The concept behind the 3 main portable hyperbaric chambers is they effect a physiological descent by inflating the air impermeable bags above ambient atmospheric pressure. The extent of the descent is dependent on the altitude at which the bag is used and the pressure to which they can be pumped. The patient is placed in the bag lying down (which can be claustrophobic), there is a window for the patient to look through, the fabric of the bag is thick but a conversation can be undertaken. If the patient has difficulty lying flat put the bag on a slope.
Oxygen can be placed inside the bag with the patient. It is worth ensuring the patient has something comfortable to lie on and has a sleeping bag if they get cold. Conversely if its day time the bag needs to be in the shade to avoid ‘boil in a bag’. The bag is zipped up and the bag inflated slowly using a foot pump until the pop-off valve hisses (at around 2 psi). The pressure then has to be maintained by continuing to pump but at a slower rate.
The patient is normally kept in the bag for about an hour, as long as they remain stable in the bag. As pressure increases, the patient needs to be warned to equalise if they are able. It may be worth giving the patient a bag to vomit in if required. Occasionally the zips burst, leading to rapid depressurization and the risk of barotrauma. When reducing the pressure to get the patient out do it slowly, the zip can normally be opened slowly when the side of the bag dimples on pressure.
What are the advantages and disadvantages of this piece of equipment?
Advantages: Lightweight well tested, robust. All the equipment weighs aproximately 7kg. Fast to use, inexpensive in comparison to the others.
Disadvantages: Still costs £1500 or so, the zip can breakdown and is the weak point. No carrying handles if you wanted to physiologically and geographically descend simultaneously.
Who makes hyperbaric chambers?
The Gamow bag is the oldest design. The other bags are the PAC and the Certec. Both as good and lighter. The Certec uses a different pumping system, which can be tiring.
Gamow Bag. The Gamow does not have handles but can be carried on a stretcher if absolutely necessary. You can read more about Gammow Bags and their inventor, Igor Gamow, scientist, classicist, professor, adventurer, at web.mit.edu/invent. Gamow is the son of the famed physicist George Gamow, a co-author of the Big Bang Theory and the first to propose the genetic code.
Where can I hire a Gamow Bag?
They can be hired from Expedition and Wilderness Medicine see our Media Support Page for more details.
More About CERTEC Bags. The present CERTEC hyperbaric chamber is an improved version of a hyperbaric chamber that was originally designed in 1989 by a French and German team.
The color of the new CERTEC hyperbaric chamber is not orange but yellow and blue.
Its design is different from all other pressure bags (Gamow, PAC, etc.) since it is comprised of two bags in one:
An outside envelope made of very strong material (to withstand tension) and good friction (for stability on any surface) , an inside envelope made of polyurethane (for airtightness)
Advantages of this double envelope design are:
it is rugged and durable
good protection of the airtight inner envelope
All air valve systems are doubled for security:
two inflation valves
two automatically opening preset valves (220 mB)
A very large window allows contact with the person in the bag.
Two full length zippers (inside and outside bags) allow easy in- and egress.
The inflation pressure is 220 mB, corresponding to a virtual descent of about 2500 m (depending on the actual altitude).
Total weight of the CERTEC Hyperbaric Chamber is 4,8 kg (carry bag and pump included).
It comes with a very efficient double effect pump (i.e. that pumps during up and downstroke) has a volume displacement of 3,7 liters for each pump cycle.
Only 4 pump cycles per minute are necessary to keep the CO2 in the bag at acceptable levels.
The price of the CERTEC Hyperbaric Chamber is $2300. It can also be rented.
Advantages: Higher pressures, though it isn’t known how clinically important/useful this is. The bag is lighter than the Gamow. The double-wall system should provide more durability.
Disadvantages: Similar to the Gamow bag, the Certec is expensive, around $2300. I have not seen the newer Certec bag, and my comments are based on the older orange model. I found the (old) pump to be quite difficult to use as it required bending over at the waist (see photo at top of page); it was very fatiguing. As in the Gamow® Bag, fresh air must be regularly pumped into the bag to prevent CO2 buildup.
More about The PAC® (Portable Altitude Chamber)
Dr. Jim Duff, an experienced climber and expedition physician, has developed a nice alternative to the Gamow® and Certec® bags. The PAC (a coated fabric bag) is about the same size and weight as the Gamow, but more of a mummy shape, so there is more room around the head and shoulders. It also develops a 2 psi pressure, equivalent to the Gamow bag. The PAC is much cheaper than the Gamow bag and is probably the most sturdiest of the three hyperbaric bags on the market.
The main design difference, however, is in the radial zipper at the head end. This opens the whole head end and makes access far easier than either the Gamow or Certec bags. This is especially important with large and/or comatose patients (ask anyone who has tried to stuff such a patient into the Gamow bag!). There is no pressure gauge, instead there is a clear pocket on the inside of the window, so you can insert an altimeter and watch it from outside.
The external, dangling pressure gauge on the Gamow Bag is vulnerable to wear/damage and subsequent leakage, something avoided in the Certec by having the pressure gauge set flush into the bag. I should note that the presence or absence of a gauge does not affect treatment; the pressure gauge or altimeter is merely a reassurance that the equipment is functional, something that is easy to ascertain in straightforward ways, ie, the bag inflates and the pop-off pressure control valves hiss.
Note that with the PAC the maximum pressure is limited by the pop-off valves to 2 psi, but you can adjust the valves to a lower pressure to accomodate patients who have trouble clearing their ears. Instructions for using the PAC are printed right on the side of the bag, as is a table showing the equivalent descent at various altitudes, a nice touch. This bag has recently been used in the HRA Pheriche clinic and seems to be durable.
Advantages: The shorter zipper and simplicity of design has resulted in a bag that is far cheaper than the other available alternatives: US$1,200 including delivery almost anywhere in the world. The end-opening design is a major advance in terms of ease of getting patients in and out
Disadvantages: No significant disadvantages.
About the author
Dr. Sean Hudson is a Fellow of the Royal Geographical Society and on the expeditionary advisory board for Summit. Sean has been involved in a wide array of expeditions over the last 18 years. During this time he has trekked across the Darien Gap, The Thar Desert, worked as a trekking guide and Chief Medic for Raleigh International in Namibia and Zimbabwe, a trauma medic in Columbia and ski field doctor in New Zealand. Since 1998 he has worked for Across the Divide Expeditions as medic and expedition medicine advisor, providing medical cover on expeditions in 21 different countries. Dogsledding to Desert trekking in Namibia. In 2002, he and his wife, expedition medic Dr. Caroline Knox, helped to established Expedition and Wilderness Medicine, which seeks to provide comprehensive training for medical professionals working as expedition medical officers in a variety extreme and remote environments.