Cephalic Angulation of Epidural Needle Insertion may be an Important Factor to Safely Approach the Epidural Space: A Mathematical Model

摘要

Regarding the mathematical study by Inoue et al. 1 , it isappropriate to mention the study by Cheng 2 published morethan half a century ago, in which the research team measuredcircular epidural space (ES) width and dura mater (DM) thick-ness. According to Cheng 2 , ES axial width at L2-L3 is 6 mm.Thus, if the puncture is performed at an angle of 30-degreeto the skin, the puncture safety margin (Image 1 A) 1 will be12 mm (sin 30o = 6 mm/A). In this line of thought, with a45-degree puncture angulation, ES safety margin (SM) will be8.6 mm, which is smaller than that of the 30-degree puncture.In the thoracic and cervical regions, there is a reduction in theepidural space, as well as the angle of the median and para-median punctures, due to bony anatomy of spinal apophysesguiding the puncture angulation. Because there is no data onthe incidence of thoracic DM perforation, it is supposed tobe lower than that of the lumbar DM. It is likely that manyanesthesiologists, based on Euclidean reasoning, prefer thelatter for the following reasons: 1) to facilitate access to theES; 2) it results in greater SM (Image 1) 1; 3) prevent DM per-foration; 4) consume less time for blockade performance 3 ; and5) facilitate catheter insertion. This reasoning is also applicablein peripheral regional anesthesia 4,5 , provided that a profoundanatomical parameter is recognized, as shown in Images 1 and2 of previous studies 4,5 .