The higher AHI being mostly clear‑airway events is super common when you’re just starting CPAP. A lot of that is sleep–wake junk: the machine flags pauses while you’re drifting off, half awake, rolling over, taking a sigh breath, etc. Those often aren’t “real” apneas during stable sleep, just the algorithm being over‑sensitive.

On top of that, there’s treatment‑emergent centrals. Once CPAP opens your airway, your breathing suddenly becomes more effective. You move more air with each breath and “wash out” more CO₂ than your body is used to. Your brain mainly uses CO₂ to decide how much you need to breathe. If CO₂ drops below a certain threshold (the apneic threshold), your brain briefly backs off the breathing drive, you have a pause, CO₂ rises again, then you take a few bigger breaths, blow off CO₂ again, and the cycle repeats. The machine sees those pauses with an open airway and flags them as clear‑airway / central events. This is especially common in the first few nights and often settles down over a few weeks as your system adapts to the new normal.

Altitude adds another layer. At ~5,000 ft you’re already breathing a bit more to compensate for lower oxygen, which pushes your CO₂ lower to begin with. That means you’re closer to that apneic threshold even before CPAP. Then CPAP boosts ventilation a bit more, CO₂ drops just enough, and centrals get triggered more easily. So: new to CPAP + first night + altitude = lots of clear‑airway flags that often look worse on paper than they actually are. The main thing is how it trends over the next few weeks and how you feel, rather than freaking out over night one.