Browsing by Author "Ferreira, David A."
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- Brain monitoring in dogs using the cerebral state index during the induction of anaesthesia via target-controlled infusion of propofolPublication . Ribeiro, Lénio M.; Ferreira, David A.; Bressan, Nadja; Amorim, Pedro; Antunes, Luis M.; Nunes, Catarina S.The aim of this study was to evaluate the correlation between the cerebral state index (CSI) and the estimated propofol plasma concentrations in dogs during induction of anaesthesia. Fifteen healthy dogs undergoing scheduled routine surgical procedures were enrolled in this study. Target controlled infusion (TCI) software, based on the pharmacokinetic model for propofol, was used to control the syringe pump and to estimate plasma propofol concentrations (PropCp) and the CSI values every five-seconds. Three electrodes placed in the centre of the forehead, on the left side of the forehead and on the left mastoid were used to collect the electroencephalographic (EEG) signal converted by the cerebral state monitor into the CSI. The cerebral electrical changes induced by increasing propofol concentrations appear to be detected by CSI monitoring in dogs. The negative correlation between CSI and PropCp demonstrates that the CSI could be used to assess electrical brain activity in dogs during the induction of anaesthesia with propofol.
- Brain tumors may alter the relationship between bispectral index values and propofol concentrations during induction of anesthesiaPublication . Ferreira, David A.; Nunes, Catarina S.; Lobo, Francisco; Casal, Manuela; Antunes, Luís M.; Amorim, PedroStudy Objective: To compare propofol-predicted effect-site concentrations (PropCe) and bispectral index (BIS) of the electroencephalogram during induction of anesthesia in patients with small brain tumors and to analyze BIS and PropCe at loss of consciousness (LOC). Design: Prospective investigation. Setting: Operating theater of a university hospital. Patients: 26 ASA physical status I and II patients, 13 of whom were scheduled for nontumor spinal surgeries, and the other 13, for brain surgery for small brain tumor removal. Interventions: Anesthesia was induced with a propofol 1% constant infusion rate of 200 mL/h until LOC. Measurements: BIS, PropCe, heart rate, and mean arterial pressure were analyzed at the beginning of the propofol infusion and every 30 seconds during induction. Main Results: The BIS values were significantly higher in patients with brain tumors in the period from 150 to 210 seconds, with PropCe similar to patients without brain tumors. Loss of consciousness occurred 3.6 ± 0.8 minutes in patients without brain tumors and 3.9 ± 0.7 minutes in patients with brain tumors. No differences were observed between groups in the time to LOC (3.6 ± 0.8 in group 1 vs 3.9 ± 0.7 in group 2) or in BIS at LOC (48.7 ± 11.4 in group 1 vs 58.6 ± 21.7 in group 2). Conclusions: For similar propofol concentrations, patients with small brain tumors show higher BIS values on induction of anesthesia with propofol.
- Clinical variables related to propofol effect-site concentrations at recovery of consciousness after neurosurgical proceduresPublication . Nunes, Catarina S.; Ferreira, David A.; Antunes, Luís; Amorim, PedroTarget controlled infusion (TCI) systems and computer data acquisition software are increasingly used in anesthesia. It was hypothesized that the use of such systems might allow retrieval of information useful to anticipate the effect-site concentrations of propofol at which patients would recover from anesthesia. The goal of the study was to identify variables related to propofol effect-site concentrations at recovery of consciousness (ROC). Sixteen patients with a Glasgow of 15, ASA 1 or 2, subjected to neurosurgical procedures, received TIVA with TCI propofol and remifentanil. Data were collected every 5 seconds from Datex AS3 and Aspect A200XP (BIS). Effect-site TCI was used for propofol (initial effect target 5.0 mg/ml) and for remifentanil (initial plasma target 2.5 ng/ml). All clinical events were noted. Variables possibly related to propofol effect-site concentration at ROC were selected. Data are expressed as mean 6 SD. Effect-site propofol concentration at ROC was 1.3 6 0.5 mg/ml. A positive correlation was found between propofol effectsite concentration at ROC and: age (49.3 6 17 years) (P = 0.003); mean remifentanil dose during surgery (0.11 6 0.05 mg/kg/min) (P = 0.003); mean propofol dose during surgery (0.12 6 0.03 mg/kg/min) (P = 0.046); and remifentanil effect-site concentration at ROC (2.85 6 2.06 ng/ml) (P = 0.002). Propofol effect-site concentrations were not correlated with: weight, height, LBM, duration of anesthesia, minimum BIS at induction (30.4 6 6.8), time till minimum BIS (4.7 6 2.2 min), mean and median BIS during surgery (38.2 6 4.5 and 37.8 6 5.3). BIS-related variables were not useful as ROC predictors. Only drug variables and age correlated with propofol effectsite concentrations at ROC.
- Controlling the hypnotic drug (propofol) to maintain a stable depth of anesthesia, in dogsPublication . Bras, Susana; Ribeiro, Lenio; Ferreira, David A.; Antunes, Luis; Nunes, Catarina S.The development of control and automatic systems is important to guarantee a stable anesthesia, with no under or over dosage, and no awareness episodes. In this study a controller for the Cerebral State Index (CSI — an electroencephalogram derived signal) was developed. This study was a simulation study, the CSI was modeled using a fuzzy logic model with two inputs the effect-site concentration of propofol and the electromyography (EMG). The controller was tested using constant and variable references in an exhaustive set of simulations. The controller developed presents a good performance in all simulations and the controlled variable seems to be influenced by electromyography level. A controller for propofol anesthesia for veterinary use is an important step towards the improvement of animal welfare. The overall aim is to improve animal safety and comfort.
