Infusão alvo-controlada com propofol e remifentanil: estudo experimental em cães

Abstract

Os modernos sistemas de infusao alvo-controlada (TCI), usados para a inducao e manutencao da anestesia, permitem que a velocidade de infusao seja ajustada atraves da utilizacao de avancados softwares alimentados com parametros farmacocineticos, de modo a assegurar uma adequada profundidade da anestesia e uma rapida e eficiente recuperacao. O objetivo inicial deste estudo foi determinar a concentracao plasmatica calculada de propofol (Cpcalculada) determinada por meio de estimulacao eletrica (50V, 50 Hz e 10 ms). Na segunda fase, o objetivo foi investigar a performance do uso de um sistema de infusao alvo-controlada de propofol usado isoladamente ou associado ao remifentanil. Paralelamente foram avaliados as respostas hemodinamicas e o periodo de recuperacao. A Performance e determinada pela Mediana da Performance do erro (MDPE), e a Mediana Absoluta da Performance do erro (MDAPE), sendo considerada clinicamente aceitavel uma MDPE de ate 20% e a MDAPE de ate 40%. Seis caes adultos saudaveis (26,6} 3,6kg) foram alocados aleatoriamente em 2 grupos com um intervalo de uma semana entre os experimentos. GI = TCI de propofol e G II = TCI de propofol + remifentanil. Os resultados foram analisados estatisticamente atraves da analise de variancia seguida pelo teste gt-Studenth. Foi considerado como significante um p<0,05. Houve uma reducao na frequencia cardiaca e indice cardiaco em GII, enquanto a pressao venosa central e a pressao de oclusao da arteria pulmonar aumentaram significativamente em GII comparado a GI. Os resultados obtidos para o grupo propofol foram de MDPE = 16,3% e MDAPE = 32,1% e para o grupo propofol+remifentanil foram de MDPE = 6,8% e MDAPE = 36,5%. A Cp50calculada foi de 2,0Êg.ml-1 (GI) e de 0,9Êg.ml-1 (GII)...

The target-controlled infusion systems (TCI), designed to keep the drug concentration in the bloodstream constant, are controlled by state-of-art software based upon pharmacokinetic models. These models have been designed for each species to produce an adequate anesthetic depth and fast and efficient recover. The aim of this study was to establish the predicted plasmatic concentration (Cppredicted) based upon electric stimulus (50V, 50 Hz and 10 ms). In a second phase, the aim was to investigate the anesthetic performance of the TCI of propofol used alone and associated with remifentanil. Moreover, haemodynamic parameters and anesthesia recovery time were evaluated. The performance was established based on the Median Performance error (MDPE < 20%) and Absolute Median Performance error (MDAPE < 40%). Six clinically normal dogs (26.6 l 3.6 kg) were randomly divided in 2 groups with at least one week between experiments. G1 = TCI of propofol alone; G2 = TCI of propofol + remifentanil. The statistical analysis was based on Student's t-distribution test, with alpha set at 0.05. Heart rate (HR) and cardiac index (CI) were significantly decreased after propofol + remifentanil (G2) infusion administration until the end, while central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) were significantly increased. The G1 group demonstrated MDPE of 16.3% and MDAPE of 32.1%, whereas the G2 group had MDPE of 6.8% and MDAPE of 36.5%. The average Cp50predict for G1 was 2,0ìg.ml-1 and for G2 was 0,9ìg.ml-1. The evaluation of these parameters and the control of the anesthetic depth suggested that the TCI stanpump could be considered clinically acceptable in dogs. The remifentanil enhances the propofol's CPpredict in an average of 56.7%; however, haemodynamic side effects were detected.