Power spectral analysis of EEG during sufentanil infusion in humans

Electroencephalographic delta/alpha frequency activity differentiates psychotic disorders: a study of schizophrenia, bipolar disorder and methamphetamine-induced psychotic disorder

Electroencephalography (EEG) has been proposed as a neurophysiological biomarker to delineate psychotic disorders. It is known that increased delta and decreased alpha, which are apparent in psychosis, are indicative of inappropriate arousal state, which leads to reduced ability to attend to relevant information. On this premise, we investigated delta/alpha frequency activity, as this ratio of frequency activity may serve as an effective neurophysiological biomarker. The current study investigated differences in delta/alpha frequency activity, in schizophrenia (SCZ), bipolar I disorder with psychotic features and methamphetamine-induced psychosis. One hundred and nine participants, including individuals with SCZ (n = 28), bipolar I disorder with psychotic features (n = 28), methamphetamine-induced psychotic disorder (MPD) (n = 24) and healthy controls (CON, n = 29). Diagnosis was ascertained with the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, 4th Edition disorders and current medication was recorded. EEG was undertaken in three testing conditions: resting eyes open, resting eyes closed and during completion of a simple cognitive task (visual continuous performance task). EEG delta/alpha frequency activity was investigated across these conditions. First, delta/alpha frequency activity during resting eyes closed was higher in SCZ and MPD globally, when compared to CON, then lower for bipolar disorder (BPD) than MPD for right hemisphere. Second, delta/alpha frequency activity during resting eyes open was higher in SCZ, BPD and MPD for all electrodes, except left frontal, when compared to CON. Third, delta/alpha frequency activity during the cognitive task was higher in BPD and MPD for all electrodes, except left frontal, when compared to CON. Assessment of EEG delta/alpha frequency activity supports the delineation of underlying neurophysiological mechanisms present in psychotic disorders, which are likely related to dysfunctional thalamo-cortical connectivity. Delta/alpha frequency activity may provide a useful neurophysiological biomarker to delineate psychotic disorders.

Interactions of propofol and remifentanil on bispectral index under 66% N(2)O: analysis by dose-effect curve, isobologram, and combination index

Background

Propofol and remifentanil are usually co-administered and have shown synergistic effect for anesthesia. However, the synergistic effect of the two drugs on hypnosis measured by bispectral index (BIS) was controversial in previous studies. The aim of this study was to identify the interaction of propofol and remifentanil on BIS and the optimal dose combinations for hypnosis under 66% N₂O during surgery.

Methods

Patients (age 55-75 and American Society of Anesthesiologists [ASA] 1-2) undergoing gastrectomy were enrolled in this study. Propofol and remifentanil were co-administered incrementally at 1 : 1 potent ratio (the P1R1 group), at 1 : 2 potent ratio (the P1R2 group), or at 2 : 1 potent ratio (the P2R1 group) using effect site target-controlled infusion and BIS was measured. 66% N₂O was concomitantly administered to all groups. The dose-effect curves, the 90% effective dose (EC₉₀) for adequate hypnosis (BIS 40), isobolograms and combination index were obtained by Calcusyn program (Biosoft) to reveal the interaction of propofol and remifentanil.

Results

The P2R1 group showed synergistic action on BIS. However, the other groups needed larger amount of each drug than the doses of additive action. The EC₉₀ of the P2R1 group was propofol, 3.34 µg/ml and remifentanil, 2.41 ng/ml under 66% of N₂O.

Conclusions

Propofol dominant co-administration is needed for dose reduction in BIS guided hypnosis.

Pharmacodynamics and pharmacokinetics of high-dose oxycodone infusion during and after coronary artery bypass grafting

OBJECTIVE

In small to moderate doses, oxycodone has similar analgesic efficacy to morphine with fewer side effects. The present study evaluated the pharmacokinetics and dynamics of high doses of oxycodone during anesthesia for primary coronary artery bypass grafting.

DESIGN

A randomized, prospective clinical evaluation.

SETTING

A major Scandinavian university clinic.

PARTICIPANTS

Two groups with 10 patients each were studied.

