Background: Syringes are commonly used in pharmacy compounding for the measurement of small volumes, especially in the preparation of sterile products for injection and infusion. However, there are no current official guidelines for the proper use of syringes in measuring small volumes. Objective: The purpose of this project was to determine the accuracy and precision of commercially available syringes in measuring small volumes during sterile product preparation to make recommendations for syringe size selection. Methods: To assess precision and accuracy of syringes, 3 separate investigators measured 5%, 10%, or 20% (n = 30 each) of the volume of a 1-, 3-, 5-, 10-, or 20-mL syringe with an attached 18G, 1½&#; needle by drawing sterile water for injection from a vial. Delivered volumes were measured gravimetrically using an electronic balance and converted to volume using the specific gravity of water (1.0). Accuracy is represented as the mean and standard deviation, while precision is represented as percent relative standard deviation. Differences were assessed using a 1-way analysis of variance with Bonferroni adjustments and significance set at P < .05. Results: Precision and accuracy were highly variable and often significantly (P < .05) different compared to the theoretical volume delivered both within and between investigators. An increased likelihood of unacceptable error (>5%) was observed when less than 20% of the labeled capacity of a syringe was measured. Mean percent error ranged from 1.4% to 18.6%, despite manufacturer specification of ±5% accuracy, suggesting proper technique as a major factor in small-volume measurements. Conclusion: In addition to proper, validated training of syringe users, we recommend that users measure no less than 20% of the indicated volume of the syringe while choosing syringes as close as possible to the desired measurement. When possible, very small volumes should be diluted to meet the minimum volume of the smallest syringe available. Implementation of these recommendations will improve accurate dosing and, ultimately, patient safety.
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Therefore, it seems necessary to develop guidelines for the proper use of syringes, especially in measuring small volumes and potent medications, to improve dosing accuracy and ultimately patient safety. Scientific evidence of the limits of accuracy should be used by pharmacists and other health care providers in medication preparation and dosing to ensure optimal patient outcomes.
Few studies have attempted to address the issue of using syringes to measure small volumes during compounding. Several studies that have been published specifically refer to the accuracy of insulin measurements in a 1-mL syringe. 4 - 6 Two published studies have looked at the accuracy of measurements in a variety of syringes but the results did not reach statistical significance to make a strong recommendation on compounding practices. 7 , 8 Lee et al 7 concluded that reproducibility increased as the measured volume increased relative to syringe capacity and that, relative to the measured volume, smaller syringes yielded more reproducible results. Similarly, Erstad et al 8 found that measurement of 0.5 mL in 3 different syringe sizes (1, 3, and 10 mL) was more accurate and reproducible in the smaller syringe.
Currently, no official guidelines exist for either minimum or maximum volumes for accurate measurement using syringes. The general rule of thumb for measuring bulk liquids using volumetric glassware is to measure at least 20% of the total volume of the measuring device while also using the smallest instrument possible to make the measurement. 1 Clinically, unsubstantiated recommendations for measurement of small volumes in syringes varies including ranges from 20%, similar to the guidelines for volumetric glassware, up to a minimum volume of 50% of the syringe capacity. These values differ significantly from the manufacturer specifications, which state a volumetric accuracy for some syringes of ±5%, in line with current ISO standards which require a tolerance no greater than ±5% at more than or equal to 50% capacity ( and ). 2 , 3 In addition to the inherent variability in instrumentation, multiple other factors can contribute to inaccurate and imprecise measurements including user skills and the volume to be measured relative to syringe capacity.
An 18G, 1½&#; needle was attached to a 1-, 3-, 5-, 10-, or 20-mL syringe, and the syringe assemblage, with needle cap removed, was weighed (W syringe ) using a calibrated analytical balance accurate to ±0.001 g (Denver Instruments, Bohemia, NY). A volume of SWFI equivalent to 5%, 10%, or 20% of the indicated nominal capacity of the syringe ( ) was drawn into the syringe, ensuring all air bubbles were removed, and the syringe assemblage was weighed again (W filled ). The contents were then expelled from the syringe and the syringe assemblage was reweighed (W expelled ). Three separate investigators repeated each measurement 30 times.
