Auto-titration of CPAP is an essential tool for
diagnosing and treating obstructive sleep apnea.
John A. Wolfe, RRT
Diagnosing and treating obstructive sleep apnea (OSA) with
continuous positive airway pressure (CPAP) is both an art and
a science. Once the nature of a patient’s OSA has been
established (central, peripheral, or mixed), clinicians face
the challenge of selecting the ideal interface and the optimal
level of CPAP. An amazing (and some might say bizarre) array
of masks and headgear have been developed in an attempt to
address the unique facial anomalies that are infinitely
variable from one patient to the next. Just as each patient
has unique facial features, the pharyngeal anatomy is slightly
different from one individual to the next. In addition, their
soft tissue may transform slightly as they adjust from one
position to another. Not surprisingly, this creates a
challenge when selecting the correct level of CPAP. There is
no magic number that applies to all patients, and the amount
of CPAP required to maintain a patent airway for any patient
may actually change from one minute to the next. For example,
higher pressures are generally needed in the supine position
and during rapid eye movement (REM) sleep.1
Auto-titration of constant positive airway pressure (APAP)
offers an important tool to optimize treatment, increase
efficacy, and enhance patient compliance. APAP devices
effectively normalize sleep while delivering a mean pressure
typically 37% lower than fixed pressure therapy.2
While insufficient pressure can not provide effective therapy,
too much pressure can increase discomfort and pressure-related
side effects, ultimately contributing to patient
noncompliance.
A summary of peer-reviewed articles conducted by a task
force appointed by the American Academy of Sleep Medicine
endorses the technology saying, “APAP can be used to treat
many patients with OSA (auto-adjusting) or to identify an
effective optimal fixed level of continuous positive airway
pressure (CPAP) for treatment (auto-titration).”3
In the diagnostic setting, auto-adjusting can make determining
the appropriate prescription levels easier and, in some cases,
more precise. For many patients, both the patient’s sleep
apnea diagnosis and an appropriate CPAP level can be
determined in one visit. It saves both time and money compared
to spending a night in the laboratory to determine OSA and
another to determine optimal CPAP. At home, APAP can be a
useful tool in the quest to optimize patient treatment and
compliance.
Because it is responsive to changes in the patient’s
pressure requirements, APAP can be used to titrate pressure
settings and may be more effective for patients with
significant medical comorbidities. Mark Petrun, MD, medical
director of the sleep laboratory for Northern Colorado
Pulmonary Associates, Fort Collins, Colo, says, “It fills an
important niche for people who we cannot titrate in the sleep
lab,” either because they can not settle into sleep at the
laboratory or have difficulty going there, or because their
insurance (or lack of insurance) may limit their options. He
emphasizes that in some cases a patient’s optimal pressure can
not be determined in a single night. In addition, it can be an
important alternative for patients who are struggling to
maintain compliance with traditional CPAP.
There is conflicting evidence as to whether APAP is more
effective in the treatment of OSA than traditional CPAP.
Although there is considerable evidence that “APAP reduced the
apnea plus hypopnea index to acceptable levels (AHI
<10/hour) in greater than 80% to 95% of OSA patients
studied,”3 the previously mentioned task force
noted that sufficient direct comparisons between CPAP, APAP,
and placebo are lacking. Importantly, many patients notice a
difference and prefer APAP therapy.
How it Works
APAP devices operate on
one of two principles:
1. Devices that use “flow limitation” analysis titrate the
patient’s pressure based on a continuous analysis of breathing
patterns (flow) and adjust pressures using a multilevel
algorithm to determine the optimal CPAP level. By making
subtle changes in pressure and effectively assessing the
impact of those changes, the machine can continually search
for the best possible pressure level for the individual.
Secondary algorithms assess and address leaks and variable
breathing patterns. Snoring, apnea, hypopnea, and leaks all
have a telltale signature the auto-titration mechanism can
recognize. Once it detects one of these situations, it raises
the pressure gradually to maintain normal breathing.
