Monoplace Delivery System
Monthly Hyperbaric Safety Notice: June 2005
Importance of Optimizing Chamber Gas Flow
In this notice, attention is focused on the importance of being fully and constantly cognizant of the state of gas flow through the chamber.
Background
The Sechrist 3200B monoplace hyperbaric chamber operates under a state of constant gas (oxygen) flow. Flow can be adjusted via a control valve located within the oxygen exhaust assembly. In the “closed” position the control valve permits approximately 240 lpm of flow. By design, and to avoid a potentially hazardous accumulation of CO2, flow cannot be completely stopped. In the fully open position, flow peaks at approximately 400 lpm. Adjustment of the control valve between these two extremes provides a corresponding flow volume ranging between 240 and 400 lpm.
This constant flow of gas serves to eliminate metabolic waste gases, and provides a useful source of temperature control for the patient. Higher flow rates act as a cooling mechanism, lower flow rates reduce the cooling effect.
However, there are additional aspects to flow control, aspects that have important patient and facility safety implications.
The Safety Issue
The principal source of oxygen for chamber compression, and constant flow, is the hospital’s bulk liquid oxygen (LOX) system. This oxygen is stored in a super-cooled and liquefied form. As it is transferred, on demand, to the hospital, it is converted into a usable gas, via an associated vaporizing system. Having boiled off from a liquid, this resulting gas is essentially dry. It contains little to no moisture.
While a dry gas has the benefit of minimizing corrosive damage to system valving and piping, it has potentially adverse effects on hyperbaric safety. A dryer atmosphere promotes a greater accumulation of static electricity. A resulting static electrical discharge may generate sufficient energy to cause ignition of volatile substances (hydrocarbon based oils and lotions, alcohol-prepped materials, hydrocarbon contaminated air, etc.).
Key Operational Issues
- Under routine operations, as the rate of gas flow through the chamber is decreased the chamber atmosphere’s relative humidity increases. This effect is the result of a greater accumulation of the patient’s evaporative moisture loss within the chamber. This is a good thing.
- If the patient complains of being cool, slow the rate of oxygen flow. Don’t provide additional blankets. This is all too frequently the action taken, yet it represents an increasing safety hazard. Should a fire occur within the chamber, more fuel is available. This could represent the difference between a fire entirely contained within the chamber versus a fire that results in catastrophic failure of the chamber, and potential damage to the entire facility, and its staff.
- If a patient complains of being too warm:
- Cover them with a sheet rather than a blanket.
- Compress the chamber at a slow rate of descent, in order to limit the effect of compression on heat production.
- Titrate chamber flow increases rate for optimal comfort, rather than opting for the widest setting, if i. and ii. above prove insufficient.
- Maintain the hyperbaric facility temperature within a range of 68-72°F.
- If a patient complains of being too cold:
- Close the exhaust valve.
- If this isn’t sufficient, switch the sheet out for a blanket.
- Get into the habit of observing the oxygen flow setting upon arrival at the ordered treatment pressure. Don’t find yourself in a position where a treatment is underway and you do not know precisely the flow setting.
Bottom Line
Know the flow rate at all times. Optimize it for patient comfort.
Contributing Author: Dick Clarke, CHT
Dick
is President of National Baromedical Services, which he founded in 1986.
His previous background included service in the British Royal Navy, diving
instructor and underwater photographer, assistant director of the seabed
habitat 'HydroLab' and several years in the offshore commercial diving industry.
Dick heads the Baromedical Research Foundation where he serves as Principal
Investigator for several international clinical trials. He is course director
for 'Primary Training in Hyperbaric Medicine' and the 'HBO 2000' series of
advanced hyperbaric symposia. Dick has been a NOAA Diving Medical Officer
Training Course faculty member since 1983. He pioneered the Certification
in Hyperbaric Technology (CHT) program, is a past president of the National
Board of Diving and Hyperbaric Medical Technology and remains active at the
committee level within the Undersea and Hyperbaric Medical Society.
