Transthoracic sonographic assessment of B-line scores during ascent to altitude among healthy trekkers

•Portable transthoracic sonography is feasible in fieldwork contexts such as trekking at altitude.•B-line incidence is increased with ascent among healthy trekkers.•The clinical relevance of field sonography for B-lines remains to be clarified. Sonographic B-lines can indicate pulmonary interstitial edema. We sought to determine the incidence of subclinical pulmonary edema measured by sonographic B-lines among lowland trekkers ascending to high altitude in the Nepal Himalaya. Twenty healthy trekkers underwent portable sonographic examinations and arterial blood draws during ascent to 5160 m over ten days. B-lines were identified in twelve participants and more frequent at 4240 m and 5160 m compared to lower altitudes (P