Accepted for more than 50 years, the initial treatment for carbon monoxide (CO) poisoning involves giving patients 100 percent oxygen until they can be placed into a hyperbaric chamber. However, a treatment developed in the 1920s produced significantly better results by using a fixed mixture of oxygen and carbon dioxide instead of just pure oxygen. Unfortunately, the technology of the day did not allow its commercialization.
Recently, researchers at the Toronto General Hospital rediscovered the older approach and set out to improve on the currently accepted practice. For patients with CO poisoning who are a long distance from a hyperbaric treatment center, an improved technique to increase the body's absorption of oxygen during transport can literally be the difference between life, death or reduced long-term side effects.
The Deadly Facts
In the industrialized world, carbon monoxide poisoning is the leading cause of fatal poisoning. In North America alone, more than 10 percent of the 70,000 patients treated annually for carbon monoxide poisoning die. For survivors, as many as 30 percent of those with severe poisoning have disabling physical and neurological symptoms that can last for years. The key to reducing these statistics is improved treatment prior to the ultimate hyperbaric chamber for those exposed to smoke inhalation during a fire, from faulty home furnaces, in industrial situations, such as a coal mine explosion and fire or from an attempted suicide.
Research testing used a standard scuba air tank regulator and a standard resuscitation bag that helped maintain the partial pressure level of CO2 (PCO2). To create a usable product, the researchers enlisted the help of Viasys' SensorMedic division. Several design criteria were developed, including the need to vary the concentration of carbon dioxide relative to the oxygen depending on the respiratory rate of the patient. In addition, when the patient's breathing level is maintaining the desired PCO2 level, the carbon dioxide flow had to be stopped. To achieve these goals, the PCO2 control needed to be automatic, passive and involve no electronic circuitry. Fail-safe operation required that in the event of loss of pressure in either the oxygen or carbon dioxide tanks, an audible alarm would sound.
Custom Valve Technology
To accomplish the project goals, the design required a mixing valve and a supply/regulator unit for the oxygen and carbon dioxide. Two valves working in tandem could maintain the optimal flow to the mixing valve and provide the regulator portion. When standard pneumatics valves failed to provide the required precision, the design team brought in experts from Humphrey Engineered Solutions.
The valve engineers determined that the valves needed to provide ON/OFF functionality in a very narrow snap pressure bandwidth. One valve design that was considered had a poppet held in the seat by pressure with a spring return. However, this type of valve, also called a TAC valve, is unbalanced and takes more force to actuate making a precise set point unobtainable. An existing 310 solenoid valve met the low mechanical force requirement, but the direct acting solenoid design was not totally pneumatic. Replacing the solenoid on the 310 valve with a modified TAC valve to function as a pilot operator provided a solution that met both criteria.
According to Dave Maurer, director of sales and marketing for Humphrey Products, “The most technically challenging aspect of the application was achieving superior and very consistent snap pressure on the pilot.” The difficulty came from the application's use of bottled oxygen and carbon dioxide that have a slow bleed-down pressure. Getting a pilot to snap under these conditions is difficult, says Maurer. However, a custom design provided the answer.
The custom design uses a lengthened push rod with a piston on top. In addition to using double springs to obtain consistent action, an adjustment allows the setting of optimal snap pressure on each assembly during manufacturing. As a result, the custom valve assembly was able to maintain the specific ON/OFF oxygen set point of 40±1 psi with a very low leak rate.
The Final Design
With a successful regulator assembly, Viasys gave Humphrey the challenge to revise and simplify the layout of the entire design. A custom manifold eliminated the tubing and fittings connecting the valves, check valves, regulators, pressure gauges and CO2 ON/OFF valve. In addition to reducing the size of the entire product down to a small brief case, the new manifold eliminated numerous leak points.
Reengineering the CO2 ON/OFF valve provided a fail-safe design. Other revisions include a new check valve for enhanced reliability and consistent operation, a unique pneumatic alarm and sintered bronze cone-shaped filters for the gas inlets to prevent contamination of the unit during use. Humphrey's assembly of the entire unit in a positive pressure, clean environment eliminates dust and other foreign materials from getting into the system. Finally, 100 percent testing of each unit ensures operation to the precise specifications.
The resulting small, portable oxygen therapy system, called ClearMate, has proven to be almost as effective as the hyperbaric chamber. For smoke inhalation during a fire, inhalation of hydrocarbon emissions from coal mine explosions and fires and other accidental industrial exposure, ClearMate provides rapid oxygen therapy for victims. Other applications include initial treatment for accidental carbon monoxide exposure due to faulty home heating systems or improper use of devices such as kerosene heaters and other flame sources and suicide attempts. In addition to providing an improved treatment for CO poisoning in the industrialized regions of the world, where the availability of hyperbaric chambers is not uncommon and the transportation to these facilities is excellent, third world regions may experience even greater benefits. In these regions, the lack of facilities with hyperbaric chambers, less stringent industrial safety regulations and the use wood, charcoal or other sources of carbon monoxide for indoor cooking and home heating make the possibility of CO poisoning and an unfavorable outcome even greater. For many of those patients, the ClearMate system could be the only alternative.