Vol. 12 •Issue 6 • Page 54
Innovations in CPAP Therapy
From Hardware to Long-term Patient Care, CPAP has Come a Long Way
In 1980, Colin Sullivan, MD, used a two-stage vacuum cleaner to create the first home continuous positive airway pressure unit. He applied positive pressure through a mask interface to a person’s airway during sleep to maintain airway patency.
Now, only 23 years later, numerous variations on this theme are available, including bilevel positive airway pressure and more recent innovations in positive airway pressure delivery. As CPAP has become an accepted form of noninvasive treatment for obstructive sleep apnea-hypopnea syndrome, patient compliance has driven the development of added features and new devices.
ADVANCES THROUGH THE YEARS
For example, ramp time was developed early on to allow the patient time to adjust to the prescribed pressure as they fall asleep. Most CPAP devices now have a ramp feature that generally includes a button on the machine that, when pushed by the patient, transiently decreases the prescribed pressure for 10 minutes to 20 minutes. This allows patients who require higher pressures to reach that prescribed pressure gradually over a period of time, thereby increasing patient comfort and compliance.
CPAP units have gone from weighing approximately 35 pounds to less than 4 pounds. They have evolved from sounding like a vacuum cleaner to ultra quiet units.
Smaller units also have improved portability for travelers. CPAP units are available that automatically adjust to higher altitudes (where more pressure is typically needed), whereas others adjust automatically to both 120 V and 220 V outlets for those traveling overseas. Some devices can be powered by a 12 VDC power source for those who enjoy camping.
One of the most common limiting factors in patient compliance has been either nasal dryness or chronic nasal congestion from the continuous forced air passing through the nasal passages. The nasal mucosa tend to become irritated and produce mucous to humidify the dry air. This irritability of the nasal mucosa can be improved if the air is humidified prior to its delivery.
Cool humidity was the only choice until 1992 when heated humidifiers for CPAP were introduced. Adjustable heated humidification may improve patient compliance because humidity requirements change during the year; there’s generally more need for humidity in winter but less need in the humid summer.
Bilevel positive airway pressure therapy allows for a means to meet specific patient needs. This device makes exhaling easier by reducing expiratory pressure below that of the prescribed inspiratory pressure. Bilevel therapy only is beneficial in specific cases, particularly in patients with neurological disorders in which work of breathing is compromised, such as in amyotrophic lateral sclerosis or Lou Gehrig’s disease.
The latest refinement in positive pressure delivery is a mode that allows for a small drop in pressure at the beginning of exhalation, yet the pressure rises back to the prescribed inspiratory pressure before inspiration begins without the use of two separate prescribed pressures (inhalation and exhalation pressure as in the bilevel mode). Indeed, the greater the expiratory effort, the greater the reduction in exhalation pressure. This device may improve compliance in patients who have difficulty tolerating the positive pressure during exhalation, such as in patients with claustrophobia.
A new variation of CPAP that may be used in some cases are the auto-titrating devices. This auto CPAP senses obstructive breathing events by monitoring inspiratory flow restrictions and adjusts the delivered pressure accordingly. Pressure requirements may change depending on body position (supine sleep typically requires more pressure than in the lateral position) or on the stage of sleep. Pressure requirements also may increase following alcohol consumption before bedtime. However, auto-CPAP devices may have disadvantages for some patient populations. Some patients don’t tolerate changing pressures and prefer a fixed pressure.
Moreover, it’s unclear how good auto-CPAP devices are in eliminating electroencephalographic (EEG) microarousals, even though frank apneas and hypopneas may be eliminated. For example, sleep professionals often see patients who require low level CPAP pressures of only 5 cmH2O to 6 cmH2O to eliminate apneas, hypopneas and snoring, yet require .9 cmH2O to 11 cmH2O pressure to eliminate inspiratory associated microarousals. None of the auto-CPAP devices available simultaneously records EEG and, therefore, they’re unable to titrate according to EEG sleep fragmentation.
With the advent of CPAP changes, the sleep field also has gained better ways to track overall compliance. Instead of relying on reports from the patient or home care providers, machines now have cards that can record the amount of time, on a nightly basis, that the individual uses CPAP. This information can be downloaded onto a computer for review and analysis.
