OBSERVATIONS ON THE EPIDURAL SPACE

Abstract

THE epidural space-the space between the dura surrounding the cord and the inner wall of the vertebral canal-extends from the sacrum to the base of the skull.It is largely filled with fat, and is traversed by the spinal nerves as they pass out through the intervertebral foramina.In order to provide intradural (spinal) analgesia, the needle must be passed through the epidural space.Fidel Pages was the first (1921) to carry out abdominal operations under extradural (epidural) analgesia, He halted the needle just short of the dura, and injected a comparatively large volume of solution which spread up and down the epidural space blocking the intercostal nerves as they ran across it.The technique was popularised in Italy by Dogliotti, and, recently, Gutierrez of Buenos Aires reported a series of cases running into five figures.Negative Pressure.Certain advantages are claimed for epidural analgesia, and certain disadvantages admitted, but it is not the purpose of this short article to discuss these.One of the disadvantages is the difficulty of knowing when the point of the needle is accurately lodged.Many writers have pointed out that there is a negative pressure in the epidural space ; and when an scttachment to the hub of the needle demonstrates negative pressure, the point lies within the space.For this purpose indicators have been used-small manometers (fig.I), or a needle with a special hub which allows aspiration of a hanging drop to be seen (fig.2).Gutierrez in his monograph on the subject gives 129 references to articles on epidural analgesia.In these, various explanations, some rather involved, have been advanced for the existence of the negative pressure in the epidural space.Considering the amount of thought which has been given to the matter it is strange that an obvious explanation has been overlooked.This is all the more surprising since two writers make observations which alone might well have put them on the right track.Thus, Dogliottil points out that the negative pressure is most marked in the thoracic region and diminishes as the sacral region is approached ; and Gutierrez, who first drew attention to the sign of the hanging drop (fig.2), tells us that the drop may be sucked in quickly or slowly, or " a simple to and fro movement may be observed.Some observations and experiments, as well as dissections we have made, appear to have a direct bearing on the subject.When injecting analgesic fluid into one paravertebral space we noticed, as many other anzsthetists have done, that some of the solution dripped from the hub of the needle lodged in the adjoining space (fig.3).