Comparison of design features and mechanical properties of commercially available Veress needles.

OBJECTIVE: To compare design features and mechanical properties of 13 commercially available Veress needles (VN).

STUDY DESIGN: In vitro biomechanical study.

SAMPLE POPULATION: Veress needles from 9 manufacturers (6 reusable, 6 disposable, and 1 with a reusable stylet combined with a disposable cannula) were included in the study.

METHODS: Veress needles are designed with a spring-loaded stylet to protect the tip of the cannula following insertion into the abdomen. Stylet forces were measured with a scale in a test jig by moving the stylet in 0.5 mm steps into the hollow cannula. Forces and spring rates were derived from force-displacement plots. Mass, mechanical dimensions, and the bevel angle and geometry were assessed. Differences between VN models were analyzed with a univariate analysis of variance. Results are reported as mean ± SD or median (range).

RESULTS: Physical and mechanical parameters differed between models. The exposed stylet length was 3.5 mm (2-7). Three bevel geometries (bias, lancet type, and back-cut) with angles between 20° and 40° were identified. Reusable VN weigh more (24.9 ± 2.2 g) than disposable designs (6.0 ± 2.3 g). The mean values for the spring rate and the residual stylet force were 0.23 ± 0.08 Nmm-1 and 0.94 ± 0.28 N, respectively. The mean force required to move the stylet to the cannula tip was 1.81 ± 0.29 N and 2.77 ± 0.54 N to move to the proximal end of the bevel.

CONCLUSION: Commercially available VN use diverse bevel geometries and have different mechanical characteristics. Studies investigating laparoscopic entry complications should explicitly report the type of VN model used.