High-Altitude Cough

Definition

High-altitude cough is a persistent, characteristically dry and often paroxysmal cough that develops during prolonged exposure to high altitude, typically above 3,000–4,000 m and near-universally on extended expeditions above 5,000 m. Its popular name, Khumbu cough, comes from the Khumbu valley on the Nepalese approach to Everest, where trekkers and climbers have described it for as long as they have been going there. It is also familiar on Kilimanjaro, Aconcagua, Denali and the Karakoram peaks.

It is not a diagnosis of exclusion by default. High-altitude cough is a clinical entity in its own right, with measurable changes in cough reflex sensitivity behind it — but because high-altitude pulmonary oedema (HAPE), chest infection and exercise-induced bronchoconstriction all cause cough at altitude too, and one of those could have dire consequences, the diagnosis is only safe once those have been actively considered.¹

Pathophysiology

The old explanation, and why it is incomplete

For decades the cough was attributed simply to cold, dry air. The reasoning is sound as far as it goes: barometric pressure falls with altitude, the hypoxic ventilatory response drives a large sustained increase in minute ventilation, and the air being moved is both very cold and almost devoid of water vapour. A climber at 5,300 m may shift several times their sea-level volume of air, mostly through the mouth, bypassing the nose's job of warming and humidifying it. The result is progressive drying of the airway surface liquid, loss of the periciliary layer that the mucociliary escalator depends on, and mechanical irritation of an exposed epithelium.

The problem is that this explanation does not survive testing. In the Operation Everest III chamber study, subjects taken to a simulated 8,848 m in a controlled environment — with temperature and humidity held at comfortable levels — still developed a marked, measurable increase in cough frequency and a significant rise in cough receptor sensitivity to citric acid challenge.² If dry air alone were the mechanism, that should not have happened. Something about hypobaric hypoxia itself sensitises the cough reflex.

What the current picture looks like

Altitude-related cough is now best understood as multifactorial, with a genuine central component:³

• Increased cough reflex sensitivity — demonstrated at altitude and in the hypobaric chamber, and the finding that most changed thinking on this condition.
• Airway drying and cooling — still contributory, particularly with high minute ventilation and mouth breathing, but not sufficient on its own.
• Bronchoconstriction in a subset, overlapping with exercise-induced bronchoconstriction, which cold dry air provokes powerfully.
• Subclinical pulmonary interstitial oedema — a plausible and much-discussed contributor, given that mild fluid shifts into the interstitium are common at altitude and sit on the same spectrum as frank HAPE.
• Upper airway inflammation and post-nasal drip, and genuine intercurrent viral infection, which is rife in crowded base camps and teahouses.

Why it becomes self-sustaining

Repeated violent coughing damages the epithelium it arises from, which lowers the threshold further — the same vicious circle that drives chronic refractory cough at sea level. That is why the cough often persists for days or weeks after descent, when the original stimulus has gone, and why treatments developed for refractory cough are the ones most likely to help the tail end of it.

Prevalence

It is close to universal on long, high expeditions. Reported rates rise steeply with altitude and duration of exposure, and on Everest expeditions the great majority of members describe a cough at some point. It is common enough among trekkers in the Khumbu that it has a place name rather than a diagnostic code, and it is a well-recognised reason for members to leave an expedition — not because the cough itself is dangerous, but because of what it does to sleep, to eating and to rib and chest-wall pain.

Causes and risk factors

• Absolute altitude and, more importantly, time spent at altitude — the cough is a feature of expeditions rather than of day trips.
• High sustained minute ventilation — hard climbing, heavy loads, and the hypoxic ventilatory response itself.
• Mouth breathing, which bypasses nasal conditioning of inspired air.
• Very cold, very dry air, particularly on early starts and summit days.
• Pre-existing asthma or exercise-induced bronchoconstriction, and current or recent smoking.
• Recent or concurrent upper respiratory tract infection — common in shared accommodation and camps.
• Dehydration, which is near-universal at altitude and worsens airway surface drying.
• A previous episode — many experienced climbers report it recurring on every trip.

Symptoms

Typical features

A dry, hacking, often paroxysmal cough that comes in prolonged bouts, characteristically worse at night, on exertion, and on breathing cold air. It is usually non-productive or produces only scant clear sputum. Hoarseness, sore throat and a raw retrosternal sensation are common companions.

