029, India
3 Prof. & Head, Department of Neuroanesthesiology, All India Institute of Medical Sciences, New Delhi- - 110029, India
|Date of Acceptance||26-Feb-2008|
|Date of Web Publication||19-Mar-2010|
H H Dash
Department of Neuroanesthesiology, CN Center, 7th floor, All India Institute of Medical Sciences, New Delhi, India-110029
Source of Support: None, Conflict of Interest: None
Previous studies have confirmed the usefulness of Bispectral index (BIS) and spectral entropy in non-neurosurgical patients. The effects of thiopentone or propofol on BIS and entropy in patients with supratentorial tumours have not been studied. To address the above issue, we carried out a prospective, randomised controlled trial to determine the correlation between BIS, Response entropy and State entropy during different stages of induction of anaesthesia in neurosurgical patients.
Twenty ASA I/II patients of either gender, aged 19-58 years undergoing excision of supratentorial tumour were selected for the study. The BIS was recorded using A-2000 BIS monitor (Aspect medical systems, Newton, MA) and entropy monitored with Datex-Ohmeda S/5 entropy module (Helsinki, Finland) at various stages of induction of anaesthesia, using either thiopentone or propofol as the induction agent.
We found that BIS and Entropy parameters correlated strongly at different stages of induction. The correlation was significant between BIS and Entropy at baseline, after fentanyl administration, after induction, and after intubation. We also noted that Entropy parameters unlike BIS are not affected by haemodynamic response due to intubation.
To conclude, Entropy may be considered a valid indicator of the effects of thiopentone and propofol during different stages of induction of general anaesthesia neurosurgical patients.
Keywords: Bispectral index; Entropy; Neurosurgical patients
|How to cite this article:|
Jagia M, Prabhakar H, Dash H H. Comparative Evaluation of Spectral Entropy and Bispectral Index during Propofol/Thiopentone Anaesthesia in Patients with Supratentorial Tumours - A Preliminary Study. Indian J Anaesth 2008;52:175-8
|How to cite this URL:|
Jagia M, Prabhakar H, Dash H H. Comparative Evaluation of Spectral Entropy and Bispectral Index during Propofol/Thiopentone Anaesthesia in Patients with Supratentorial Tumours - A Preliminary Study. Indian J Anaesth [serial online] 2008 [cited 2020 Jul 8];52:175-8. Available from: http://www.ijaweb.org/text.asp?2008/52/2/175/60617
| Introduction|| |
Monitoring the adequacy of depth of anaesthesia is of vital importance in neurosurgical patients so as to prevent arousal and awareness during anaesthesia and surgery. Haemodynamics and electroencephalography (EEG) monitoring are widely used to monitor depth of anaesthesia. EEG is predominantly quantified by Fourier's analysis based techniques, which include power spectrum, coherence and bispectral analysis  . Bispectral index (BIS) monitoring is used widely, and is based on the correlation of the phase between frequency components of the EEG  . Entropy is a new EEG-based technology to measure the depth of anaesthesia. It measures irregularity, complexity or unpredictability of a signal. Entropy module (Datex-Ohmeda S/5, Helsinki, Finland) does computation by choosing the length of the time window for each particular frequency  . It has two components, Response entropy (RE) and State entropy (SE). RE is computed over a frequency range of 0.8 Hz to 47 Hz with response time of 1.92 seconds to 15.36 seconds, while SE is computed over frequency range of 0.8 Hz to 32 Hz in time window of 15 seconds to 60 seconds. Previous studies have confirmed the usefulness of BIS and spectral entropy in non-neurosurgical patients ,,, .Although Vakkuri and colleagues  , have studied the effects of thiopentone or propofol anaesthesia on spectral entropy and BIS in general surgical patients, the effects of thiopentone or propofol on BIS and entropy in patients with supratentorial tumors have not been studied. To address the above issue, we carried out a prospective, randomised controlled trial to determine the correlation between BIS, RE and SE during different stages of induction of anaesthesia in neurosurgical patients.
| Methods|| |
After institutional ethics committee approval, informed consent was obtained from 20 ASA I/II patients of either gender, aged 19-58 years undergoing excision of supratentorial tumour. As our trial was a preliminary one, the sample size of 20 patients was chosen after discussing with the statistician. All consecutive patients with supratentorial tumours were enrolled for the study. Patients with cardiovascular disorders, diabetes mellitus, metabolic disorders or alcohol abuse were excluded from the study.
