Flow characteristics of Luer and non-Luer spinal needles

We investigated the flow rates of 25-G and 27-G spinal needles, of 90-mm and 120-mm lengths, from Vygon, BD, B. Braun and Pajunk; the needles had either a Luer connector, or a Surety^® or UniVia^® non-Luer connector. We used a bench-top model of entering the spinal space, pressurised to 35 cmH₂ O to simulate cerebrospinal fluid pressure in the sitting position. We examined the time to first appearance of simulated cerebrospinal fluid in the needle hub, as well as the amount of fluid collected over 120 s after the needle was introduced. The mean (SD) times to first appearance of fluid in the needle hub of Luer spinal needles varied from 0.36 (0.22) s for the 25-G 90-mm BD to 3.14 (0.72) s for the 27-G 120-mm B. Braun, and in the non-Luer spinal needles from 0.22 (0.17) s for the 25-G 90-mm B. Braun to 2.99 (0.71) s for the 27-G 120-mm Pajunk. There was a significant difference in the time to first appearance of fluid in the needle hub between Luer and non-Luer needles of the same type for seven of 14 comparisons made, of which four showed slower appearance of fluid in the non-Luer version. In some of these cases, the time to appearance of fluid was nearly twice as long with the non-Luer counterpart. The mean (SD) weight of fluid collected in 120 s using the Luer spinal needles varied from 0.21 (0.05) g for the 27-G 120-mm Pajunk to 1.21 (0.18) g for the 25-G 90-mm Vygon, and using the non-Luer spinal needles from 0.25 (0.05) g for the 27-G 120-mm Pajunk to 1.55 (0.05) g for the 25-G 90-mm B. Braun. All of the needle types showed a greater weight of fluid collected using the non-Luer compared with the Luer version, with six of the 14 needle types showing a significant difference. Significant variations in flow were also seen between the same needle type from different manufacturers. We conclude that changing from Luer to non-Luer versions of spinal needles does not merely change the hub design and connection, but may introduce important differences in function.