User experience and syringe-and-needle combination impacts accuracy and precision of small-volume medications

To evaluate the accuracy and precision of user groups using common syringe-and-needle combinations found in small animal general practice.

30 participants were divided into 3 groups (novice, beginner, and expert) based on level of experience. Participants prepared 180 syringes (sixty 0.5-mL insulin syringes, sixty 1-mL tuberculin syringes with 25-gauge needle, sixty 1-mL tuberculin syringes with 22-gauge needle) with 3 volumes of sterile water (0.02, 0.12, and 0.43 mL). Accuracy and precision were calculated, and mixed-effect modelling was used to evaluate the impact of syringe type, volume, and participant characteristics.

The greatest precision was seen with the smallest needle for the smallest volume. All participants tended to overfill volumes with larger syringe-and-needle combinations. The 1-mL syringe with larger needles was the least accurate. However, with larger volumes the percent difference in prepared versus expected volume (ie, the effect of overfilling) was reduced compared to smaller volumes. The beginner group was nearly 2 times as likely to prepare an accurate volume within ± 20% of the intended volume compared to experts (OR, 2.29; 95% CI, 1.33 to 3.93).

Errors in volume preparation ± 20% of expected, especially with the smallest volumes, were most common when larger needles were used. Smaller syringe-and-needle combinations improved precision.

Clinical practitioners should be aware of the inaccuracies encountered when preparing small volumes of injectable medications frequently used in veterinary practice. Greater experience does not guarantee greater accuracy. Clinically significant errors of at least ± 20% are common, especially when preparing very small volumes.