Browsing by Author "Antunes, Luís"
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- 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.
- EEG entropy monitoring of depth of anaesthesia: pharmacokinetic and dynamic modellingPublication . Castro, Ana; Bressan, Nadja; Antunes, Luís; Nunes, Catarina S.Because of the difficulty in analyzing raw electroencephalographic signal, several electroencephalographic monitors have been developed to aid anaesthetists on their task to maintain adequate anaesthesia. Spectral Entropy is used as a measure of electroencefalographic effects of drugs in human patients, and is a valuable tool to predict depth of anaesthesia. Monitors with implemented entropy algorithms, process the electroencephalogram (EEG) and are in current use at the operating room. In this study we used the EEG collected in rats and applied the Shannon entropy over the signal. The information obtained was used as an indicator of depth of anaesthesia. The main objective was to model the relation between the depth of anaesthesia in rats (entropy) and the propofol infusion rates, with the purpose of obtaining a closed-loop control for propofol infusions. Five adult rats were sedated with isoflurane, cannulated and equipped for the EEG collection. After the preparation, anaesthesia was induced with propofol infusions, using different infusion rates on each rat. The collected EEG (125Hz) was processed using an entropy algorithm developed in MATLAB R 7 that determined the entropy value at each second using the preceding 15s of signal. Pharmacokinetic models were fitted for each rat using bi and tri-compartmental models; the pharmacodynamic phase was also modelled for each rat. The relation between obtained propofol effect-site concentrations and the entropy values was modelled by a Hill Equation. The model obtained for the relation between infusion rates and entropy values was evaluated using the mean absolute deviation (MAD) and the relative mean square error (RMSE) for models comparative analysis.
- 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.
- 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.
- Propofol and remifentanil: contributions to the improvement of target controlled infusion and BIS monitoringPublication . Ferreira, David A.; Nunes, Catarina S.; Antunes, Luís; Amorim, Pedro
- Recent advances in BIS guided TCI anesthesiaPublication . Ferreira, David A.; Antunes, Luís; Amorim, Pedro; Nunes, Catarina S.
- Simulação social para otimização das políticas de serviços de emergência médicaPublication . Calado, Mateus Padoca; Antunes, LuísFrequentemente, as políticas públicas, concebidas apenas, podem ser avaliadas só quando já se encontram implementadas. A simulação à priori dessas políticas apresenta vários benefícios: o design pode ser ajustado aos objectivos dos decisores políticos de forma mais exacta; as políticas podem reflectir melhor as motivações dos indivíduos envolvidos em diversos papéis (utilizadores, médicos, enfermeiros, funcionários públicos, auditores, decisores políticos); as ligações micro-macro e as mediações são representadas explicitamente; a simulação pode permitir a melhoria sucessiva das políticas, de tal forma que as mesmas aquando da sua implementação estejam aperfeiçoadas; os decisores e intervenientes podem conhecer melhor o território de decisão para melhor reagir em situações de contingência. Defendemos a simulação baseada em multi-agentes como forma de orientar a especificação de políticas. Os sistemas multi-agente permitem a representação de agentes racionais heterogéneos e fornecem uma abordagem para criar modelos dinâmicos complexos de fenómenos sociais. Neste artigo, descreve-se como podemos atacar o problema de optimização das políticas de serviços de emergência médica, quando há uma diferença clara entre a concepção dessas políticas e o uso que as pessoas lhes dão. Apresenta-se o cenário e um modelo para a simulação, identificando os actores envolvidos, as ligações e relações entre eles, as medidas necessárias para avaliar os resultados multi-dimensionais da simulação e como se podem afinar as políticas e simulá-las antes da sua implementação no mundo real.