title: EEG entropy values during isoflurane, sevoflurane and halothane anesthesia with and without nitrous oxide.
abstract: We hypothesized that like bispectral index, entropy may be anesthetic agent specific. We carried out a study to assess the entropy values of different anesthetics at equi-minimal alveolar concentrations (MACs) with air and nitrous oxide as carrier gases. Thirty adult patients undergoing spine surgery were randomized to receive halothane, isoflurane, or sevoflurane, in 2 stages, (a) with air/oxygen mixture (2:1) and (b) in nitrous oxide/oxygen (2:1). Heart rate, mean arterial blood pressure, response entropy (RE), and state entropy (SE) were noted at 1.0 and 1.5 MACs for each agent. Statistical analysis was done using the 2-way analysis of variance followed by Bonferroni correction and Student t test for paired data. P value of less than 0.05 were considered significant. The demographics and baseline values of heart rate, mean arterial blood pressure, RE, and SE were comparable. Changing from air/oxygen as carrier gas to 66% nitrous oxide in oxygen resulted in significant increase in both RE and SE at 1.0 MAC for all the agents (P<0.05). Among the agents, it was found that both RE and SE values were significantly higher during halothane anesthesia as compared with sevoflurane and isoflurane (P<0.05). At 1.5 MAC for all agents, after addition of nitrous oxide, there was an insignificant reduction in both RE and SE (P>0.05). Again the values of RE and SE remained high for halothane as compared with isoflurane and sevoflurane. In conclusion, our data suggest a possibility of misinterpretation of anesthetic hypnosis when entropy values increase with addition of nitrous oxide to 1 MAC isoflurane and sevoflurane.
authors.affiliation: Department of Neuroanaesthesiology, Neurosciences Center All India Institute of Medical Sciences, New Delhi, India. prabhakarhemanshu@rediffmail.com
authors.forename: Hemanshu
authors.initials: H
authors.lastname: Prabhakar
authors.forename: Zulfiqar
authors.initials: Z
authors.lastname: Ali
authors.forename: Parmod K
authors.initials: PK
authors.lastname: Bithal
authors.forename: Gyaninder P
authors.initials: GP
authors.lastname: Singh
authors.forename: Pradip K
authors.initials: PK
authors.lastname: Laithangbam
authors.forename: Hari H
authors.initials: HH
authors.lastname: Dash
mesh_terms: D000293:Adolescent; D000328:Adult; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation; D004569:Electroencephalography / Q000187:drug effects*; D019277:Entropy; D005260:Female; D006221:Halothane; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D007530:Isoflurane; D008297:Male; D008738:Methyl Ethers; D008875:Middle Aged; D009609:Nitrous Oxide; D011650:Pulmonary Alveoli / Q000378:metabolism; D000077149:Sevoflurane; D013131:Spine / Q000601:surgery; D055815:Young Adult
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane; D009609:Nitrous Oxide; D006221:Halothane