Anestesia espinal parte III. Mecanismos de acción / Spinal anesthesia part III. Mechanisms of action

Spinal anesthesia is a widely used technique in medical practice nowadays. Generally, nervous blockage is determined by three main factors. The first of them is the distribution of the local anesthetic in the cerebrospinal fluid (CSF), which can be affected by numerous factors, the most important of them being CSF volume. The second is absorption, which is greatest at the sites with higher drug concentration: this is the result of the accessibility, lipidic content and vascular irrigation of each area. The last of these factors is elimination, mediated mainly by the irrigation of the different compartments, and whose order differs from the mirror image of the onset's action order. The previously mentioned elements are the main sources of variation for the time needed to achieve desired effects, order in which fibers are affected and differential blockage. This text describes the principal mechanisms through which spinal anesthesia works, and the factors which can result in variations of its results.

La anestesia espinal es una técnica ampliamente utilizada en la práctica clínica. Por lo general, el bloqueo nervioso está determinado por tres factores principales. El primero es la distribución del anestésico local en el líquido cefalorraquídeo (LCR), que a su vez se ve afectado por una gran variedad de factores, destacando entre estos el volumen de LCR. El segundo es la absorción, la cual es mayor en los sitios en donde la concentración del fármaco también lo es: para esto afecta la accesibilidad, el contenido lipídico y la irrigación vascular de cada zona. El último factor es la eliminación, mediada principalmente por la irrigación de los distintos compartimentos, y cuyo orden es distinto a la imagen especular del inicio de acción. Los factores mencionados son los principales determinantes de los tiempos de demora de los bloqueos, el orden en el que se logra su acción en las distintas fibras y el bloqueo diferencial. Este texto pretende describir los principales mecanismos de acción mediante los cuales actúa la anestesia espinal y los factores que pueden determinar diferencias en los resultados de esta.

Comunicación masiva del ramo superficial del nervio radial con el nervio cutáneo antebraquial lateral, implicancias anatomo-clínicas: reporte de un caso / Massive communication between the superficial branch of radial nerve and lateral cutaneous nerve of the forearm, anatomical and clinical implications: a case report

La distribución de los ramos nerviosos sensitivos en el borde lateral y en el dorso de la mano han sido descritos con mayor exactitud en las últimas décadas, debido al avance de las técnicas de electrodiagnóstico que ofrecen un alto rendimiento, las cuales han permitido detectar que alrededor del 40 por ciento de la población examinada presenta algún grado de variación anatómica en el territorio de distribución de los nervios involucrados. En este caso presentamos una variación anatómica bilateral extremadamente rara, que involucra al ramo superficial del nervio radial (NRS) y al nervio cutáneo antebraquial lateral (CABL); donde NRS se conecta de forma íntegra con el ramo medial de CABL, formándose así un tronco común (TC) que se distribuye por la región dorsal de la mano. Por su parte, el ramo lateral de CABL se distribuye por el borde lateral de la mano, ocupando el territorio cutáneo de NRS; situación que aparece descrita en la literatura especializada sólo una vez. El hallazgo de estas variaciones anatómicas en los cadáveres disecados con fines docentes en nuestro Departamento de Anatomía, tienen un valor formativo indiscutible para nuestros alumnos de pregrado y especialmente para los de postgrado, quienes pueden comprobar de primera mano la enorme variabilidad del ser humano, valorando las implicancias en la clínica diaria de este conocimiento anatómico.

The distribution of the sensory nerve branches in the lateral and the back of the hand have been described more accurately in the past decades due to advancement of high performance electro-diagnostic variation techniques, which indicate that approximately 40 percent of the population examined have some degree of anatomical variation in the distribution area of the nerves involved. In this case we present an extremely rare, bilaterally detected variation, involving the superficial branch of the radial nerve (SBRN) and lateral antebrachial cutaneous nerve of the forearm (LABCN), where the SBRN is connected integrally with the medial branch of LABCN, forming a common trunk (CT) distributed by the dorsal region of the hand. Furthermore, the lateral branch of the LABCN is distributed in the lateral border of the hand, occupying the area of the skin of the SBRN, an event that is described only once in the literature. The discovery of these anatomical variations in dissected cadavers for teaching purposes, in the Department of Anatomy, have an undeniable educational value for our undergraduate students and especially for the graduate who can observe the enormous variability of human beings first hand, and value implications of this anatomical knowledge in daily clinic.

Hipoxemia nocturna después de cirugía abdominal: factores asociados y rol de la oxigenoterapia / Nocturnal hypoxemia after abdominal surgery: associated factors and usefulness of oxygen therapy

Fifteen elective patients (6 M, 9 F, 51+-8 years old) scheduled for laparotomy (n=8) or laparoscopy (n=7) were studied. Ventilatory parameters and pulse oximetry were measured pre and postoperatively. Patients were randomly assigned to receive oxygen by nasal cannula either during the first or the second postoperative night. PONH (Sat2 85) developed in seven patients (47 per cent)of which four had undergone laparoscopic surgery. PONH was more frequent in mildly obese patients and those presenting preoperative hypoxemia (p=0.03). Peak flow was lower in patients presenting PONH (p=0.04). In five patients, PONH was associated with significant tachycardia. Oxygen administration was associated with a higher SatO2 and prevented PONH in 6/7 patients. PONH is a common event in patients older than 40 years scheduled for open or laparascopic abdominal surgery, and develops more frequently in those with preoperative nocturnal hypoxemia and greater ventilatory impairment. PONH can be prevented, most of the time, with oxygen administration