Is HAPO the exclusive diagnosis of pulmonary oedema at HA

Dear Editor, The article on extreme altitude pulmonary oedema (EAPO) in acclimatised soldiers published in MJAFI 2012; 68: 339–345 by Maj I. D. Khan suggests that the soldiers were expected to be “acclimatised” after 39 ± 13.79 days of stay at 19,000–23,000 ft. Lowlanders never acclimatise to extreme altitude and some changes that constitute some acclimatisation at this altitude occur over much longer periods of time.1 The title of the article is thus misleading. HAPO is known to occur in acclimatised individuals and usually follows an event like gain in altitude or respiratory infection.2,3 Its de novo occurrence in 21 soldiers, resident at a given altitude for weeks, is intriguing. That 71% cases were native highlanders is interesting since native highlanders of Ladakh have minimal musculature in the pulmonary artery which mitigates acute pulmonary hypertension which is central to the pathophysiology of HAPO.4 In view of the atypical setting and the large number of cases reported, we request the author to clarify the following: 1. A number of conditions like bronchitis, acute MI and pulmonary embolism may mimic HAPO.5 How were these conditions ruled out? 2. What were the values of vital signs and SpO2 in the patients and healthy soldiers at that altitude? 3. Did investigations at Base Camp/Siachen hospital confirm the diagnosis? 4. Over what time period did the 31 cases occur? 5. What is the validity of using SpO2 <75% as a criterion for diagnosing HAPO? 6. Why were acetazolamide and dexamethasone used to treat HAPO instead of internationally accepted treatment modalities2,5 7. Why and on what basis was Nifedipine administered to only four “select” patients? 8. How were the symptoms/signs of HAPO (predominantly pulmonary) confusing with those of AMS (predominantly neurological)? We also wish to correct certain factual inaccuracies in the manuscript: 1. Hypertension and orthopnoea are not features of HAPO. 2. Stage I “Acclimatisation” begins at/above 9000 ft and not below 9000 ft as depicted in Table 2. 3. HAPO bag therapy does not reset the patients' physiology to lower altitude. It improves oxygenation and residual benefits may last for a few hours outside. 4. The descent simulated by the HAPO bag has been overstated in the example of Mt Everest. 5. Compression increases the PO2 and not the oxygen concentration (FiO2) inside the bag. 6. Some HAPO bags are designed to be carried as stretchers (DRDO bags).