Loading...
4 results
Search Results
Now showing 1 - 4 of 4
- Electromyographic assessment of blink reflex throughout the transition from responsiveness to unresponsiveness during induction with propofol and remifentanilPublication . Ferreira, Ana Isabel Leitão; Vide, Sérgio; Felgueiras, João; Cardoso, Márcio; Nunes, Catarina S.; Mendes, Joaquim; Amorim, PedroGeneral anesthesia is a reversible drug-induced state of altered arousal characterized by loss of responsiveness due to brainstem inactivation. Precise identification of the moment in which responsiveness is lost during the induction of general anesthesia is extremely important to provide information regarding an individual's anesthetic requirements and help intraoperative drug titration. To characterize the transition from responsiveness to unresponsiveness more objectively, we studied neurophysiologic-derived parameters of electromyographic records of electrically evoked blink reflex as a means of identifying the precise moment of loss of responsiveness. Twenty-five patients received a slow infusion of propofol until loss of corneal reflex while successive blink reflexes were elicited and recorded every 6 s. The level of anesthesia was assessed using an adapted version of the Richmond Agitation-Sedation Scale. Different variables of the blink reflex components were calculated and compared to the adapted version of the Richmond Agitation-Sedation score and the estimated effect-site propofol concentration. Baselines of the blink reflex responses were similar to those in literature. After propofol infusion started, the most susceptible component of the blink reflex to propofol was R2 (EC50 = 1.358 (95% CI 1.321, 1.396) µg/mL) and the most resistant was R1 (EC50 = 3.025 (95% CI 2.960, 3.090) µg/mL). Most of the patients (24 out of 25) lost the R1 component when they were still responsive to shaking and shouting and corneal reflex could be elicited clinically (time = 102.48 ± 33.00 s). Habituation was present in R2 but not in R1. The R1 component of the blink reflex was found to have a strong correlation with the adapted version of the Richmond Agitation-Sedation Scale, with amplitude correlating better than areas (ρ = - 0.721 (0.123) versus ρ = - 0.688 (0.165)). We found a strong correlation between the R1 component with the estimated propofol effect-site concentration, with amplitude correlating better than areas (ρ = - 0.838 (0.113) versus ρ = - 0.823 (0.153)) and between the clinical scale and the propofol concentration (ρ = 0.856 (0.060)). The area and amplitude of the R1 component showed to be indicators of predicting different levels of anesthesia (Pk = 0.672 (0.183) versus Pk = 0.709 (0.134)) and these are connected to the propofol concentrations (Pk = 0.593 (0.10)). Our results suggest that electrically evoked blink reflex could be used during the induction of anesthesia as a surrogate of the Richmond Agitation-Sedation Scale to provide an objective endpoint as far as a - 4. At this point, at the moment of loss of R1, the propofol infusion may be stopped, as overshooting increases slightly the effect-site concentration afterward and eventually reaching loss of responsiveness. If the desired target is not achieved, the infusion can then be resumed.
- Usefulness of the blink reflex to assess the effect of propofol during induction of anesthesia in surgical patientsPublication . Ferreira, Ana Isabel Leitão; Nunes, Catarina S.; Mendes, Joaquim; Amorim, PedroThe aim of this study was to investigate the relation between the blink reflex evoked by an electrical stimulus and the depth of anesthesia induced with intravenous anesthetic drug propofol. The blink reflex was stimulated before the propofol infusion started (baseline) and after, every 6 s. The electromyographic responses and the level of sedation/anesthesia scores as well as the estimated effect-site concentration of propofol were recorded in 11 patients. The blink reflex responses were abolished when patients were still conscious. The clinical scale of anesthesia increased with increasing concentrations of propofol. To predict the level of sedation/anesthesia a multinomial logistic regression was performed using blink reflex extracted features at the frequency domain. Several features proved to be good predictor estimates and the model showed to be useful. This information could be helpful to assess the moment of loss of consciousness and thus personalize anesthesia.
- Patterns of hysteresis between induction and emergence of neuroanesthesia are present in spinal and intracranial surgeriesPublication . Ferreira, Ana Isabel Leitão; Correia, Rui; Vide, Sérgio; Ferreira, Ana Dias; Kelz, Max B.; Mendes, Joaquim; Nunes, Catarina S.; Amorim, PedroRecovery of consciousness is usually seen as a passive process, with emergence from anesthesia depicted as the inverse process of induction resulting from the elimination of anesthetic drugs from their central nervous system sites of action. However, that need not be the case. Recently it has been argued that we might encounter hysteresis to changes in the state of consciousness, known as neural inertia. This phenomenon has been debated in neuroanesthesia, as manipulation of the brain might further influence recovery of consciousness. The present study is aimed at assessing hysteresis between induction and emergence under propofol-opioid neuroanesthesia in humans using estimated propofol concentrations in both spinal and intracranial surgeries.
- Propofol administration in the induction phase of general anesthesia in PortugalPublication . Ferreira, Ana; Mendes, Joaquim; Nunes, Catarina S.; Amorim, PedroIntrodução: A administração adequada de propofol por via intravenosa durante a indução da anestesia geral implica um bom conhecimento da farmacocinética e da farmacodinâmica, um bom entendimento de como a anestesia altera a consciência e a habilidade de interpretar corretamente a monitorização dos sinais vitais. Este trabalho pretende avaliar a prática usual dos anestesiologistas em Portugal no que diz respeito à administração de propofol por via intravenosa durante a indução da anestesia geral. Material e Métodos: Estudo observacional transversal, descritivo e analítico realizado através de um questionário enviado por correio eletrónico a todos os médicos internos e especialistas em Anestesiologia de vários hospitais portugueses. O questionário apresentava um cenário convencional (Sujeito do sexo masculino, 50 anos, 60 kg, 160 cm, ASA I, submetido a anestesia geral com propofol a 1%) e incluía 10 questões relacionadas com a administração de propofol durante a indução. Foi realizada análise descritiva dos dados obtidos através do programa SPSS 23.0®. Resultados: Responderam ao inquérito 118 médicos, sendo que, a maioria eram especialistas há mais de 5 anos (56,9%). Baseados no cenário apresentado, a maioria dos anestesiologistas administraria uma dose de 60 mg de propofol na indução, a uma velocidade superior a 1200 mL/horas, avaliariam a perda de consciência através da perda do reflexo palpebral, o que se refletiria num índica BIS de 60. A maioria dos participantes medem a pressão arterial do doente a cada 5 minutos e nunca utilizaram sistemas de infusão alvo-controlada. Discussão: Os resultados do inquérito mostraram que existe uma grande variedade de métodos para avaliar a perda de consciência, uma diversidade no manuseamento e doses de propofol na indução, uma falta de experiência no uso de sistemas de infusão alvo-controlada e na avaliação da relação entre a dose, a velocidade e a concentração de propofol. Neste trabalho apresentaram-se também algumas sugestões para os anestesiologistas ponderarem implementar nas suas práticas clínicas. Conclusão: Parece haver uma diversidade na quantidade e na forma como os anestesiologistas portugueses utilizam o propofol na indução da anestesia geral.