Fluidic Connectors Go With the Flow

By Amy Goetzman | May 15, 2018

Connectors that carry fluid or air through a bore, paired with connectors that carry signal and power, are a critical component in modern medicine.

Medical feature

Electronic connectors typically handle power and signal. In the world of medical equipment, however, connectors can often take on additional jobs, carrying fluid, gases, and light. These specialty or hybrid connectors, which incorporate traditional fluidic, media, or bore connectors within a standard connector shell, transmit fluid or gases along with the traditional electronic media. A small hole, or bore, in the center of the connector permits the flow of liquid or gas through flexible tubing. This combination of media allows product designers working in modern medicine to specify a single connector for both fluids and electronics. Companies such as LEMO USA, Fischer Connectors, Staübli, CPC, Arrow, Caton, and Nextron offer hybrid connectors.

Transmitting Liquids and Gases

Machines such as respirators and continuous flow anesthesia machines deliver oxygen or anesthetic vapors to a patient through a series of tubes and valves. Pneumatic connectors are used between these tanks and their tubing, and at other junctures in the system. To permit the uncontaminated flow of the air or gas through the system, the housings for these connectors must be resistant to the ingress of both moisture and outside air. In a simpler system, a blood pressure cuff pumps air from a flange to an inflatable cuff. In this case, the connectors help seal off outside air and control the proper flow of air into the cuff, without allowing it to deflate while a reading is being obtained. They permit airflow in only one direction, or at controlled times.

Staübli’s CombiTac modular connectors combines power, signal, data, thermocouple, coaxial, fiber-optic, pneumatic, and hydraulic connections in a single compact frame or housing.

Connectors that handle fluids have similar requirements. Fluidic connectors used in enteral applications — equipment that moves fluids into a patient — are designed to seal out moisture or fluids from the outside, yet permit the proper flow of liquids through flexible lines and into a device. They are used to deliver medications, remove bodily fluids, and move water through hoses. Many critical medical machines depend on these connectors.

Other systems that use bore connectors draw fluids away from a patient, such as catheter machines or suction vacuums used in surgical theaters. Dialysis machines draw blood from a patient, clean it of impurities, and mix it with a therapeutic solution before pumping it back into the patient’s bloodstream at a regulated rate of flow. The connectors in these systems must handle a variety of liquids without mixing them or permitting air or contaminants to enter the tubing at any point. Feeding tubes, IV machines, epidural lines, wound drains, and other critical care applications depend on these connectors. Dentistry also depends on bore or fluidic connectors.

Hybrid connectors enable machines to manage the electronic functions at the same time as it handles fluid or gases. Fischer Connectors produces hybrid connectors for medical applications that handle fluid and signal, or fluid and power.  These connectors are usually custom design-and-build projects to make sure the customer has a perfect match for the application. However, standard designs in the Fischer Core Series line are available to order.

“There are little to no differences in the design of a connector that is used for fluids versus one used for gases,” says Steven Lassen, senior customer application manager at LEMO USA. “We work with the customer to determine what kind of medium will be used in the application. If it’s something that has corrosive potential, for instance, then we can look at different materials, maybe select stainless steel instead of brass, or different O-ring materials.”

A hybrid receptacle by Fischer Connectors. The white tube in the center is for the fluid line, and other contacts are for power or signal.

Fluidic and pneumatic connectors can include a wide variety of metals and plastics, including durable, flexible plastics such as ABS, PEEK, nylon, and polysulfide. Metal parts include lightweight aluminum, chrome-plated brass, and die-cast zinc. These connectors must also coordinate with the tubing that carries the air or liquid in the system. The inner diameter of the tube corresponds with the bore in the connector. Fine-gauge tubing is increasingly popular, which means that these connectors must do a lot in a very small package. Lassen says the inner diameter of the bore typically ranges from 1.8 to 4mm for medical applications that incorporate a shut-off valve, and 0.9 to 1.6mm for ones without a shut-off valve. He also notes that O-rings need to be selected for longevity and compatibility with the medium that will pass through the system. “It might work perfectly at first, but after a little while in the field, it can develop leakage, so the ability to do a field replace is important.”

Although small and lightweight, these connectors must be highly durable. Since they need to withstand shock, vibration, rough handling, and temperature shifts, their construction should protect other components from movement of the air or fluid. They must also be easily cleaned and either resist deterioration by cleaning fluids or be designed for sterilization in an autoclave machine or gamma ray sterilizer. They may also need to be disposable.

LEMO’s Redel P self-latching plastic connectors for medical applications features an alignment key for additional safety.

Fluid connectors may feature integrated valves to control flow rates and pressure changes. These valves also prevent the entry of air into the system and prevent leaking upon disconnection. Connectors with integral precision flush-face valves are called dry-break connectors. Intelligent or integrated connectors may handle power, signal, fluids, air, and additional information, such as radio frequency identification (RFID) technology to allow data exchange at the point of connection.

“You also need to think about the cable. It should be made from durable, kink-proof material and the electrical contacts should be well insulated. The whole system that surrounds the connector needs to be considered,” says Lassen.

In a busy healthcare setting, ease-of-use is another critical factor. Personnel should be able to quickly mate or unmate connectors to activate or discontinue a treatment in time-sensitive situations. Even so, it’s important that these connections require some time and thought.

Non-Standard by Design

CPC’s hybrid connector with twist-latch locking can handle power, signal, fluids, and gases.

In an environment where multiple lines are available within a single patient’s room or operating theater, there is a real risk that a practitioner will attach the wrong connectors. In tragic cases, patients have been mistakenly given the improper treatment because the equipment used standardized, compatible connectors. To prevent this, fluid connectors follow the ISO 80369 standard, which seeks to prevent the erroneous mismating of connectors used in hospital settings.

As medicine becomes more reliant on technology, the risk of misconnection has risen. The FDA has issued guidance to manufacturers urging them to design equipment to prevent such incidents with designed incompatibility. The use of color-coding, labeled, specially keyed, and proprietary connectors is encouraged to help providers make the correct connections every time.

“Some of the safety options we offer include precision keying, color-coding and other visual cues, and positive latching, so the operator will hear a click when the connection is engaged. We also design them to be scoop-proof so that if you come at the connection from an angle, you can’t short it out because they are recessed within the outer shell,” says Lassen. “When we work with a designer on an overall system, we can suggest things like alignment keys and different keys on the same panel, so there’s no way mismating can occur.”

Ultimately, the safety of both patients and care providers is the guiding principal behind these unique connectors.

Amy Goetzman
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