The Effects of Passage Through Vaccine Vial Septa on Needle Sharpness

Abstract

Veterinarians anecdotally report changing needles before injection after drawing up a vaccine due to concerns for needle dulling. However, there is little information on the impact on needles during passage through vial septa, and the CDC does not recommend this practice. Sharps are considered medical waste and their disposal incurs regulatory burden while recapping a needle to remove it represents a hazard to veterinary personnel. Due to the large volume of vaccines administered in shelters, the cost to dispose and repurchase needles can be high. The aim of this study was to determine whether needles commonly used by veterinarians dull after passage through vial septa. A survey to determine the most common brands and gauges of needles, as well as needle-changing practices, was promoted to veterinarians and staff via social media from 5/5-5/12/23 (IRBAZ-5222). A Wagner FDIX ForceOne force gauge was used to measure peak force required to penetrate 0.020” thick Abrasion-Resistance Polyurethane Rubber (ISO 7864) for new needles, needles passed through 1 vial septum, and needles passed through 2 via septa (0, 1, 2) across 3 different brands (a, b, c) and 4 sizes (20, 22, 25 G) of single-use veterinary hypodermic needles. Needle tip and surfaces were visualized via 3D infinite focus microscopy (Bruker Alicona InfiniteFocusSL) with a 5XAX objective and subsequent deviation maps were created in Zeiss Inspect Professional (formerly GOM) to facilitate defect identification. Multivariable linear regression was used to determine the association between peak force and number of passages through a vaccine vial septum while controlling for needle brand, gauge, and vaccine vial penetration force (VVPF) and logistic regression to determine associations between gross defects and brand, gauge, and VVPF. Of the 482 survey respondents, 76% reported changing needles used to draw up a vaccine, primarily due to concerns about needle dulling. The peak force through a standard material was measured for 330 needles. The mean VVPF through the first septum was 2.1±0.7 N (range 0.4-5.0). New 20 G needles of brand a (referent) required 1.05 N to penetrate the standard material. One pass through a septum at the lowest recorded VVPF required an additional 0.09 N, an increase of 9% from baseline P < 0.0001, while 2 passes, both at the lowest recorded VVPF, required additional 0.21 (19%) N of force (P <0.0001). Compared to brand a, brand b and c required an additional 0.12 (11%) and 0.10 (10%) N, respectively, both P <0.0001. Smaller needles required less force, with 22, 25, and 29 G needles requiring -0.06 (-6%), -0.23 (-22%), and -0.47 (-45%) N, respectively (all P <0.003). VVPF increased the peak force by 0.03 N for each additional 0.5 N (P=0.003) during the first septum penetration, but was not significant for a second penetration (P=0.337). Fifty-two needles were scanned with the InfiniteFocus SL microscope after one and two passages through a vial septum. Twenty-one of 52 needles had visual defects after 1 passage and 27 had visual defects after 2 passages, which was not different (P = 0.241). Only VVPF was significant for predicting visual defects (OR 4.6; P = 0.001). Passage once or twice through vial septa resulted in less than a 20% change in force required to penetrate standard material. The impact of other factors, including brand, needle size, and force used to penetrate the vial, all had a greater impact on force than passage through a single vial septum. The clinical significance of these peak force differences is unknown.