1
Introduction
Positive airway pressure (PAP) therapy is the standard modality for treating moderate and severe obstructive sleep apnea (OSA) in adults. It was first described by Colin Sullivan, an Australian pulmonologist, in 1981.
There are several theories as to how PAP therapy relieves airway obstruction. Intuitively, it makes sense to think of it as a pneumatic splint that keeps the airway open by increasing the intraluminal pressure above the critical pressure at which the pharynx collapses (P crit ). Potentially, there are additional mechanisms. For instance, it has been suggested that PAP may stimulate mechanoreceptors leading to an increase in airway tone, in addition to its pneumatic stenting role.
It is clear that moderate and severe OSA, and for some even mild OSA, are significant, independent cardiovascular (CV) risk factors. In the Busselton Study, a population-based study in Australia that followed people with all degrees of OSA, one-third of the patients with untreated moderate and severe OSA died during the 15 years of monitoring. Patients with no or mild OSA had a statistically significant lower mortality rate. The weakness of the study was the small number of subjects and observational nature.
Observational studies also demonstrate that PAP therapy markedly reduces the cardiovascular risk associated with untreated moderate and severe OSA. In another population-based study by Marin et al., patients with untreated severe OSA had an approximately fivefold increase in fatal and nonfatal CV events over a 15-year period. However, patients with severe OSA who were treated with PAP therapy had the same risk of fatal and nonfatal CV events as patients without significant OSA.
The efficacy of PAP therapy in ideal settings is clear, but adherence to PAP may limit its effectiveness in the home setting. Adherence rates range from 30% to 60%. It is the treating physician’s role to understand the nuances of PAP therapy in an attempt to maximize adherence to a potentially lifesaving, and life-enhancing, treatment.
2
Types of PAP Machines
There are different ways to deliver PAP. The initial one was CPAP, where “C” stands for continuous. With this modality, constant pressure is delivered by the machine’s pump. The pressure is transmitted via tubing to the facial interface and into the patient’s airway ( Fig. 8.1 ).
BiPAP, or bilevel positive airway pressure, has two fixed, preset inspiratory and expiratory pressures. The airway is opened by a higher inspiratory pressure. The machine senses when inspiration is complete and then the pressure is decreased to the fixed expiratory pressure. This cycle is repeated breath after breath.
There are two autoadjustable machine classes: auto-PAP (more commonly known as autoadjustable positive airway pressure or APAP ) and auto-BiPAP. In these machines, fixed pressures are not set; rather, a range is input into the device.
With APAP, we set a lower and an upper range that limit the amount of pressure that can be delivered. The machine cannot deliver pressure below the set lower limit or above the set upper limit. The machine senses when there is increased resistance and increases the pressure in an attempt to lower the resistance and open the airway. Different APAP machines use different algorithms and sensing triggers to modulate treatment pressure and thus may not all be equally effective. Treatment algorithms are proprietary and vary from machine to machine.
With auto-BiPAP, we set an IPAPmax (inspiratory PAP maximum), EPAPmin (expiratory PAP minimum), and a pressure support. The pressure support is the differential between inspiratory and expiratory pressures during an individual breath. It must be at least 4 cm H 2 O.
Evidence is lacking for efficacy of one type of machine over another. However, there are reasons why a particular type of machine would be ordered in an individual patient. If during a PAP titration study an optimal pressure is identified, a CPAP machine is generally ordered. If during a titration study, the patient has persistent respiratory events at CPAP ≥15 cm H 2 O or if the patient complains of difficulty exhaling against the pressure, he or she can be switched to BiPAP. BiPAP will generally deliver less overall pressure than CPAP on a given night, which may theoretically reduce some of the side effects related to higher CPAP settings. In addition, BiPAP decreases the work of breathing. It tends to be beneficial for patients with severe OSA, obesity, and high pressure requirements.
If optimal pressure is not identified during a PAP titration study, then an APAP machine can be ordered, unless the patient breathed better on BiPAP than CPAP, in which case an auto-BiPAP could be ordered. Alternatively, a CPAP machine can be requested at an empiric setting, or the patient can return to the sleep laboratory for a repeat titration study.
As noted later, if the patient does not undergo a titration study and, therefore, an optimal pressure is not known, an APAP machine is generally ordered.
