Traditional syringes require users to visually estimate syringe volume, resulting in adverse effects on dosing accuracy, precision, and speed. This is especially problematic when the user must simultaneously focus on other visual information, deliver multiple small volumes, or for procedures requiring a great level of accuracy and precision. Injecting Botox via cystoscope while observing the procedure on a monitor, for example, often leads to unequal and non-accurate delivery of Botox in different spots in the bladder. We have designed an Incremental Syringe1 (IS) which provides an audible “click” and tactile resistance from the plunger feedback after each increment (one ml) of injection. Here we compare the dosing accuracy, precision and speed of the incremental syringe to those of a traditional syringe.

We converted half of 10 ml traditional syringes to IS by replacing their plungers. Incremental plungers were prototyped with increments every 1.0 mL and to fit the 10 mL syringes. Fourteen graduate student volunteers tested syringes with three needle sizes (14, 18, and 23 gauges). Each operator tested all syringe type and needle size combinations by dispensing 1.0 mL at a time for 8 consecutive injections. Each injection was weighed on a balance and converted to volume using the specific gravity of water. The precision of dose volumes was compared using Bartlett’s Test for unequal variances. A standard one-way or Welch’s ANOVA was used to compare differences in accuracy depending on equality variances.

Traditional and IS dose volumes were off by -3.2% and -2.5% respectively. Accuracy differences were identified between syringe types with 14 and 18 gauge needles, but not with 23 gauge. The coefficient of variation was 3.5% for traditional syringes and 1.2% for IS, which was significantly different for all three needle sizes.

Statistically different variation in dose volumes was found between needle sizes and between users for traditional syringes, but not for IS. Thirteen of 14 individuals were more accurate and 13/14 were more precise with the IS. In addition, pilot data suggests ISs are approximately 50% faster.

While the Incremental Syringe’s main advantage lies in simple handling, it is also more accurate, reducing dosing variation within individuals, across individuals, and across needle sizes. IS is a promising medical device for difficult situations like Botulinum toxin injection into the detrusor when multiple precise injections and monitoring the screen are needed at the same time.