INTERVENTIONS

Invasive hemodynamics, echocardiograms, and electrocardiograms were monitored. Oxycodone kinetics, histamine liberation, and plasma cortisol levels were measured. Anesthesia was induced with 1.0 mg/kg of oxycodone and, thereafter, in a random order, maintained with a continuous infusion of oxycodone at a rate of either 0.5 mg/kg/h (group OX 0.5, 10 patients) or 1.0 mg/kg/h (group OX 1.0, 10 patients). An additional bolus dose of 0.5 mg/kg (OX 0.5) or 1.0 mg/kg (OX 1.0) of oxycodone was given before the incision. Enflurane was administered according to hemodynamic criteria.

MEASUREMENTS AND MAIN RESULTS

The induction of and the course of anesthesia were hemodynamically stable in all patients. Enflurane was given to every patient. The mean total doses of oxycodone were 3.5 mg/kg (OX 0.5) and 6.2 mg/kg (OX 1.0). The median t(1/2) of oxycodone varied from 5.1 to 5.9 hours. No hemodynamic differences were found between the groups. No histamine liberation was detected. During anesthesia, the predominant waves in the EEG were theta;- and delta-waves. The mean times to awakening were 3.8 hours and 7.0 hours in the groups OX 0.5 and 1.0, respectively. All patients were intubated until the first postoperative morning. No recall of awareness was reported.

CONCLUSION

A combination of oxycodone and enflurane provides hemodynamically stable anesthesia. No advantages were gained with the higher dose. Elimination of oxycodone was slower than reported previously.

Measurement of opioid-induced sedation

One of the major side effects of opioid analgesics is sedation. Despite the fact that neither a universal definition nor a gold standard for the measurement of opioid-induced sedation exists, various neurophysiologic and psychomotor measures are used to quantify the sedative effects of opioids. This report reviews the strengths and weaknesses of various approaches that are used to measure opioid-induced sedation. The first section summarizes various neurophysiologic measures (i.e., electroencephalogram, autonomic reflexes, and evoked responses), and the second section reviews psychomotor measures (i.e., visual analog scales, observer assessments, motor performance tests, tests of perceptual processes, tests of information processing, tests of memory, and composite tests) that are used to evaluate the sedative effects of opioids. Implications for future research on opioid-induced sedation are discussed.

Definition of and mechanism for opioid-induced sedation

Although sedation is acknowledged to be one of the most common side effects of opioid analgesics, the mechanisms and characteristics of this phenomenon remain elusive, and research in this area is extremely limited. This report integrates research findings on the mechanism of action of opioids with research findings on the phenomenon of consciousness to develop a model of how opioids may act in the central nervous system to produce sedation. Based on this integration, a definition of opioid-induced sedation is proposed to encourage dialogue and research on this perplexing and clinically significant phenomenon.

Interaction modeling of propofol and sufentanil on loss of consciousness

STUDY OBJECTIVES

To examine the possible pharmacodynamic interaction of propofol and sufentanil with respect to the induction of loss of consciousness.

DESIGN

Prospective, randomized, double-blinded study.

SETTING

University hospital.

PATIENTS

30 female, ASA physical status I and II patients undergoing elective gynecologic surgery.

INTERVENTIONS

Patients were allocated randomly to receive an individual combination of propofol (1, 2, 3, 4, 5, or 6 micrograms/ml) and sufentanil (0.1, 0.2, 0.3, 0.5, or 1.0 ng/ml) target blood concentrations using target-controlled infusions.

MEASUREMENTS AND MAIN RESULTS

Study endpoint was loss of consciousness, which was tested by response to verbal commands and classified as responder or nonresponder, as assessed by the anesthetist, who was blinded to the drugs' target blood concentrations. Nonlinear association (interaction) of both drugs was accomplished with logistic regression analysis using the maximum likelihood method, based principally on the hypothesis of interaction: In [p/(1-p)] = beta 0 + beta 1 x Cprop + beta 2 x Csuf + beta 3 x Cprop x Csuf with a p-value < 0.05 for coefficient estimates considered significant. In the logistic regression model, sufentanil and propofol showed no supra-additive interaction regarding loss of consciousness (p = 0.5916).

CONCLUSIONS

Our results give no evidence of additional hypnotic properties of sufentanil compared to the other fentanyl congeners, although logistic regression may be of limited value in modeling interaction of hypnotic-analgesic combinations.

