Duration
Field Safety Reference (Pre-Trip Planning & Active Trail Use)
Max Altitude
High Himalayan Passes (5,400m–5,650m) & Base Camps
Difficulty
Essential Knowledge (Life-Safety & Medical Protocols)
Best Season
Applicable Year-Round (Autumn, Spring, Winter & Monsoon)
Age Range
All High-Altitude Trekkers & Climbers (14 to 75 Years)
Destination
Nepal Himalaya (Khumbu, Annapurna, Manaslu, Langtang, Rolwaling)
Activities
AMS Self-Assessment, Diamox Protocols, HAPE/HACE Rescue, Water Filtration, Wound Care
Accommodation
Teahouse Aid Stations, HRA Field Posts & Base Camp Medical Tents
Transportation
Ground Foot Descent, Gamow Hyperbaric Chambers, Helicopter Evacuation
1. The Physiology of Altitude: Hypoxia & Acclimatization
The air we breathe contains roughly 20.9% oxygen at every elevation on Earth. What changes as you climb higher is barometric pressure. At sea level, the weight of the atmosphere compresses air molecules, resulting in an atmospheric pressure of roughly 760 mmHg. At Namche Bazaar (3,440m), barometric pressure drops to approximately 510 mmHg, delivering roughly 67% of sea-level oxygen per breath. At Thorong La Pass (5,416m) and Everest Base Camp (5,364m), pressure drops by half, providing only 50% of the effective oxygen molecules available at sea level.
When your body experiences this hypoxic stress, it initiates immediate compensatory mechanisms. You breathe deeper and faster (hyperventilation), your resting heart rate rises, and your blood vessels dilate. However, rapid hyperventilation blows off carbon dioxide (CO2), causing blood pH to become excessively alkaline (respiratory alkalosis). True acclimatization is the process where your kidneys excrete bicarbonate into the urine over 48 to 72 hours, rebalancing your blood pH and allowing your brain to continue breathing rapidly without feeling like you are over-ventilating.
Expedition Essentials
Assume Altitude First:
Any sickness or physical discomfort above 2,500 meters is altitude sickness until proven otherwise. Never attribute headaches or nausea to dehydration or fatigue alone.
Stop Ascent with Symptoms:
Never ascend to sleep at a higher altitude with active symptoms of Acute Mountain Sickness (AMS). Stop, rest at your current camp, and give your body time to adapt.
Descend Immediately if Worsening:
If symptoms worsen or fail to resolve within 24 hours of rest, descend immediately by at least 500 to 1,000 meters. Delaying descent is the primary cause of fatalities.
Never Leave a Patient Alone:
Never send a sick trekker downhill unaccompanied. High altitude can cause sudden cognitive confusion, disorientation, and loss of motor coordination.
2. Acute Mountain Sickness & The Lake Louise Score
Acute Mountain Sickness (AMS) is the body's natural warning signal that ascent has outpaced acclimatization. Symptoms typically emerge 6 to 24 hours after arriving at a new, higher sleeping elevation. The international medical standard for diagnosing and tracking AMS is the Lake Louise Score (2018 Consensus).
A diagnosis of AMS requires the presence of a headache plus a score of at least 3 points from the four core symptom categories:
Headache
- 0: None
- 1: Mild headache
- 2: Moderate headache
- 3: Severe, incapacitating headache
Nausea / Loss of Appetite
- 0: Normal appetite, no nausea
- 1: Poor appetite or mild nausea
- 2: Moderate nausea or occasional vomiting
- 3: Severe nausea with frequent vomiting
Fatigue / Weakness
- 0: Normal energy
- 1: Mild fatigue or tiredness
- 2: Moderate fatigue or weakness
- 3: Severe fatigue or weakness, bedridden
Dizziness / Lightheadedness
- 0: None
- 1: Mild dizziness
- 2: Moderate dizziness
- 3: Severe dizziness, impaired balance
Mild AMS
Rest at current altitude. Take ibuprofen (400mg) for headache and drink oral rehydration fluids. Do not climb higher until score is 0.
Moderate AMS
Rest for 24 hours. Consider Diamox (250mg twice daily). If symptoms do not improve by morning, initiate physical descent of 500 meters.
Severe AMS
Immediate descent required. High risk of progression into life-threatening HAPE or HACE. Do not delay descent waiting for medical supplies.
3. Life-Threatening Illnesses: HAPE & HACE Protocols
While mild AMS is uncomfortable, High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema (HACE) are lethal conditions that can progress to death within 6 to 12 hours if ignored.
