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Hyperbaric Treatment

Table of Contents

The Gamow® Bag
The Certec® Bag
The PAC®(Portable Altitude Chamber)

Introduction

Several portable hyperbaric chambers are now available, and are very helpful in treating severe forms of altitude illness. They all are all similar to the extent that they are air-impermeable bags that completely enclose the patient, and are inflated to a significant pressure above ambient atmospheric. This effects a physiological "descent." This can be demonstrated with an altimeter inside the bag, and marked improvements in oxygen saturation are measurable with a pulse oximeter. The extent of the descent depends on the altitude at which the bag is used; as an example, at 4250m (14,000 ft), the inside of the bag is equivalent to 2100m (7,000 ft).

Typical treatment protocols are to put the patient into the bag, pump it up until the pop-off valves hiss, and keep the patient at pressure for one hour. Unless your bag has a CO2 scrubber system, you need to continue pumping several times per minute to flush fresh air through the system (consult the specific manufacturers' information to determine how frequently). At the end of the hour, the patient is removed from the bag and reassessed. Additional cycles of "descent" and reassessment are continued as needed until either the patient is clinically improved enough to not need further hyperbaric treatment, or is able to actually descend. Experience has shown that HAPE typically requires 2-4 hours of hyperbaric treatment, and HACE typically requires 4-6 hours of hyperbaric treatment.(Taber 1990)
Compressing and decompressing the bag should be done slowly, while talking to the patient. Slow down if s/he experiences ear pain. Despite the concerns about tympanic membrane barotrauma, however, I have not personally seen this happen nor heard any reports of it happening.
Patients with severe HAPE may not tolerate lying flat; this problem is readily addressed by putting the bag on a rigid surface (such as a bed) and propping one end up 30-40 cm (12-16 inches). However, it is so much easier for these patients to breathe inside the bag once it is pressurized, that this maneuver is usually not necessary.
For maximum therapy, it is possible to put patients inside the bag with oxygen on (I suggest 4-6 l/min); obviously the bottle must be inside the bag with them. Do not hook oxygen up to the pump intake.
Remember to put a sleeping bag in with the patient - it can get very cold lying motionless for an hour at high altitude! Conversely, if you are outside in the sun, remember to shade the hyperbaric bag, as the sun is intense at altitude and will "cook" the patient.
Absolute contraindications to using the bag include lack of spontaneous respirations, as you can't ventilate the patient from outside the bag. There is a "Gamow Tent" which is about twice the diameter of the standard bag, and accommodates two patients simultaneously. This is useful for treating a critically ill patient with a medical person present, or treating a child with a parent present.

Relative contraindications to using the bag are middle ear congestion (small risk of barotrauma), inability to protect the airway in a deeply comatose patient (consider intubation), and claustrophobia.




The Gamow® Bag

The Gamow® Bag and Certec® Bag compared

The Gamow® bag in use

The Gamow® Bag (left) and
The Certec® Bag (old version, right) compared.

The Gamow® Bag in use.

This is the original portable hyperbaric bag, invented by Dr. Igor Gamow at the University of Colorado. It is a bright red coated nylon fabric cylinder with a long zipper to allow entry. Small clear windows allow viewing in/out of the chamber. Conversation is slightly muffled by the fabric, but it is easy to talk to patients. Inflation is with a raft foot-pump, to 2 psi (105 mmHg) above ambient pressure. At the HRA clinic in Pheriche (4250 m/14000 ft) the equivalent "elevation" inside the bag is roughly 2100m/7000 ft.

The patient is placed completely within the bag, the zipper sealed shut, and the bag is inflated with the foot pump. Two pop-off pressure valves set to 2 psi (not adjustable) start to hiss when maximum pressure is reached, and prevent over-pressurization of the bag.

All of the currently available bags must be continuously pumped (about once every 5 seconds) while someone is inside, not to maintain pressure, but to flush fresh air through the bag to prevent CO2 buildup - this is a significant effort at 4000 - 5000 m.

Advantages: Well tested. Relatively lightweight (the bag, pump, and daypack carrying case is roughly 7 kg/15 lbs.). Fast and easy, you can have someone in the bag and "descended" in one to two minutes.

Disadvantages: Cost is US$2400. The zipper takes a lot of wear, and is the weak point - this is where leaks eventually show up (see photo of a well-used Gamow Bag, above). On the other hand, Gamow bags receive daily use in the HRA clinic and last several years. Due to the location of the reinforcing straps (yellow in photo above), it can be difficult to get a patient in and out of the bag.

Gamow purchase and rental information




The Certec® Bag

The new and old Certec® bags compared
The new bag (yellow) next to the old one (orange)

Here is some information on the Certec bag received
from Dr. Jean-Piere Herry:

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.

Certec purchase and rental information




The PAC® (Portable Altitude Chamber)

The Portable Altitude Chamber
The 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 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.

PAC purchase information


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Copyright© Thomas E. Dietz, MD
Emergency & Wilderness Medicine

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Last modified 26-Apr-2001