For each of the syringe sizes tested, the %RSD decreased as the percentage of the measured syringe capacity increased toward 20%, although the results were generally not statistically significant (P > .05) except for the 5-mL syringe ( ). This trend was observed for the overall pooled data as well as for each individual investigator. The average %RSD, reflecting the reproducibility of the measurements, was below 5% for each syringe tested at 20% capacity ( ). However, the accuracy of the measurements was frequently greater than 5% and varied significantly between investigators, suggesting the technique as an important variable in measurement accuracy ( and ).
Significant differences (P < .05) were observed in the accuracy between the 3 investigators especially with smaller volumes, with 2 of the investigators tending to over-measure while the third was usually within 5% error range ( ). However, as the syringe size increased, measurements tended to approach the desired volume for all investigators, especially as percentage of the nominal capacity measured increased. Additionally, the difference between investigators also decreased as syringe size increased, especially at the 5% capacity measurement.
For all syringe sizes tested, the accuracy improved as the percentage of the nominal volume measured increased (P < .005; ). Additionally, the total number of measurements with greater than 5% error decreased while the percentage of measurements with an acceptable error (&#;5%) increased with increasing percentage nominal capacity measured ( ). Comparison between different syringe sizes showed wide variability in accuracy. Generally, the accuracy of measurements improved as syringe size increased except for the 5-mL syringe. The MPE varied significantly between syringe sizes, the percentage (5%, 10%, or 20%) of the instrument capacity measured, and the investigator performing the measurements ( ).
Technical data provided by the manufacturer indicate tolerance within ±5% for the syringes used in this study ( ).2 Sánchez-Rubio Ferrández et al9 investigated the error associated with the measurements at full syringe capacity in 10-, 20-, and 50-mL syringes and found that in all cases, the error was less than 5%, which is in line with the inherent variability of accuracy as stated by the manufacturer. Similarly, Lee et al7 measured the accuracy and reproducibility of 2 brands of 1-, 3-, 10-, and 12-mL syringes (primarily >20% nominal capacity) and found that the MPE (accuracy) was less than 5% and the %RSD (reproducibility) was less than 1% for all measurements. Although we investigated only one brand, it is expected that syringes supplied by other manufacturers should have the same tolerance because all syringes are manufactured to the same ISO standards (ISO -1-). Per ISO -13 standards, the tolerance of all syringes when measuring less than 50% of nominal capacity (Vnominal) is ±[1.5% Vnominal + 2% Vexpelled] for syringes with a nominal capacity less than 5 mL and ±[1.5% Vnominal + 1% Vexpelled] for syringes more than 5 mL. Tolerances of ±5% or less are only required when the expelled volume is at least 50% of the nominal volume. However, manufacturers may employ more stringent tolerances to their product, as with the Becton Dickinson (BD) syringes used in the study, for which the manufacturer states a ±5% tolerance without regard to volume except for the 1-mL syringe.2 It is important to note that the tolerances for syringes refer only to the syringe and not to its use with an attached needle or injection via a Leur-Lok connector on an intravenous administration set.
At partial capacity (5%-20%) volumes used in this study, a range of accuracy of 1.4% to 18.6% was observed, suggesting that factors beyond the acceptable syringe tolerance contributed to mismeasurement. In this study, both accuracy and reproducibility improved as both syringe size and the percentage of nominal capacity measured increased. However, measurement error was frequently greater than 5% ( ), suggesting that the technique also played a significant role in measurement accuracy. Mean percentage error tended to decrease as syringe size increased except for the 5-mL syringe, possibly due to the graduations on the syringe barrel, which fell between graduation marks for the 5% and 10% capacity measures. Thus, these volumes were estimated measurements, contributing to decreased accuracy (up to 20%; ). However, the error in this syringe at 20% nominal capacity, which fell directly on a graduation mark, was still high relative to other syringes tested. Additionally, the 5% capacity measures for both the 3- and 10-mL syringes also fell between the graduation marks but did not appear to have as significant an impact on the overall accuracy as compared to the 5-ml syringe. Thus, estimation between graduation marks may not be as much of a contributor to overall measurement error as appropriate instrument selection and compounder technique. Indeed, a significant difference in error was observed between the 3 investigators in this study for most of the syringe measurements ( ).
