To meet the needs of today's ever-changing hospital environments, medical equipment manufacturers are under pressure to design smaller, lighter and more portable devices without compromising functionality. Medical device engineers are challenged with integrating components that meet design specifications, yet also deliver the high performance expected for critical applications.
A capnography monitor, for example, is a medical device used by anesthesiologists in the operating room or in intensive care units to capture, measure and display readings on the exhaled carbon dioxide (CO2) of a patient.
There are two methods used by capnography monitors to measure exhaled CO2:
- Mainstream capnography uses an in-line infrared CO2 sensor connected directly to the airway, between the endotracheal tube and the breathing circuit.
- Sidestream capnography pulls a sample of the patient’s exhaled gas from the breathing circuit through tubing to the infrared sensor located in a remote monitor.
This blog examines the challenges medical device engineers face when designing next generation sidestream capnography monitors and presents fluidic component solutions to these problems.
Since its introduction in the 1950s, capnography has continued to advance and has rapidly become the standard of care in anesthesia and respiratory therapy. Capnography is non-invasive, easy to use, and offers great promise in the assessment of acute and critically ill patients. The success of capnography depends largely on how well manufacturers underscore its functionality by improving fluidic controls.
Fluidic components used in sidestream capnography
Sidestream capnography requires a vacuum source, usually a diaphragm or sampling pump to pull a sample of exhaled air from the patient’s breathing circuit, through a length of tubing, into the remote monitor and across the CO2 sensor. The CO2 sensor requires regular calibration to ensure accuracy and system integrity. This is done through “auto-zeroing” the sensor by switching a solenoid valve in line with the sensors to expose it to ambient air (atmosphere). The sensor auto-zero valve acts to shut off flow from the system to the differential pressure and CO2 sensors in order for the sensors to self-calibrate.
Depending on the complexity of the capnograph, the equipment can also include other solenoid valves that divert the airflow of the pump away from the sensor and perform a purge of the tubing to prevent occlusion.
The increased use of capnography monitors combined with the life science industry’s evolving design requirements has resulted in the need for enhanced devices with complex technology and more advanced fluidic controls. Some of the design challenges engineers face include:
Next generation of capnography monitors are smaller and designed for portability. To support this trend, fluidic components should meet these requirements without compromising key performance characteristics such as flow rate, pressure capability, and leak integrity.
To address the continued rise in healthcare costs, manufacturers are designing capnographs with longer life expectancy. Consequently, component life is becoming a concern. Engineers must source components capable of operation in excess of 5,000 hours.
When developing a system, engineers must coordinate the integration of several sub-components into a functional layout to fit within a reduced device footprint.
The need for sidestream CO2 OEM modules drives requirements for remote purging and more advanced sensor technologies which require valves for calibration
Portable devices that run on battery power requires lower power consuming components that maintain a high level of performance without loss of functionality.
Combining miniaturization, low power, and high performance
Parker Precision Fluids addresses the sidestream capnography monitor design challenges with lightweight valves and pumps that offer reduced power requirements, high performance, and are small enough to fit in the palm of your hand.
Parker’s T2-05 pump combined with miniature X-valves are ideal for sidestream capnography devices and offer:
- Small size
- Low power consumption
- Long life
- Easy integration
The compact T2-05 Micro Diaphragm Pump is uniquely designed to fit in tight spaces where other pumps cannot, minimizing overall device weight. Also, the valve design has been optimized to provide the highest flow rates available with the lowest current draw — only 0.36 Watts is consumed if operated at full voltage. This results in longer battery life and extends the portable range of the system. Other features include:
- Prolonged life expectancy ranges up to 10,000 rated hours, depending on motor type options.
- Ideal for portable applications
- RoHS compliant
The X-Valve Miniature Pneumatic Solenoid Valve is a compact, lightweight 8 mm PBT plastic valve commonly used for calibration of the CO2 sensor. The valve is rated for 25 million cycles of operation. Given the infrequency of sensor calibration over its life, the X-Valve exceeds the life requirements of the capnography module. Other features include:
- Direct PC and side-to-side mounting enables compact and efficient system design
- Large range of pressure options (6, 30 and 100 psi) to meet various application requirements
- Light weight valve construction is ideal for portable applications
- Available low power model (0.5 Watt) for continuous duty applications
- RoHS compliant
This blog was contributed by Richard Whipple, marketing communications manager, Parker Precision Fluidics Division.