Comparative Phantom Study on Epidural Anesthesia Needle

The purpose of the current study was to evaluate the clinically used epidural anesthesia needles based on quantitative comparative data. Precise measurement of the tip shape and puncture force analysis were conducted on six different needles. Tip angle (alpha+beta) and tip length (L) were measured by X-ray computed tomography (CT). The one-axial puncture force through a silicone phantom (thickness of 3 mm) was obtained by a load cell. The speed was set at 4 mm/s, which equals the average of anesthesiologists´ technique. The needle punctured twice at the same position to separate cutting and friction force. The X-ray CT revealed that 1) the alpha+beta ranged from 27.5 degrees to 38.8 degrees (average of 33.8 degrees), 2) the higher alpha+beta resulted in the lower L (ranges from 2.13 mm to 3.27 mm; average of 2.62 mm), and 3) the most popular needle was the one with average tip angle and length (the alpha+beta of 33.6 degrees, the L of 2.57 mm.). Puncture force analysis showed that 1) the peak value related the L (correlation coefficient of r2=0.65), and the most popular needle was the third-largest value, 2) the slope of increasing force related the alpha+beta (correlation coefficient of r2=0.79), and 3) the averaged force to cut of the most popular needle was the second-smallest value, which means less resistance for cutting