Syringe and needle size, syringe type, vacuum generation, and needle control in aspiration procedures

Abstract

Purpose: Syringes are used for diagnostic fluid aspiration and fine-needle aspiration biopsy in interventional procedures. We determined the benefits, disadvantages, and patient safety implications of syringe and needle size on vacuum generation, hand force requirements, biopsy/fluid yield, and needle control during aspiration procedures.

Materials and methods: Different sizes (1, 3, 5, 10, and 20 ml) of the conventional syringe and aspirating mechanical safety syringe, the reciprocating procedure device, were studied. Twenty operators performed aspiration procedures with the following outcomes measured: (1) vacuum (torr), (2) time to vacuum (s), (3) hand force to generate vacuum (torr-cm2), (4) operator difficulty during aspiration, (5) biopsy yield (mg), and (6) operator control of the needle tip position (mm).

Results: Vacuum increased tissue biopsy yield at all needle diameters (P<0.002). Twenty-milliliter syringes achieved a vacuum of -517 torr but required far more strength to aspirate, and resulted in significant loss of needle control (P<0.002). The 10-ml syringe generated only 15% less vacuum (-435 torr) than the 20-ml device and required much less hand strength. The mechanical syringe generated identical vacuum at all syringe sizes with less hand force (P<0.002) and provided significantly enhanced needle control (P<0.002).

Conclusions: To optimize patient safety and control of the needle, and to maximize fluid and tissue yield during aspiration procedures, a two-handed technique and the smallest syringe size adequate for the procedure should be used. If precise needle control or one-handed operation is required, a mechanical safety syringe should be considered.

Figure 1. Different Sizes of Reciprocating Procedure Device (RPD)

The RPD mechanical syringe (1 ml, 3 ml, 5 ml, 10 ml, and 20 ml RPD) device injects when the thumb presses the dominant plunger and aspirates when the accessory plunger is pushed. The index and middle fingers do not change position on the finger flanges when transitioning from injection to aspiration.

Figure 2. Linear Displacement Method for Measuring Syringe and Needle Control

A rigid polystyrene marker is placed on the needle to a preset indelible mark on the needle, and then the needle is advanced into the target surface until the needle tip is at the desired location and polystyrene marker is touching the surface. The physician operator then performs the aspiration procedure. Loss of control in the forward direction (penetration) pushes the polystyrene marker posteriorly on the needle past the indelible mark, permitting precise measurement in mm of loss of control in the forward direction.

Figure 3. Vacuum Generation with the Conventional Syringe

Vacuum in Torr (mm Hg) are shown as a function of plunger displacement and syringe size. As can be seen each syringe size has its unique vacuum - plunger displacement curve with the 20 ml syringe generating the greatest vacuum. However, along each curve, the plunger displacement to a particular volume generates the identical vacuum regardless of syringe size.

Figure 4. Vacuum Generation with the Reciprocating Procedure Device (RPD)

Vacuum in Torr (mm Hg) are shown as a function of plunger displacement and RPD size. As can be seen each RPD size has its unique vacuum - plunger displacement curve with the 20 ml device generating the greatest vacuum; however, the curves generated with the RPD are identical to those with the conventional syringe - thus the RPD and conventional syringe are identical in vacuum-generation characteristics.

Figure 5. Vacuum Generation as a Function of Needle Diameter

Vacuum in Torr (mm Hg) are displayed as a function of time with 4 different needle diameters (measured in gauge) using a 20 ml RPD to generate vacuum. As can be seen, smaller diameters of needles have a lag time of several seconds before generation of maximum vacuum.

Figure 6. Vacuum Generation as a Function of Force

Vacuum in Torr (mm Hg) are displayed as a function of force required to displace the plunger to various volumes. The solid line represents the near-linear relationship of vacuum to force for each syringe or RPD size. The fine dotted lines demonstrate the force required to generate maximum vacuum with a particular syringe size. The bold dotted lines indicate the corresponding force necessary to generate the same level of vacuum with the 20 ml RPD or syringe. As can be seen, it requires much more force to generate the same level of vacuum with larger syringes.

Figure 7. Operator Difficulty Generating Maximum Vacuum

Vacuum in Torr (mm Hg) are displayed as a percentage of individuals able to generate maximum vacuum (fine dotted horizontal lines) with a particular syringe or RPD size. The conventional syringe is the bold dotted line, and the RPD the solid bolded line. As can be seen, it is much easier for operators to generate high level of vacuum with the RPD compared to a conventional syringe due to the pulley mechanism of the RPD.

Figure 8. Needle Control as a Function of Syringe Size

The undesirable characteristic of unintended forward penetration (loss of control of the needle in the forward direction) for each syringe size during aspiration procedures with the conventional syringe used with one hand is shown. The 1 ml device corresponds to a vacuum of −120 Torr, 3 ml −250 Torr, 5 ml −334 Torr, 10 ml −441 Torr, and 20 ml −517 Torr. Control of the conventional syringe was improved if vacuum was generated and the device controlled with two hands (p < 0.002), but most improved in terms of needle control with the RPD mechanical syringe (p < 0.002).