A Gamow bag is a portable, inflatable chamber that treats altitude sickness by simulating a descent of 5,000 to 6,000 feet without the patient actually moving downhill. It works by increasing the air pressure around the person inside, effectively giving their body the same oxygen-rich environment they’d find at a much lower elevation. The device weighs about 14 pounds and is carried by trekking groups and expeditions heading into remote, high-altitude areas where a quick descent might not be possible.
How a Gamow Bag Works
The bag is essentially a sealed, human-sized tube made of heavy-duty fabric. A person lies inside, the chamber is zipped shut, and an attendant uses a foot pump to pressurize the interior. The pump raises the pressure inside the bag by about 2 PSI above the surrounding atmosphere. At high altitude, where the air is thin and oxygen levels are low, this modest pressure increase replicates the atmospheric conditions found roughly a mile lower in elevation.
That difference matters enormously for someone whose body is struggling with low oxygen. Altitude sickness develops because there’s less oxygen in every breath you take at elevation. By compressing the air around the patient, the Gamow bag increases the amount of oxygen available with each breath, giving the body the relief it needs to stabilize. The effect is immediate: symptoms often begin improving within minutes of pressurization.
What It Feels Like Inside
The chamber is snug. You lie flat inside a cylindrical tube with limited room to move, and the fabric inflates tightly around you. It can feel claustrophobic, especially for someone already anxious from feeling sick at altitude. The noise from the foot pump is constant, since someone outside must keep pumping at a rate of 10 to 20 pumps per minute for the entire treatment session.
One sensation most people notice is pressure on their ears, similar to what you feel during airplane descent. The rapid pressure change inside the bag can cause ear pain or a feeling of fullness. Swallowing, yawning, or gently blowing against a pinched nose (the same technique divers use) helps equalize the pressure in the middle ear. If someone can’t equalize, the pressure difference can bruise or, in rare cases, rupture the eardrum.
Treatment sessions typically last one to several hours. During that time, the person inside exhales carbon dioxide, which builds up in the sealed chamber. A relief valve releases used air while the attendant continuously pumps fresh air in. This cycle keeps the CO2 levels safe, but it means someone must stay at the pump the entire time. A Gamow bag is not a set-it-and-forget-it device.
When a Gamow Bag Is Used
The bag is a temporary rescue tool, not a cure. It’s used when someone develops serious altitude sickness and getting them to lower ground quickly isn’t realistic, whether because of nightfall, severe weather, difficult terrain, or the person being too sick to walk. The three forms of altitude illness it addresses range from mild to life-threatening:
- Acute mountain sickness (AMS): headache, nausea, fatigue, and dizziness, typically above 8,000 feet. This is the most common form, and while it often resolves with rest and hydration, severe cases benefit from pressurization.
- High altitude pulmonary edema (HAPE): fluid accumulates in the lungs, causing breathlessness, a persistent cough, and extreme fatigue. Without treatment, it can be fatal.
- High altitude cerebral edema (HACE): the brain swells due to low oxygen, leading to confusion, loss of coordination, and altered consciousness. This is a medical emergency.
For HAPE and HACE, descent is the definitive treatment. The Gamow bag buys time. It stabilizes the patient enough to make evacuation possible, or it holds them through the night until a helicopter or ground descent can happen at first light. Symptoms often return after the person is removed from the bag if they remain at the same altitude, so the goal is always to get them lower as soon as conditions allow.
Practical Considerations at Altitude
The bag and pump together weigh about 14 pounds, which is significant when every ounce matters on a high-altitude trek. Most independent trekkers don’t carry one. You’re more likely to find Gamow bags at established base camps, remote medical posts, and with organized expeditions that plan for altitude emergencies. Some trekking agencies on popular routes like Everest Base Camp or Kilimanjaro keep them at key elevations.
The effectiveness of the simulated descent depends on starting elevation. At 18,000 feet, pressurizing the bag simulates dropping to roughly 12,000 or 13,000 feet. At 12,000 feet, the same pressure increase simulates a drop to around 6,000 or 7,000 feet. The higher you start, the more dramatic the benefit, because oxygen levels fall steeply with each additional thousand feet of elevation.
Operating the pump is physically demanding. Maintaining 10 to 20 pumps per minute for hours requires rotating attendants, which means you need multiple healthy team members available. At extreme altitude, where everyone is somewhat affected by thin air, this labor adds up quickly. Groups need to plan for the reality that running a Gamow bag is a team effort, not a solo task.
Limitations Worth Knowing
A Gamow bag does not replace descent. It mimics the effect temporarily, and symptoms frequently rebound once the patient exits the chamber if they haven’t moved to a lower elevation. It’s a bridge, not a solution. For someone with HACE who is confused or vomiting, being zipped into a tight chamber also raises practical concerns: the attendant outside can’t easily monitor the patient or intervene if they vomit and risk aspiration.
The bag also requires continuous manual effort to maintain pressure and cycle fresh air. If the pump fails, or if there aren’t enough healthy people to keep pumping, the treatment stalls. In extremely cold or windy conditions, securing the bag to the ground with its built-in straps prevents it from shifting, but the attendant pumping outside is fully exposed to the elements.
Despite these constraints, the Gamow bag remains one of the most important pieces of emergency equipment in high-altitude wilderness medicine. When descent isn’t immediately possible, it can stabilize a deteriorating patient and buy the hours needed to organize a safe evacuation.