Glycopyrrolate 0.2 mg intramuscularly was given to all the patients as premedicant. Phenytoin sodium 100 mg intravenously was given 2 hours prior to the surgery to all the patients. In the operation theatre, an intravenous line was secured and basic monitoring (i.e. ECG, heart rate, non-invasive blood pressure, and pulse oximetry) was initiated. The skin of forehead was then cleansed thoroughly with ether before application of BIS and entropy sensors. Both the sensors were applied on the forehead, one above the other on side contralateral to the tumor location. The BIS was recorded using A2000 BIS monitor (Aspect medical systems) and entropy monitored with Datex-Ohmeda S/5 entropy module. In a noise free environment, baseline values of BIS, RE, SE, heart rate and mean blood pressure were recorded every minute for five minutes and mean calculated. Fentanyl 2 mcg.kg -1 was given intravenously to all patients and study parameters were recorded again every minute for five minutes. Based on a computer generated randomization table, patients were then randomly induced with either thiopentone (3-5 mg.kg -1 ) or propofol (1.52.5 mg.kg -1 ). After recording the study parameters, rocuronium 1 mg.kg -1 was used to facilitate tracheal intubation. Post-intubation all the study parameters were once again noted. Both BIS and Entropy were monitored for 10 minutes after intubation. We recorded the values each minute and calculated the mean value for statistical analysis. Intraoperative monitoring of BIS and entropy was not possible because of the preparation of the forehead for raising skin flap during craniotomy.
The demographic data between the groups were compared using the paired 't' test. One way analysis of variance (ANOVA) test was used to compare responses of BIS, RE and SE at baseline, after fentanyl administration, post-induction with thiopentone/propofol and after intubation, both in patients within the group and between the two groups. Pearson correlation coefficient was used to determine the relationship between BIS, RE and SE at different stages of induction during anaesthesia between the two groups.
| Results|| |
In the present study, patients' age, gender, weight and location and type of tumours in the two groups were comparable [Table 1]. Likewise, the baseline values of BIS, RE, SE, heart rate and mean arterial pressure were comparable in both groups. Though there was a reduction in BIS, RE and SE after fentanyl administration in all the patients, the reduction in BIS values in the thiopentone group was statistically significant. However, the rise in BIS values after intubation was significant in both groups. The decrease in RE and SE after thiopentone and propofol administration were comparable. We noticed that there was a rise in mean Entropy values after intubation in propofol group, while the Entropy values decreased in the thiopentone group. The changes were, however, not statistically significant [Table 2]. The changes in haemodynamic parameters were also comparable in both the groups [Table 3]. There was a strong and significant correlation between BIS and RE and between BIS and SE at different stages of induction. The correlation was significant between BIS and Entropy at baseline, after fentanyl administration, after induction, and after intubation [Table 4].
| Discussion|| |
Our study compared the performance of BIS, RE and SE at different stages of induction with thiopentone or propofol in neurosurgical patients with supratentorial tumours. BIS and Entropy parameters correlated strongly at different stages of induction. Previous studies have shown comparison of BIS and Entropy but these studies had excluded neurosurgical patients. In the present study, the sensors were placed on the side of forehead contralateral to the tumour location in all patients. In our study we observed that in patients with supratentorial tumours, the baseline values of BIS and Entropy were in normal range of wakefulness. In our study, pre-induction noise free environment was kept in the operation theatre. Minimal noise in the operating room can lead to a rise in the BIS and Entropy parameters. The BIS sensor was applied above the Entropy sensor on the forehead. Davidson and co-workers  have shown in their study that superiorly placed BIS sensors did not affect the BIS readings. After fentanyl administration, BIS reduced upto 30 (30-97). Opioids are known to cause reduction in the EEG activity. The BIS, RE and SE decreased after administration of thiopentone and propofol, but the decrease was more in the latter group although the result was not statistically significant. The rise in BIS value after intubation was significant in both the study groups. Nakayama and co-workers  had observed significant increase in heart rate, mean arterial pressure and BIS after fentanyl-propofol. Guignard and colleagues also reported similar observations after remifentanilpropofol anaesthesia. We recorded an insignificant rise in mean RE and SE values in propofol group after intubation and a statistically insignificant decrease in the two values in the thiopentone group. Increase in BIS, RE or SE values can occur due to deficit in analgesic or hypnotic action, but significant rise in BIS compared to RE and SE in similar groups of patients shows the possibility of affection of BIS by haemodynamic variability. Entropy parameters are not affected by haemodynamic variables, as Entropy algorithm does not consider it. BIS algorithm has not been published; hence degree of effect of haemodynamics on BIS cannot be ascertained.
Pearson's correlation coefficient showed a strong and significant correlation between BIS and RE and SE at baseline, after fentanyl, after induction agent and after intubation. Previous studies ,, in non-neurosurgical patients have also shown significant correlation between BIS and Entropy parameters with different anaesthetic agents like thiopentone  , sevoflurane ,, , propofolremifentanil  , ketamine  and propofol  .Our study shows the effect of opioids and thiopentone on BIS and Entropy and also the strong correlation between the two monitoring modalities in neurosurgical patients. A recent study by Paola et al also demonstrates that spectral entropy provides a reproducible hypnosis index for patients undergoing supratentorial neurosurgical procedures  .
In conclusion, Entropy may be considered a valid indicator of the effects of thiopentone and propofol during different stages of neurosurgical patients. Entropy correlates strongly with BIS during different stages of induction. Entropy parameters unlike BIS do not seem to be affected by haemodynamic response due to intubation. Further detailed evaluation may be needed to justify this observation and validate our results.
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[Table 1], [Table 2], [Table 3], [Table 4]