Strain derivative inside skin during epidural needle insertion calculated with finite element analysis

Abstract

 Patients feel much pain during epidural needle insertion, due to deformation of the skin before puncturing. In order to develop a painless epidural insertion needle, purpose of the current study was quantification of pain by calculation of strain derivative inside the skin with finite element analysis（FEM）. A mimicked skin for epidural insertion training was employed. Epidural needle insertion experiment against the mimicked skin showed actual insertion force and skin deformation. Results of the FEM matched with the experimental data satisfactory. When the epidural needle was inserted 0.8 mm into the mimicked skin, strain derivative was calculated as 0.49/mm in the location of 0.5 mm from the surface. The strain derivative with the epidural needle showed 1.5 times value as large as the strain derivative with an indenter for rubber stiffness. Thus, pain intensity could compare not only by visual analogue scale method, but also by the calculated strain derivative inside skin.