Because of its proven benefits to patient outcomes, continuous positive airway pressure (CPAP) is quite likely to keep its status as a mainstay of obstructive sleep apnea (OSA) treatment. But according to Charles W. Atwood Jr, MD, many sleep medicine practitioners overstate the effect of CPAP therapy on some of these outcomes, from improving quality of life to eliminating cardiovascular risk.
“We think it does everything,” said Dr. Atwood, Associate Professor of Medicine in the Division of Pulmonary, Allergy, and Critical Care Medicine at the University of Pittsburgh. “We think it is the greatest thing ever.” However, in a lecture at the American College of Chest Physicians 2008 Annual International Scientific Assembly, he pointed out that in some areas, this contention is not borne out.
SORTING OUT THE LITERATURE
It is not clear whether CPAP’s positive effect on patients’ apnea-hypopnea index (AHI) and daytime sleepiness translates into an improvement in quality of life. In one study, Dr. Atwood noted, patients with OSA and congestive heart failure who received CPAP showed large and significant improvements on some, but not all, components of the Short Form 36 (SF-36) and Guyatt’s chronic heart failure questionnaire, compared with patients who received usual care. However, a 2006 Cochrane database showed less favorable results for CPAP’s ability to improve quality of life as shown on the SF-36.
“For most of the included studies, the confidence intervals cross the zero line, indicating that the effect is not statistically significant or questionably so,” he said. “Therefore, quality of life is not shown conclusively to improve with CPAP.”
Similarly, CPAP’s effect on cardiovascular function may not be as far-reaching as was once thought. In a 2003 study, researchers found that CPAP significantly improved left ventricular end systolic dimension after only one month among patients randomized to CPAP treatment as opposed to medical therapy only; however, blood pressure was improved only slightly. Prospective studies have reported positive findings, and while Dr. Atwood called such studies “provocative,” the conclusions are not irrefutable.
WHAT IS THE USE OF AUTOCPAP?
Despite the uncertainty over which benefits CPAP provides, OSA diagnostic activity increased by more than 300% between 2001 and 2006, said Dr. Atwood. CPAP prescriptions are increasing as well, and although fixed-pressure, in-laboratory polysomnography remains the standard, the use of autotitration CPAP (autoCPAP) machines is gaining in popularity.
A 2004 study by Masa et al provides the best evidence for use of autoCPAP machines, according to Dr. Atwood. In that study, there was no difference in AHI or subjective daytime sleepiness among patients who received standard, autoadjusted, or predicted-formula titration. However, it is unlikely that use will be able to increase as long as the Healthcare Common Procedure Coding System code does not differentiate between fixed-pressure and autotitration machines, even though higher reimbursement for the more expensive autoCPAP is justified. “As long as fixed pressure and autotitration have the same reimbursement, then home care companies are just not that interested in prescribing autoCPAP,” Dr. Atwood pointed out.
Among its advantages, an auto-CPAP machine can be used in a limited fashion to determine the pressure to be programmed into a long-term-use fixed-pressure machine. “There are some data for this, and the data look pretty good,” said Dr. Atwood, although he acknowledged that different autoCPAP machines can have varying readings. In a 2003 study, Kessler et al found differences in titration between autoCPAP machines as great as 3.5 cm.
“It is probably not a good idea for you to use four or five different autoCPAP machines, unless you are obsessed with knowing all the differences about them,” Dr. Atwood recommended. “You should use a machine you are comfortable with and get to know it well.”
Another possible use of autoCPAP on the horizon is to directly tie in treatment with diagnosis. In a study by Senn et al, patients were allowed to get comfortable with CPAP for two hours in the laboratory before being sent home with a CPAP device. If after two weeks the patient used the device for more than two hours per night and wanted to continue treatment, a diagnosis of OSA was made. Through use of this method, 58% of patients were diagnosed with OSA, with 80% sensitivity, 97% specificity, and reasonable positive and negative predictive values. Although most clinicians would not like to approach diagnosis this way, Dr. Atwood noted that insurers like Medicare and Medicaid Services are beginning to consider it.
“The machine that works for the patient is the right type of positive airway pressure therapy, whether it is fixed or auto,” concluded Dr. Atwood. “I think autoCPAP is something you are going to need to become familiar with, because your patients are going to ask for it.”