Power spectral analysis of the electroencephalogram during increasing end-expiratory concentrations of isoflurane, desflurane and sevoflurane

We studied the effects of increasing end-expiratory concentrations of isoflurane (0.3, 0.6, 0.9, 1.2 vol.%) (n = 12 patients), desflurane (1.5, 3.0, 4.5, 6.0 vol.%) (n = 12 patients) and sevoflurane (0.5, 1.0, 1.5, 2.0 vol.%) (n = 12 patients) on power spectral analysis of the electroencephalogram (EEG). Spectral edge frequency (SEF), total power (TP) and relative power in the delta, theta, alpha and beta band were calculated. EEG changes were very similar within the three groups. SEF decreased, TP and relative power in the delta and theta band increased, power in the beta band decreased in a dose-dependent fashion with comparable regression lines. This indicates that MAC equivalent administration of isoflurane, desflurane and sevoflurane in clinically applied dose ranges is associated with equipotent EEG suppression.

40 Hz auditory steady-state response and EEG spectral edge frequency during sufentanil anaesthesia

PURPOSE

The auditory steady-state evoked response (ASSR) is an evoked potential which provides a sensitive measure of the effects of general anaesthetics on the brain. We used pharmacokinetic-pharmacodynamic (PK-PD) modelling to compare the effects of sufentanil on the amplitude of the ASSR with its effect on spectral edge frequency (SEF) of the electroencephalogram.

METHODS

Nine patients scheduled for elective cardiac surgery participated. Midazolam (70 micrograms.kg-1 i.m.) was given 60 min before entering the operating room. Anaesthesia was induced with 5 micrograms.kg-1 sufentanil at a rate of 0.83 microgram.kg-1.min-1. The ASSR, SEF and plasma sufentanil concentrations were measured for 30 min after induction of anaesthesia before surgery. The half-life between the central and effect site compartments (t1/2Keo), the 50% inhibitory concentration (IC50) and the slope factor (gamma) were computed.

RESULTS

The amplitude of the ASSR increased during the first three minutes of infusion of sufentanil by up to 40%. This was followed by a rapid decrease between the fourth and fifth minutes to 16% of baseline. The SEF decreased progressively during the first five minutes of infusion to 18% of baseline. Both measures subsequently showed modest recovery. The parameters gamma, IC50 and t1/2Keo for ASSR were (mean +/- SD) 6.0 +/- 3.7, 2.1 +/- 1.2 ng.ml-1 and 7.3 +/- 2.4 min. For SEF the values were 5.9 +/- 5.2, 1.4 +/- 0.7 ng.ml-1 (P < 0.05 compared with ASSR) and 6.8 +/- 2.4 min.

CONCLUSION

The sensitivity of ASSR to sufentanil is less than that of the SEF.

Neuromonitoring in the operating room: why, when, and how to monitor?

This review considers the main principles and indications of EEG and evoked potential (EP) neuromonitoring in the operating room. Neuromonitoring has a threefold purpose: to warn the surgeon that he has to adjust his strategy, to confirm his decision, and to help him improve subsequent procedures. The pathophysiology of intraoperative events liable to alter the EEG or the EPs is first considered. The usefulness of neuromonitoring in preventing neurological complication relies on its ability to detect neurological dysfunction at a reversible stage. This applies especially to ischemia and compressive damage. The anesthetic influences on EEG and EPs are then considered. Knowledge of them is essential to disentangle these neurophysiological alterations due to intraoperative events from those merely due to anesthesia and to use neurophysiological parameters to evaluate the depth of anesthesia. Third, the main indications and limitations of neuromonitoring are considered: prevention of ischemic brain or spinal cord damage, prevention of mechanical injuries of the brain, spinal cord or peripheral nerve, and localization of the motor cortex in cortical neurosurgery or of cranial nerves in posterior fossa surgery. Finally, the 3 levels of neuromonitoring (neurophysiological feature extraction, neurophysiological pattern recognition, clinical integration of the neurophysiological patterns) are discussed together with the rules that should guide the dialogue between the surgeon, the anesthesiologist, and the neurophysiologist.

Dose-response to anaesthetic induction with sufentanil: haemodynamic and electroencephalographic effects

PURPOSE

To determine the effect of a five-fold variation in sufentanil dose on the haemodynamic and electroencephalo graphic (EEG) response to anaesthetic induction and tracheal intubation.

METHODS

Thirty-four patients undergoing elective coronary artery bypass grafting (CABG) participated in this randomized double-blind study. Patients in Group L (n = 17) received 3 micrograms.kg-1 sufentanil and those in Group H (n = 17) 15 micrograms.kg-1. Premedication was 60 micrograms.kg-1 lorazepam po. Anaesthesia and neuromuscular blockade were induced by infusing sufentanil and 0.15 mg.kg-1 vecuronium i.v. over five minutes. Haemodynamic data and the electroencephalographic (EEG) spectral edge were acquired by computer and compared at Control, Induction and Intubation.