Overall, reproducibility improved as syringe size decreased relative to the measured volume, which is consistent with the literature. Thobani and Steward10 measured volumes of 1, 3, or 5 mL in syringes ranging from 1- to 20-mL capacity (percentage of nominal capacity measured ranged from 5% to 100%). The authors found that although less than 5% in all cases, the MPE tended to be higher when less than 20% of the nominal capacity was measured (1 mL measured in a 10- or 20-mL syringe). Reproducibility also decreased as the syringe size increased, which the authors attributed to increased internal diameter of the barrel.
Erstad et al hypothesized that using large-volume syringes to measure small volumes would result in increased error. The authors measured 0.5 mL in 1-, 3-, or 5-mL syringes (10%-50% nominal capacity) and found that as syringe size increased, reproducibility and accuracy decreased.8 Accuracy was acceptable (<5%) for only the 1- and 3-mL syringes, while reproducibility fared worse with an acceptable error observed only for the 5-mL syringe. Similar to Thobani and Steward,10 the authors hypothesized that the increase in internal diameter for larger syringes made accurate measurement more difficult in addition to human perception of the plunger position. In another study, Raju and Weinberg11 measured 0.05 mL (5% capacity) and 0.10 mL (10% capacity) doses in 1-mL syringes. The authors found that for the smaller volume, 22% of the measurements had more than 20% error and only 44% of the measurements were within 10% of the desired volume. As the volume increased to 10% of syringe capacity, 71% of the measurements were within 10%, with only 7% having more than a 20% error.
Casella et al4 investigated the accuracy and precision of low-dose insulin syringes by measuring 0.5 units (0.005 mL) to 2.0 units (0.02 mL) in 0.3- or 0.5-mL insulin syringes. The authors found that an unacceptable error (>10%) was achieved when less than 2.0 units of insulin were measured regardless of syringe size and that doses tended to be over-measured in all cases. Because of the inaccuracy of low-dose insulin measurements and the lack of availability of more precise measuring devices, the authors recommended dilution of the drug product for all doses less than 2.0 units (6.7% and 4% of nominal capacity, respectively, for 0.3 and 0.5 mL syringes). Keith et al12 measured 1 (0.01 mL), 2 (0.02 mL), and 5 (0.05 mL) unit insulin doses in 2 brands of 30-unit insulin syringes, equivalent to 3.3% to 16.7% nominal capacity. Doses were generally over measured, and accuracy was poor (mean error >10%) for volumes less than 10% nominal capacity, and similar to Casella et al, the authors recommend predilution of insulin before low-dose measurement. However, both precision and accuracy improved as the volume measured increased, with less than 5% error for the 5-unit dose. Similarly, Lteif and Schwenk13 found that when patients were asked to measure low-dose insulin (&#;5 units) using 0.3- or 0.5-mL insulin syringes, the mean error in the measurements was 9.9% ± 2.4%.
Other contributing factors to mismeasurement that have been identified in the literature include size of dead space relative to the syringe capacity, calculation errors, infrequent use of syringes in daily routine, number of years of professional experience, and fatigue.14,15 Each of these factors can be linked back to appropriate didactic and practical training skills necessary for preparing competent sterile products.
One type of syringe comprises two parts: (1) the plunger and (2) the barrel. Having these essential parts, we call this syringe the 2 part syringe. Compared with a 3 part syringe, the 2 part syringe is without a gasket.
Syringe anatomy of 2-part syringeBasically, a syringe is a medical device used to inject or remove fluids from the body. That fluid could be in the form of blood or medication.
Syringe plunger
The plunger is responsible for pushing or pulling any form of liquid in or out of the barrel. It is basically made up of a straight plastic rod, which is in turn made up of polypropylene. So, it is actually a piston-type rod that could go down and up the barrel.
Syringe barrel
The barrel is the hollow and tube-like part of the syringe that holds the fluid to be injected or aspirated.
