Overpressure bag

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A positive pressure bag , also known as a hyperbaric chamber , is a device used to treat altitude sickness . In principle, it is a portable (de) compression chamber , with the help of which the patient is exposed to higher air pressure .

Working principle

A positive pressure bag is an inflatable airtight envelope that is large enough to hold a person lying down. To do this, the patient is completely placed in the sack and then closed. By inflating the bag with a foot pump , the internal pressure is increased, which physiologically corresponds to the patient descending to a lower altitude. The extent of the simulated descent achieved depends not only on the excess pressure achieved, but also on the altitude above sea level , since the decrease in air pressure with altitude is not linear (see barometric altitude formula ): At greater altitude, a greater descent can therefore be simulated. With an overpressure of 200 millibars at an altitude of 4000 meters , you can achieve an air pressure like that at 1650 meters, at 6000 meters you can simulate a descent to 3100 meters and at 8000 meters to 4500 meters.

The improved oxygen supply by the increased partial pressure of oxygen in the interior leads to an improvement of the symptoms of acute altitude sickness ( acute mountain sickness , AMS ) of the high altitude pulmonary edema ( high-altitude pulmonary edema , HAPE ) and the height of edema ( high-altitude cerebral edema , HACE ).

Areas of application

The first choice in the case of altitude sickness is always a real descent. The positive pressure bag is only used when it is no longer possible, for example due to the poor condition of the patient. Overpressure bags are available in high-altitude shelters or can be carried on larger expeditions . On smaller expeditions or trekking tours, however, it is hardly common to carry pressure bags with you due to the high weight and high costs.

The only clear contraindications for overpressure treatment are respiratory and circulatory arrest .

application

The correct implementation of a treatment with the positive pressure bag requires training of the helper, but also practice of the patient, in order to e.g. B. to avoid claustrophobic states .

When preparing for the treatment, attention must be paid to a balanced thermoregulation : Both hypothermia in the cold mountain air and overheating in sunlight must be avoided, the patient's clothing must be able to tolerate the increasing humidity in the sack. Furthermore, a surface must be available that allows damage to the bag to be avoided. Before being locked in the sack, the patient must equalize the pressure ; in the case of a blocked Eustachi tube , the administration of nasal drops is indicated, which allow the nasal mucosa to swell and facilitate pressure adjustment. The sack is then spread out flat or with the head part slightly raised, the patient is enclosed and the sack is inflated until air escapes through the pressure relief valve.

If a patient is inside the sack, a sufficient supply of fresh air must be ensured through continuous pumping. This pumping can be a great burden for the helpers at great heights, usually several resilient and experienced helpers have to be available. It is difficult or mostly impossible to transport it away while it is in the sack. During the treatment, the patient must be monitored through a viewing window.

Usually the patient remains in the sack for about one to a maximum of two hours before the air is slowly let out and his condition is checked again. This time is often sufficient for the symptoms to improve so much that an independent descent or at least removal is possible. This should be done as quickly as possible, as the therapy with the positive pressure bag usually does not last long. If necessary, the treatment can be repeated.

Construction forms and models

Hyperbaric chambers for the treatment of acute altitude sickness have been known for a long time, especially in the Asian high mountains they have long been used in the military sector. The first mobile hyperbaric chamber was presented in Germany as early as 1919. It was not until 1988, however, that Igor Gamow from the University of Colorado presented the first transportable overpressure bag as it is today.

The Gamow sack , named after its inventor, has a cylindrical shape, is made of airtight nylon fabric and has a longitudinal zipper for getting in and out. Side windows allow visual contact. Two overpressure valves limit the overpressure to 138 mbar (2 psi ). The sack weighs 7 kg.

The Certec sack is a French product that weighs 4.8 kg and is lighter than the Gamow sack thanks to its double cover . At 220 mbar, the maximum pressure is higher than that of the Gamow sack, and a sideways zipper should make it easier to get in.

The Australian Portable Altitude Chamber (English for "portable altitude chamber", PAC ) consists of coated fabric and is considered the cheapest overpressure bag. It is a little more spacious and easy to enter thanks to its all-round zip. The maximum overpressure is 138 mbar, but can also be set lower if necessary (e.g. in the event of pressure equalization problems due to a closed Eustachi tube).

Complementary treatment and alternatives

Basically, bottled oxygen or a combination therapy of oxygen and medication is usually the method of choice for altitude sickness . One advantage of the positive pressure bag compared to oxygen, however, is that it can be operated with muscle power and can be refilled indefinitely from the ambient air. The hyperbaric bag can also be combined with drug therapy or oxygen by taking an oxygen cylinder with you in the bag.

For cases in which the patient needs to be looked after during treatment, there are now tent-sized positive pressure bags that can accommodate an assistant in addition to the patient. Another new development is the TAR helmet (Thin Air Rescue) , an overpressure bag restricted to the head area, which can be operated by the patient himself and which maintains his mobility during treatment.

literature

Individual evidence

  1. ↑ a b c d e Robert Koch: Use of the TAR (Thin Air Rescue) helmet at extreme heights. In: bergleben.de. July 10, 2006, archived from the original on June 20, 2010 ; Retrieved May 6, 2011 .
  2. ↑ a b c d e f g h Franz Berghold , Wolfgang Schaffert: Handbook of Trekking and Altitude Medicine . Practice of altitude adjustment - therapy of altitude sickness. Guidelines of the Austrian Society for Alpine and Altitude Medicine and the German Society for Mountain and Expedition Medicine . Ed .: DAV Summit Club. 7th edition. Munich 2015, ISBN 978-3-00-025756-8 , pp.  86-92 .
  3. ↑ a b c d e Hyperbaric Treatment. In: The High Altitude Medicine Guide. Retrieved May 6, 2011 .
  4. ↑ a b Gamow Bag. In: trekkingguide.de. Retrieved May 6, 2011 .
  5. ↑ Ulrike Wagner, Christina Hohmann: Travel and Infectious Diseases . In: Pharmaceutical newspaper . Govi-Verlag, 2004, ISBN 978-3-7741-0987-2 , ISSN  0936-658X , p. 208-209 ( Google Books ).
  6. ↑ A self-contained life support system designed for use with a portable hyperbaric chamber ; Biomed Sci Instrum .; 1989; 25: 79-81, cf. Robert Koch: Using the TAR (Thin Air Rescue) helmet at extreme heights. bergleben.de, July 10, 2006, archived from the original on June 20, 2010 ; Retrieved May 6, 2011 .