EEG Entropy Values During Isoflurane, Sevoflurane and Halothane Anesthesia With and Without Nitrous Oxide

We hypothesized that like hispectral index, entropy may he anesthetic agent specific. We carried out a study to assess the entropy values of different anesthetics at equi-minimal alveolar concentratioin (MACs) with air and nitrous oxide as carrier gases. Thirty adult patients undergoing spine surgery wen 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 (SF) Were noted at 1 0 and 1.5 MACs for each agent. Statistical analysis was done using Be 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 6600 nitrous oxide in oxygen resulted in significant increase in both RE and SF 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 or 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.