Browsing by Author "Antunes, Luís M."
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- 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.
- Neuro-fuzzy techniques to model pharmacodynamic interactions between anesthetic drugs on the bispectral index: a preliminary studyPublication . Nunes, Catarina S.; Ferreira, David A.; Mendonça, Teresa F.; Amorim, Pedro; Antunes, Luís M.The aim of this preliminary study was to try to identify the effect of propofol and remifentanil on bispectral index of the electroencephalogram (BIS), and to determine if a model can be generalized between different patients. We used the data from three patients under stable propofol and remifentanil anesthesia for neurosurgical procedures. A Takagi-Sugeno-Kang (TSK) fuzzy model was used to describe the effect of interaction of propofol and remifentanil on BIS. An Adaptive Network-Fuzzy Inference System (ANFIS) was used to obtain the parameters of the TSK model. The ANFIS was able to optimize the parameters of the fuzzy TSK model. The obtained TSK model reflected the data trend and was able to capture the synergistic interaction between propofol and remifentanil during the maintenance phase of anesthesia. The model was trained with the data of two patients and tested with the data of a third patient. Different patients have different physiological responses and this preliminary study results suggested that the BIS values were independent of patients’ variability. This result should be improved using a larger set of data with more patients.
- Remifentanil bolus dose is a safe procedure to control intense noxious stimuli in hypertensive neurosurgical patientsPublication . Ferreira, David A.; Nunes, Catarina S.; Lobo, Francisco; Antunes, Luís M.; Amorim, PedroPatients with hypertension may be more prone to develop hypotension as a consequence of opioid administration under general anesthesia. The hemodynamic and bispectral index responses to a remifentanil bolus in neurosurgical hypertensive patients under target-controlled infusion with propofol and remifentanil are addressed. Ten healthy patients and 10 patients with diagnosed hypertension under pharmacological treatment were studied. A 2 µg/kg remifentanil bolus was administered to all patients before skin incision under target-controlled infusion with propofol and remifentanil. Mean arterial pressure, heart rate, and the area under the curve for the bispectral index of the electroencephalogram were analyzed within the groups and compared between them every 30 seconds for two minutes following the bolus. Two minutes after the remifentanil bolus, remifentanil predicted effect-site concentrations reached maximum values of 8.46±0.91 ng/ml and 9.74±1.29 ng/ml in the healthy and hypertensive patients, respectively. Both groups showed a significant decrease in mean arterial pressure, heart rate, and in the area under the curve for the bispectral index. Mean arterial pressure decreased by 17.3±10% and 24±9%, heart rate by 11.1±8% and 12±8%, and the bispectral index by 13±9.2% and 8.6±8.4% in the healthy and hypertensive patients, respectively, 120 seconds after the remifentanil bolus. In a clinical situation in which high remifentanil doses may be required, hypertensive patients are expected to have hemodynamic and bispectral index responses similar to those observed in healthy patients.