Five doses of 0.5 ml are withdrawn from a new 10 ml multi-dose injection bottle .
Example A Using any needle and syringe with a standard discard volume of 0.05 ml per injection .
5 x 0.5 ml = 2.5 ml drug administered 5 x 0.5 ml = 0.25 ml drug wastage recorded
Total volume withdrawn = 2.75 ml , leaving 7.25 ml in the bottle .
Example B Using 1 ml syringes with a 21G needle and the proposed needle / syringe dead-space volume of 0.11 ml .
5 x 0.5 ml = 2.5 ml drug administered 5 x 0.11 ml = 0.55 ml drug wastage recorded
Total volume withdrawn = 3.05 ml , leaving 6.95 ml in the bottle .
Example C Using 3 ml syringes with a 21G needle and proposed needle / syringe dead-space volume of 0.16 ml .
5 x 0.5 ml = 2.5 ml drug administered 5 x 0.16 ml = 0.80 ml drug wastage recorded
Total volume withdrawn = 3.3 ml , leaving 6.70 ml in the bottle .
Figure 5 . Examples of controlled drug record book calculations using different needle and syringe combinations and proposed discard volumes to illustrate the effect on record accuracy .
A significant difference was found between different syringe sizes . Median losses for all needle / syringe combinations were higher than the typically recommended value of 0.05 ml [ 8 ] . Therefore , the use of 0.05 ml as a standard discard volume cannot be recommended .
Mirroring the findings of Cambruzzi and Macfarlane [ 9 ] , the results of this study highlight the necessity for different discard volumes dependent on the syringe used ( Table 3 ). Analysis indicated no significant difference in dead-space volumes based on syringe fill volume , which is expected as the dead space associated with a syringe is due to the volume of liquid that remains in the syringe hub and between the syringe end and the plunger , so should be unaffected by syringe fill .
Overall , this study found no significant difference in the dead-space volume between the three needle sizes . However , if data were collected with largergauge needles or longer needles , it is anticipated that a significant difference would be identified due to the increase in needle gauge / length resulting in an increase in equipment dead space .
In comparison , the study by Cambruzzi and Macfarlane [ 9 ] found no significant difference between 21G and 23G needle dead space ( the reported value was 0.05 ml for both ). They also reported a dead-space volume for 18G needles of 0.07 ml , highlighting the need for further research with a wider range of needle gauges .
As the volume of CDs prescribed in small animal practice is often below 1 ml , the effect of needle size on combined needle / syringe dead space was explored . This analysis did not indicate a statistically significant difference in dead-space volume between 23G and 25G needles combined with 1 ml syringes . However , there was a statistically significant difference between 21G needles and 23 / 25G needles with 1 ml syringes , with an additional median loss of 0.03 ml .
Practices should therefore consider using the smallestgauge needle possible to reduce CD wastage . Low dead-space syringes are also available , which can further reduce drug wastage . However , they were not included in this study due to supply limitations at the time of the investigation .
The results of this study mirror the current literature regarding the variations in dead-space volumes [ 9 – 11 ] . All studies identified significant differences in deadspace volumes in a variety of syringe sizes . The study conducted by Cambruzzi and Macfarlane [ 9 ] reported similar results to this study : their mean dead-space loss for syringes was between 0.03 ml and 0.14 ml , and their mean dead-space loss for 21G and 23G needles was 0.05 ml . Their study would report an overall deadspace volume of between 0.08 ml and 0.19 ml if results for needle and syringe dead space were combined .
The volume of needle / syringe dead space poses a question of whether drug overdose is possible if this volume is not accounted for . Bhambhani et al . [ 11 ] conducted a study into an inadvertent overdose of human neonates due to dead-space volumes . They stated that this occurred due to dilution of the drug for intravenous administration , which led to the deadspace volume being withdrawn into the syringe when the additional sterile saline was drawn up after the drug into the same syringe . Their study estimated dead-space volumes as 0.07 ml . Therefore , potentially , a neonate prescribed 0.02 ml digoxin received 0.09 ml once diluted .
In veterinary medicine , it is normal practice to administer pre-medication drug combinations in the same syringe , which may inadvertently cause an overdose of drugs if they are sequentially withdrawn into the same syringe .
Volume 38 ( 2 ) • April 2023
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