Loading...
67 results
Search Results
Now showing 1 - 10 of 67
- Effect of propofol and remifentanil on a somatosensory evoked potential indicator of pain perception intensity in volunteersPublication . Castro, Ana; Amorim, Pedro; Nunes, Catarina S.; Almeida, Fernando Gomes deSomatosensory evoked potentials (SEPs) have been linked to noxious activation and stimulus intensity. In this exploratory study we investigated the impact of anaesthetic drugs on SEPs and pain ratings, to assess their applicability as an objective measure of the nociception/anti-nociception balance. Following institutional approval and written informed consent, 10 healthy adult volunteers were enrolled (29.5 ± 9.1 years, 63.0 ± 8.9 kg and 171.4 ± 7.2). Median nerve electrical stimulation was adjusted according to volunteers' sensitive, motor and painful thresholds (PT). Baseline SEPs were registered, and remifentanil and propofol administered using a stair scheme TCI. For each drug combination a 1.3×PT stimulus was administered, and volunteers evaluated pain intensity in a numerical rating scale (0-10). SEPs' amplitudes and latencies were normalized by the baseline values, reducing volunteers' intervariability. Stimulation currents varied between 6-52 mA (1.3×PT) and pain ratings between 0 and 9. Cortical SEPs latencies were decreased for higher stimulus intensities (P < 0.01), accompanied by increased pain ratings (P < 0.01). An individually adjusted/normalized ratio based on cortical SEPs amplitude and interpeak latency is proposed([Formula: see text]): [Formula: see text] and NSR were significantly correlated in three out of nine subjects, and [Formula: see text] and remifentanil Ce were significantly correlated in two (low number of evaluation points). [Formula: see text] was shown to decrease with increasing doses of propofol and remifentanil (P < 0.05). The proposed metric was depressed by anaesthetics and reflected pain evaluations. Further research is necessary to increase the number of volunteers and drugs' combination, to assess its applicability during surgically adequate anesthetic leves.
- A novel multivariate STeady-state index during general ANesthesia (STAN)Publication . Castro, Ana; Almeida, Fernando Gomes de; Amorim, Pedro; Nunes, Catarina S.The assessment of the adequacy of general anesthesia for surgery, namely the nociception/anti-nociception balance, has received wide attention from the scientific community. Monitoring systems based on the frontal EEG/EMG, or autonomic state reactions (e.g. heart rate and blood pressure) have been developed aiming to objectively assess this balance. In this study a new multivariate indicator of patients' steady-state during anesthesia (STAN) is proposed, based on wavelet analysis of signals linked to noxious activation. A clinical protocol was designed to analyze precise noxious stimuli (laryngoscopy/intubation, tetanic, and incision), under three different analgesic doses; patients were randomized to receive either remifentanil 2.0, 3.0 or 4.0 ng/ml. ECG, PPG, BP, BIS, EMG and [Formula: see text] were continuously recorded. ECG, PPG and BP were processed to extract beat-to-beat information, and [Formula: see text] curve used to estimate the respiration rate. A combined steady-state index based on wavelet analysis of these variables, was applied and compared between the three study groups and stimuli (Wilcoxon signed ranks, Kruskal-Wallis and Mann-Whitney tests). Following institutional approval and signing the informed consent thirty four patients were enrolled in this study (3 excluded due to signal loss during data collection). The BIS index of the EEG, frontal EMG, heart rate, BP, and PPG wave amplitude changed in response to different noxious stimuli. Laryngoscopy/intubation was the stimulus with the more pronounced response [Formula: see text]. These variables were used in the construction of the combined index STAN; STAN responded adequately to noxious stimuli, with a more pronounced response to laryngoscopy/intubation (18.5-43.1 %, [Formula: see text]), and the attenuation provided by the analgesic, detecting steady-state periods in the different physiological signals analyzed (approximately 50 % of the total study time). A new multivariate approach for the assessment of the patient steady-state during general anesthesia was developed. The proposed wavelet based multivariate index responds adequately to different noxious stimuli, and attenuation provided by the analgesic in a dose-dependent manner for each stimulus analyzed in this study.
