Relationship between bispectral index values and volatile anesthetic concentrations during the maintenance phase of anesthesia in the B-Unaware trial.
ABSTRACT Hypnotic depth during anesthesia affects electroencephalography waveforms and electroencephalogram-derived indices, such as the bispectral index (BIS). Titrating anesthetic administration against the BIS assumes reliable relationships between BIS values, electroencephalogram waveforms, and effect site concentration, beyond loss of responsiveness. Associations among BIS, end-tidal anesthetic concentrations (ETAC), and patient characteristics were examined during anesthetic maintenance, using B-Unaware trial data.
Pharmacokinetically stable ETAC epochs during intraoperative anesthetic maintenance were analyzed. A generalized estimating equation determined independent relationships among BIS, ETAC (in age-adjusted minimum alveolar concentration equivalents), patient characteristics, and 1-yr mortality. Further individual and population characteristics were explored graphically.
A total of 3,347,523 data points from 1,100 patients were analyzed over an ETAC range from 0.42 to 1.51 age-adjusted minimum alveolar concentration. A generalized estimating equation yielded a best predictive equation: BIS = 62.9-1.6 (if age younger than 60 yr) -1.6 (if female) -2.5 (if American Society of Anesthesiologists physical status more than 3) -2.6 (if deceased at 1 yr) -2.5 (if N2O was not used) -1.4 (if midazolam dose more than 2 mg) -1.3 (if opioid dose more than 50 morphine equivalents) -15.4 × age-adjusted minimum alveolar concentration. Although a population relationship between ETAC and BIS was apparent, interindividual variability in the strength and reliability of this relationship was large. Decreases in BIS with increasing ETAC were not reliably observed. Individual-patient linear regression yielded a median slope of -8 BIS/1 age-adjusted minimum alveolar concentration (interquartile range -30, 0) and a median correlation coefficient of -0.16 (interquartile range -0.031, -0.50).
Independent of pharmacokinetic confounding, BIS frequently correlates poorly with ETAC, is often insensitive to clinically significant changes in ETAC, and is vulnerable to interindividual variability. BIS is therefore incapable of finely guiding volatile anesthetic titration during anesthetic maintenance.
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ABSTRACT: Patients with a history of intraoperative awareness with explicit recall (AWR) are hypothesized to be at higher risk for AWR than the general surgical population. In this study, the authors assessed whether patients with a history of AWR (1) are actually at higher risk for AWR; (2) receive different anesthetic management; and (3) are relatively resistant to the hypnotic actions of volatile anesthetics. Patients with a history of AWR and matched controls from three randomized clinical trials investigating prevention of AWR were compared for relative risk of AWR. Anesthetic management was compared with the use of the Hotelling's T statistic. A linear mixed model, including previously identified covariates, assessed the effects of a history of AWR on the relationship between end-tidal anesthetic concentration and bispectral index. The incidence of AWR was 1.7% (4 of 241) in patients with a history of AWR and 0.3% (4 of 1,205) in control patients (relative risk = 5.0; 95% CI, 1.3-19.9). Anesthetic management did not differ between cohorts, but there was a significant effect of a history of AWR on the end-tidal anesthetic concentration versus bispectral index relationship. Surgical patients with a history of AWR are five times more likely to experience AWR than similar patients without a history of AWR. Further consideration should be given to modifying perioperative care and postoperative evaluation of patients with a history of AWR.Anesthesiology 10/2013; · 5.16 Impact Factor
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ABSTRACT: Clinical signs are unreliable for guiding anaesthetic administration and it is suggested that using the bispectral index can improve anaesthetic delivery. In the current study, isoflurane administration was guided to a bispectral index range of 55-60. Intra-operative responsiveness, as assessed by the isolated forearm technique, was compared with whether the bispectral index predicted/identified a patient's appropriate hand movements in response to commands. Thirty-four women underwent major gynaecological surgery with isoflurane/air and atracurium. Eleven women responded on 32 occasions with appropriate hand movements to commands given during surgery, of which the bispectral index detected 17 (sensitivity 53%). The bispectral index suggested consciousness 660 times in the absence of any movement responses (specificity 69%). The positive predictive value of the bispectral index was 3%. The median (IQR [range]) bispectral index value associated with an intra-operative response was significantly lower than that associated with eye opening after surgery: 60 (50-68 [36-83]) vs 77 (75-84 [59-90]), respectively (p = 2.25 × 10(-8)). Conversely, end-tidal isoflurane concentration was significantly higher at intra-operative response than at eye opening: 0.3 (0.3-0.4 [0.2-0.9]) vs 0.2 (0.1-0.2 [0.1-0.3]), respectively (p = 7.36 × 10(-8)). For patients who responded more than once during surgery, the bispectral index value associated with a response was not constant. No patient had recall for surgery or the taped commands, and only one could remember dreaming (a good dream). Titrating isoflurane to target a bispectral index range of 55-60 may result in an unacceptable number of patients who are conscious during surgery (albeit without recall).Anaesthesia 10/2013; 68(10):1010-20. · 3.49 Impact Factor
- Anesthesia and analgesia 11/2013; 117(5):1039-41. · 3.08 Impact Factor