Browsing by Author "Bressan, Nadja"
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- 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.
- 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.
- 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.
- 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.
- 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.
- Nonlinear modeling of cerebral state index in dogsPublication . Bras, Susana; Bressan, Nadja; Ribeiro, Lenio; Ferreira, David A.; Antunes, Luis; Nunes, Catarina S.The Cerebral State Index (CSI) is an electroencephalogram derived signal representing the depression of central nervous activity produced by anesthetic drugs. In this study, a nonlinear model was developed to describe the CSI tendency during general anesthesia in dogs, by evaluating the effect of the anesthetic drug propofol. The model was based on a compartmental and Hill Equation structure with individually identified parameters. The clinical data of 14 dog surgeries were collected and used for modeling and testing. The model presented good results, following the CSI trend. A model for drug-effect for veterinarian anesthesia is an important step when developing advisory, educational and control systems. The overall aim is to improve animal safety and comfort.
- 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.
- Synchronization software for automation in anesthesiaPublication . Bressan, Nadja; Castro, Ana; Bras, Susana; Oliveira, Helder P.; Ribeiro, Lenio; Ferreira, David A.; Antunes, Luis; Amorim, Pedro; Nunes, Catarina S.This work presents the development of a software for data acquisition and control (ASYS) on a clinical setup. Similar to the industrial Supervisory Control And Data Acquisition (SCADA) the software assembles a Target Controlled Infusion (TCI) monitoring and supervisory control data in real time from devices in a surgical room. The software is not a full controller since the TCI systems comprehend permanent interaction from the anesthesiologist. Based on pharmacokinetic models, the effect-site and plasma concentrations can be related with the drug dose infused and vice versa. The software determines the infusion rates of the drug which are given as commands to the infusion pumps. This software provides the anesthesiologist with a trustworthy tool for managing a safe and balanced anesthesia. Since it also incorporates the acquisition and display of patients brain signals.
- Target controlled infusion algorithms for anesthesia: Theory vs practical implementationPublication . Bressan, Nadja; Moreira, A. Paulo; Amorim, Pedro; Nunes, Catarina S.Target Controlled Infusion (TCI) systems are based in drug pharmacokinetic and pharmacodynamic models implemented in an algorithm to drive an infusion pump. Infusion control algorithms have been designed, implemented and validated for several anesthetic drugs, devices and controllers. The maintenance phase in these algorithms is represented by an equation that compensates the loss of drug from the central compartment and maintains the set target concentration. The goal of the current study was to improve existing TCI software with a new method for the maintenance phase. We compared and analyzed two different methods to find the more efficient method for the maintenance phase in an open-loop control TCI system.