2. Devices that use an acoustic-based algorithm analyze
vibrations from the pharyngeal wall to determine the
appropriate pressure. In effect, they react to snoring and
adjust the pressure up or down in reaction to the patient’s
needs. They can also change the pressure within a specific
breath if a problem is detected. If solely dependent on
vibration, these devices may not work in nonsnorers or
patients who have undergone upper-airway
surgery.3
“No studies have systematically compared the efficacy of
one APAP technology with another,”3 and devices
using different technology may not produce the same results in
a given patient.
A Patient’s Perspective
Dick Goodman
used a fixed CPAP system for 9 years, and was generally
satisfied with the setup. About a month ago, he agreed to
replace his old equipment after discussions with his home care
clinician and physician. They had all agreed there was some
room for improvement and he decided to try out an APAP system.
Because he had been having some problems with a stuffy nose,
and consequently kept opening his mouth, they also switched
from a nasal mask to a face mask that covered both his nose
and mouth. He was already using a humidifier. He was at first
reticent to try the face mask, thinking it would be
uncomfortable. “I didn’t think I would like [the mask], but I
adjusted to it really quick,” the patient says.
He was pleased with the auto-titration feature as well.
“It’s quieter and more compact than my old unit,” he says. He
also noted that it does not seem to blow as hard. “If I’m
stopped up, I thought [the machine] should be blowing harder,”
he says, but that was decidedly not the case. “It doesn’t seem
to have the [same] pressure the other one did—it doesn’t blow
as hard,” he says, adding that the quality of his sleep was as
good as or better than ever. “Overall, I’m very pleased,” he
adds.
Surprisingly, the lower noise level was not a benefit to
him and actually created a problem for his wife, who had grown
accustomed to sleeping with the “white noise” drone of the old
unit. “So we still run [the old unit] at night,” he chuckles,
“because my wife sleeps better with it running.”
Conclusion
OSA continues to be widely
undiagnosed and untreated. Once it is diagnosed, the benefits
of CPAP in the treatment of OSA are well documented and
unimpeachable. It has long been recognized as the most
effective treatment for patients with moderate to severe
OSA.4-6 Treating OSA with CPAP is considerably more
challenging and time-consuming than treating a condition with
pharmaceutical drugs. Patient education, clinical assessment,
support during treatment (especially during the initiation
phase), and continuous follow-up are important cornerstones to
successful CPAP treatment. Because the mean pressure is often
lower than the optimal fixed CPAP pressure, APAP can increase
comfort and compliance for some patients. Every patient’s
experience is different, but it may be hypothesized that APAP
will be most effective in those who experience the biggest
difference between CPAP and APAP levels.
APAP is not a “magic bullet,” but rather an important tool
that may be underutilized. A manager of a nationally
affiliated home medical equipment company said that while
physicians are generally aware of the benefits of APAP, they
frequently need to be reminded to consider it. He said, “When
we report back to them that the patient is having difficulty
adjusting to their CPAP and we suggest trying APAP, they often
ask me, ‘Why didn’t I think of that in the first place?’”
John A. Wolfe, RRT, is a contributing writer for
Sleep Review.
References
1. Oksenberg A, Silverberg
DS, Arons E, Radwan H. The sleep supine position has a major
effect on optimal nasal continuous positive airway pressure:
relationship with rapid eye movements and non-rapid eye
movements sleep, body mass index, respiratory disturbance
index, and age. Chest. 1999;116:1000-1006.
2. Teschler H,
Berthon-Jones M. Intelligent CPAP system: clinical experience.
Thorax. 1998;53(suppl 3):S49-S54.
3. Berry R, Parish J,
Hartse K. The use of auto-titrating continuous positive airway
pressure for treatment of adult obstructive sleep apnea: an
American Academy of Sleep Medicine Review. Sleep.
2002;25:148-173.
4. Loube DI, Gay PC, Strohl KP, Pack AI,
White DP, Collop NA. Indications for positive airway pressure
treatment for adult obstructive sleep apnea patients: a
consensus statement. Chest.1999;115: 863-866.
5. Sullivan
CE, Issa FG, Berthon-Jones M, Eves L. Reversal of obstructive
sleep apnea by continuous positive airway pressure applied
through the nares. Lancet. 1981;1:862-865.
6. ATS
Statement. Indications and standards of use of nasal
continuous positive airway pressure (CPAP) in sleep apnea
syndromes. Am J Respir Crit Care Med.
1994;150:1738-1745.