Journal: Anesthesiology 106(3):472-483, 2007. 65 References
Reprint: Northwestern University, Departments of Anesthesiology and Neurological Surgery, Ward Building, Room No. 13-179, 303 East Chicago Avenue, Chicago, IL 60611 (DK Gupta, MD)
Faculty Disclosure: Abstracted by T. Tilton, who has nothing to disclose.
Processed electroencephalographic (PEEG) parameters are gaining popularity as intraoperative monitors of depth of anesthesia. Some reports showed that the PEEG is insensitive to opioids. The authors sought to identify how the addition of opioids sufficient to change the clinical level of sedation influenced PEEG as measured by Bispectral Index (BIS) or A-Line Auditory Evoked Potential Index (AAI). It was hypothesized that a relatively small change in PEEG due to remifentanil added to sevoflurane would not adequately reflect the substantial change in the clinical anesthetic state and that the co-administration of remifentanil and sevoflurane (attempting to maintain BIS at 40-60 or AAI at 20-30) would result in an excessively deep state of clinical anesthesia.
Twenty-four volunteers were recruited for this study to assess drug interactions. They received a target-controlled infusion of remifentanil (predicted effect site concentrations of 0.5-15 ng/mL) or sevoflurane (0.3-6 vol% end-tidal alveolar concentration) as the primary agent with the other drug as the secondary agent. Adequate anesthesia was defined as: modified Observer’s Assessment of Alertness/Sedation Score (OAA/SS) ≤ 1; no movement in response to a 5 sec, 50mA electric tetanic stimulation; and no change in HR (> 20%) in response to the same electrical stimulation.
Demographics were similar between groups with respect to age, weight, and height, but the sevoflurane group contained equal numbers of males and females, whereas the remifentanil group was predominantly males. Most volunteers were sedated (OAA/SS ≤ 1) at sevoflurane concentrations > 1.5 vol%. Adequate sedation was not achieved with remifentanil in the clinical range (5-10 ng/mL) but was achieved at concentrations > 20 ng/mL. Results clearly demonstrated that the addition of remifentanil (2.5 ng/mL) resulted in an increase in the target BIS and AAI needed to produce clinically adequate sedation or anesthesia. BIS and AAI were both insensitive to observed changes in the clinical sedation state after the addition of a small to large dose of remifentanil to sevoflurane suggesting that sevoflurane/remifentanil anesthetics titrated to traditional BIS or AAI targets may result in deeper than necessary anesthetic levels. The "optimum" target combinations of sevoflurane and remifentanil that provided adequate surgical anesthesia (for anesthetics ranging from 0.5-24 hours) and minimize recovery time were: 1.10-0.75% and 4.1-6.1 ng/mL (infusion rates of 0.15-0.22 mcg/kg/min) in typical adults, respectively.
BIS and AAI monitoring were not sensitive to the addition of even moderate doses of remifentanil so that targeting a BIS < 60 or AAI < 30 may result in an excessively deep anesthetic level. It is suggested new targeted PEEG values may allow for more precise anesthetic levels and further research is indicated. |