RESULTS

Sufentanil dose did not affect the haemodynamic or EEG response at end-induction. No bradyarrhythmias occurred, and the incidence of hypotension was 12% in both groups. However, during induction apparent electromyographic artifacts and a transiently greater increase in heart rate were observed in Group H. The serum sufentanil concentration at Induction was 6.1 +/- 1.8 ng.ml-1 in Group L and 25.4 +/- 8.8 ng.ml-1 in Group H, and did not correlate with haemodynamic changes. No patient recalled any intraoperative event.

CONCLUSION

Increasing sufentanil dose from 3 to 15 micrograms-1 does not influence the ultimate haemodynamic response to induction. Combined with lorazepam premedication, 3 micrograms-1 sufentanil produces near-maximal haemodynamic and EEG effects and is adequate for induction and tracheal intubation of patients undergoing CABG. Sufentanil 15 micrograms.kg-1 is no more efficacious, and causes transient cardiovascular stimulation.

EEG-controlled "overdosage" of anesthetics in a patient with a history of intra-anesthetic awareness

In spite of the ever-growing pharmacologic arsenal available for induction and maintenance of anesthesia, to our knowledge no treatment regimen exists that will provide full protection against intraoperative awareness. To date, no single monitoring technique is able to detect awareness or predict recall. Although the frequency of these complications is rare, the occurrence of any such event can be very distressful for the patient. Based on our clinical experience with a patient with a history of recall and a marked resistance to benzodiazepines, we present electroencephalogram-based anesthetic management as a technique to address this difficult problem.

Neural networks and nonlinear regression modelling and control of depth of anaesthesia for spontaneously breathing and ventilated patients

Various attempts have been made to control the depth of anaesthesia by observing different variables. In some studies, depth of anaesthesia has been correlated with inferential parameters and the control has been made through these inferred parameters. No single system has been reported which provides a fully developed architecture to control the depth of anaesthesia. This study is concerned with the development of controllers and patient models via Artificial Neural Networks and regression analysis. Two types of data sets were used for the training and development of models and controllers. The first set was for spontaneously breathing and the second set for ventilated patients. All of the controllers and patient models gave satisfactory results when tested individually. Later these two sets of controllers and patient models were studied in closed-loop modes. The robustness to the sensitivity of the regression patient model was also investigated. Various tests were performed with these closed-loop situations. Results and performance of these tests are discussed in the paper.

Intracranial pressure during induction of anaesthesia and tracheal intubation with etomidate-induced EEG burst suppression

This study was designed to determine if induction of anaesthesia with etomidate titrated to an early EEG burst suppression pattern would produce minimal changes in cerebral perfusion pressure, and prevent increases in intracranial pressure (ICP) associated with tracheal intubation. Eight patients, 18-71 yr, with intracranial space-occupying lesions, were studied. In each patient ICP was monitored via a lateral ventriculostomy catheter placed preoperatively. In the operating room, an ECG, a radial arterial line, and a two-channel computerized EEG were placed. Control (awake) measurements of MAP (mmHg), ICP (mmHg), CPP (mmHg), heart rate (HR-bpm), EEG power (picowatts-pW), and spectral edge frequency (SEF, Hz) were obtained. Anaesthesia was induced with etomidate, 0.2 mg.kg-1 iv, followed immediately by an etomidate infusion, 20 mg.min-1, iv, and vecuronium 0.2 mg.kg-1 iv. When early burst suppression was achieved, the etomidate infusion was stopped and tracheal intubation performed. The etomidate dose (bolus plus infusion) required to reach burst suppression was 1.28 +/- 0.11 mg.kg-1. Compared with awake control values (mean +/- SE), the period from induction to burst suppression was associated with a 50% decrease in ICP (22 +/- 1 vs 11 +/- 1 mmHg, P less than 0.01), but there were no changes in MAP, CPP, or HR. The decrease in ICP was maintained during the first 30 sec and the following 60 sec after intubation as MAP and HR remained unchanged. Our results suggest that when etomidate was administered to early burst suppression pattern on EEG, minimal changes in CPP occurred during induction of anaesthesia and a marked reduction in ICP was maintained following tracheal intubation.