If the plunger is pushed down the barrel, the liquid will be forced out of the syringe. If it is pulled out, the fluid will be drawn inside the barrel. The barrel has an opening at the bottom end. This opening is provided with a tapering tip where the needle is eventually attached.
To know the volume of fluid currently inside the syringe, we can find the graduation lines marked on the side of the barrel. These graduation lines are expressed in terms of milliliters or fractions of a milliliter, depending on the size of the syringe. The larger the size is, the more prominent will be the interval between the graduation lines.
The syringe tips could be in the form of a Luer slip.
Luer slip syringe
In the Luer slip syringe tip, the needle is held in place by the force of friction. The needle is reasonably secure, but there is a possibility that it may come off if not firmly or snugly attached or if considerable pressure is applied to it.
2 part syringe with eccentric needleUnder this type of 2-part syringe, there are two sub-types: (1) the centric and (2) the eccentric.
In the centric style, the syringe tip is at the center of the bottom end.
In the eccentric type, the syringe tip is off-center. This is used when the needle needs to be parallel with the injection plane, such as in the intradermal route of administration or puncturing superficial blood vessels.
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Syringes are available in different sizes ranging from 1 to 60 ml. The basic rule is that when the size of the syringe to be used is being determined, the capacity of the syringe, which is next in a size larger than the volume to be measured, should be selected. For instance, if the fluid volume to be injected is 2.3 ml, then a 3 ml syringe should be used. If 3.8 ml of fluid needs to be injected, then a 5 ml syringe should be selected.
Through this method, the graduation marks on the syringe to be used will be in the smallest possible increments for the volume to be measured, leading to a more accurate measurement of the needed volume. In addition, as a precaution, a syringe should not be filled to its maximum capacity when aspirating a fluid because the plunger may be dislodged from the barrel.
A 2-part syringe cannot discharge its essential functions if a needle is not attached to its tip. Thus, there is a need to discuss the proper selection of a needle.
From the diagram of a needle, we can see that there are three essential parts of a needle: (1) the hub, (2) the shaft, and (3) the bevel.
Diagram of a needleThe hub of needle is located at one end of the needle, and it is the structure that attaches to the syringe tip. The hub is made of PP.
The shaft is the long and slender stem of the needle that is beveled at one end to form a point. It is made of stainless steel.
The bore of the needle shaft, which is hollow and cylindrical, is known as the lumen.
The size of a needle is based on the length and gauge. The length is measured in inches from the meeting point of the hub and the shaft up to the tip of the point. The lengths of needles range from 5/16 to 3 ½ inches. For some particular uses, some needles are available in longer lengths. On the other hand, the gauge of a needle that actually measures the lumen&#;s size ranges from 31 (the finest) up to 13 (the largest).
Selection of the needle size
In the selection of the needle size to use, two bases will be considered.
(1) the viscosity or rate of flowing of the solution and
(2) the nature of the rubber closure on the vial(s) of the medications.
A fluid is said to be very viscous if its rate of flowing is very slow. Thus, an oily medication is considered a viscous substance because it flows very slowly. For drugs considered viscous, needles with larger lumens (lower gauges) should be used.
If the rubber closure is easier to puncture, then needles with smaller lumens (higher gauges) should be used. Suppose needles with larger lumens are used for easily pierced rubber closure. In that case, tearing of the rubber could take place, and it will contaminate the medication.
2 part syringeNeedle gauge recommendations
The following table shows the most appropriate gauges of the needle for a particular situation.
GaugeAppropriate UseComments16-18IV infusion:Liaoning KANGYI Medical Equipment Co., Ltd was founded in and is one of the leading manufacturers of IV sets, syringes, and medical parts in China. Quality is our highest priority, and our quality assurance system is certified and meets the standards of the Chinese National Medical Products Administration, ISO , and the European Union&#;s CE mark.
We produce over 600 million pieces per year. Our products are sold across China and exported worldwide, to destinations including Europe, South America, Russia, Africa, and the Middle East.
Our company employs over 300 staff, including 50 people working in engineering and technical management. Our premises occupy an area of 20,000 square meters, with a construction area of 15,000 square meters. This space includes a 100,000-class purification workshop that occupies 8,000 square meters.
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Types Of Syringe
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