Dunn ’ s pairwise post-hoc analysis ( adjusted using the Bonferroni correction ) indicated very strong evidence of a difference between the combined needle / syringe dead-space volume for 1 ml syringes with a 21G versus 25G needle ( p < 0.001 ), and for 1 ml syringes with a 21G versus 23G needle ( p = 0.006 ), but not for 23G versus 25G ( p = 1.000 ). The median combined needle / syringe dead-space volume for 1 ml syringes with a 21G needle was 0.11 ml ( IQR 0.09 – 0.12 ml ), and with a 23G or 25G needle it was 0.08 ml ( IQR 0.07 – 0.10 ml ). For all other syringe sizes ( 3 – 20 ml ) there was no evidence of needle gauge significantly affecting the combined needle / syringe dead-space volume ( p > 0.05 ) ( Figure 4 ).

The combined needle / syringe dead-space distribution was significantly affected by syringe size ( H = 145.26 , p < 0.001 ). There was very strong evidence ( p < 0.001 ) of a difference between the dead-space volume for 1 ml syringes versus all other sizes ( 3 – 20 ml ). There was also strong evidence of a difference between the dead-space volume for 3 ml syringes and 5 ml syringes ( p = 0.006 ), between 3 ml and 10 ml syringes ( p = 0.017 ), and between 3 ml and 20 ml syringes ( p < 0.001 ).

There was no evidence of a difference between the 5 ml , 10 ml or 20 ml syringes ( p > 0.05 ). The median combined needle / syringe dead-space volume for 5 – 20 ml syringes was 0.19 ml ( IQR 0.16 – 0.21 ). The proposed CDR dead-space discard volumes for multidose injectables are shown in Table 3 . There was no effect of syringe fill on dead-space discard volume ( Z = – 0.69 , p = 0.488 ).

Table 3 . Proposed discard volumes for controlled drug registers ( CDRs ) based on data analysis .

Equipment

1 ml syringe with 23G or 25G needle

1 ml syringe with 21G needle

3 ml syringe with 21 – 25G needle

5 – 20 ml syringe with 21 – 25G needle

Discussion

New volume to be recorded in CDR ( ml )

0.08

0.11

0.16

0.19

The findings of this study suggest that the practice of using a standard needle / syringe dead space estimate of 0.05 ml for recording CD wastage from multidose injection bottles is inaccurate and will result in inadequate wastage records . Figure 5 demonstrates the impact of using the previously proposed deadspace discard volume of 0.05 ml , when compared with the volumes reported in this study for 1 ml versus 3 ml syringes . In this example , when five doses are withdrawn , 0.30 – 0.55 ml would be unaccounted for . This may seem like an acceptable loss but , after 10 dose withdrawals , this unaccounted wastage would increase to 0.60 – 1.10 ml , meaning over 10 % of the total drug volume would have been lost and unaccounted for .

0.00

1 3 5 10 20 Syringe size ( ml )

Figure 4 . Boxplot of calculated dead-space volume for each syringe size and needle gauge combination .

26 Veterinary Nursing Journal