Learning outcomes
This article aims to enable VNs to :
• Recognise the impact a standard dead-space discard volume may have on the accuracy of controlled drug records .
• Understand the impact of syringe size , needle size and syringe fill on dead-space discard volume .
• Create a practice-specific action plan to improve the accuracy of controlled drug records through deadspace discard volume records .
Materials and methods
To investigate the variation in dead-space volume , a variety of sizes of syringes and needles commonly used in small animal veterinary practice were investigated . Five syringe volumes were used : 1 ml , 3 ml , 5 ml , 10 ml and 20 ml . All syringes were manufactured by Henry Schein ( Melville , NY , USA ), except for the 5 ml syringes , which were manufactured by Aniject ( Millpledge , UK ). Three sizes of needles were used in this study , 21G , 23G and 25G ; all were 5 / 8 ’’ ( 15.9 mm ) length and manufactured by Henry Schein .
To measure the volume of dead space present in the needle and syringe combinations , two bottles of Water for Injection 100 ml ( Norbrook , UK ) were used in the study . Water for Injection was selected because 1 ml of water weighs 1 g , allowing weight to be used as a measure of liquid loss due to syringe / needle dead space .
Ten sets of data collection were performed by one investigator ( the first author ) for consistency . Data collection was performed in a room with an approximate ambient temperature of 20 ° C ( a temperature-controlled room was not available , although this reflects the majority of UK veterinary clinics ).
In each set , combinations of syringe and needle sizes were used so that all available sizes were tested against each other – for example , the 1 ml syringe was used with 21G , 23G and 25G needles . This was initially performed with 10 % of the syringe volume withdrawn , then repeated with 100 % of the syringe volume ( e . g . the 5 ml syringe was initially filled to 0.5 ml , then to 5 ml ).
The injection bottle was weighed prior to syringe filling and the required volume was then withdrawn into the needle and syringe and set aside . An Ascher Digital Pocket Scale ( RUIYI Tech , UK ) was used for measurements , which has an accuracy of ± 0.01 g . The injection bottle was reweighed and the difference between the pre-weight and post-weight was calculated to determine the change in bottle weight .
To calculate the volume of dead space , the volume of water withdrawn from the bottle ( as measured by the syringe ) was first converted from ml to g ; for example , 0.5 ml is equal to 0.5 g . The weight of water withdrawn ( as measured by the syringe ) was then subtracted from the change in bottle weight , to calculate the combined weight of the needle / syringe dead-space volume , and this was converted back to ml .
Statistical analysis was performed using SPSS v28 ( IBM Inc ., Armonk , NY , USA ). Descriptive statistics were calculated for each syringe / needle combination , and data were tested for normality using the Shapiro – Wilk test . The impact of syringe fill ( 10 % versus 100 %) on dead-space volumes was investigated using the Mann – Whitney U test .
The effect of syringe size on dead-space volume , and the effect of needle size on dead-space volume ( for each individual syringe size , and all syringe sizes combined ) were both investigated using the Kruskal – Wallis test , with post-hoc analysis using Dunn ’ s pairwise tests ( adjusted using the Bonferroni correction ) to identify significant differences between syringe sizes . Significance was indicated by p < 0.05 .
Results
A total of 300 measurements were recorded from the various syringe / needle combinations , with an overall median calculated dead-space volume of 0.16 ml ( interquartile range ( IQR ) 0.12 – 0.20 ml , range 0.05 – 0.28 ml ). Median losses based on syringe size were identified as : 1 ml = 0.09 ml , 3 ml = 0.16 ml , 5 ml = 0.18 ml , 10 ml = 0.19 ml , 20 ml = 0.20 ml ( Table 2 ).
Table 2 . Overall descriptive statistics ( median , interquartile range ( IQR ) and overall range ) for calculated needle / syringe combination dead-space volume by syringe size . Each dead-space volume was measured 30 times per syringe size .
Syringe size ( ml )
Median ( IQR )
Range
1 0.09 ( 0.07 – 0.10 ) 0.05 – 0.15 3 0.16 ( 0.12 – 0.18 ) 0.06 – 0.23 5 0.18 ( 0.15 – 0.21 ) 0.10 – 0.27 10 0.19 ( 0.14 – 0.20 ) 0.07 – 0.28 20 0.20 ( 0.17 – 0.23 ) 0.10 – 0.27
Overall , the combined needle / syringe dead-space volume was not affected by the needle gauge ( H = 2.66 , p = 0.264 ). For 1 ml syringes , the combined needle / syringe dead-space distribution was significantly affected by different needle gauges ( H = 18.07 , p < 0.001 ).
Volume 38 ( 2 ) • April 2023
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