Combined effect of shearing and cooling rate on the rheology of organogels developed by selected gelators.

In this study we investigated the combined effect of shearing and cooling rate in the rheology of organogels developed in high oleic safflower oil by (R)-12-hydroxystearic acid (HSA), its primary amide derivative [(R)-12-hydroxyoctadecanamide, HOA], and the N-octadecyl derivative of HOA [(R)-N-octadecyl-12-hydroxyoctadecanamide, OHOA]. The experimental set up to develop the organogels involved: 1). The use of quiescent (0s-1) or shearing (300, 600, and 1200s-1) conditions during cooling the gelator solutions (2%) just until achieving the gelator's melting temperature (TM) in the vegetable oil, to then continuing the cooling under static conditions until achieving 15°C) The use of cooling rate protocols involving a constant cooling rate of 1°C/min (CR1) or 10°C/min (CR10) in the shearing and static stages, or variable cooling rates in each stage (i.e., VR1-10 or VR10-1). The elasticity of the organogels (G') was measured while cooling under static conditions, once the systems achieved 15°C, and after 60min at this temperature. The rheological results obtained at 15°C showed a cooling rate and molecular weight-dependent effect of shearing on G'. We propose that the molecular relaxation time of gelator molecules, and its increase as molecular weight increases and as temperature decreases, plays an important role on the gelator's susceptibility to go through a shear induced crystallization process. Therefore, high molecular weight molecules like OHOA (551.97Da) would remain stretched by shearing longer times than HSA (300.49Da) and HOA (299.49Da). Thus, when shearing was applied while cooling at the higher cooling rate (i.e., CR10 and VR10-1), the stretched OHOA molecules would lead to the development of mesophase precursors that upon further cooling under quiescent conditions, crystallize developing a well-structured organogel. In contrast, stretched low molecular weight molecules (i.e., HSA and HOA) with shorter relaxation time would dissolve back to the isotropic state during cooling. Additionally, the rheological results of HSA and HOA organogels suggested that the shear induced crystallization process might be dependent on the gelator polarity also. These results show that the application of shear and the extent of its application as temperature decreases until achieving TM, have important implication on the self-assembly of gelator molecules, and therefore in the organization and rheology of the three-dimensional crystal network of the organogel.

Cirugía selectiva bajo anestesia local para el tratamiento de los adenomas paratiroideos / Selective surgery under local anesthesia for parathyroid adenomas

Introducción. El hiperparatiroidismo primario por adenoma, identificado y localizado por ecografía y gammagrafía, puede ser tratado mediante un acceso limitado, bajo anestesia local y sedación, con la condición de controlar el efecto de la exéresis mediante la dosificación intraoperatoria de la parathormona intacta (PTH-i), y respetar las limitaciones y/o contraindicaciones de esta técnica. Pacientes y método. Se analizan los resultados obtenidos en el tratamiento de 14 pacientes afectados por un hiperparatiroidismo ocasionado por un adenoma de paratiroides (localizado por ecografía y gammagrafía) mediante cirugía selectiva bajo anestesia local y sedación con monitorización intraoperatoria de la PTH-i. Resultados. La anestesia local y la posición operatoria fueron bien toleradas y no hubo complicaciones locales ni re currenciales. La exéresis del adenoma en el orden técnico, no planteó ninguna dificultad. El éxito de la operación se confirmó durante el acto operatorio al comprobar la normalización de los valores de PTH-i a los 30 y 60 minutos tras la exéresis lesional. Conclusiones. La cuestión que subyace es si este método podrá sustituir al acceso quirúrgico tradicional. No obstante, la adenomectomía selectiva paratiroidea, con anestesia local y sedación constituye, en caso de monitorización de la PTH-i, el preludio de una cervicotomía estándar bajo anestesia general (AU)

[Induction-intubation sequence in neuroanesthesia. Usefulness of vecuronium in fractionated doses]. / Secuencia de inducción-intubación en neuroanestesia. Utilidad del vecuronio en dosis fraccionadas.

Muscular relaxant vecuronium bromide (Norcuron R, Organon Teknika Española, S.A.) was administered to 20 patients undergoing intracranial surgery with general anesthesia at a dose of 0.01 mg/kg weight followed by 0.1 mg/kg (intubation dose) four minutes later. Two minutes after the second dose and under careful manual mechanical ventilation with O2 100%, a laryngoscopy was performed to evaluate the conditions for intubation. Mean arterial pressure, heart rate, PaO2, and PaCO2 were measured at baseline and immediately before laryngoscopy. Neuromuscular function was monitored observing the response to a train of four stimuli applied on the cubital nerve. During the operation a continuous infusion of vecuronium at a rate of 1 microgram/kg/min was maintained. Conditions for intubation were excellent in 18 patients and good in two cases. Mean heart rate and PaCO2 did not show significant variations. In contrast, during prelaryngoscopy mean arterial pressure decreased and PaO2 increased with respect to the baseline values. During surgery all patients showed a good clinical relaxation. Thus, we believe that vecuronium is a good muscular relaxant agent, safe, and effective to be used in neurosurgery.