Sensation : 2 A Subjective and Objective Prospective Study of Dural Puncture Forces 3 Using Fine-Gauge Spinal Needles 4 5

Background We hypothesized that the click perceived when puncturing the dura-arachnoid with fine-gauge spinal needles can be subjectively identified, and investigated whether it may be distinguishable among different needle types. Methods Subjective and objective evaluations were performed. First, physicians punctured the polyamide film or porcine dura mater (n = 70 and n = 20, respectively) with seven types of spinal needles and numerically evaluated the perceived click sensations. Using an 11-point numerical rating scale (from “0” for “no click sensation” to “10” for “the strongest click perceived”) data, subjective differentiation among needle types was assessed. Second, in the objective part of the study, total forces elicited by polyamide film or porcine dura mater punctures with each needle were measured using a biomechanical testing device, and load-displacement curves evaluated. Third, the results of subjective and objective evaluations were compared. Results All participants recognized the click and could discriminate among needles of different tip shape. The load-displacement curves for polyamide film and porcine dura mater were similar and needle-specific. The subjective numerical rating scale values corresponded well with the objectively measured changes in total forces (R2 = 0.862 and R2 = 0.881 for polyamide film and porcine dura mater, respectively), indicating that an increase in the largest drop in total force value of 0.30 N or 0.21 N would produce an increase of numerical rating scale value of 1 for polyamide film and porcine dura mater, respectively. Conclusions We provide an objective proof of the click sensation felt upon dural puncture using different fine-gauge spinal needles. Click recognition could be used as an additional indicator of successful spinal puncture.

5 100 substitute material for the artificial dura mater. Fresh PDM was collected as a by-product 101 from a meat-processing plant (Tokyo Shibaura Zoki Co., Ltd.; Tokyo, Japan), and excised 102 from the spinal cord within 1 h after the pigs (Duroc, Landrace, and Large White Yorkshire 103 breeds, approximately 6 months old) were sacrificed. Samples of fresh PDM cut lengthwise at 104 4-cm intervals were stored in the physiological saline solution at 2-4°C until immediately 105 before experimental use. All samples were used within 24 h of preparation, and the thickness 106 of each excised dura sample measured using a micrometer. The equipment used in this study 107 was loaned by the Unisis Corporation (Tokyo, Japan).

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The seven spinal needles were inserted through a 20-G introducer needle fixed in a 117 hard sponge block. The needles were set-up to enable the perpendicular puncture of either the 118 synthetic or porcine dura (Fig 1a). Both dura were fixed in position by rubber sheets with a 119 middle excised portion.

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In the single-blind experimental settings, the participants were first instructed on the 136 defined NRS range. Next, they were asked to puncture the dura with the Dr. Japan  needle, 137 with an assigned score of 10, and then to perform punctures with the remaining six needles in 138 a random order. The needle types were not disclosed and the participants, blinded to the six 139 needles, assigned the NRS scores according to their subjective click sensations. After each set 140 of seven punctures, when a participant needed an additional puncture to assign the final NRS 141 score, the dura was slightly moved (approximately 5-10 mm) to ensure that each puncture was 142 performed in a clean part of the dura. Punctures with each spinal needle could be repeated as 143 many times as required; however, to avoid potential "material fatigue" and attachment of film 150 Shimazu Corporation, Kyoto, Japan). Samples (4 cm × 4 cm in size) of either the 50 m-PA 151 film or PD were mounted with pins onto the testing device. The spinal needles were loaded so 152 that the needle punctured the dura at 90° at a constant velocity of 200 mm min -1 (Fig 1b).  164 PAF -PA film, PDM -porcine dura mater.

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In the preliminary studies, the results obtained for PAF were more consistent (smaller 167  SD from mean) for all needles than those of PDM (larger  SD from mean); therefore, in 168 the final bench experiment, the number of PAF punctures was set to 10 per needle type and 169 the number of PDM punctures set to 20 per needle type. In PDM experiments, each needle 170 was not used >10 times due to an observed tendency towards increased measured forces when 171 the same needle was used ≥20 times. The puncture loci on either PAF or PDM were randomly 172 selected.  (Table 1a). Among all 70 238 participants in the PAF group, two (2.8%) reported not perceiving the click with the 27 G 239 cutting needle, resulting in a score of 0 (Table 1a). Scores >10 or equal to 0 were not assigned 240 by participants in the PDM group (Table 1b).
241    287 needle had only one marked peak of force values, which, compared to other needles, was also 288 the highest for both PAF and PDM (Fig 2).

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Load-displacement curve shapes of synthetic and porcine dura mater revealed visual 290 similarities between the corresponding curve shapes produced by each spinal needle (Fig 2). 302 the x-axis compared to PAF curves (Fig 2 and Fig 3) for the respective needle. Differences in 303 values of the mean peak force, plateau, and depth of displacement for PAF and PDM are 304 shown in Figure 2. Mean peak forces and plateaus tended to be lower for each needle 305 puncturing PDM compared to PAF but mean depths of displacement were higher for PDM 306 than PAF. 323 27 G cutting needle (Fig 2).

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Among all fine spinal needles and data items obtained from the objective part of the

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The load-displacement curves obtained for both PAF and PDM were needle-type-345 specific: closer similarities were observed between PAF and PDM curves obtained for the 346 same needle than for other needles (Fig 3).

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At the defined point on the load-displacement curve, the total force elicited on the 348 needle could be expressed as:  (Fig 4a), the force acting on the needle is due to the elastic 357 deformation of the membrane which is represented as F elastic . After the puncture (Fig 4b), 358 F resistive is added to represent the forces produced by membrane viscosity, similar to frictional 359 forces. This F resistive can be observed when force converges to the plateau where the effect of 360 F elastic becomes minimal.