High Altitude Pulmonary Edema (HAPE)
Caused by uneven vasoconstriction in the lungs under extreme hypoxia, creating localized high pressure that forces fluid through capillary walls into air sacs.
Warning Signs: Extreme breathlessness while resting in bed, rapid breathing (>25 breaths/min), fast resting pulse (>110 bpm), dry cough progressing to a wet rattling cough with pink or blood-tinged sputum, and blue/gray lips.
Field Protocol: Immediate descent is mandatory. Even dropping 500 to 1,000 meters dramatically reduces pulmonary artery pressure. Administer high-flow oxygen (2–4 L/min) or place the patient in a Gamow hyperbaric bag. If descent is delayed, administer Nifedipine (extended-release 20mg–30mg).
High Altitude Cerebral Edema (HACE)
Caused by severe hypoxic dilation of cerebral blood vessels, causing fluid leakage across the blood-brain barrier and dangerous intracranial swelling.
Warning Signs: Loss of motor coordination (ataxia: inability to walk heel-to-toe in a straight line), severe confusion, slurred speech, irrational behavior, hallucinations, and progressing lethargy to coma.
Field Protocol: Immediate descent of at least 1,000 meters. Administer Dexamethasone immediately: 8mg initial dose (oral or IM), followed by 4mg every 6 hours until low altitude is reached. Dexamethasone buys hours of consciousness to enable walking down; it does not replace descent.
The 10-Step Tandem Gait Test for Ataxia
If a trekker appears unusually sluggish, clumsy, or irritable above 3,500 meters, test for HACE immediately using the Tandem Gait Test. Have the person walk ten paces in a straight line, placing the heel of the leading foot directly in contact with the toes of the trailing foot. If they sway, step sideways, or stumble, treat immediately as HACE and begin descent with an escort.
4. Diamox (Acetazolamide) Protocols & Evidence
Acetazolamide (Diamox) speeds up your body's natural acclimatization. It forces the kidneys to excrete bicarbonate, acidifying the blood and stimulating your brainstem to increase ventilation during rest and sleep. It does not mask symptoms or improve physical stamina.
| Regimen | Standard Dosage | Timing & Administration | Clinical Indication |
|---|---|---|---|
| Prevention | 125mg twice daily | Start 24 hrs prior to 2,800m; continue to high point | Standard preventative protocol for high ascents |
| Treatment | 250mg twice daily | Administer at rest upon AMS diagnosis | Active treatment combined with mandatory rest |
| Pediatric Protocol | 2.5 mg/kg every 12 hrs | Max 125mg per individual dose | Prescription only; consult pediatrician pre-trip |
Expected Side Effects vs. Contraindications
- Paresthesia: Tingling or numbness in fingertips, toes, and lips (completely harmless).
- Frequent urination due to bicarbonate diuresis (stay hydrated).
- Altered carbonation taste: Carbonated sodas and beer will taste flat.
- Known severe allergy to sulfonamide drugs (sulfa antibiotics).
- Pre-existing severe renal failure or advanced liver dysfunction.
- Pregnancy (first trimester contraindication).
5. The Himalayan Rescue Association (HRA) Aid Posts
Founded in 1973, the Himalayan Rescue Association (HRA) is a non-profit voluntary organization that reduces altitude casualties in Nepal. During peak autumn and spring trekking seasons, the HRA operates two field aid posts:
Pheriche Aid Post (4,240m)
Khumbu / Everest Base Camp RouteStaffed by volunteer Western and Nepali high-altitude physicians. Equipped with supplemental oxygen cylinders, Gamow hyperbaric bags, automated external defibrillators (AED), and digital diagnostic tools.
Manang Aid Post (3,519m)
Annapurna Circuit TrailFull-time medical post operating since 1981. Provides outpatient clinical consultations, pulse oximetry testing, Gamow bag therapy, and emergency helicopter evacuation coordination.
Attending the daily lectures at Pheriche (1:00 PM) and Manang (3:00 PM) gives you real-time pass snow reports, resting pulse oximetry checks, and clinical consultations with volunteer mountain physicians.
