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Nightly use of continuous positive airway pressure (CPAP) did not prevent cardiovascular events in high risk patients with obstructive sleep apnea, according to a large randomized trial. The SAVE study suggests that CPAP has no cardiovascular benefits for the millions of people using it less than 4 hours a night. However, those using CPAP for more than that might still get health benefits.
What They Did
Investigators in Europe and Australia randomized 2,717 patients aged 45-75 with established coronary or cerebrovascular disease and moderate or severe obstructive sleep apnea to receive either nightly CPAP or not, along with usual care. They used a composite primary endpoint of cardiovascular death or cardiovascular events. Patients were followed for an average of 3.7 years. Patients with excessive daytime somnolence or hypoxemia were excluded (for ethical and safety reasons). The study was published in the New England Journal of Medicine.
What They Found
Slightly more patients in the CPAP group reached the primary outcome (229 vs 207, hazard ratio 1.1). The patients using CPAP did feel significantly better during the day, with less sleepiness and better quality of life. Patients only used CPAP 3.3 hours per night.
What it Means
Sleep medicine experts were quick to point out that many of the centers were not experienced in the diagnosis and treatment of sleep apnea. Treatment (or at least counseling) by sleep specialists has been shown to improve adherence with CPAP.
Adherence was in fact the major limitation of confidence in the trial's conclusions: three hours of nightly CPAP use might have been an inadequate dose to reduce cardiovascular events, editorialists argued.
There's some support for this theoretical dose response for CPAP in OSA with regard to cardiovascular disease:
- 244 patients with OSA with significant coronary artery disease who had just been revascularized were randomized to CPAP or none, followed for almost 5 years on average. There was no improvement in the composite cardiovascular endpoint overall. However, those who used CPAP >4 hours did have a significant reduction in cardiovascular events, while nonadherent patients did not.
- Similar results were found among 723 patients with OSA, without prior cardiovascular disease. The patients using CPAP > 4 hours per night had better outcomes than the nonadherent patients.
That being said, the SAVE trial reflected the reality of CPAP use outside clinical trials. Most patients prescribed CPAP use it not at all, or less than 4 hours per night.
What about those patients who were excessively sleepy during the day, who were excluded from the SAVE trial? Might they have had reduced cardiovascular risk even with a mere 3 hours of nightly CPAP usage? We'll never know.
The SAVE study will lend support to the increasingly common deployment of wireless communication-enabled CPAP machines loaded with spyware that transmit usage data to the payer, without action by the patient. Patients who use their CPAP machine will get to keep it; nonadherent patients may have it repossessed. High deductibles for CPAP or differential cost share according to usage are other methods being used by payers to squeeze nonadherent patients.
Whether consistent use of CPAP (>4 hours a night) leads to improved cardiovascular outcomes is still unknown, but it should now be considered absolutely, positively, 100% certain that CPAP doesn't help when it is not connected to the patient.
Read more: CPAP for Prevention of Cardiovascular Events in Obstructive Sleep Apnea. N Engl J Med. 2016 Sep 8;375(10):919-31.