Bispectral Index During Maintenance of Total Intravenous Anesthesia: Frequency of Out of Recommended Range and Impact of Patients’ Characteristics: A Brief Report Little is known about respecting the recommended range of bispectral index (BIS) in practice. This exploratory retrospective analysis of 138 robotic surgical patients having received total intravenous anesthesia shows that BIS was between 40 and 60 during 61.3% ± 25.2% (mean ± standard deviation [SD]) of maintenance, >60 during 3.1% ± 5.5%, and <40 during 35.7% ± 26.9%. Burst suppression was present during 17.8% ± 22.2%. Female sex is associated with increased periods of BIS <40 (P = .002) as is body mass index (BMI) <26 (P = .012). Increased age is associated with increase in burst suppression (P = .005). A larger study is required to confirm the role of patients’ factors on the number of periods of low BIS. Accepted for publication May 23, 2019. Funding: This work was supported by grants from Hospital Foch. Conflicts of Interest: See Disclosures at the end of the article. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website (www.anesthesia-analgesia.org). Reprints will not be available from the authors. Address correspondence to Marc Fischler, MD, Department of Anesthesiology, Hospital Foch, 40 Rue Worth, Suresnes, France. Address e-mail to m.fischler@hopital-foch.org. © 2019 International Anesthesia Research Society