- Remifentanil analgesic interpatient variability assessed through pupillary reflex dilationPublication . Vide, Sérgio; Nunes, Catarina S.; Correia, Rui P.; Teixeira, J.; Antunes, P.; Rego, J.; Amorim, Pedro
- Feedforward adaptive control of the Bispectral Index of the EEG using the intravenous anaesthetic drug propofolPublication . Nunes, Catarina S.; Mendonça, Teresa; Lemos, João M.; Amorim, PedroThe problem of controlling the level of unconsciousness measured by the Bispectral Index (BIS) of the EEG of patients under anaesthesia is considered. The manipulated variable is the infusion rate of the hypnotic drug propofol. In order to tackle the high uncertainties present in the system, the predictive adaptive controller MUSMAR is used. The performance of the controller is illustrated by means of simulations with 50 patient individual adjusted models (nonlinear models), which incorporate the effect of the drugs interaction on BIS. This work presents a feasibility study of the control of the BIS exploring the above ideas. These results show that such a control structure can be adequate to control the BIS signal during total intravenous anaesthesia. The controller was able to adequately achieve and maintain the BIS signal with different patient dynamics, reference values and noise. A major challenge for the automation of anaesthesia consists of replicating the experience of the anaesthetist. Clearly, this calls for the use of feedforward from measurable signals correlated with disturbances (e.g. electromyography—EMG, analgesic drug). The results also show that the analgesic and EMG have different influences on the performance and therefore carry different but relevant information.
- Anaesthesia synchronization software: target controlled infusion system evaluationPublication . Bressan, Nadja; Moreira, A. Paulo; Amorim, Pedro; Nunes, Catarina S.Target Controlled Infusion (TCI) systems are based in drug Pharmacokinetic (Pk) and Pharmacodynamic (Pd) models implemented in an algorithm to drive an infusion device. Several studies had compare manual titration of anesthesia and TCI system use; some studies evaluate the performance of the control algorithms for TCI systems, and a considerable number of studies assess the performance of Pk/Pd models implemented into TCI systems. This study presents a set of tests to validate the performance of a TCI system as a computer-aided. The goal of the current study was to assess the performance of the TCI system, Anaesthesia Synchronization Software (ASYS), on clinical set up to evaluate communication consistence (computer - infusion device) and controller performance in real time. These measures provided quantitative and qualitative evidences of software robustness and accuracy to be used at clinical environment.
- Do we have today a reliable method to detect the moment of loss of consciousness during induction of general anaesthesia?Publication . Ferreira, Ana Isabel Leitão; Nunes, Catarina S.; Mendes, Joaquim; Amorim, PedroThis review aims to give an overview of the current state of monitoring depth of anaesthesia and detecting the moment of loss of consciousness, from the first clinical signs involved in anaesthesia to the latest technologies used in this area. Such techniques are extremely important for the development of automatic systems for anaesthesia control, including preventing intraoperative awareness episodes and overdoses. A search in the databases Pubmed and IEEE Xplore was performed using terms such anaesthetic monitoring, depth of anaesthesia, loss of consciousness, as well as anaesthesia indexes, namely BIS. Despite the several methods capable of monitoring the hypnotic state of anaesthesia, there is still no methodology to accurate detect the moment of loss of consciousness during induction of general anaesthesia.