What it does to people

The consequences are mostly mechanical and are the reason it matters:

• Sleep disruption, compounding the poor sleep altitude already causes, with knock-on effects on judgement and performance.
• Chest wall and intercostal muscle pain, sometimes severe.
• Rib and costal cartilage fractures. Cough-induced rib fracture at extreme altitude is described in the literature and is not rare in expedition medicine.⁴ A climber with sudden localised chest pain after a coughing bout, tender over a single rib, has probably fractured it.
• Vomiting, cough syncope, stress incontinence and inability to eat during bouts.
• Loss of the summit — a practical outcome worth naming, since it drives people to self-medicate hard.

Warning signs — the distinction that matters

Diagnosis

How it is diagnosed

Clinically, and largely by pattern and by exclusion of the dangerous alternatives. A dry paroxysmal cough that appeared during ascent, in someone whose exercise tolerance, resting breathing and oxygen saturation are appropriate for the altitude, needs no investigation on the mountain. The diagnostic work is the differential, not the confirmation.

What to rule out

After the expedition

A cough that persists more than a few weeks after return to sea level should be investigated as it would be in anyone else — because at that point it is no longer altitude-related, whatever started it. Consider post-infectious cough, newly unmasked asthma, reflux, and the possibility of an undiagnosed rib fracture maintaining the cycle through pain and splinting. Spirometry with reversibility testing is a reasonable first step; see spirometry and chronic cough.

Management

On the mountain

There is no strong trial evidence for any specific treatment of high-altitude cough, and it is honest to say so — what follows is expedition practice and extrapolation from cough physiology, not guideline-grade recommendation.

• Reduce the stimulus. A heat-and-moisture-exchange mask, buff or balaclava over the mouth and nose warms and humidifies inspired air and is the single most-used measure. Nose breathing wherever the workload allows does the same job.
• Hydration, deliberately and continuously — thirst is an unreliable guide at altitude.
• Humidify the sleeping space where practical, and avoid stove fumes and smoke, which are potent irritants in enclosed teahouses.
• Simple demulcents — lozenges, honey, warm drinks. Modest effect, no downside, and they matter more than that sounds at 3 a.m.
• Bronchodilator trial where wheeze or chest tightness suggests bronchoconstriction.
• Antibiotics only for genuine infection, not for a dry cough.
• Descent is the definitive treatment, and resolves it — which is worth stating plainly to someone deciding whether to continue.

Cough suppressants — with a caution

Codeine-based and other centrally acting suppressants are widely carried on expeditions and often help sleep. The caution is real: opioids depress the ventilatory response to hypoxia, which is the very mechanism keeping a climber oxygenated at altitude, and they sedate. Suppressing a cough also removes a protective reflex and can mask the change in character that signals HAPE. They are a considered decision with a doctor, not a routine.

Preventing it

Graded ascent with adequate acclimatisation, mask or buff from the outset rather than after the cough starts, disciplined hydration, treating a URTI before departure rather than climbing with it, hand hygiene in shared camps, and pre-existing asthma optimised and reviewed before travel.

Multi-system manifestations

Musculoskeletal

The main source of morbidity: intercostal and abdominal muscle strain, costochondral injury and frank rib fracture,⁴ with secondary splinting, reduced tidal volume and impaired clearance — which in turn worsens cough. This is the point at which physiotherapy becomes directly useful.

Sleep and cognition

Cough-related sleep fragmentation adds to periodic breathing and hypoxaemia, and the combined effect on judgement, coordination and decision-making at altitude is a genuine safety issue rather than a comfort one.

Nutrition

Coughing bouts during meals, nausea and vomiting compound the appetite suppression and weight loss already characteristic of high altitude.

Voice and upper airway

Hoarseness and laryngeal irritation are common, occasionally with troublesome persistent dysphonia after return.

Living with it, and afterwards

During the expedition

Expect it, plan for it, and treat the mask and the water bottle as equipment rather than optional comfort. Distinguishing a nuisance cough from an emergency is a skill worth briefing the whole team on before the trip, not looking up at 5,000 m.

Coming home

Most cases settle within days to a couple of weeks of descent. Where it does not, the cough has usually become self-perpetuating through reflex hypersensitivity and epithelial irritation, and that is treatable — see below.

Going back up

Recurrence is common and does not indicate anything sinister. Prevention is more effective than treatment, so the next trip is planned with the mask, hydration and ascent profile in place from day one.

Prognosis

Excellent. High-altitude cough resolves with descent and leaves no lasting lung damage. Its risks are indirect — the fractured rib, the lost sleep, the impaired judgement, the abandoned climb, and the missed diagnosis of HAPE hiding behind an assumption. A minority carry a hypersensitive cough reflex home with them for weeks, and a small number develop genuinely refractory chronic cough that needs the same approach as any other.

Role of the physiotherapist

Most of what physiotherapy offers here happens before and after the mountain rather than on it.

