No relationship between COVID19 and altitude sickness

There have been proposals to treat covid-19 with medications that are used for HAPE, because of suggestions that covid-19 pneumonia is similar to HAPE. Both conditions can cause non cardiogenic pulmonary oedema and hypoxemia with characteristic findings on computer tomography. Main difference is that HAPE occur in hypobaric conditions and covid-19 pneumonitis is normobaric disease. Both cause pulmonary oedema but pathophysiology is very different.

Pulmonary oedema in HAPE is caused by increased pulmonary artery pressures, in viral pneumonia the pulmonary oedema is infectious and usually referred to as acute respiratory distress syndrome (ARDS). Proinflammatory markers are probably triggered by the virus. Crucially, patients with HAPE, respond rapidly and dramatically to oxygen therapy and do not require mechanical ventilation unlike in patients with covid-19 who may require non-invasive, or even invasive ventilation, including extracorporeal support.

Ground glass appearance on chest CT in both HAPE and covid-19 is not due to similar pathophysiology. Ground glass appearance on CT is a common finding in viral and bacterial pneumonia as well as in ARDS.

There are also anecdotal reports among patients with covid-19 of variability in hypoxic pulmonary vasoconstriction (HPV) and hypoxic ventilatory response (HVR). Variability in HPV and HVR is also found amongst HAPE patients. Both HPV and HVR are genetically determined. Variability due to genetic variation is a common finding in human populations that does not imply a common pathophysiology.

Increasing the inspired oxygen is the best treatment for HAPE. In many cases, increased oxygen is easily provided by descent to a lower altitude. Oxygen is a true antidote to HAPE that reverses pulmonary hypertension. In covid-19, oxygen is required to treat hypoxaemia, but is not a cure especially in the absence of other effective treatment modalities that are currently being investigated. 

Nifedipine is a calcium- channel blocker that is commonly used adjunctively with oxygen in HAPE to decrease pulmonary artery pressure. Use of nifedipine is likely to be counterproductive in ARDS due to covid-19, because decreasing HPV may worsen ventilation-perfusion matching causing increased hypoxaemia. Phosphodiesterase inhibitors also limit HPV and may cause the same deleterious results. Acetazolamide, the most commonly used medication in the prevention and treatment of acute mountain sickness (AMS), has no role in covid-19 treatment. AMS is a neurological condition that is not associated with pulmonary disease. 

There is no logical reason to treat covid-19 using medications intended for AMS or HAPE, a disease with a completely different aetiology. The use of medications for high altitude illness to treat covid-19 is likely to be unhelpful and could have a potentially dangerous outcome. These are desperate times, but we should not try treatments for which there is no good rationale. Primum non nocere.

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