In this study, electrochemical impedance spectroscopy (EIS) is evaluated as a novel application in the biodiesel purification process. EIS is proposed as a tool to study the behavior of charge carriers produced from side reactions or dissociations of some impurities during the gravitational separation of glycerol dispersed in crude biodiesel after the transesterification process. In the present study, EIS combined with a simple capacitor of two parallel plates made of stainless steel ASTM 304 with an area of 7.0 cm2 and a gap between the plates of 0.8 mm is demonstrated to be a promising technique to monitor the biodiesel/glycerol separation as a function of time. From the analysis of the impedance data, collected during the separation process, it was found that the biodiesel resistance increases up to a maximum value and then decreases to a value which corresponds to the final equilibrium state. Considering that the maximum resistance represents the less contaminated biodiesel as a criterion, the proper average biodiesel/separation time of 4 h 14 min ± 1 h 11 min was determined. Another finding from the EIS results suggests that a growing absorbed film exists on the plate surface of the capacitor used as an impedance sensor.

Biodiesel, unlike diesel, is highly susceptible to autoxidation. This autoxidation is a major concern for a biodiesel producer. Various methods have been developed to estimate the degree of oxidative stability of biodiesel. These methods are useful to compare and estimate the oxidative stability between different biodiesel samples. However, an absolute value of the oxidative state will be more useful. In this study, we describe a method of estimating a figure that can be used as an indicator of the oxidation level. This indicator was determined from the thermal decomposition curve of biodiesel, as obtained from the thermogravimetric test. Biodiesel from waste cooking oil was oxidized at 80, 100 and 120 ºC using different exposure areas (19.6, 63.6, and 153.9 cm2). The percentage of oxidation, measured from low (80 ºC, 19.6 cm2) to highly aggressive conditions (120 ºC, 153.9 cm2), was in the range of 0.4 ± 0.1 and 23.5 ± 3.3. Kinematic viscosity was also measured for the oxidized samples, and a strong correlation (R2=0.96) was observed between the percentage of oxidation products and kinematic viscosity. In addition, the oxidative effect of temperature and area of exposure on the biodiesel samples was confirmed by ultraviolet spectroscopy.

Hace cincuenta años se describió por primera vez el hiperaldosteronismo primario que hasta hace poco se consideraba un síndrome infrecuente y una causa excepcional de hipertensión arterial. De cada 10 pacientes hipertensos habrá en promedio uno de ellos con este padecimiento, convirtiendo a tal grupo de enfermedades en la causa más frecuente de hipertensión potencialmente curable. Este incremento en la prevalencia se debe quizás al aumento en la sensibilidad de las pruebas de tamizaje utilizadas. Si bien es cierto, los nuevos hallazgos no implican necesariamente el tamizaje generalizado de la población de hipertensos; es importante que el médico que la controla esté familiarizado con el tema para que lo considere y lo sospeche en el manejo y seguimiento de sus pacientes.

Primary aldosteronism was first described fifty years ago, and until recently it was considered uncommon and an exceptional cause of hypertension. Now we know that approximately one out of every 10 patients with hypertension will have some form of hyperaldosteronism, making this group of diseases the number one cause of potentially curable hypertension. This increase in prevalence is probably due to improved screening strategies. Although, these new findings do not necessarily imply the need to screen all the patients with hypertension, it is fundamental that physicians treating hypertensive patients be familiarized with primary hyperaldosteronism so that they consider this possibility as they manage and follow this individuals patients.

Justificación y objetivo: La laparoscopía es el abordaje de elección para la colecistectomía y tiene grandes beneficios sobre la colecistectomía abierta, que incluyen una mejor recuperación. También se sabe que puede realizarse en forma ambulatoria. Sin embargo, en el sistema de seguridad social costarricense no se ha implementado aún un programa de colecistectomía laparoscópica ambulatoria. El objetivo de este trabajo es demostrar que en Costa Rica, en un hospital clase A, se puede realizar la colecistectomía laparoscópica ambulatoria de una manera segura y de rutina. Métodos: De febrero a julio de 2005, en el Servicio de Cirugía Uno del Hospital San Juan de Dios, se seleccionaron 100 pacientes de 16 a 61 años, previo consentimiento informado, con colelitiasis, sin comorbilidades de importancia, sin colecistitis ni vesículas escleroatróficas. Los pacientes ingresaron a las 6 de la mañana, se operaron durante las siguientes 4 horas, fueron egresados a las 4 de la tarde y evaluados a los quince días después de la cirugía en la Consulta Externa. Resultados: Se operaron 100 pacientes, de los cuales 6 requirieron ser hospitalizados. Como única complicación hubo una fístula biliar. No hubo reintervenciones ni mortalidad. Conclusiones: La colecistectomía laparoscópica es un procedimiento de cirugía mayor que puede realizarse de forma segura y ambulatoria en los hospitales clase A de Costa Rica, si previo a esto existe una adecuada evaluación preoperatoria de los pacientes y un adecuado manejo transoperatorio y postoperatorio.

Background: It is well known that a laparoscopic approach is the election of choice for cholecystectomies, this is due, among other things, to the great benefits that it has over open surgery regarding patients recovery. It is also known that to do so in an ambulatory setting is reasonable in a subgroup of selected patients. Even though this has become a common practice in other countries, Costa Rica´s social security system does not have a program for ambulatory cholecystectomy. Aim: To demonstrate that in Costa Rica, laparoscopic cholecistectomy can be done safely in an ambulatory setting. Methods: Between february and july of this year a total of 100 patients with cholelithiasis, with ages between 16 and 61 and a previous ly signed informed consent, were included in a program of ambulatory laparoscopic cholecystectomy at the Surgery One Service at the Hospital San Juan de Dios. In general, these patients had no previous comorbilities. There were no patients with cholecystitis or thicken gallbladder walls on ultrasonography. The patients were admitted at 6am and had the procedure done some time during the next 4 hours, they were discharged at 4pm and seen 15 days later. Results: Of the 100 patients, 6 had to be hospitalized. The only complication was a biliary fistula. There were no reinterventions and there was no mortality. Conclusions: In Costa Rica, laparoscopic cholecystectomy can be done safely in an ambulatory setting, with an adecuate preoperative selection of patients and an adequate postoperative management.