By: M. ALEXANDER OTTO, Family Practice News Digital Network
PHOENIX – For uncomplicated, moderate to severe obstructive sleep apnea, autoadjusting positive airway pressure is as effective as continuous positive airway pressure titrated in a sleep laboratory, according to Dr. Neil Freedman, a sleep medicine specialist and pulmonologist in Bannockburn, Ill.
Randomized controlled trials comparing lab-titrated continuous positive airway pressure (CPAP) to autoadjusting positive airway pressure (APAP) in unattended settings have shown similar compliance, apnea-hypopnea index (AHI), and daytime sleepiness improvements (Sleep 2010;33:267-71).
That raises the possibility of sending uncomplicated obstructive sleep apnea patients home with APAP machines to see how they do, instead of to a sleep lab. With insurance companies, among others, interested in that option, "in the near future patients who need CPAP – if they have uncomplicated sleep apnea – are going to get an unattended APAP trial whether they’re going to be treated long-term with it or they are going to be pushed to CPAP. It’s not inappropriate, as long as you know what you’re doing," Dr. Freedman said at a meeting on sleep medicine sponsored by the American College of Chest Physicians.
APAP machines don’t provide continuous pressure, but instead detect and respond to changes in upper airway flow or resistance patterns; the idea is to use the minimal effective pressure needed to maintain airway patency, which can change for various reasons, even body position.
Initially, machines are typically set to a minimum pressure of 4 cm H2O and a maximum pressure of 20 cm H2O. Dr. Freedman starts on the higher side with obese patients and those with worse symptoms, and also includes heated humidification and a gradual ramp-up to therapeutic pressures at the start of sleep.
"The overwhelming majority" of patients are going to need pressure of 8 to 12 cm H2O. If patients need more than 14 cm H2O, "there’s probably something else going on," he said.
Despite APAP’s effectiveness, that there are several unresolved issues, he cautioned.
First, the machines use different technologies and algorithms to treat events, so data from one APAP study is specific to the device used in that trial, and cannot be generalized to other machines. It’s important for clinicians to know their device and its weaknesses, but "provider knowledge, patient education, and early follow-up are more important than the type of device used." If patients still complain about snoring, being sleepy during the day, or other issues despite treatment, "look for problems. When in doubt, send them back to the lab," Dr. Freedman said.
Some machines can have trouble distinguishing true obstructive apneic events and central sleep apnea – apneic episodes despite an open airway – and misestimate the apnea-hypopnea index.
Patients may come in with a high AHI and events marked that "should be obstructive events" but that didn’t get better with increased pressure, which suggests central apnea. "If you inappropriately increase the pressure, you may actually make things worse for the patient," he noted. Excessive mask leaking can artificially inflate the AHI as well, so it’s important to use the mask or breathing apparatus recommended for a given machine. A proper fit also helps ensure the machines accurately capture snoring data, a measure of mask vibration, Dr. Freedman said.
Most APAP machines are flow based, which means they rely on the absence of flow back at the machine to detect events. A different approach, the forced oscillation technique (FOT), also is available to differentiate obstructive events from central apneic events. FOT reads changes in patterns of resistance; an absence of flow, despite low resistance, likely indicates a central event.
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