Pain and mechanical injury of human skin following needle insertions

Needle insertion is a very common invasive procedure, but little has been done to study how pain is related to the mechanical properties of the needle insertion, and how pain from the procedure may be minimized. The aim of the present study was to investigate the pain evoked by standardized needle insertion into the human skin. Needle insertions were performed with continuous registration of the mechanical force on the needle. Forty consecutive needle insertions to the depth of 8 mm with 27G and 30G needles, 2 and 19 mm/s velocities, and at 45 and 90 degree angles to the skill surface were performed in a randomized and blinded design in 30 healthy volunteers. The occurrence, intensity and quality of pain, as well as the maximum mechanical needle penetration force and the total mechanical workload were registered. The mechanical parameters of needle insertions were significantly related to needle size and velocity of insertion. Occurrence of pain and bleeding were significantly related to the needle size. High needle insertion velocity was significantly related to a higher rate of sharp and pricking pain, and low insertion velocity to a significantly higher rate of dull and burning pain. The present study provides quantitative data on pain and mechanical parameters of standardized needle insertions through normal human skin.