Oncology nurses, compounding pharmacists, and others who handle hazardous drugs, such as chemotherapy drugs, are put at risk of exposure. This is due to the antineoplastic agents with adhesive properties within these drugs that cause contamination of the workplace. Exposure to these agents has been linked to side effects ranging from skin irritation, birth defects, and miscarriage, to cancer in some cases.

Fig. 1 – Pressure equalization diagram showing the movement of liquids and air through the system.
To prevent hazardous drug exposure, healthcare practitioners use certain safety measures including wearing protective gowns, using double gloves, and working with the drugs under a biological safety cabinet. However drug aerosols, vapors, and liquids can easily escape regular syringes used in oncology practice and cause significant contamination of the workplace.

As part of the solution to combat hazardous drug exposure, a growing number of healthcare facilities are using single-use devices called Closed System Transfer Devices (CSTDs). According to the U.S. Centers for Disease Control and Prevention’s National Institute for Occupational Safety and Health Alert: Preventing Occupational Exposures to Antineoplastic and Other Hazardous Drugs in Health Care Settings, CSTDs “mechanically prohibit the transfer of environmental contaminants into the system and the escape of hazardous drug or vapor concentrations outside the system.”

CSTDs provide an added layer of protection to healthcare workers. However, there are various design approaches employed, making some devices more effective than others.

In considering the design of a CSTD, engineers have two main problems to solve. First, which design choices will allow the device to close off all routes of exposure and all potential routes of exposure and provide the highest level of safety? Second, what will make this device easier for healthcare practitioners to use?

Safety First: A Fully Closed System

To understand the design needs of a CSTD, one much first understand the challenges and risks that need to be addressed.

The direct routes of exposure include:

  • drug aerosols and vapors escaping from the system
  • drug residuals found on the connector pieces between the syringe and drug vial or IV bag
  • contamination of the syringe plunger

To eliminate these risks, a CSTD requires a full pressure equalization system, the ability to perform “dry connections,” and a syringe plunger designed to prevent its contamination by drug residuals.

Full Pressure Equalization

A full pressure equalization system is the essence of a closed system. When a syringe is used to withdraw liquids from a drug vial, there must be a store of sterile air to replace the volume of liquid that was removed. Conversely, when liquids are entered into the drug vial to reconstitute a powdered drug, there must be storage area for contaminated air that prevents the escape of hazardous drug aerosols and vapors.

There are three existing approaches to solving this problem. The first involves the use of a filtering system. When liquids are withdrawn, air is vented into the system to equalize the pressure, replacing the equivalent volume of liquids removed. While this is acceptable from a contamination standpoint, the reverse scenario becomes problematic.

When liquids are entered into a drug vial, there must be storage space for contaminated air. However, a vented system has contaminated air pass through the filter and out to the surrounding environment. While some of the contaminants are caught within the filtering system, hazardous vapor can still escape into the surrounding environment and may be inhaled or form condensate on surfaces such as the working area and the IV bags. These are then sent for administration to the wards and may contaminate the surrounding environment.

The second approach uses an external balloon to store sterile air that replaces the removed volumes of liquid, or as a place for contaminated air to be held to prevent over-pressurization of the system. This design is effective at solving the pressure equalization issue from a safety perspective. However, these systems can be cumbersome to use, as they require an initial injection of air into the external balloon.

The final approach involves building the pressure equalization system into the syringe barrel. This provides a selfcontained storage area for sterile or contaminated air. The syringe barrel must be fully encapsulated at the top to ensure that it is airtight. This also prevents accidental removal of the syringe plunger, which could cause major spills of hazardous drugs—a potential route of exposure.

Furthermore, there must be a double needle built into the syringe itself which allows the withdrawal or insertion of liquids through one needle, and the replacement of sterile air, or the removal of contaminated air through the smaller, parallel needle.

When it comes to a achieving the combination of safety and ease-of-use, the third option accomplishes both by creating a fully closed pressure equalization system with a sleek design, unencumbered by an external balloon, which is both bulky and requires additional steps for its use. (See Figure 1)