Effect of epidural bupivacaine on the relationship between the bispectral index and end-expiratory concentrations of desflurane

New developments in cerebral monitoring

In past years, cerebral monitoring was mostly focused around global cerebral perfusion and metabolism monitoring, with the use of transcranial Doppler recordings, jugular bulb oximetry and near-infrared spectroscopy. Most of the recently introduced cerebral monitoring modalities, such as brain tissue partial oxygen tension monitoring and cerebral microdialysis, offer new opportunities by providing regional information on the specific brain area in which the probe is inserted. Ideally, these probes should be inserted in that area of the brain that is most vulnerable to ischaemia, but that may be salvageable with appropriate therapy. In this case, the combination of global and regional cerebral monitoring might offer the best information on which to base patient management. Also, the introduction of more clinically useful, functional neuroimaging techniques may be a valuable adjunct to future neurological critical care management.

Bispectral index does not correlate with observer assessment of alertness and sedation scores during 0.5% bupivacaine epidural anesthesia with nitrous oxide sedation

The bispectral index (BIS) has been used as a measure of the degree of sedation and level of hypnosis for IV hypnotics and sedatives, potent volatile anesthetics. We evaluated the effect of increasing concentrations of nitrous oxide (N2O) on BIS and compared it with the Observer's Assessment of Alertness and Sedation (OAA/S) scale in patients undergoing regional anesthesia. We studied 48 unpremedicated, ASA physical status I-II adult patients scheduled for lower extremity surgery under lumbar epidural anesthesia. N2O was given in oxygen to achieve measured end-tidal concentrations of 33%, 50%, and 67% N2O by a tight-fitting facemask, and each N2O concentration was maintained for 20 min. Paired measurements of BIS and OAA/S scores were obtained just before each increase in N2O concentration. Forty of the 48 subjects completed the study. Increasing N(2)O concentrations produced no changes in BIS despite a significant decrease in OAA/S scores at 50% and 67% N2O concentrations. The prediction probability for BIS and OAA/S calculated by Somers' d(x.y) were 0.60 and 0.84, respectively. Anesthesiologists should be aware that the BIS monitor may not be sensitive enough to provide an adequate measure of the depth of sedation and hypnosis when using N2O alone for sedation. It may be better to monitor sedation clinically (e.g., with the OAA/S scale) to determine the dose requirement and the adequacy of depth of sedation and hypnosis.

Comparison of 1% and 2% lidocaine epidural anaesthesia combined with sevoflurane general anaesthesia utilizing a constant bispectral index

BACKGROUND

The authors compared the effects of epidural anaesthesia with lidocaine 1% and lidocaine 2% on haemodynamic variables, sevoflurane requirements, and stress hormone responses during surgery under combined epidural/general anaesthesia with bispectral index score (BIS) kept within the range 40-50.

METHODS

Thirty-three patients undergoing lower abdominal surgery were randomly divided into two groups to receive lidocaine 1% or 2% by epidural with sevoflurane general anaesthesia. Sevoflurane was adjusted to achieve a target BIS of 40-50 during maintenance of anaesthesia with nitrous oxide 60% in oxygen. Measurements included the inspired (FI(SEVO)) and the end-tidal sevoflurane concentrations (E'(SEVO)), blood pressure (BP), and heart rate (HR) before surgery and every 5 min during surgery for 2 h. Plasma samples were taken immediately before and during surgery for measurements of catecholamines, cortisol, and lidocaine.

RESULTS

During surgery, both groups were similar for HR, BP and BIS, but FI(SEVO) and E'(SEVO) were significantly higher and more variable with lidocaine 1% than with 2%. Intraoperative plasma concentrations of epinephrine and cortisol were found to be higher with lidocaine 1% as compared with 2%.

CONCLUSIONS

To maintain BIS of 40-50 during combined epidural/general anaesthesia for lower abdominal surgery, sevoflurane concentrations were lower and less variable with lidocaine 2% than with 1%. In addition, the larger concentration of lidocaine suppressed the stress hormone responses better.

Isoflurane dosage for equivalent intraoperative electroencephalographic suppression in patients with and without epidural blockade

We conducted a prospective, randomized, controlled trial to establish the effect of epidural blockade on isoflurane requirements for equivalent intraoperative electroencephalographic (EEG) suppression. Fifty patients undergoing abdominal hysterectomy received combined epidural and general anesthesia or general anesthesia alone with isoflurane and alfentanil. Isoflurane was administered by computer-controlled closed-loop feedback to maintain an EEG 95% spectral edge frequency of 17.5 Hz, a target chosen on the basis of a pilot study. In epidural patients, end-tidal isoflurane concentration (FE'(ISO)) was 0.19% smaller (95% confidence interval [CI], -0.32% to -0.06%; P < 0.01), mean arterial blood pressure was 17 mm Hg lower (95% CI, -24 to -9 mm Hg; P < 0.0001), and body temperature was 0.4 degrees C lower (95% CI, -0.7 to 0 degrees C; P < 0.05) than in controls. EEG bispectral index (BIS) was 4 points higher (95% CI, 1 to 7; P < 0.05). EEG median frequency and heart rate were similar in both groups. Epidural patients were 76% more likely (95% CI, 58% to 94%; P < 0.001) to require metaraminol for hypotension and were 28% more likely (95% CI, 3% to 53%; P < 0.05) to require glycopyrrolate for bradycardia. After surgery, the time to eye opening in epidural patients was 2.3 min shorter (95% CI, -4.2 to -0.5 min; P < 0.05). Time to eye opening correlated better with FE'(ISO) in the last 30 s of anesthesia (FE'(ISO) = 0.07 x time to eye opening + 0.31; r(2) = 0.59; P < 0.0001) than with BIS from the same period (BIS = 64 - 1.25 x time to eye opening; r(2) = 0.22; P < 0.001) (P < 0.0001). To maintain similar intraoperative spectral edge frequency, patients receiving combined epidural and general anesthesia require 21% less isoflurane than those receiving general anesthesia alone. This smaller isoflurane dose is associated with faster emergence from anesthesia.

IMPLICATIONS

The dose of general anesthetic required to maintain similar intraoperative suppression of brain electrical activity is 21% less in patients with nerve blockade than in those without. This dose reduction results in faster waking times in patients with nerve blockade, which may reflect lighter intraoperative anesthesia. The dose of general anesthetic required to maintain similar intraoperative suppression of brain electrical activity is 21% less in patients with nerve blockade than in those without. This dose reduction results in faster waking times in patients with nerve blockade, which may reflect lighter intraoperative anesthesia.