Mask Leaks
Introduction to Leak
Air enters the CPAP machine from your room. It is drawn in through a filter, and is blown out in a controlled manner. Air blown out of the CPAP machine eventually leaves the machine - tubing - interface - person system and returns to your room. There are four possible routes by which air is returned to the room:
(1) A defect in the equipment, or equipment defectively assembled. This is always bad, and should be guarded against by frequent inspection, and periodic listening and feeling for extraneous airflow.
(2) Intentional venting. Virtually all commercial CPAP interface systems are designed so that air ALWAYS blows through them. This enables the moisture-laden, oxygen depleted, and carbon dioxide-rich air which you exhale into the interface to be continually "washed out" so that it is not re-inhaled. This venting is part of the interface design, with greater volumes of air being vented at higher pressures. Most manufacturers provide information as to how much leak will occur at various pressure levels. While often referred to as "leak," this normal, intentional venting should not be confused with "unintentional" leak.
(3) Seal leak. Virtually every interface device involves some sort of contact, a "seal," between a plastic "cushion" or "pillow" and the user's skin. Air can easily leak out through these seal contact points, particularly as the user moves around during the course of the night. This is the first type of "unintentional leak" which should ideally be minimized.
(4) Mouth leak - the second type of "unintentional lead" which should ideally be minimized. Since the mouth and the nose are connected in the pharynx, unless a "Full Face Mask" (or other special interfaces which cover both the mouth and the nose) is used, air which enters the nose may leak out of the mouth. This can occur in several different ways (or in combinations) which may more-or-less affect the effectiveness of CPAP, and which may require different strategies for dealing with the leak:
(a) with "mouth breathing," in which unpressurized room air is inhaled - and exhaled - through the mouth,
(b) with "open mouth flow," in which air pressurized air entering through the nose more-or-less continually escapes through an open mouth, or
(c) with "mouth exhalation," in which pressurized CPAP air which is inhaled through the nose is partially or totally exhaled through the mouth.
What Harm Does Leak Do?
There are three mechanisms by which unintentional leak can detract from CPAP therapy. One or more of these mechanisms may be present. None are "all or nothing" phenomenon - the nature, extent and freqeuncy of leak will determine the negative effect - if any - of the leak. It may accurately be stated that, "Leak is a problem only if leak is a problem."
(1) Disruption of Sleep. Leak involves the blowing of air where air "should not" be blowing. This is usually related to seal leak, but may also be applicable to mouth leak. If air is blowing across the face or into the eyes, this is likely to arouse or awaken you from sleep. Blowing air also creates sound, ranging from rushing torrents to "musical" tones when the edges of the plastic cushion vibrate. These sounds too can arouse or awaken you, interfering with sleep.
(2) Drying of the Airway. Mouth leak has the special disadvantage of the leak taking place AFTER the pressurized air is already within the body. While all leak involves additional airflow, mouth leak produces additional airflow within the nose and mouth. This often results in drying of the membranes. If the nasal membranes become dried and irritated, increased resistance to breathing may ensue, with resultant congestion. Drying of the mouth may be uncomfortable, and add to sleep disruption.
(3) Pressure Loss. This problem is sometimes overemphasized and often misunderstood. To understand it properly, a bit of physics needs to be reviewed. In a small, passive, closed, pressurized system (think of a car tire, perhaps), the pressure is everywhere the same. If a "small" leak develops in the system, the pressure drops, though it remains the same everywhere in the tire, regardless of the site of the leak. CPAP is a "small" system, and for all practical purposes the pressure everywhere - in the tubing, in the mask, in your airway - is always instantaneously the same, regardless of where the leak originates. But CPAP is not a "passive" system. The technology works by increasing or decreasing air flow in order to maintain the target pressure the machine is trying to deliver. This is important: CPAP "uses" airflow but CPAP "works" by maintaining airway pressure. Leak is the loss of airflow, but leak does not necessarily result in any loss of pressure. Modern CPAP machines are robust, and can compensate for significant loss of airflow from leaks by increasing their output airflow. In this way they maintain their desired pressure, even in the presence of substantial leak, and regardless of the location of that leak. (Thus a "mouth leak" is not necessarily any more relevant in terms of pressure than is a "seal leak.") However, if the leak is too large, it may overwhelm the machine's ability to compensate and maintain pressure. This is arguably the most severe and important consequence of leak, though its frequency may be exaggerated. It takes a LOT of leak to result in failure of the machine's ability to maintain pressure and/or the ability of the machine's sensors to accurately detect pressure and flow information. When this happens, however, the effectiveness of CPAP therapy can be markedly compromised.
Respironics documentation summarizes the above information nicely: "System leak is a combination of intentional and unintentional air leak. Intentional leak is the expected leak at the exhalation port. Some leak is required to minimize CO2 rebreathing. Unintentional leak occurs around the patient interface. If there is a large increase in the amount of leak .... the patient may need a mask refitting. Leaks that should be fixed include leaks into the eyes, leaks that bother the patient, or leaks that affect pressure stability."
How Do I Know If I'm Leaking?
