Finite Element Analysis of Hepatic Radiofrequency Ablation Probes using Temperature-Dependent Electrical Conductivity

BACKGROUND: Few finite element models (FEM) have been developed to describe the electric field, specific absorption rate (SAR), and the temperature distribution surrounding hepatic radiofrequency ablation probes. To date, a coupled finite element model that accounts for the temperature-dependent electrical conductivity changes has not been developed for ablation type devices. While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed. METHODS: The results of four finite element models are compared: constant electrical conductivity without tissue perfusion, temperature-dependent conductivity without tissue perfusion, constant electrical conductivity with tissue perfusion, and temperature-dependent conductivity with tissue perfusion. RESULTS: The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures. These errors appear to be closely related to the temperature at which the ablation device operates and not to the amount of power applied by the device or the state of tissue perfusion. CONCLUSION: Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100°C

INSTRUMENTO DE COMUNICAÇÃO DE ENFERMAGEM. Estudo da implantação de um modelo de comunicação escrita entre as equipes de enfermagem das unidades cirúrgicas e do centro cirúrgico

A study to introduce a nursing communication toot to make easier the continuity of nursing care of the surgical patient in the pre, per and postoperative periods. The communication tool consists in two parts: preoperative and peroperative notes form. This tool was aplied to 327 patients undergoing surgical treatment who were interned in three general surgical units and in three specialized units in a general hospital. The application of the tool was made by nursing staff of the surgical units and the operating room of the hospital. It was verified, by the analysis of results, that the frequency of the filling-in items on the preoperative form was higher than 83%, above the 70% established in this present study. The percentage of items registered on the peroperative form was above 85%, excepting pulse rate and blood pressure that showed less than 70%. The frequency of the filling-in of the items on the two forms, preoperative and peroperative, was analyzed separately for each six surgical units. The percentual variation of the filling-in was between 83 and 100% which makes possible the inference that this nursing communication tool is certainly applicable to patients undergoing general specialized surgery.Estudo da implantação de um Instrumento de Comunicação de Enfermagem que propicie a continuidade de assistência ao paciente cirúrgico, nos períodos pré, trans e pós-operatório. O Instrumento de Comunicação compreende duas partes: Ficha Pré-operatória de Enfermagem e Ficha Transoperatória de Enfermagem. O instrumento foi aplicado, pelas equipes de enfermagem das unidades cirúrgicas e do centro cirúrgico, a 327 pacientes submetidos a tratamento cirúrgico, internados em três unidades cirúrgicas gerais e três especializadas, em um hospital geral. Pela análise dos resultados apresentados, verificou-se que a freqüência de preenchimento dos itens propostos na Ficha Prê-operatória de Enfermagem obteve percentual acima de 83%, superior ao estabelecido neste estudo (70%). O percentual de preenchimento dos itens da Ficha Transoperatória de Enfermagem foi acima de 85%, exceto o dos itens pulso e pressão arterial, que se apresentou abaixo de 70%. A freqüência de preenchimento dos itens das Fichas Pré-operatória e Transoperatória de Enfermagem foi analisada separadamente, em relação a cada uma das seis unidades cirúrgicas de internação. A variação do percentual quanto à freqüência de preenchimento dos itens propostos foi de 83% a 100% nas seis unidades cirúrgicas, o que permite inferir que o Instrumento de Comunicação de Enfermagem é passível de aplicação, tanto aos pacientes submetidos a cirurgias gerais como a especializadas