Bispectral Index Changes during Acute Brainstem TIA/Ischemia

We describe a 76-year-old patient who suffered a brainstem TIA just before being anesthetised for cardiac surgery. The TIA was registered on BIS and resulted in a drop in BIS to a value of 60. When consciousness returned spontaneously, the BIS increased to 85. The relative use of the BIS during an operation is discussed. We believe that the lack of input from the brainstem to the frontal cortex resulted in the reduced cortical electrical activity as registered with the BIS

Multi-level approach to anaesthetic effects produced by sevoflurane or propofol in humans: 1. BIS and blink reflex.

Contains fulltext : 53194.pdf (publisher's version ) (Closed access)BACKGROUND: The relative roles of forebrain and brainstem in producing adequate anaesthesia are unclear. METHODS: We simultaneously analysed the effects of sevoflurane (Group S; n = 18) or propofol (Group P; n = 29) on the bispectral index (BIS) and the first component of the blink reflex (R1). The dose of anaesthetic agent was increased until loss of blink reflex. After discontinuation and reappearance of blink reflex activity, the amount was increased again. The area under curve R1 (area-R1) of the electromyogram of the orbicularis oculi muscle after electrical stimulation of the supraorbital nerve was measured. Using a sigmoid E(max) model and a first-order rate constant k(e0), we characterized the dose-response relationships for BIS and area-R1. RESULTS: Concentration-dependent depression of BIS and area-R1 was adequately modelled. The concentration that causes an effect midway between minimum and maximum (EC50) for area-R1 was smaller than EC50 for BIS in both groups [0.34 (0.19) vs 1.29 (0.19) vol% and 1.78 (0.65) vs 2.69 (0.67) mug ml(-1); mean (sd)]. At doses of sevoflurane and propofol with equivalent depression of BIS, sevoflurane depressed area-R1 more than propofol. The k(e0) for area-R1 was about half that for BIS in both groups: 0.24 (0.19-0.29) vs 0.48 (0.38-0.60) min(-1) for Group S; 0.28 (0.23-0.34) vs 0.46 (0.40-0.54) min(-1) for Group P, geometric mean (95% CI). CONCLUSIONS: The blink reflex (brainstem function) is more sensitive to sevoflurane or propofol than BIS (forebrain function). Sevoflurane suppresses the blink reflex more than propofol. Different k(e0)s for blink reflex vs BIS indicate different effect sites

Decoding motor responses from the EEG during altered states of consciousness induced by propofol

Contains fulltext : 157484.pdf (publisher's version ) (Open Access)Objective. Patients undergoing general anesthesia may awaken and become aware of the surgical procedure. Due to neuromuscular blocking agents, patients could be conscious yet unable to move. Using brain–computer interface (BCI) technology, it may be possible to detect movement attempts from the EEG. However, it is unknown how an anesthetic influences the brain response to motor tasks. Approach. We tested the offline classification performance of a movement-based BCI in 12 healthy subjects at two effect-site concentrations of propofol. For each subject a second classifier was trained on the subject’s data obtained before sedation, then tested on the data obtained during sedation (‘transfer classification’). Main results. At concentration 0.5 μ g ml -1 , despite an overall propofol EEG effect, the mean single trial classification accuracy was 85% (95% CI 81%- 89%), and 83% (79%-88%) for the transfer classification. At 1.0 μ g ml -1 , the accuracies were 81% (76%-86%), and 72% (66%-79%), respectively. At the highest propofol concentration for four subjects, unlike the remaining subjects, the movement-related brain response had been largely diminished, and the transfer classification accuracy was not significantly above chance. These subjects showed a slower and more erratic task response, indicating an altered state of consciousness distinct from that of the other subjects. Significance. The results show the potential of using a BCI to detect intra-operative awareness and justify further development of this paradigm. At the same time, the relationship between motor responses and consciousness and its clinical relevance for intraoperative awareness requires further investigation.9 p

Towards a novel monitor of intraoperative awareness: Selecting paradigm settings for a movement-based brain-computer interface

Contains fulltext : 103039.pdf (publisher's version ) (Open Access)During 0.1-0.2% of operations with general anesthesia, patients become aware during surgery. Unfortunately, pharmacologically paralyzed patients cannot seek attention by moving. Their attempted movements may however induce detectable EEG changes over the motor cortex. Here, methods from the area of movement-based brain-computer interfacing are proposed as a novel direction in anesthesia monitoring. Optimal settings for development of such a paradigm are studied to allow for a clinically feasible system. A classifier was trained on recorded EEG data of ten healthy non-anesthetized participants executing 3-second movement tasks. Extensive analysis was performed on this data to obtain an optimal EEG channel set and optimal features for use in a movement detection paradigm. EEG during movement could be distinguished from EEG during non-movement with very high accuracy. After a short calibration session, an average classification rate of 92% was obtained using nine EEG channels over the motor cortex, combined movement and post-movement signals, a frequency resolution of 4 Hz and a frequency range of 8-24 Hz. Using Monte Carlo simulation and a simple decision making paradigm, this translated into a probability of 99% of true positive movement detection within the first two and a half minutes after movement onset. A very low mean false positive rate of <0.01% was obtained. The current results corroborate the feasibility of detecting movement-related EEG signals, bearing in mind the clinical demands for use during surgery. Based on these results further clinical testing can be initiated.9 p

Patient state index vs bispectral index as measures of the electroencephalographic effects of propofol.

