Browsing by Author "Ferreira, D. A."
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- Comparison of neural networks, fuzzy and stochastic prediction models for return of consciousness after general anesthesiaPublication . Nunes, Catarina S.; Mendonca, T. F.; Amorim, Pedro; Ferreira, D. A.; Antunes, L.This paper presents three modeling techniques to predict return of consciousness (ROC) after general anesthesia, considering the effect concentration of the anesthetic drug at awakening. First, several clinical variables were statistically analysed to determine their correlation with the awakening concentration. The anesthetic and the analgesic mean dose during surgery, and the age of the patient, proved to have significantly high correlation coefficients. Variables like the mean bispectral index value during surgery, duration of surgery did not present a statistical relation with ROC. Stochastic regression models were built using the variables with higher correlation. Secondly, fuzzy models were built using an Adaptive Network-Based Fuzzy Inference System (ANFIS) also relating different sets of variables. Thirdly, radial basis function (RBF) neural networks were trained relating different sets of clinical values with the anesthetic drug effect concentration at awakening. Clinical data was used to train and test the models. The stochastic models and the fuzzy models proved to have good prediction properties. The RBF network models were more biased towards the training set. The best balanced performance was achieved with the fuzzy models.
- Correlation between clinical signs of depth of anaesthesia and cerebral state index responses in dogs during induction of anaesthesia with propofolPublication . Ribeiro, L. M.; Ferreira, D. A.; Brás, S.; Castro, A.; Nunes, Catarina S.; Amorim, Pedro; Antunes, L. M.The cerebral state index (CSI) is used for monitoring EEG and depth of anaesthesia. The objective of this study was to analyse the correlation between ocular reflexes, CSI and estimated propofol plasma concentrations (PropCP) in dogs during induction of anaesthesia with propofol. Fourteen dogs were premedicated with acepromazine 0.05 mg kg1 IM. Anaesthesia was induced with a 200 ml h1 propofol 1% constant infusion rate until loss of corneal reflex using RugLoop II software with Beths’ pharmacokinetic model to estimate PropCp. Palpebral reflex (PR) and the corneal reflex (CR) were tested every 30 s and classified as present (+) or absent (), and eyeball position was registered as rotated ventromedialy (ERV) or centred (EC). Heart rate (HR), mean arterial pressure (MAP) and CSI values were analyzed from baseline before the beginning of propofol infusion (T0) until loss of CR; CSI and PropCp, CSI and anaesthetic planes, and PropCp and anaesthetic planes were compared using correlation analysis. PropCp reached 7.65 ± 2.1 lg ml1 at the end of the study. CSI values at T0 were 89.2 ± 3.8. Based on the observation of ocular reflexes and eyeball position, it was possible to define five anaesthetic planes: A (superficial) to E (deep), being A (PR+/CR+/EC), B (PR+/ERV/CR+), C (PR/ERV/CR+), D (PR/EC/CR+) and E (PR/EC/CR). There was a significant correlation between PropCp and the anaesthetic planes (R = 0,861; P < 0.01). No significant correlation was observed between CSI and the anaesthetic planes or between CSI and PropCp. MAP decreased significantly from T0 until loss of corneal reflex (from 98 ± 14 mmHg to 82 ± 12 mmHg); HR did not change significantly (from 101 ± 30 bpm to 113 ± 16 bpm). The CSI monitoring was not consistent with the clinical observations observed in the different stages of depth anaesthesia. This could limit the use of CSI for monitoring depth of anaesthesia with propofol.
- EMG contributes to improve cerebral state Index modeling in dogs anesthesiaPublication . Brás, S.; Ferreira, D. A.; Antunes, L.; Ribeiro, L.; Nunes, Catarina S.; Gouveia, S.Cerebral State Index (CSI) is a measure of depth of anesthesia (DoA) developed for humans, which is traditionally modeled with the Hill equation and the propofol effect-site concentration (Ce). The CSI has been studied in dogs and showed several limitations related to the interpretation of EEG data. Nevertheless, the CSI has a lot of potential for DoA monitoring in dogs, it just needs to be adjusted for this species. In this work, an adapted CSI model is presented for dogs considering a) both Ce and EMG as inputs and b) a fuzzy logic structure with parameters optimized using the ANFIS method. The new model is compared with traditional Hill model using data from dogs in routine surgery. The results showed no significant impact in the model performance with the change of model structure (Fuzzy instead of Hill). The residuals of the Hill model were significantly correlated with the EMG, indicating that the latter should be considered in the model. In fact, the EMG introduction in CSI model significantly decreased the modeling error: 11.8 [8.6; 15.2] (fuzzy logic) versus 20.9 [16.4; 29.0] (Hill). This work shows that CSI modeling in dogs can be improved using the current human anesthesia set-up, once the EMG signal is acquired simultaneously with the CSI index. However, it does not invalidate the search of new DoA indices more adjusted to use in dog’s anesthesia.