- Electroencephalogram-based indices applied to dogs' depth of anaesthesia monitoringPublication . Brás, Susana; Georgakis, A.; Ribeiro, L.; Ferreira, David A.; Silva, A.; Antunes, L.; Nunes, Catarina S.Hypnotic drug administration causes alterations in the electroencephalogram (EEG) in a dose-dependent manner. These changes cannot be identified easily in the raw EEG, therefore EEG based indices were adopted for assessing depth of anaesthesia (DoA). This study examines several indices for estimating dogs' DoA. Data (EEG, clinical end-points) were collected from 8 dogs anaesthetized with propofol. EEG was initially collected without propofol. Then, 100 ml h−1 (1000 mg h−1) of propofol 1% infusion rate was administered until a deep anaesthetic stage was reached. The infusion rate was temporarily increased to 200 ml h−1 (2000 mg h−1) to achieve 80% of burst suppression. The index performance was accessed by correlation coefficient with the propofol concentrations, and prediction probability with the anaesthetic clinical end-points. The temporal entropy and the averaged instantaneous frequency were the best indices because they exhibit: (a) strong correlations with propofol concentrations, (b) high probabilities of predicting anaesthesia clinical end-points.
- Fuzzy logic model to describe anesthetic effect and muscular influence on EEG Cerebral State IndexPublication . Brás, S.; Gouveia, S.; Ribeiro, L.; Ferreira, David A.; Antunes, L.; Nunes, Catarina S.The well-known Cerebral State Index (CSI) quantifies depth of anesthesia and is traditionally modeled with Hill equation and propofol effect-site concentration (Ce). This work brings out two novelties: introduction of electromyogram (EMG) and use of fuzzy logic models with ANFIS optimized parameters. The data were collected from dogs (n = 27) during routine surgery considering two propofol administration protocols: constant infusion (G1, n = 14) and bolus (G2, n = 13). The median modeling error of the fuzzy logic model with Ce and EMG was lower or similar than that of the Hill with Ce (p = 0.012-G1, p = 0.522-G2). Furthermore, there was no significant performance impact due to model structure alteration (p = 0.288-G1, p = 0.330-G2) and EMG introduction increased or maintained the performance (p = 0.036-G1, p = 0.798-G2). Therefore, the new model can achieve higher performance than Hill model, mostly due to EMG information and not due to changes in the model structure. In conclusion, the fuzzy models adequately describe CSI data with advantages over traditional Hill models.
- Hemodynamic and bispectral index responses to high doses of remifentanil in patients with brain tumors submitted to neurosurgical proceduresPublication . Ribeiro, Lénio; Ferreira, David A.; Amorim, Pedro; Lobo, Francisco; Nunes, Catarina S.; Antunes, Luís
- Individual effect-site concentrations of propofol at return of consciousness are related to the concentrations at loss of consciousness and age in neurosurgical patientsPublication . Nunes, Catarina S.; Ferreira, David A.; Antunes, Luís; Lobo, Francisco; Santos, Isabel A.; Amorim, PedroStudy Objective: To investigate whether a patient's propofol effect-site concentration at return to consciousness (ROC) was related to the propofol effect-site concentration at loss of consciousness (LOC) and to patients' individual demographic parameters. Design: Prospective study. Setting: Operating room. Patients: 31 ASA physical status I and II neurosurgical patients with Glasgow Coma Score N 15, and scheduled to receive total intravenous anesthesia with effect-site target controlled infusion (TCI) of propofol and remifentanil. Interventions: A constant propofol infusion was administered until LOC. At LOC, remifentanil started with a plasma concentration target of 2.5 ng mL 1 . Main Results: Propofol concentration at LOC was 4.9 ± 1 μg mL 1 . At ROC, propofol and remifentanil concentrations were 1.16 ± 0.3 μg mL 1 and 3.41 ± 1.5 ng mL 1 . Significant correlation was observed between propofol concentrationa at ROC and LOC, between propofol concentration at ROC and patient age (48.7 ± 15 yrs), and between propofol concentrations at ROC and LOC, divided by patient's age. Conclusions: The correlation between propofol concentrations at ROC and LOC was improved by inclusion of patient age data.
- Modeling anesthetic drugs' pharmacodynamic interaction on the bispectral index of the EEG: the influence of heart ratePublication . Nunes, Catarina S.; Mendonca, Teresa; Bras, Susana; Ferreira, David A.; Amorim, PedroThe effect of drugs’ interaction on the brain signal Bispectral Index (BIS) is of great importance for an anesthesia control drug infusion system. In this study, the objective was to inspect the influence of patient’s heart rate on the effect of the drugs on BIS. With this goal, the patient’s heart rate was incorporated in an drug interaction model. The model was fitted per patient during anesthesia induction, and tested for prediction under surgery. The results showed that the model with time changing parameters incorporating patient’s heart rate has a better performance than a non adjusted model. Three clusters of models were also identified using the fuzzy cmeans algorithm. These clusters will help to distinguish between different patients’ dynamics.
- Modelling drugs' pharmacodynamic interaction during general anaesthesia: the choice of pharmacokinetic modelPublication . Nunes, Catarina S.; Mendonça, Teresa F.; Antunes, Luís; Ferreira, David A.; Lobo, Francisco; Amorim, PedroThe effect of drugs’ interaction on the brain signal Bispectral Index (BIS) is of great importance for an anaesthesia control drug infusion system. In this study, two renowned pharmacokinetic (PK) models for propofol are compared, in order to evaluate its influence on the performance/predictably of a drug interaction model for BIS, considering data of 45 patients. The model was fitted per patient during anaesthesia induction, and tested for prediction under surgery. The results showed that the choice of PK model had influence on the overall performance. In the prediction phase, only one PK model presented good results with small errors.