Unfortunately, we're not always aware of whether or not, or of how significantly, we may be experiencing unintentional leakage. The blowing of air, or the sound created by blowing air, doesn't always awaken us. We may now be aware of, or remember being aware of, a dry mouth caused by mouth leak (particularly if the leak is intermittent).
Fortunately, chances are that if leak is not frequent enough or large enough to cause symptoms, it's probably not significant enough to be of concern. Still, the possibility of an unrecognized large leak, which can interfere with effective therapy, cannot be discounted entirely.
Many CPAP machines provide an audible "Leak Alert" alarm function. If given a choice, and unless there is a particular reason NOT to use it, this option should generally be turned "on."
Many ResMed (S7, S8) machines offer a "Leak Alert" which can be enabled or disabled. "When enabled, leaks > 0.7 L/s for > 20s result in an audible alert and a high leak message in the LCD. Note: when Leak Alert is enabled, SmartStart/Stop is automatically disabled." We will talk more, in a subsequent section, about what these numbers mean. For the present, we might simply note that 0.7 liters per second (equal to 42 liters per minute) is a sizeable airflow. Given that a typical adult breath moves about 500 cc of air (Tidal Volume), and that we might perhaps be taking 10 breaths per minute, the amount of air moved by normal breathing is about 5 liters per minute, or 0.08 liters per second. Thus, the machinery quite reasonably becomes concerned when leakage accounts for over eight times more air movement that is produced by our breathing. Particularly for AutoPAP machines, ResMed notes that "When the leak exceeds this level, the autotitrating algorithm ceases to perform optimally."
Again, simply to keep this number in context (pending more detailed discussion below), ResMed notes that "Generally, a leak rate of more than 0.4 L/s (24 L/min) is associated with patient discomfort, disturbed sleep, and reduced efficacy of treatment."
Many Respironics machines (M-Series) also provide a "Mask Leak Alert" feature: "Mask Leak Alert – This flashing text displays on the Active Display screen if the Mask Alert setting is enabled and the device detects an excessive mask leak. .... If this feature is enabled, then the [ ] symbol flashes on the Active display screen if a significant mask leak is detected, and an audible alert sounds." Unfortunately, available Respironics documentation does not define their criteria for "excessive" or "significant" leak.
What Does My Machine Tell Me About My Leak?
(in progress)
What Does Software Tell Me About My Leak?
(in progress)
What Can (And Should) I Do About Leaking?
(in progress)
Mouth breathing and mouth leaks are closely related, but not necessarily the same thing.
Mouth breathing must occur when the nasal passages are blocked, so the only way for any air to get into the lungs is through the mouth. People with blocked noses breathe through their mouth, not through their nose. The solution to mouth breathing is to use a full face mask. Some effort and time may be required to find the best full face mask, fit it, and adjust to it. Use of nasal irrigation and humidified CPAP, especially with nasal pillows, may open nasal passages that were previously chronically blocked. The person can then learn to breathe through the nose.
Mouth leaks may occur if the person is breathing through their nose, but opens their mouth during sleep. If leakage through the mouth is a persistent problem, CPAP treatment can be rendered completely ineffective. CPAP air detouring out the mouth does nothing to keep the airway open. Either mouth breathing or mouth leakage can also cause feelings of suffocation from apneas still happening and/or just the choking feeling of air rushing out the mouth unexpectedly. The safest solution to mouth leakage is to use a full face mask.
http://www.cpaptalk.com/viewtopic/t23863/Why-dont-more-people-use-a-full-face-mask.html
Other remedies including using a homemade or commercial chinstrap in hopes that the tongue will maintain an airtight seal inside the mouth if the jaw is kept up. Many people find that chinstraps don’t work to prevent mouth leakage.
Another remedy is to use the tongue to maintain an airtight seal inside the mouth. Some people train the tongue by positioning the tip of the tongue behind the upper front teeth or on the roof of the mouth, and let the tongue spread out in back to seal the throat air passage, even if the lips open. Others use a dental splint, custom made by a dentist, or a do-it-yourself mouth guard to help the tongue maintain an airtight seal.
“The safety of taping the mouth shut has not been proven and there are potential risks of regurgitation and aspiration of food and of suffocation.” TS Johnson MD et al, Sleep Apnea – The Phantom of the Night, p. 167. Mouth taping is especially dangerous for anyone who ever gets blocked nasal passages during the night. If air can’t get in through the nose, it needs to get in through the mouth. Mouth taping is also risky in case of a hose disconnect or power outage.
Warning against mouth leakage
Whether you use a nasal mask or nasal pillows (or any other kind of mask except a full face), if air leaks out through your mouth, the PAP therapy will not work. There are two safe options. The first is to learn to keep your mouth closed while sleeping. Since the feel of pressurized air exiting your mouth is an unpleasant sensation, PAP aids in this. Some people position the tongue behind the top teeth and let it spread out in back to cover the throat opening and make a seal so the PAP works. The second option is to use a full face mask. If you are a mouth breather, breathing in through your mouth instead of your nose, a full face mask is required. An alternative practice for mouth leaks, mouth taping or sealing, is understandable but not advisable, and is not safe if your nose gets stuffy at night, you have acid reflux, need to regurgitate; or you have a hose disconnect or lose machine power and need to breathe through your mouth.
See also Mask Leaks Blow onto Partner