Closed system transfer devices (CSTDs) are used to safely transfer hazardous drugs from one receptacle to another.

For example, to prepare and administer chemotherapy drugs, which contain hazardous antineoplastic agents, the drugs need to be transferred from the original vial to a syringe and from a syringe to an IV infusion bag. Each transfer creates the possibility for exposure to the hazardous drugs.

The importance of a fully closed system cannot be overstated. Exposure to hazardous drugs can cause serious health complications for those who are exposed to them over time. These risks range from skin irritation, to birth defects, and even various cancers.

Without using a CSTD, studies have shown hazardous drug residue on surfaces in the workplace, including on counters, and doorknobs, and even in unlikely places like a secretary’s desk. This is due to the adhesive properties of hazardous drugs. Using a CSTD, the rates of residue, as well as exposure to harmful vapor, diminish drastically.

All of these considerations came into play when designing the EQUASHIELD system. The device was designed and manufactured by Equashield, which is a spinoff of PlastMed, an Original Equipment Manufacturer (OEM) that specializes in the R&D and manufacture of complex medical devices made of plastics.

The device incorporates elements across multiple disciplines, such as plastic injection, ultra sonic processes, extrusion, insert and over molding.

To understand the design choices of the EQUASHIELD system, one must understand the functional needs of those using CSTDs.

First, in order to prevent leaks, spills, escape of vapors and aerosols, there must be a way to equalize the pressure within the system when fluids are withdrawn or injected into vials. In fact, pressure equalization systems are the essence of closed systems, preventing the ambition of drug to escape.

Since drug vapors pass unhindered by any filter, venting pressure to the outside environment through a filter is not an applicable solution. Other existing solutions to the problem of pressure equalization are often cumbersome to setup and use. For example, one such CSTD has an external balloon to hold air that can be entered into the vial when fluid is removed, and when fluid is added. During setup of this system, air needs to be injected, bearing the risk that contaminated air can enter the drug vial.

Figure 1: EQUASHIELD syringe and vial adaptorsThe EQUASHIELD system design was created to simplify the design of a CSTD, while simultaneously creating a sleek and elegant device.

The EQUASHIELD transfer device system is a fully closed syringe, with a lid encapsulating the rear section of the syringe cylinder, which acts to isolate the plunger rod and the syringe barrel from the environment.

Instead of a cumbersome balloon external to the system, Equashield developed an encapsulated syringe with an internal, self-contained pressure equalizer and sterile air chamber.

The syringe barrel itself provides the reservoir of air needed to fill the vacuum that is created when drugs are drawn out; and, when liquid is inserted into the vial, the natural place for the over-pressurized air to go is into the syringe barrel.

To channel the fluids, each syringe unit incorporates a dual needle air-to-liquid exchange system. The short "liquids needle" draws drug out of the vial, while the long "air needle" replaces the volume of medication with an equal volume of sterile air from the air chamber.

This innovative approach allows sterile air from the barrel to enter the vial when fluid is removed. Alternatively, if fluid is added to a vial, contaminated air is drawn into the barrel in equal measure, and contained within the system so as not to release any of the hazardous material.

Figure 2: Pressure equalizationThe second feature that is unique to EQUASHIELD's system revolves around one of the major routes of exposure for those handling hazardous drugs.

A regular syringe is made of plastic, with the plunger sides often touching the inside wall of the barrel. This is a major route of exposure because the design of a standard plastic plunger results in contamination with almost every use. As such, the person handling a syringe like this can be exposed to residues of the hazardous drug that infiltrated onto the surface of the plunger. Furthermore, regular syringe plungers can be pulled out completely, which can lead to major spills.

To solve these problems, the EQUASHIELD system uses a stainless steel rod as a plunger that extends through the lid of the syringe cylinder. The plunger rod is sealed with an EPDM rubber O-ring that allows the plunger to be moved axially while the syringe remains airtight. Due to its small diameter the rod is a great distance from the contaminating syringe inner walls, thereby preventing the drug infiltration onto the plunger rod. Furthermore, since the metal rod is sealed in, it cannot be removed from the cylinder, while the O-Ring provides a double jacket protection to the plunger.  

The final major innovation of Equashield's CSTD is the connection mechanism. To transfer liquids, the EQUASHIELD syringe connects to a variety of Equashield adaptors that are attached to vials, infusion bags or infusion tubing. Each adaptor and the syringe are equipped with a rubber septum (membrane) docking port for safe connection.

During the connection process, the membrane of the syringe unit and the membrane of an adaptor are pressed tightly together and become one piece of rubber, which remain locked in this pressed position throughout the drug transfer. The locked membranes are moved over the stationary needles which pierce them through to establish a fluid path. The needles never move; they are permanently recessed inside housing and are out of reach, preventing needle sticks.

The sleek design of the connector mechanism performs with a single axial motion all the five steps of:

  1. Pressing membranes
  2. Locking membranes
  3. Enabling movement of membranes
  4. Moving membranes over needles
  5. Holding components connected

Thereby the syringe connector is made of only 2 plastic parts and a membrane, while the adaptor ports are made of only 1 plastic part and a membrane.

Figure 3: Locking mechanism sequenceUnlike other mechanisms that use simple spring to press and hold membranes together, the Equashield mechanism uses solid locking of compressed membranes in a defined position. The spring provides poor control of membranes compression throughout the connection steps, since it is sensitive to unpredictable forces created by needle friction with membranes, thereby allowing performance irregularities and leaks.

During retraction, the needles wipe against the elastic membranes. The membranes are unlocked and separated from each other only after full removal of the needles from the membranes. The outer surfaces of the membranes at no stage, during connection or disconnection, come in contact with the drug; therefore the outer surface contact area remains dry and clean of drug residuals, is leak-proof, needle-safe and provides a highly effective microbial barrier.

Equashield's system was designed to be sleek and easy to use. In fact, its innovations –the self-contained pressure equalizer and sterile air chamber, the sealed plunger and the double membrane connectors—create a system in which the user doesn't even realize the complexity of the system because the design streamlines the use-process.

The simplicity, elegance and ease of use are what set this CSTD apart. With hundreds of customers around the globe, Equashield proves how the right design is critical to the adoption of new, innovative medical devices.