Browsing by Author "Lobo, Francisco"
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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.
- 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.
- 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.