Loading...
15 results
Search Results
Now showing 1 - 10 of 15
- 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.
- 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.
- EEG signatures at the transition between conscious and unconscious state during induction of general anesthesia with remifentanil and propofolPublication . Ferreira, Ana Isabel Leitão; Mendes, Joaquim; Amorim, Pedro; Nunes, Catarina S.The precise identification of the moment of Loss Of Consciousness (LOC) during the induction phase of general anesthesia is of extreme importance for the individualization of drug doses. In the lack of an objective method to assess this moment, the development of a new methodology is needed. In this observational study, Electroencephalogram (EEG) signatures that were associated with the moment of LOC are examined as a starting point, so as to create a robust model for tracking the dynamic changes between conscious and unconscious states. The data from 12 patients under general anesthesia for neurosurgical procedures with remifentanil and propofol, are used is this study. Multitaper spectrograms were computed to observe the dynamics of EEG oscillations before and after LOC. At LOC, a decrease in gamma power and an increase in delta and alpha bands were identified.
- Usefulness of brain signals for the detection of loss of consciousness in anesthesia: overview of the problem and results from a Clinical StudyPublication . González, Carmen; Mendes, Marina; Amorim, Pedro; Mendes, Joaquim; Nunes, Catarina S.Loss of consciousness (LOC) detection is essential for better anesthesia guidance. Clinical signs and brain monitoring are currently used in operating rooms to assess the state of consciousness. However, a patientindependent, accurate and reliable indicator of LOC is not currently available. We studied 69 patients undergoing general anesthesia, investigating a possible relationship between loss of consciousness and BIS and EMG signals registered during induction. Neither BIS and EMG values at LOC, nor their abrupt fall proved to be good indicators of loss of consciousness. Further work needs to be done in order to reliably detect loss of consciousness.
- Automation in anesthesia: computer controlled propofol infusion and data acquisitionPublication . Bressan, Nadja; Castro, Ana; Braga, Carlos; Lages, Jose; Silva, Nuno R.; Portela, Paulo; Miranda, Pedro; Oliveira, Sergio; Mendes, Joaquim; Amorim, Pedro; Nunes, Catarina S.This work presents the improvement of a software for a clinical setup, the Anesthesia Synchronization Software (ASYS). The first version presented the data acquisition from cerebral monitors and a partial control with Target Controlled Infusion (TCI) system. Based on pharmacokinetic models, the effect-site and plasma concentrations can be related with the drug dose infused and vice versa. This later version comes with the implementation of the hemodynamic monitor always present in operating rooms and with the full TCI system developed to determine the infusion rates of the drug which are given as commands to the infusion pumps.
- Usefulness of the blink reflex to assess the effect of propofol during induction of anesthesia in surgical patientsPublication . Ferreira, Ana Isabel Leitão; Nunes, Catarina S.; Mendes, Joaquim; Amorim, PedroThe aim of this study was to investigate the relation between the blink reflex evoked by an electrical stimulus and the depth of anesthesia induced with intravenous anesthetic drug propofol. The blink reflex was stimulated before the propofol infusion started (baseline) and after, every 6 s. The electromyographic responses and the level of sedation/anesthesia scores as well as the estimated effect-site concentration of propofol were recorded in 11 patients. The blink reflex responses were abolished when patients were still conscious. The clinical scale of anesthesia increased with increasing concentrations of propofol. To predict the level of sedation/anesthesia a multinomial logistic regression was performed using blink reflex extracted features at the frequency domain. Several features proved to be good predictor estimates and the model showed to be useful. This information could be helpful to assess the moment of loss of consciousness and thus personalize anesthesia.
- Comparison of two pharmacokinetic–pharmacodynamic models of rocuronium bromide during profound neuromuscular block: analysis of estimated and measured post-tetanic count effectPublication . Couto, Mafalda; Vide, Sérgio; Marco-Ariño, Nicolás; Troconiz, Iñaki F.; Esteves, Simão; Nunes, Catarina S.; Amorim, Pedro; Mendes, JoaquimBackground: Profound neuromuscular block (NMB) is important in surgeries where complete immobility is considered essential to improve tracheal intubation and surgical conditions. Rocuronium bromide is a commonly used NMB agent. This work describes a noninvasive approach for estimation of post-tetanic count (PTC) based on two pharmacokinetic (PK) models, the Saldien and the De Haes models. The aim was to investigate the rocuronium bromide PKepharmacodynamic (PD) relationship in estimating the PTC effect during profound NMB. Methods: In this prospective, non-randomised, observational study, an induction bolus of rocuronium bromide was administered followed by continuous infusion for maintenance of a PTC of 1-2. measured every 3 min. Measurements were analysed as discrete categorical data and by applying the nonlinear mixed-effect modelling approach. Performance of the selected models was evaluated through simulation model-based diagnostics, further assessing the precision of the parameter estimates and the performance of the models at the individual level. Results: Data from 30 adult patients undergoing elective abdominal or neurosurgical procedures were included. Posttetanic count response profiles during rocuronium bromide infusion were successfully characterised using the population PD analysis. The models showed a good performance for all PTC categories, albeit with a moderate over-prediction of PTC >6. Conclusions: Our findings indicate that using plasma concentrations of rocuronium bromide estimated with either of the two models, combined with a PD model, provides equal model performance when predicting PTC. These promising results may provide an important advance in guiding rocuronium bromide administration when profound NMB in routine clinical practice is desired.
