Mouth Leak and CPAP

The following information is provided by: Fisher & Paykel Healthcare

By Dr. Vanessa MB Jordan Ph.D., Research Scientist, Fisher & Paykel Healthcare

Definitions

Mouth Leak: The mouth being partially or fully open during nasal positive pressure ventilation may result in a mouth leak. Instead of air, once it has entered the nares, flowing down into the respiratory tract, a fraction of the air alternatively flows through the verolingual sphincter into the virtual oral cavity and then out through the lips . Thus it does not reach the lungs and does not contribute to ventilation. This air is following the path of least resistance and results in a leak.

Mouth Breathing: Mouth breathing is when air enters through the mouth or nares, flows down through the glottis into the respiratory tract and down into the lungs. Here O2 and CO2 are exchanged and then the air flows back up and exits through the mouth.

Importance of Mouth Leaking

Nasal symptoms, congestion, dry nose and throat, sore throat and bleeding nose, are commonly noted as a side effect when using CPAP. Studies have shown that roughly 68% of CPAP users report having a dry congested nose. These symptoms can be reproduced by mouth breathing during CPAP. Therefore it is probable that the presence of unidirectional airflow caused by either mouth leak or mouth breathing causes these nasal symptoms.

It is considered likely that if someone on positive pressure ventilation is mouth breathing then they are probably mouth leaking. Logically if the mouth is open then some of the air will follow the path of least resistance and exit through the oral cavity. Alternatively, it is quite possible that people mouth leak without mouth breathing.

Previous Studies

Teschler and colleagues when using nocturnal nasal bilevel ventilatory support for respiratory failure had noticed that mouth leak was a major problem. The mouth leak, which appeared to be ever present, caused sleep fragmentation due to irritation and reduction in the effectiveness of the ventilation. Teschler showed that if the leak was abolished the subjects had a decreased arousal index, increased REM sleep and inconsistent changes in slow wave sleep but there was no effect on sleep duration, efficiency or latency.

Another study had some of the subjects involved simulate a mouth leak. It was demonstrated that mouth leaking resulted in increased phasic EMG activity and thus an increase in the level of work that was necessary.

It has also been shown that mouth leak during non-invasive positive pressure ventilation causes oxygen desaturations in individuals with kyphoscholiosis. This change in oxygen saturation resulted in a change in sleep stage 76% of the time, this in turn resulted in oromotor activity which decreased or eliminated the leakage.

Teschler's group have observationally noted that the percentage of mouth leakers in non-invasively ventilated patients maybe 100%. Another group has reported that 84% of children with OSA were mouth breathers and therefore logically would also have a mouth leak during nCPAP.

The percentage of CPAP users that mouth leak/breath is relatively unknown, although it is thought it could be relatively high as indicated above. A question that needs addressing concerns the amount of time during a sleep period that a person has a mouth leak, will nasal problems be caused regardless of time or must a leak be present for a substantial percentage of the sleep time to result in the aforementioned symptoms. Additionally, as mouth leak during positive pressure ventilation appears to cause sleep fragmentation, oxygen desaturation and decreased REM sleep, it would be advantageous to establish any means of minimizing the time a person mouth leaks.