- The Blink Reflex as a useful approach for assessing the effect of propofol during the induction phase of anesthesiaPublication . Ferreira, A.; Nunes, Catarina S.; Felgueiras, J.; Cardoso, M.; Mendes, J.; Amorim, Pedro
- The effect of a remifentanil bolus on the bispectral index of the EEG (BIS) in anaesthetized patients independently from intubation and surgical stimuliPublication . Ferreira, D. A.; Nunes, Catarina S.; Antunes, L. M.; Santos, I. A.; Lobo, F.; Casal, M.; Ferreira, L.; Amorim, PedroBackground and objective: Remifentanil boluses are used in different clinical situations and the effects on bispectral index monitoring are unclear. We analysed the effect of a remifentanil bolus on the bispectral index of the electroencephalogram (bispectral index) under total intravenous anaesthesia with propofol and remifentanil. Methods: ASA I–III patients were included in this study. All patients received a 2 µg kg 1 remifentanil bolus in a period free from stimuli. Bispectral index and haemodynamic data were collected from an A-2000XP bispectral index monitor (every second) and an AS/3 Datex monitor (every 5 s). Bispectral index data were analysed using the area under the curve. Mean arterial pressure and heart rate were averaged at each 30-s period and analysed using analysis of variance. Results: A total of 240 bispectral index values were obtained per patient. The area under the curve between 90 and 120 s after the bolus was significantly lower than the basal area under the curve (average of all areas before the bolus, P 0.05). Mean arterial pressure and heart rate were significantly reduced from 96.4 19.9 mmHg at the time of the bolus to 74.2 16.6 mmHg 120 s after, and from 70 16.4 bpm at the time of the bolus to 61 13.6 bpm after (P 0.001), respectively. Conclusions: There was a significant reduction in the areas under the curve between 90–120 s following the bolus. Heart rate and blood pressure also showed significant reductions. Thus, remifentanil bolus given under total intravenous anaesthesia with propofol and remifentanil decreases bispectral index, an effect independent of intubation and surgical stimuli.
- Electromyographic assessment of blink reflex throughout the transition from responsiveness to unresponsiveness during induction with propofol and remifentanilPublication . Ferreira, Ana Isabel Leitão; Vide, Sérgio; Felgueiras, João; Cardoso, Márcio; Nunes, Catarina S.; Mendes, Joaquim; Amorim, PedroGeneral anesthesia is a reversible drug-induced state of altered arousal characterized by loss of responsiveness due to brainstem inactivation. Precise identification of the moment in which responsiveness is lost during the induction of general anesthesia is extremely important to provide information regarding an individual's anesthetic requirements and help intraoperative drug titration. To characterize the transition from responsiveness to unresponsiveness more objectively, we studied neurophysiologic-derived parameters of electromyographic records of electrically evoked blink reflex as a means of identifying the precise moment of loss of responsiveness. Twenty-five patients received a slow infusion of propofol until loss of corneal reflex while successive blink reflexes were elicited and recorded every 6 s. The level of anesthesia was assessed using an adapted version of the Richmond Agitation-Sedation Scale. Different variables of the blink reflex components were calculated and compared to the adapted version of the Richmond Agitation-Sedation score and the estimated effect-site propofol concentration. Baselines of the blink reflex responses were similar to those in literature. After propofol infusion started, the most susceptible component of the blink reflex to propofol was R2 (EC50 = 1.358 (95% CI 1.321, 1.396) µg/mL) and the most resistant was R1 (EC50 = 3.025 (95% CI 2.960, 3.090) µg/mL). Most of the patients (24 out of 25) lost the R1 component when they were still responsive to shaking and shouting and corneal reflex could be elicited clinically (time = 102.48 ± 33.00 s). Habituation was present in R2 but not in R1. The R1 component of the blink reflex was found to have a strong correlation with the adapted version of the Richmond Agitation-Sedation Scale, with amplitude correlating better than areas (ρ = - 0.721 (0.123) versus ρ = - 0.688 (0.165)). We found a strong correlation between the R1 component with the estimated propofol effect-site concentration, with amplitude correlating better than areas (ρ = - 0.838 (0.113) versus ρ = - 0.823 (0.153)) and between the clinical scale and the propofol concentration (ρ = 0.856 (0.060)). The area and amplitude of the R1 component showed to be indicators of predicting different levels of anesthesia (Pk = 0.672 (0.183) versus Pk = 0.709 (0.134)) and these are connected to the propofol concentrations (Pk = 0.593 (0.10)). Our results suggest that electrically evoked blink reflex could be used during the induction of anesthesia as a surrogate of the Richmond Agitation-Sedation Scale to provide an objective endpoint as far as a - 4. At this point, at the moment of loss of R1, the propofol infusion may be stopped, as overshooting increases slightly the effect-site concentration afterward and eventually reaching loss of responsiveness. If the desired target is not achieved, the infusion can then be resumed.
- Incidência de BIS superior a 60 durante anestesia com propofol/remifentanil para cirurgia da coluna cervical e possível ocorrência de awareness, comparando bloqueio neuromuscular standard e profundoPublication . Amorim, Pedro; Saúl, Raquel; Nunes, Catarina S.