- TOF-Watch NMB monitoring misleading display output during moderate neuromuscular blockadePublication . Couto, Mafalda; Nunes, Catarina S.; Amorim, Pedro; Mendes, JoaquimIn general anesthesia, Neuromuscular Blockade (NMB) agents are administered to ensure intubation quality and complete immobilization. Monitoring NMB, based on the evoked response evaluation after a peripheral nerve stimulation, is essential to provide insight on medication dosing and suitable approaches for NMB reversal. Professionals often rely on the data displayed on the monitor screen after TOF stimuli, assuming measurements present the expected fade and a TOF-ratio > 90% is enough to rule out residual paralysis. This can be inaccurate and mislead the clinician to extubate before adequate NMB curarization. Data from 31 patients that underwent general anesthesia were retrospectively analyzed. All patients received a standard dose of rocuronium (0.6 mg/kg) for intubation, during maintenance additional rocuronium boluses were administered if solicited. NMB monitoring was done continuously applying TOF stimuli at the adductor pollicis with TOF-Watch SX®. Two types of monitoring display errors were studied: (1) valid TOF value without fade effect (invalid T1 > T2 > T3 > T4); (2) in the 30 min before extubation a valid TOF-ratio value > 90% (without error type 1) with T1 < 70%. Results show a mean (SD) of type 1 error on 42.0 (17.5)% of valid TOF measurements, type 2 error in 63 (45)%. Only 9 patients (29%) presented a TOF with no errors before extubation. These results may increase the distrust in the NMB monitoring devices, however its use should not be rejected when NMB agents are administered. Careful evaluation of the NMB is recommended and additional efforts should be placed in the accuracy of monitors data display to avoid errors.
- Implementation of neural networks to frontal electroencephalography for the identification of the transition responsiveness/unresponsiveness during induction of general anesthesiaPublication . Ferreira, Ana Isabel Leitão; Vide, Sérgio; Nunes, Catarina S.; Neto, Joaquim; Amorim, Pedro; Mendes, JoaquimObjective: General anesthesia is a reversible drug-induced state of altered arousal characterized by loss of responsiveness (LOR) due to brainstem inactivation. Precise identification of the LOR during the induction of general anesthesia is extremely important to provide personalized information on anesthetic requirements and could help maintain an adequate level of anesthesia throughout surgery, ensuring safe and effective care and balancing the avoidance of intraoperative awareness and overdose. So, main objective of this paper was to investigate whether a Convolutional Neural Network (CNN) applied to bilateral frontal electroencephalography (EEG) dataset recorded from patients during opioid-propofol anesthetic procedures identified the exact moment of LOR. Material and methods: A clinical protocol was designed to allow for the characterization of different clinical endpoints throughout the transition to unresponsiveness. Fifty (50) patients were enrolled in the study and data from all was included in the final dataset analysis. While under a constant estimated effect-site concentration of 2.5 ng/mL of remifentanil, an 1% propofol infusion was started at 3.3 mL//h until LOR. The level of responsiveness was assessed by an anesthesiologist every six seconds using a modified version of the Richmond Agitation-Sedation Scale (aRASS). The frontal EEG was acquired using a bilateral bispectral (BIS VISTA (TM) v2.0, Medtronic, Ireland) sensor. EEG data was then split into 5-second epochs, and for each epoch, the anesthesiologist's classification was used to label it as responsiveness (no-LOR) or unresponsiveness (LOR). All 5-second epochs were then used as inputs for the CNN model to classify the untrained segment as no-LOR or LOR. Results: The CNN model was able to identify the transition from no-LOR to LOR successfully, achieving 97.90 +/- 0.07% accuracy on the cross-validation set. Conclusion: The obtained results showed that the proposed CNN model was quite efficient in the responsiveness/unresponsiveness classification. We consider our approach constitutes an additional technique to the current methods used in the daily clinical setting where LOR is identified by the loss of response to verbal commands or mechanical stimulus. We therefore hypothesized that automated EEG analysis could be a useful tool to detect the moment of LOR, especially using machine learning approaches.
- Systematic review on Rocuronium continuous infusion for deep neuromuscular blockadePublication . Couto, Mafalda; Couto, J. Guilherme; Nunes, Catarina S.; Vide, Sérgio; Amorim, Pedro; Mendes, JoaquimBackground: Rocuronium is a muscle relaxant with increased use due to its binding relation with the reversal agent sugammadex. The purpose of this review entails the investigation of its use for the maintenance of Deep Neuromuscular Block (NMB) via continuous infusion. Methods: Based on PRISMA systematic search guidelines, databases included PubMed, ISI Web of Science, Cochrane Library and Google Scholar. This comprehensive search addresses surgical patients under deep muscle relaxation via continuous rocuronium infusion. The main indicators were the rocuronium administration, NMB monitoring approaches and effects in order to maintain the deep level of relaxation, as well as reversal time after a standard dose of sugammadex. Results: Despite the variance in approaches found in the literature, findings show the overall maintenance of deep NMB requires approximately 0.758 mg.kg-1h-1 of rocuronium (according to the PTC target of 0-10, 0-5 and 1-2, mean estimates are 0.445, 0.65 and 0.833 mg.kg-1h-1 respectively), suggesting that a lower range and a smaller maximum of PTC response require higher amount of rocuronium for its maintenance. The standard dose of sugammadex (4 mg/kg), administered at the end of the surgery takes longer [2.85 (1.17) min] than when they are administered after moderate NMB recovery [1.68 (0.47) min]. Conclusion: Continuous infusion for deep NMB presents inherent advantages in terms of maintenance and stability of muscle relaxation. Monitoring and rocuronium administration approaches are fundamental and intrinsically connected to provide a stable and improved maintenance of deep NMB.