Which finding is least likely to be present in a patient experiencing acute mountain sickness?

Acute mountain sickness (AMS) occurs due to rapid ascent to high altitudes, typically above 8,000 feet, where lower oxygen levels can cause various symptoms. The key symptoms associated with AMS include headaches, light-headedness, insomnia, and gastrointestinal issues like vomiting.

When considering the symptoms, crackles in the lungs are not commonly observed in patients with AMS. This finding indicates potential pulmonary edema or other respiratory conditions that would not be typical of the symptoms associated purely with AMS. Instead, the presence of crackles usually points towards underlying lung issues, which are not a primary concern of acute mountain sickness.

Light-headedness aligns with the decreased oxygen availability experienced at high altitudes, indicating the body's difficulty in acclimating. Insomnia is also frequently reported due to changes in sleep patterns at altitude, and vomiting is a gastrointestinal response to the stress of altitude. Therefore, among the listed options, crackles in the lungs are the least likely finding in a patient experiencing acute mountain sickness.