Wireless solutions are making it simpler for medical equipment OEMS with l foot-control issues to eliminate the potential for tripping over cables and running them over with carts and tables, the most common cause of foot-switch failure. Wireless options are also making it easier to locate switches with the end user in mind. And when it comes to cleaning and storage, wireless is the way to go.

Wireless designs permit greater freedom of foot control location.

The ability to achieve these design objectives is prompting OEMs to design equipment for use with a wireless foot switch or to accept a wireless foot switch as a pre-sale or post-sale option. Such designs introduce two new elements into the design of the medical device.

The first set of design considerations revolve around the use of wireless foot controls. Here the design considerations are relatively straightforward and are driven primarily by:

• Choice of wireless protocol.
• Choice of batteries.
• Replacement and recharging technique for ease-of-use.

The second set of design considerations involves the associated wireless receiver located on, or in, the medical device. There are several considerations that can influence the receiver design:

• Receiver location.
• Receiver signal protocol to the host device.
• "Pairing" of the receiver and foot control.
• Optimal use of foot control "status" information.

Selecting protocol
Today's technologies present OEMs with an array of wireless protocols from which to choose. A sampling includes ZigBee, BlueTooth, Infrared, WLAN, and customized protocols designed expressly for medical applications.

When selecting the protocol, the following factors need to be considered:

• Power consumption and power management, which affects the frequency of the required recharging and battery replacement and the choice of the type and size battery for powering the foot control.
• Ability to minimize or eliminate the potential for interference from other "like" systems or from other wireless equipment in the environment.
• Nature of the medical device and its related risk assessment.
• Ability to transmit ancillary, noncontrol information such as medical device OEM identification, medical device identification, real-time state of battery condition (voltage, current, charge status, temperature, and number of experienced recharge cycles). This may be an important parameter as assessed risk increases or interruption of a procedure due to a power loss becomes unacceptable.
• Need for bidirectional vs. unidirectional communications capability.
• Desired transmission distance, though for most medical devices this is likely to be less than 10 meters.
• Number of "like" wireless systems in the same local environment.
• General inherent reliability.
• Cost, which will typically be driven by the technical requirements of the application and/or the level of acceptable risk aversion.

Table 1. Click image to view larger

Wireless choices
Several commercially available "wireless" technologies are available for consideration:

• Infrared (IR)
• DECT (Digitally Enhanced Cordless Telecommunications)
• WLAN (Wireless LAN)
• ZigBee
• BlueTooth
• STEUTE "Wireless 2.4-MED"

Each of these has its own unique attributes, which should be considered in the context of the risk assessment associated with the medical device function and application. See Table 1.

Where the level of assessed risk is low,” almost any wireless technology may be suitable, depending upon cost-performance requirements such as response time, desire for signal confirmation, consequence of erroneous or lost signals, and need for worldwide acceptance.