Contains fulltext : 89815.pdf (publisher's version ) (Open Access)BACKGROUND: The patient state index (PSI) and the bispectral index (BIS) quantify anaesthetic depth based on the EEG using different algorithms. We compared both indices with regard to the prediction of the depth of propofol anaesthesia. METHODS: In 17 patients, propofol was infused until burst suppression occurred and stopped thereafter until BIS recovered to values above 60. This was repeated; afterwards, patients were intubated, for subsequent surgery. Without surgical stimulus, PSI and BIS were measured simultaneously and compared with the estimated effect-site concentrations of propofol. These were derived from simultaneous pharmacokinetic and -dynamic modelling in an individual two-stage and a population-based NONMEM approach. RESULTS: A close sigmoid relationship was observed between the propofol effect-site concentration and both PSI [coefficient of determination rho(2)=0.91 (sd 0.05)] and BIS [rho(2)=0.92 (0.03)], which was significantly steeper for PSI [gamma=2.2 (0.6)] than for BIS [gamma=1.8 (0.4)], and reached significantly lower values for PSI [E(max)=0.3 (1.1)] than for BIS [E(max)=5.3 (6.7)] at maximal propofol concentrations. A significantly smaller k(e0) was obtained for PSI [0.09 (0.03) min(-1)] compared with BIS [0.10 (0.02) min(-1)]. PSI and BIS correlated significantly with each other (rho(2)=0.866) and predicted propofol effect-site concentration with a comparable probability [P(K)=0.87 (0.05) and 0.86 (0.05), respectively]. NONMEM revealed E(0)=89.3 and 92.3, E(max)=1.9 and 8.6, C(e50)=1.38 and 1.92 microg ml(-1), gamma=1.6 and 1.48, and k(e0)=0.103 and 0.131 min(-1) as typical values for PSI and BIS, respectively. CONCLUSIONS: The PSI and the BIS monitors performed equally well in predicting depth of propofol anaesthesia. However, PSI was lower than BIS by approximately 10-15 points at high propofol concentrations.1 augustus 201

Electromyographic assessment of blink and corneal reflexes during midazolam administration: useful methods for assessing depth of anesthesia?

Item does not contain fulltextBACKGROUND: There are at least three components of the anesthetic state: loss of consciousness, amnesia and obtundation of reflex responses to noxious stimuli. To investigate the third component, we used a standard electrical stimulus to evoke a blink reflex, which was electromyographically recorded. These data may give information on the anesthetic state. METHODS: The relation between the electrically evoked blink and corneal reflexes and the depth of sedation and anesthesia induced with intravenous midazolam was investigated. Ten patients received i.v. increments of midazolam (1 mg, 2 mg, 3 mg, 3 mg, 3 mg, etc., until a 21-mg total dose) to create a step-wise deepening of sedation and anesthesia. Depth of anesthesia was assessed by the Observer's Assessment of Alertness/Sedation (OAAS) scale, ranging from 5 ( = awake and alert) to 0 ( = no motor response to tetanic stimulation). RESULTS: Latency of the first (R1) and second (R2) blink components and the corneal (C) reflex component increased, whereas duration and area decreased with increasing depth of sedation and anesthesia. R1 was last seen at an OAAS score [mean (SD)] of 1.8 (0.8), R2 at a score of 3.1 (1.1), C at a score of 3.8 (0.8), and R3 at 4.8 (0.5). These end-points were all statistically different from each other, except R2 vs. C. CONCLUSIONS: Our results suggest that the differential sensitivity of the components of the blink reflex could be useful to monitor depth of sedation and light levels of anesthesia during the administration of midazolam

Detection of attempted movement from the EEG during neuromuscular block: proof of principle study in awake volunteers.

Brain-Computer Interfaces (BCIs) have the potential to detect intraoperative awareness during general anaesthesia. Traditionally, BCI research is aimed at establishing or improving communication and control for patients with permanent paralysis. Patients experiencing intraoperative awareness also lack the means to communicate after administration of a neuromuscular blocker, but may attempt to move. This study evaluates the principle of detecting attempted movements from the electroencephalogram (EEG) during local temporary neuromuscular blockade. EEG was obtained from four healthy volunteers making 3-second hand movements, both before and after local administration of rocuronium in one isolated forearm. Using offline classification analysis we investigated whether the attempted movements the participants made during paralysis could be distinguished from the periods when they did not move or attempt to move. Attempted movement trials were correctly identified in 81 (68-94)% (mean (95% CI)) and 84 (74-93)% of the cases using 30 and 9 EEG channels, respectively. Similar accuracies were obtained when training the classifier on the participants' actual movements. These results provide proof of the principle that a BCI can detect movement attempts during neuromuscular blockade. Based on this, in the future a BCI may serve as a communication channel between a patient under general anaesthesia and the anaesthesiologist