6. Trailside Illnesses: GI Bugs, Blisters & Cold Injuries
Gastrointestinal infections, foot blisters, and knee strain account for most non-altitude medical issues on Nepal's trekking routes:
Trekker's Diarrhea & Giardiasis Management
Bacterial enteritis (predominantly Campylobacter and E. coli) is the most common illness in Nepal. Because fluoroquinolone resistance is widespread across South Asia, Azithromycin (500mg once daily for 3 days) is the preferred first-line treatment. If symptoms persist longer than seven days with sulfur-tasting belches, bloating, and watery stool without fever, suspected Giardia lamblia should be treated with Tinidazole (2g single oral dose) or Metronidazole (400mg three times daily for 5 days).
Blister Prevention & Friction Management
Never ignore a foot hotspot. The moment friction heat is detected, stop immediately and apply Leukotape P directly over the dry skin. For formed blisters, puncture the lower margin using a sterile flame-sterilized needle to express fluid while leaving the protective skin roof completely intact. Cover with a hydrocolloid pad and secure with tape.
Descent Knee Trauma (Patellofemoral Pain Syndrome)
Descending thousands of vertical meters down stone staircases (such as the 1,656m drop from Thorong La or the Ulleri stairs) places immense stress on the patellar tendon. Adjust dual trekking poles so elbows form a 90-degree angle, lock wrist straps to transfer 20% of your body weight into upper pectoral and shoulder muscles, and take small, disciplined steps.
7. Wilderness Medical Kit Packing Matrix
Pharmacies in Thamel (Kathmandu) and Lakeside (Pokhara) stock almost all common mountain medications over the counter. Pack your medical kit in a labeled, waterproof dry pouch:
| Category | Medication / Item | Primary Indication | Field Guidance |
|---|---|---|---|
| Altitude Medications | Acetazolamide (Diamox 125mg & 250mg) | Prevention (125mg bid) and treatment of mild to moderate AMS | Check for sulfa drug allergies before administration. |
| Altitude Emergency | Dexamethasone (4mg tablets) | Emergency treatment for HACE (8mg initial, then 4mg every 6 hours) | Buys time for physical descent; does not replace descent. |
| Altitude Emergency | Nifedipine (Extended-Release 20mg–30mg) | Emergency reduction of pulmonary artery pressure in HAPE | Administer when descent is impossible; monitor blood pressure. |
| Gastrointestinal | Azithromycin (500mg tablets) | Broad-spectrum antibiotic for bacterial trekker diarrhea (Campylobacter) | Single 500mg daily dose for 3 days; superior to ciprofloxacin in Nepal. |
| Gastrointestinal | Tinidazole (2g) or Metronidazole (400mg) | Treatment for suspected Giardiasis (sulfur burps, chronic watery diarrhea) | Tinidazole 2g single dose or Metronidazole 400mg tid for 5 days. |
| Rehydration | Oral Rehydration Salts (Jeevan Jal / Electral) | Restoring electrolytes during diarrhea, vomiting, and high perspiration | Mix 1 packet per 1 liter of purified drinking water. |
| Pain & Inflammation | Ibuprofen (400mg) & Paracetamol (500mg) | Managing altitude headaches, musculoskeletal pain, and fever | Take ibuprofen with food; alternate with paracetamol for breakthrough pain. |
| Wound & Blister Care | Leukotape P & Hydrocolloid Dressings | Blister prevention, hotspot protection, and sterile blister sealing | Apply Leukotape directly over hotspots before blisters form. |
| Diagnostics | Fingertip Pulse Oximeter | Tracking blood oxygen saturation (SpO2) and resting heart rate | Warm fingers before testing; cold hands give falsely depressed readings. |
8. Emergency Helicopter Evacuation Protocols
For severe HAPE, HACE, or complex fractures, helicopter evacuation is the only fast transit out of high Himalayan valleys. Knowing how dispatch works prevents critical delays:
1. Satellite Communication & Coordinates
Never rely solely on cellular networks above 4,000 meters. Carry a two-way satellite messenger (such as a Garmin inReach or ZOLEO). When requesting an emergency rescue, provide exact GPS coordinates, local village name, surrounding terrain landmarks, and local weather conditions (cloud base height, fog, wind).
2. Insurance Authorization & Direct Billing
Under Civil Aviation Authority of Nepal (CAAN) rules, helicopter operators require guaranteed payment or direct insurance clearance before launching. Ensure your travel insurance policy explicitly covers search, rescue, and air ambulance up to 6,000 meters without requiring cash deposits upfront. Keep your policy number and 24/7 emergency assistance phone number written in your passport.