- Hydroxyethyl starch 130/0.4 can be useful to prevent a hemodynamic response to a single dose of remifentanilPublication . Ferreira, D. A.; Santos, I. A.; Nunes, Catarina S.; Amorim, Pedro; Antunes, L. M.El propofol y el remifentanilo se utilizan frecuentemente para la anestesia intravenosa. El uso combinado de las dos drogas tiende a causar depresión hemodinámica. Describimos, en dos pacientes, la ausencia de efectos hemodinámicos en respuesta a la administración de propofol y remifentanilo al combinarlo con la infusión de hidroxietilalmidón (HES) 130/0,4. Durante la inducción de la anestesia y debido a la necesidad de reponer el volumen sanguíneo, dos pacientes de 62 y 65 años recibieron una solución intravenosa de HES 130/0,4. A continuación, les fue administrado un bolus de 2 µg Kg–1 de remifentanilo bajo anestesia intravenosa total (TIVA) con propofol y remifentanilo, antes de la colocación del cabezal de Mayfield®. No observamos cambios en la presión arterial media ni en la frecuencia cardiaca como respuesta al bolus de remifentanilo en los pacientes que recibieron HES 130/0,4 bajo TIVA con propofol y remifentanilo. El HES 130/0,4 puede tener un papel activo en la prevención de la respuesta hemodinámica al remifentanilo al combinarlo con propofol. Para confirmar estos resultados es necesario realizar un estudio randomizado.
- Modelling the dynamics of depth of anaesthesia: cerebral state index in dogsPublication . Bressan, Nadja; Castro, A.; Bras, S.; Ribeiro, L.; Ferreira, D. A.; Silva, A.; Antunes, L.; Nunes, Catarina S.The goal of this study was to obtain models that described the relation between the anaesthetic drug infusions (propofol) and an electroencephalogram (EEG) derived index (Cerebral State Index - CSI) during general anaesthesia in dogs. The first phase integrated the adaptation of hardware for EEG acquisition and exploration for the best electrodes position in dogs skull. The clinical protocol implementation and data collection were the next steps followed by CSI modeling. CSI showed adequate response to changes in drug infusion, reflecting the changes of depth of anaesthesia in dogs. The models obtained adjusted well to the original CSI data and also predicted the CSI trend during surgery. Using this monitor in current practice might improve quality in the anaesthesia procedure providing a useful tool to administer a correct sedation.
- Radial basis function neural networks versus fuzzy models to predict return of consciousness after general anesthesiaPublication . Nunes, Catarina S.; Mendonca, T. F.; Amorim, Pedro; Ferreira, D. A.; Antunes, L. M.This paper presents two modelling techniques to predict return of consciousness (ROC) after general anaesthesia, considering the effect concentration of the anaesthetic drug at awakening. First, several clinical variables were statistically analysed to determine their correlation with the awakening concentration. The anaesthetic and the analgesic mean dose during surgery, and the age of the patient, proved to have significantly high correlation coefficients. Variables like the mean bispectral index value during surgery, duration of surgery did not present a statistical relation with ROC. Radial basis function (RBF) neural networks were trained relating different sets of clinical values with the anaesthetic drug effect concentration at awakening. Secondly, fuzzy models were built using an Adaptive Network-Based Fuzzy Inference System (ANFIS) also relating different sets of variables. Clinical data was used to train and test the models. The fuzzy models and RBF neural networks proved to have good prediction properties and balanced results.
- A step towards effect-site target-controlled infusion with propofol in dogs: a ke0 for propofolPublication . Brás, S.; Bressan, Nadja; Ribeiro, L.; Ferreira, D. A.; Antunes, L.; Nunes, Catarina S.Target-controlled infusion (TCI) anesthesia using target effect-site concentration rather than plasma concentration provides less drug consumption, safer anesthesia, less undesired side effects and improved animal welfare. The aim of this study was to calculate the constant that converts propofol plasma into effect-site concentration (ke0) in dogs, and to implement it in a TCI system and compare it with the effect on the central nervous system (CNS). All dogs were subjected to general anesthesia using propofol. Fourteen dogs were used as the pilot group to calculate ke0, using the tpeak method. Fourteen dogs were used as the test group to test and validate the model. Rugloop ii® software was used to drive the propofol syringe pump and to collect data from S/5 Datex monitor and cerebral state monitor. The calculated ke0 was incorporated in an existing pharmacokinetic model (Beths Model). The relationship between propofol effect site concentrations and anesthetic planes, and propofol plasma and effect-site concentrations was compared using Pearson’s correlation analysis. Average tpeak was 3.1 min resulting in a ke0 of 0.7230 min−1. The test group showed a positive correlation between anesthetic planes and propofol effect-site concentration (R = 0.69; P < 0.0001). This study proposes a ke0 for propofol with results that demonstrated a good adequacy for the pharmacokinetic model and the measured effect. The use of this ke0 will allow an easier propofol titration according to the anesthetic depth, which may lead to a reduction in propofol consumption and less undesired side effects usually associated to high propofol concentrations in dogs.
- 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.