Before. Pre-travel assessment of anyone with asthma, exercise-induced bronchoconstriction, dysfunctional breathing or a history of the cough on a previous trip. Nasal-breathing drills and breathing pattern retraining reduce the volume of unconditioned air reaching the lower airway. Conditioning for the load and altitude planned is ordinary cardiorespiratory training, and inspiratory muscle training may be considered where breathing pattern is the limiting factor — see inspiratory muscle training.

Afterwards, for the cough that will not stop. This is where the evidence actually is. Non-pharmacological cough suppression — education, cough control and suppression techniques, breathing retraining, laryngeal hygiene and psychoeducation — produced significant improvement in refractory chronic cough in a multicentre randomised controlled trial of physiotherapy and speech and language therapy intervention,⁷ and earlier randomised work in speech pathology management showed the same.⁸ The mechanism those interventions target — a sensitised cough reflex maintained by repeated coughing — is exactly what a persistent post-expedition cough is. It is the most transferable evidence base we have for this problem.

Rehydrating the airway. If the mechanism is partly loss of airway surface liquid, then restoring it is a rational target — and nebulised hypertonic saline is the tool physiotherapy already uses to do exactly that. It draws water osmotically onto the airway surface, restoring the periciliary layer the mucociliary escalator depends on, improving mucus rheology and, in the airway diseases where it has been trialled, reducing cough and improving clearance. For a dry, hypersensitive post-expedition cough it is worth a supervised trial, and it pairs naturally with the cough-suppression work above.

⚠ Two honest caveats. First, this is extrapolation, not evidence: hypertonic saline is well studied in cystic fibrosis and bronchiectasis,⁹ and there is no trial of it in altitude-related cough at all. The physiological rationale is good and the intervention is low-risk, but it should be offered as a reasoned trial rather than an established treatment. Second, hypertonic saline can provoke bronchoconstriction — it is used as a bronchial provocation agent for that reason — but it does not always, and in most people it does not. That is precisely why the first dose is a supervised trial: it establishes whether this particular airway reacts, rather than assuming it will. A bronchodilator beforehand where there is a history of asthma or exercise-induced bronchoconstriction, then observe the response and decide on the strength of it.

⚠ It is not a mountain treatment. A nebuliser needs power, a clean water supply and time, none of which a high camp has. On the hill, the equivalent measures are the heat-and-moisture-exchange mask and disciplined hydration described above. Hypertonic saline belongs to the after, when someone comes home with a cough that will not settle.

For the chest wall. Rib and costochondral injury from coughing responds to the ordinary management of chest wall pain — analgesic advice, positioning, supported cough technique, graded return to load, and breathing exercises to counter the splinting and hypoventilation that pain produces. Where secretions are retained behind that splinting, airway clearance with attention to pain control applies.

What physiotherapy does not do is treat HAPE, or replace the judgement about whether someone should continue climbing. Both belong with the expedition doctor, and the physiotherapist's most valuable contribution before departure may simply be teaching the team the difference between a dry cough and a wet one.

Part 1 · References

1. Barry PW, Pollard AJ. Altitude illness. BMJ 2003;326(7395):915–919.
2. Mason NP, Barry PW, Despiau G, Gardette B, Richalet JP. Cough frequency and cough receptor sensitivity to citric acid challenge during a simulated ascent to extreme altitude. Eur Respir J 1999;13(3):508–513.
3. Mason NP, Barry PW. Altitude-related cough. Pulm Pharmacol Ther 2007;20(4):388–395.
4. Litch JA, Tuggy M. Cough induced stress fracture and fracture of the ribs at extreme high altitude. Aviat Space Environ Med 1998;69(11):1104–1105.
5. Luks AM, Auerbach PS, Freer L, et al. Wilderness Medical Society clinical practice guidelines for the prevention and treatment of acute altitude illness: 2019 update. Wilderness Environ Med 2019;30(4S):S3–S18.
6. Basnyat B, Murdoch DR. High-altitude illness. Lancet 2003;361(9373):1967–1974.
7. Chamberlain Mitchell SAF, Garrod R, Clark L, et al. Physiotherapy, and speech and language therapy intervention for patients with refractory chronic cough: a multicentre randomised control trial. Thorax 2017;72(2):129–136.
8. Vertigan AE, Theodoros DG, Gibson PG, Winkworth AL. Efficacy of speech pathology management for chronic cough: a randomised placebo controlled trial of treatment efficacy. Thorax 2006;61(12):1065–1069.
9. Wark P, McDonald VM. Nebulised hypertonic saline for cystic fibrosis. Cochrane Database Syst Rev 2009;(2):CD001506.

References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.