Multiplace Delivery System
Monthly Hyperbaric Safety Notice: September 2005
The Hyperbaric Ventilator
Background
Cradle to grave cardiopulmonary embarrassments can present a complex array of life-threatening conditions some of which can challenge and confound even the most seasoned clinician. This applies to hyperbaric practitioners who must also contend with the effects of their unique environment. On the patient and the equipment used to support them.
The hyperbaric ventilator has long been something of an issue in terms of the continuity of critical care support and its appropriateness under conditions of hyperbaric hyperoxia.
The Safety Issue
Minimal supportive documentation exists for mechanical ventilators specific to employment in ClassA (multiplace) hyperbaric chambers. Two types of ventilators are commonly employed. They are the pneumatically pressure driven ventilators taken into the chamber with the patient or conventional ventilators that remain outside the chamber and connect to the patient circuit via ‘through-hull’ penetrations. In either case, little formal documentation is available to support their use in the hyperbaric setting. I have located only two ventilators that have a manufacturer’s warranty permitting their use in a pressurized environment (even though other makes are in common use). They are the Penlon pressure ventilator (last produced in 1985) and the TXP military transport ventilator (which remains in production today).
Key Operational Issues
Given that the Penlon ventilator has been out of production for 20 years, a limited supply of spare parts exists (and you have to know where to look). The ‘TXP’ is in production and readily available, as are its parts. It is capable of both hypo and hyperbaric operation. Manufacturer testing indicates that the TXP performance is not materially compromised even at pressures in excess of 3.0ATA. If a particular unit is dedicated to hyperbaric service, it is a good idea to recalibrate the frequency range to encompass the physiological ‘band width’ encountered while under pressure. The TXP model must always be physically located within the same ambient environment as the patient. Should it be driven by a remote gas source, that source must be increased to the ventilator by 15 psi for each atmosphere of treatment pressure. Careful ‘hyperbaric’ calibration of each particular unit is important.
The TXP has partial altitude compensation designed into its timing function. This is present up to altitudes of 8,000 feet. Adjustment of tidal volumes becomes necessary beyond 8,000 feet. Impressively, the TXP will compensate even under the most extreme circumstances, such as an immediate (several seconds) loss of cabin pressure during a medical evacuation.
Bottom Line
Numerous ventilators are in hyperbaric use. They include models manufactured by Bird, Magellan, Penlon, Siemens Servo900C and the above discussed TXP. As some of these models are not supported by a manufacturer-specific warranty for hyperbaric environments, questions may be raised regarding safety and compliance issues. The hyperbaric safety director would be well advised to look into this issue, perhaps contacting the manufacturer of their particular make for guidance.
Contributing Author: Kevan Corson, CHT
Kevan
serves as Vice-President for OxyHeal Health Group, a California based hyperbaric
equipment manufacturer and service provider. Following 14 years in the military,
Kevan spent several years as a research assistant at the University of Texas
Health Science Center before involving himself in hyperbaric medicine. Kevan’s
first stop was The University of Texas Medical Branch, in Galveston. Under the
mentorship of the late Dr. Jon Mader, Kevan became an accomplished technologist
and researcher with several peer-reviewed publications to his credit. Kevan is
active in numerous diving and hyperbaric technology, education and safety organizations.
Full Panel of Safety and Technical Correspondents
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