One Drug, Two Altitudes
Acetazolamide has strong evidence for one of this patient's two breathing problems and thin evidence for the other — and the two are easy to conflate because they share a chemoreceptor mechanism.
D.V. has guided mountaineering expeditions for fifteen years, most recently leading groups up peaks above 6,000 meters twice a year, and came in not because of anything wrong on the mountain but because his partner finally insisted he get his snoring and daytime fatigue checked at sea level. The sleep study found something he wasn't expecting: central sleep apnea, AHI 22, entirely central rather than obstructive in pattern, with a structurally normal heart on echocardiogram and an EF of 60% — no heart failure, no obvious structural driver, a genuinely idiopathic finding in an otherwise fit 39-year-old.
He has two separate questions for this visit, and they sound like one question because they share a drug and a mechanism. The first is about an expedition in six weeks, above 5,500 meters, where he wants prophylaxis against the periodic breathing that disrupts sleep at altitude in even healthy climbers. Acetazolamide induces a mild metabolic acidosis through carbonic anhydrase inhibition, widening the carbon dioxide reserve and stabilizing ventilatory drive, and the American Academy of Sleep Medicine's 2025 central sleep apnea guideline does suggest it for altitude-related CSA. The second question is about the idiopathic CSA this same study just found — and here the assumption he arrived with, strong evidence on the mountain and thin evidence at home, turns out to be the wrong way round. That same guideline suggests acetazolamide for primary CSA, which is precisely what an AHI of 22 with no structural driver makes his, and rates that recommendation at low certainty while rating the altitude recommendation he was counting on at very low certainty. Schmickl and colleagues' 2020 meta-analysis pooled fifteen controlled sea-level trials and found a mean AHI reduction near sixteen events per hour. Neither indication rests on strong evidence; both rest on weak evidence pointing the same way, and the one he assumed was sturdier is formally the less certain of the two. What actually separates his two questions is not evidence quality but duration and interpretability — a short prophylactic course for a six-week, self-limited exposure is a different commitment from open-ended therapy for a chronic finding, and starting both at once would leave nobody able to say afterward which problem the drug had been treating.
Pre-expedition sleep medicine consultation
Both problems he's describing come down to the same central chemoreceptor pathway — acetazolamide stimulates ventilatory drive through carbonic anhydrase inhibition regardless of whether the trigger is altitude hypoxia or an idiopathic drive instability at sea level. Given that shared mechanism, I don't see a reason not to treat both with the same drug.
The mechanism argument is real, and I'd have said what you just said until I looked the certainty ratings up. The 2025 AASM guideline suggests acetazolamide for both of his problems. It rates primary CSA — his sea-level finding — at low certainty, and it rates the altitude indication at very low certainty. Schmickl's 2020 meta-analysis pooled fifteen controlled sea-level trials and found about a sixteen-event-per-hour AHI reduction. So the sea-level evidence is not the thin half of this.
Which means I can't support your conclusion by the route you took to it. You argued from a shared mechanism to a single prescription covering both. I'd get to a narrower place by a different road: the guideline backs each use separately, on weak evidence either way, so nothing about the sea-level indication needs to borrow strength from the altitude one. What it does need is a reason to start now rather than after he gets back, and "we're writing the prescription anyway" isn't one.
I'd finish the thought the primary care physician started, because it settles the timing question rather than leaving it open. If we start him on acetazolamide for the baseline CSA now and he also takes it up the mountain, then when he comes back and we repeat his sleep study, we will not be able to say what we are looking at — his idiopathic CSA on treatment, or residual altitude effect, or acclimatization. The one number that would tell us whether his primary CSA is drug-responsive gets destroyed by running both indications through the same six weeks. That's not a reason never to treat it; it's a reason to treat it after we have a clean baseline.
And on the expedition course itself I'd add what neither of you has: acetazolamide is a carbonic anhydrase inhibitor with a real diuretic effect, and dehydration at altitude is already a known hazard. The prescription needs a written hydration and electrolyte plan attached to it, not just a mechanistic rationale — the pulmonologist's argument tells us the drug should work, and says nothing about what it does to a climber's fluid balance at 5,500 meters.
Agreed: acetazolamide prescribed for altitude prophylaxis only, with an explicit written hydration and electrolyte plan for the expedition; his baseline idiopathic central sleep apnea is not treated with ongoing acetazolamide at this visit, with a repeat sleep study planned after he returns.
Not fully agreed: the pulmonologist accepted the deferral on attribution grounds but maintained that the shared mechanism makes eventual treatment of the baseline CSA likely rather than merely possible, and would have been willing to start it today; the primary care physician, having found the guideline's certainty ratings ran opposite to the referral's assumption, was unwilling to treat any part of this as settled enough to act on twice in one window. Neither position was overruled — what closed the question for today was the clinical pharmacologist's point that running both indications through the same six weeks destroys the one measurement that would tell them whether his primary CSA responds to the drug at all. Both physicians accepted that as the reason for sequencing, without agreeing on what the repeat study will show.