Myth 4: APAP is a set-it and forget-it system
Rachel Vicars, senior clinical research scientist at Fisher & Paykel, says both CPAP and APAP are not set-and-forget. Both require follow-up with patients to address issues like mask fit, compliance, and humidity. Some clinicians restrict the minimum and maximum pressure ranges to something they feel comfortable with, but this comes down to clinician experience.
Myth 5: All APAPs are the same
Each individual manufacturer has its own proprietary APAP algorithm, and each performs at a different level, responding differently to different breathing patterns, Malecha says.
Vicars says, “They are based on slightly different technology and respond to events differently. It is important you are using a manufacturer that has clinically validated its algorithms to ensure adequate treatment. These validations should be available for review. An important distinction between algorithms is the way they use events to ensure a timely response to sleep-disordered breathing events. For example, flow limitation is a precursor to other more severe sleep-disordered breathing events. An AutoCPAP needs to be able to respond to these flow-limited events in a timely manner to ensure that the more severe sleep-disordered breathing events (apnea and hypopnea) are minimized.”
Malecha adds, “In addition to differing APAP algorithms from manufacturer to manufacturer, there is now differentiation between APAP solutions for patients with OSA versus central sleep apnea. It is crucial for clinicians to understand the variability of products so they can select a product they feel is most appropriate for their patient.”
Myth 6: All AHIs are the same
According to Vicars, all machines report AHI, but not all machines are measuring the same thing. “How you define apnea and hypopnea greatly affects the AHI ‘number’ that you will see. The AASM defines an apnea as a reduction in flow of ?90% for ?10 s,1-2 but the definition for hypopnea is different depending on the year the standard was published, and whether you are using the recommended or alternative scoring methods. In all cases, the definition of hypopnea has both a flow component (ie, a reduction in flow of 30-90% for ?10 s)2 AND an oxygen desaturation or arousal component (ie, ?3% oxygen desaturation or associated with an arousal2). CPAP machines only use one measure to calculate the AHI—the airflow. They do not have the additional measures to calculate oxygen desaturation, or arousal as defined by AASM.
“Therefore, no CPAP machine can give you the same AHI as a PSG. Instead you are getting the manufacturer’s version of the AHI. No definition is more ‘correct’ than another—what is important is that the machine correlates with PSG-AHI (ie, a higher AHI indicates more events than a lower AHI) and that it is validated to treat.”
Myth 7: APAPs are good for everyone
Several studies have shown that AutoCPAP is equivalent to fixed pressure CPAP in treating OSA,3 Vicars says. “These studies are in a general OSA population, and therefore individual patient differences may not be taken into account. It is important to use caution when using AutoCPAP in certain populations, such as chronic heart failure, central sleep apnea, and obesity hypoventilation syndrome, as the algorithms may not have been validated to treat in these populations, and may not respond appropriately to the patient’s flow signal.”
So let’s put the last of those myths to bed.
Peter Blais, RPSGT, is a registered sleep technologist with the Center for Sleep Disorders at St. Mary’s Regional Health System in Auburn, Me. This is his first article for Sleep Review.
1. Iber C, Ancoli-Israel S, Chesson A, Quan SF, et al. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. 1st ed. Westchester, Ill: American Academy of Sleep Medicine; 2007.
2. Berry RB, Budhiraja R, Gottlieb DJ, et al. Rules for scoring respiratory events in sleep: update of the 2007 AASM Manual for the Scoring of Sleep and Associated Events. Deliberations of the Sleep Definitions Task Force of the American Academy of Sleep Medicine. J Clin Sleep Med. 2012;8(5):597-619.
3. Ip S, D’Ambrosio C, Patel K, et al. Auto-titrating versus fixed continuous positive airway pressure for the treatment of obstructive sleep apnea: a systematic review with meta-analyses. Syst Rev. 2012;1:20.