When Dr. Sullivan tested his CPAP prototype, he used masks that were individually molded and glued to the patients’ faces. Today’s masks are designed to fit the majority of facial types. There are numerous mask types, ranging from ones that cover the nose with the use of a forehead rest, to ones that cover just the nose without a forehead rest, to full-face masks covering both the nose and mouth.
The last several years even have brought masks that are modeled after the design of the nasal oxygen cannula. This mask type has two nasal prongs that are inserted into each nasal vestibule, and the connecting tubing passes over the ears, thereby eliminating the need for extensive headgear. Other devices are available that deliver positive pressure and aid in the reduction of bruxism by using bite blocks. Oral delivery devices are options for patients who consistently breathe through their mouth.
Once a physician places an individual on nasal CPAP, several major questions arise: When does a patient potentially require a re-evaluation to determine if the prescribed nasal CPAP pressure continues to be adequate for the patient’s need? In other words, do the pressure needs of a patient change over time? And if they may change, what are the clinical clues to suggest that the patient may require a re-evaluation?
Although pressure needs may decrease transiently after the first several weeks or months of CPAP use, nasal CPAP pressure requirements tend to increase over time. The severity of sleep-disordered breathing generally worsens with advancing age and weight gain.
Sleep-disordered breathing often begins with nocturnal snoring, and, over time, this snoring may disrupt sleep architecture leading to frequent inspiratory-associated arousals typical of upper airway resistance syndrome. With further advancing age and weight gain, frank OSA with recurrent episodic hypoxia may ensue eventually.
Given this history of worsening sleep-disordered breathing over time in most patients, a clinician needs to recognize clinical signs that the patient’s nasal CPAP pressure requirements may now be inadequate. Sleep-disordered breathing is a risk factor for hypertension, cardiac arrhythmias such as atrial fibrilation, congestive heart failure (CHF) exacerbations, pulmonary hypertension, transient ischemic attacks (TIAs), stroke, gastroesophageal reflux disease (GERD) and morning headaches. It also can trigger migraine headaches, erectile dysfunction, cognitive impairment and depression. Symptoms of the above disorders that appear in a patient who has been compliant on nasal CPAP therapy should prompt one to question whether the current CPAP pressure remains adequate.
Excessive daytime sleepiness usually is the first symptom to reappear. The patient may say to the physician, “At first I felt great with this CPAP, but now I feel sleepy during the day again, and it reminds me of how I felt before starting my CPAP therapy.”
After ruling out equipment failure, lack of compliance or chronic nasal congestion, a good sleep history is required to rule out poor sleep hygiene, such as chronic sleep deprivation. An examination of other possible factors, such as depression, or other medical conditions, such as hypothyroidism, may need to be addressed.
Generally, there are additional clues other than excessive daytime sleepiness to suggest that the patient’s pressure needs may have increased. There may have been a weight gain of 20 pounds or more. The patient’s blood pressure, which was previously under good control with antihypertensive medication, may now be elevated once again. Morning headaches, night sweats, unrefreshing sleep, worsening of GERD symptoms, new onset atrial fibrilation, TIAs, worsening of short-term memory or sudden increase in CHF exacerbations all may be additional clues that sleep-disordered breathing may once again be problematic and that the current nasal CPAP pressure may be inadequate.
Nasal CPAP therapy for sleep-disordered breathing usually is a lifelong treatment, especially because the disorder worsens with age. Many CPAP devices and mask interfaces now are available to fit the needs of most patients.
Once a patient is placed on CPAP, one should never assume that the original pressure setting prescribed will remain optimal or even adequate. When optimal CPAP pressure requirements change, patients often become discouraged with the therapy, falsely assuming that the device isn’t helping them.
Long-term follow-up is necessary to ensure optimization of nasal CPAP therapy, to maintain patient compliance, and to prevent the .consequences of sleep-disordered breathing.
Dr. Schmidt is director of research at Ohio Sleep Medicine and Neuroscience Institute and adjunct assistant professor at Ohio State University, Columbus.