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Luis A Gonzalez, Thomas R Friberg; Factors associated with variability of delivered volume during standard intravitreal injection.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4461.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate variables associated with differences in volume delivered during intravitreal injections with different syringe and needle combinations.
Ten weight measurements of four different empty 1-ml syringe-needle combinations [Tuberculin(Tb)/30G½, Tb/32G½, Luer-Lock(LL)/ 30G½, LL/32G½] were obtained with a Mettler AM50 scale. Residual volume (RV) was determined by weight by first aspirating and priming sterile water to the 0.05cc mark of the syringe (initial volume - IV) and then emptying the contents with the plunger. Delivered volume (DV) was calculated by the difference between the IV and RV. Syringes and needles were also weighed separately. Statistical analysis was performed with nonparametric Wilcoxon-Mann-Whitney and Kruskal-Wallis tests.
We found significant differences in the initial and residual volumes, but no significant difference in the total delivered volume (DV) (Tb/30G.058±.007, Tb/32G .057±.003, LL/30G .056±.004, LL/32G .057±.004, p=.79) between the four syringe/needle compounds. A RV in filtered loading needles was not measurable. RV between 30G ½ and 32G ½ needles was statistically significant different (.028±.006 vs .0184±.008, p<.01), and no difference between the Tb and LL syringes was noted (.047±.006 vs .046±.007, p=.43). Further analysis showed a significant larger IV and RV with the 30G needle vs the 32G needle (0.137±.006 vs .124±.004, <.001 and .028±.006 vs .018±.008, <.01). These differences held true when volumes were measured in the needle separately or as part of a syringe/needle compound (regardless of type of syringe).
To improve cost efficiency of intravitreal injections, new alternative techniques for reducing drug wastage have been studied. Standardizing the steps of intravitreal injection preparation (e.g., loading drug, switching needles, priming) may decrease medication wastage. Our results suggest that the use of smaller gauge needles decreases the amount of medication needed to attain the target delivered volume. Preloaded syringe/needle compounds would decrease medication wastage by eliminating steps needed to prepare the injections (i.e., loading needles). In clinical practice, the authors have also noted dripping of the anti-VEGF out of needles prior to injection. We are evaluating whether drug viscosity, needle capillarity, syringe/needle compound pressures are contributing factors to injection volume variability.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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