Syringes are widely used in the medical field for the administration of sterile fluids. The fluids administered to patients by means of a syringe may be plain physiological solutions such as physiological saline and dextrose 5% to compensate for fluid losses, they may contain a medicament to treat a disease, they may be a blood product to compensate for the shortage or loss of a blood component, or they may contain nutrients. These fluids may be administered with a syringe by direct intravenous (IV) push injection or as an infusion. Generally, if the fluid must by administered slowly in more than 5 min to 10 min, it is referred to as an infusion. For that purpose, special pumps are available that can accommodate a syringe.
Syringes are commercially available in sizes ranging from smaller than 1 ml to over 50 ml from many different manufacturers. Syringes of approximately 1 ml may be intended for specific purposes such as the administration of, for example, insulin or tuberculin and may have an integral needle. Syringes have a plunger with a piston that may be made of natural or silicone rubber slidable in a body or barrel and lubricated with a lubricant such as polydimethylsiloxane. The barrel is usually manufactured from a plastic such as polypropylene, polystyrene, or styrene/acrylonitrile copolymer. The barrel is provided with graduation lines and with a nozzle. The nozzle usually constitutes a male luer or luer-lock connector and may be fitted with a nozzle or tip cap to guard against accidental contamination. After packaging, this syringe is sterilized, usually by ETO-gas or by gamma or beta radiation and is supplied ready for one-time use.
The requirements that syringes must meet are described in many standards, especially ISO. ISO sets standards for the materials of the syringe, the manufacture, accuracy, performance etc. Also, ISO and other organizations set standards for the male luer or luer-lock connector that is provided on the syringe. ISO also sets standards for female luer connectors, thereby guaranteeing a leaktight fit of the connector on the syringe with any device with a female luer connector.
The state of the art in administering a sterile fluid in a syringe to a patient is to first fill the syringe with the solution to be administered. This solution may be held in a container made of a rigid material such as glass, of a semi-rigid material such as polyethylene or polypropylene, or of a flexible material such as polyvinylchloride. These containers usually have a port with a rubber septum or membrane that can be punctured with a needle to introduce in or withdraw fluid from the container.
To maintain the sterility of both the solution to be taken or sampled and the solution in the syringe, transfer is preferably performed under aseptic conditions in a LAF-cabinet by personnel trained in aseptic techniques and wearing special clothing. First, a needle is placed on the syringe. Needles usually have a female luer connector and therefore can be connected to the male connector of the syringe. Then, with the needle, the rubber membrane of the container is punctured. By applying force to the plunger, the required volume of solution is drawn into the syringe. Air is then expelled from the syringe. Subsequently, the needle is withdrawn from the container and the fluid may be administered to the patient immediately if preparation takes place at the bedside, or, after removal of the needle, a cap may be put on the nozzle of the syringe. After capping, the syringe may be labelled and packaged and sent to the ward for administration to the patient.
If the solution is intended for direct intravenous push injection, after removal and disposal of the cap, a needle is placed on the nozzle again, and the solution may be injected into a vein or may be injected into a running administration system. If the solution is intended for slow administration over more than 5 min it usually is administered with the aid of a syringe pump. For that purpose, the cap is removed from the syringe and disposed of and the nozzle is connected to a tube with a female luer connector. The tube is connected to the administration system of the patient with a needle via an injection port or a gum rubber injection site. For slow administration of sterile fluids in a volume up to 50 ml, the use of a syringe with a syringe pump is often preferred for reasons of accuracy, reliability, ease of use, and the presence of alarms on the pumps.
Although the use of a syringe may be the preferred way for the administration of small volumes of up to 50 ml of medical fluids to patients, it has some serious drawbacks. The main drawback results from the fact that the syringe must be filled in an open system, that is with the aid of a needle in an aseptic procedure. In an open, aseptic procedure, foreign material may be introduced into the fluid in the syringe as well as in the fluid in the container. Also, in such a procedure, there is a high incidence of leakage and spillage due to needle drips and aerosols.
During filling, micro-organisms may accidentally be introduced into the syringe or into the container from which the syringe is being filled. For that reason, sterile fluids that have been sampled, in this case both the fluid in the syringe and the fluid in the container from which the syringe was filled, usually are regarded as contaminated and have a limited shelf life. Depending upon the nature of the product, the storage conditions and the policy of the hospital, the stability period for both the fluid in the syringe and the fluid in the container is limited to 1 day to 7 days.
However, this limited shelf life itself does not preclude the microbiological contamination of the fluid in the syringe no of the fluid in the container that is being sampled. Another drawback of the method of filling a syringe is that a needle is required for the procedure. Use of a needle frequently leads to needle sticks. Also, the needle may accidentally cut through the wall of the IV container and the needle may lead to coring or laceration of the rubber membrane of the IV container and thus to particulate contamination of the IV fluid. Finally, the use of a needle requires considerable force to fill the syringe, as the needle presents a substantial restriction in the system. The use of a needle, and thus an open system, may also lead to contamination of the environment with the product that is being filled in the syringe. This contamination may occur through needle drips, aerosols that are formed, spillage and leakage.
The problems that result from the use of a needle in an open, aseptic system to fill the syringe will be illustrated with three examples illustrating the consequences of contamination of the fluid in the syringe, contamination of the fluid in the container and contamination of the environment with the fluid.