3. Landing Zone Safety & Visual Signals
Clear the landing zone of all loose items, plastic bags, trekking poles, and tarps. Strong rotor downwash can blow loose gear into the rotor blades. Stand with your back to the wind, raise both arms in a "Y" shape (indicating "Yes, land here"), and do not approach the helicopter until the pilot signals and the blades have stopped rotating.
High-Altitude First Aid FAQs
Evidence-based answers regarding Diamox usage, pulse oximeter readings, HAPE vs HACE symptoms, and emergency evacuation.
What is the difference between AMS, HAPE, and HACE?
Acute Mountain Sickness (AMS) is the mild to moderate form of altitude illness characterized by headache, nausea, fatigue, and dizziness. High Altitude Pulmonary Edema (HAPE) is a life-threatening condition where fluid accumulates inside the lungs, causing extreme breathlessness at rest, a wet cough, and rattling chest sounds. High Altitude Cerebral Edema (HACE) is a life-threatening swelling of the brain characterized by ataxia (loss of physical balance and inability to walk in a straight line), severe confusion, hallucinations, and coma. Both HAPE and HACE require immediate physical descent.
How does Diamox (Acetazolamide) work, and what is the proper dosage?
Diamox is a carbonic anhydrase inhibitor. It forces the kidneys to excrete bicarbonate in the urine, acidifying the blood. This metabolic acidosis stimulates the brainstem to increase ventilation (breathing deeper and faster), especially while sleeping, raising oxygen levels in the blood. The standard preventative dosage recommended by the Wilderness Medical Society is 125mg taken orally twice daily (every 12 hours), starting 24 hours before ascending above 2,800 to 3,000 meters and continuing until reaching maximum altitude and descending.
Can you take Diamox if you have a sulfa allergy?
Diamox is a sulfonamide derivative. Trekkers with documented severe allergic reactions to sulfonamide antibiotics (such as anaphylaxis, hives, or Stevens-Johnson syndrome) should avoid Diamox due to the risk of cross-reactivity. Consult an allergist or travel medicine physician before departure; alternatives like low-dose dexamethasone can be considered for non-sulfa-tolerant individuals under clinical guidance.
What is the tandem gait (heel-to-toe) test for HACE?
The tandem gait test is the standard field test for High Altitude Cerebral Edema (HACE). Have the trekker walk in a straight line for 10 steps, placing the heel of the front foot against the toes of the back foot with eyes open. A healthy person walks without swaying. If the trekker stumbles, steps sideways, or cannot stay on the line (ataxia), assume HACE immediately. Administer emergency dexamethasone and begin descent with an escort.
What should your resting pulse oximeter reading (SpO2) be at high altitude?
At sea level, normal blood oxygen saturation (SpO2) is 95% to 100%. As elevation increases, oxygen saturation naturally drops due to lower atmospheric pressure. At Namche Bazaar (3,440m), typical resting SpO2 is 82% to 88%. At Dingboche or Pheriche (4,300m–4,400m), it is typically 75% to 82%. At Base Camp (5,364m), it can drop to 70% to 78%. A reading below 65% accompanied by extreme breathlessness or rapid resting pulse (>110 bpm) indicates poor adaptation.
What is a Gamow bag and how does it work in mountain rescue?
A Gamow bag is an airtight, portable fabric hyperbaric chamber large enough to hold a patient. Using a foot pump, the chamber is pressurized to 2 pounds per square inch (psi) above ambient atmospheric pressure. This pressure increase raises the partial pressure of oxygen inside the bag, simulating an immediate descent of 1,500 to 2,000 meters. A patient inside a Gamow bag at 5,000 meters experiences an internal altitude equivalent to roughly 3,200 meters, stabilizing them until weather permits a helicopter evacuation or physical descent.
How do you coordinate an emergency helicopter evacuation in Nepal?
To initiate an emergency helicopter evacuation, communicate via satellite messenger (Garmin inReach, ZOLEO, or satellite phone) or local cellular network to your trekking agency, insurer, or direct rescue coordinators. You must provide the patient exact GPS coordinates, current altitude, symptom details (suspected HAPE/HACE), weather conditions at the landing site, and insurance policy verification. Review our Emergency Contacts Directory for 24/7 rescue hotlines.
Evidence-Based Wilderness Safety
Our altitude illness and wilderness first aid guidelines are compiled by the Medical & Expedition Desk in alignment with Wilderness Medical Society (WMS) clinical consensus and Himalayan Rescue Association (HRA) field records. Read our Editorial Policy or report updated clinic operations in our anonymous Reader Survey.