Finally, with respect to machines to treat sleep-disordered breathing (SDB), adaptive servoventilation (ASV) should also be discussed. More than 50% of patients with heart failure have SDB. The majority of these patients have central sleep apnea (CSA) as opposed to OSA. Only 50% of patients with CSA respond to CPAP. Patients with heart failure who have CSA have a life expectancy of 45 months, whereas in those without CSA, it is 90 months. Therefore it is felt that treating the CSA in patients with heart failure could improve survival, as well as other quality-of-life measures. The mainstay of treatment for these patients has been ASV. It basically works by stabilizing the breathing pattern with ventilation during periods of decreased breathing and decreased support during periods of hyperventilation and normal breathing.
Unfortunately, an Urgent Field Safety Notice was issued for these machines in the spring of 2015. Patients with a decreased left ventricular ejection fraction of <45% had a higher mortality rate with ASV usage than without. Therefore the treatment of CSA in heart failure patients with a poor ejection fraction is still not clear and further work is clearly needed in this area.
Almost all PAP machines now have humidifiers. Higher airway pressures, without humidification, may dry out the mucous membranes through which the delivered air passes. Humidification minimizes this. Some patients opt not to use the humidification option, however.
PAP machines also have an optional ramp-up period that can be set. When the machine is first turned on, a pressure lower than the set pressure is delivered. As the patient is falling asleep, the pressure slowly increases until it reaches the final set pressure. Keep in mind that patients need PAP delivered to keep their airway open when they are sleeping, not when they are awake. In fact, high PAP delivered when someone is awake may prevent that person from falling asleep. The ramp-up period can be as long as 45 minutes. It should be set to match the patient’s typical sleep latency, that is, how long it usually takes them to fall asleep.
3
Interfaces
There are three typical interfaces: nasal “pillows,” nasal masks, and full-face masks ( Figs. 8.2–8.4 ). In general, nasal masks or nasal pillows are preferred and initially attempted on patients. If the patient has significant nasal congestion, then a full-face mask may be required.
If the patient does not have nasal congestion yet still opens the mouth at night, air leakage may occur through the mouth. This can lead to a decrease in delivery of adequate pressure to open the airway, awakening of the patient and/or bed partner, and dry mouth. This can be addressed either by changing to a full-face mask or using nasal mask/nasal pillows in conjunction with a chin strap. A chin strap, to some degree, is similar to a wide rubber band that goes from below the chin to the top of the head ( Fig. 8.5 ). It does not allow the mouth to drift open during sleep. However, if a patient awakens at night and feels that they are having difficulty breathing, it takes very little effort to open and breathe through the mouth.
It is not always clear a priori which interface an individual will tolerate best. However, certain characteristics of an individual patient may lead you in one direction. For instance, patients with claustrophobia, unusual nasal bridge anatomy, or a mustache may do better with nasal pillows.
Identifying the correct interface for PAP therapy is crucial. It is probably the most limiting factor for success with PAP therapy other than having the correct machine with the appropriate settings.
4
Initiating PAP Therapy
After a patient is diagnosed with OSA, a treatment plan is formulated. Patients with moderate or severe OSA, by definition, have obstructive sleep apnea syndrome (OSAS) and, similar to patients diagnosed with hypertension, should probably be treated even if they have, or perceive they have, no symptoms referable to OSA at this time.
Patients with mild OSA and either symptoms or comorbidities, such as excessive daytime sleepiness (EDS) or underlying CV disease, are also considered to have OSAS. They should be offered treatment to see if it helps their symptom(s) and/or ameliorates their comorbidities.
As stated earlier, PAP therapy is the gold-standard treatment for OSA. So how does a patient go from being diagnosed with OSA to being treated? There are two paradigms to offering treatment.
The traditional route to treatment has been an in-laboratory PAP titration study. In this procedure, the patient spends a night, or a day if he or she is a shift worker and generally sleeps during the day, in the sleep laboratory.
One may include a split-night sleep study in this paradigm where the first half of the night is a diagnostic portion and the second half of the night is a therapeutic titration study. The value of this is that the patient can be diagnosed and treatment decided upon in one night. This has value in patients with a very high risk of OSA or patients who were previously diagnosed with OSA and need a new diagnostic study to get a new machine ( Figs. 8.6 and 8.7 ).
