Abdominal bloating or air in the stomach is a common complaint of many CPAP users. Though it does not affect every single user, it still affects many and often becomes one of the major reasons for stopping CPAP therapy.
Difference Between Aerophagia and Gastric Insufflation
Bloating from CPAP use is mainly caused not by any digestive gas but by room air that is forced into the stomach through LES (Lower Esophageal Sphincter). Just like digestive gases, this air also goes into vents and intestines.
The LES is essentially a group of muscles situated at the lower portion of the esophagus, where it joins the stomach. Proper LES closure results in stomach contents and air being unable to travel backward into the esophagus from the stomach and stay in their rightful place.
With regards to CPAP use, the term generally used is aerophagia, which is very different from bloating. Aerophagia essentially means swallowing air which can happen when one eats very fast, chews gum or cries uncontrollably. One of the normal functions of LES is swallowing and swallowing of air is part of this process. However, when room air is forced into the stomach through LES, it is known as Gastric Insufflation, which is not a normal function of LES and should be treated medically.
Importance of Gastric Insufflation
Aerophagia is essentially not given enough importance by the medical community and is considered more of a nuisance, a process which can be easily controlled. Aerophagia rarely causes any serious injury to a human being. Gastric insufflation, on the other hand, is a serious medical issue and doctors often relate it to anesthesiology where leakage of the gas from the mask forces it through the stomach.
Gastric insufflation is considered serious medical condition as it can result in colon being perforated which would lead to the contents of colon getting into the abdominal cavity, which can cause serious infection. Survival of a person depends on whether the person has got a serious or mild infection. It has been estimated that more than 37% of the patients who had a serious infection due to perforated colon usually succumbed to their illness while those with mild infection generally lived through to tell their story.
This high rate of fatalities has resulted in the medical fraternity taking the gastric insufflation condition very seriously. Though there are studies which link gastric insufflation and CPAP, it is mostly in the realm of anesthesiology and some studies about paramedics using lung inflation bags.
Gastric insufflation can result in severe abdominal pain mainly on account of intestines having kinks which can block the digestive matters and gas. Until the block in the intestine is removed, the person would continue to have severe pain. Once enough gas has leaked through, the intestine would start relaxing. This, however, can take a lot of time, hence the need for medical evaluation and follow up action.
The GERD Connection
Gastroesophageal Reflux Disease or GERD can have a link with LES. Patients having GERD (either in the past or currently) tend to have compromised LES. LES which is incompletely closed can result in stomach contents (acidic in nature) to backflow into the esophagus. This can result in LES unable to stop the air from Bi-PAP or CPAP machine from entering into the stomach.
Though there is no definitive link between using CPAP and GERD, it is worth mentioning that sustained episodes of GERD can cause permanent damage to LES. Treatment of GERD using medications can help in healing the LES which can result in LES functioning better, leading to reduced instances of abdominal bloating.
People can also have something called “Silent GERD” of “Silent Reflux” which does not cause any known symptoms of reflux. Backflow of pepsin (digestive enzymes and stomach acid) can result in severe damage to esophagus as well as other organs. Since it is widely misunderstood and misdiagnosed, silent GERD has assumed epidemic proportions.
Both GERD and silent GERD essentially damages the LES and treatment for the same can help in LES performing better.
CPAP and Gastric Insufflation
Sleep technicians and sleep apnea patients try various tricks in the trade to ensure that patients have very minimum discomfort during the use of CPAP. The most common thing in this regard is lowering the threshold level of the CPAP machine. If pressure settings are maintained below the threshold limits, the chances of patients not having gastric insufflation is high.
The threshold limit is however linked to each individual and what is suitable for one patient might not be effective for another. For example, if a person keeps his fixed CPAP machine setting at 10, he might end up becoming heavily inflated and have severe pain in the abdominal area. This might not be case with another user, who would feel 10 is very low and might raise the setting.
If a person using fixed CPAP feels like he is bloated and starts feeling severe pain or any other discomfort in the stomach area since using the CPAP, he should immediately bring it to the notice of his MD as well as his sleep doctor. If the person is using CPAP, the sleep doctor can consider switching him to APAP. APAP helps in automatically adjusting the pressure required for keeping the upper airways open depending upon the constant changes during the nighttime ( temperature drop, turning to sides while sleeping etc.)
Will APAP Work For Me?
APAP has a broad pressure range (typically in the 4-20 range) and therefore requires correct pressure settings (high and low limits) to be set in the machine. When the limits are not set properly, the effectiveness of the treatment would be impacted. A generally agreed range among APAP users is 6-8, though some might prefer 10 or even 4.
Several studies have shown that there is not much difference between APAP and CPAP systems and what ultimately tilts the user towards a particular system is the cost and the preference of the machine.
Though a broad pressure range needs correct pressure setting, what the broad range does is it allows the user to test settings to determine the level at which the user can set LES threshold. Keeping the pressure below the threshold has been revealed in studies to control gastric insufflation, provided the LES is working as well as it should.
If the user finds the initial setting is working fine for him, then he can maintain that setting and not tinker with it. However, if the pressure setting is not effective enough, then a re-look at the pressure numbers would be necessary. If the user has the software and the SD card then pressure numbers (over a sustained period of time) and time for the following should be looked at:
The peak reached and the time spent at the peak. If a person is spending more than usual time, then it is not necessarily a high. The high attained here is essentially the time spent on waiting for the apneic event to clear. On the other hand, if the peak is reached below the maximum pressure settings, then the user has enough room to reduce the pressure setting.
Lowest setting reached and the time spent in that setting is important. If too much time is spent on the lowest setting than the user can reduce the setting even further depending upon his comfort level. If the time spent is less than, the pressure setting can be increased.
Typically, setting below 5 makes people feel as if they are gasping for air, hence they set the limit between 6 and 8. Ultimately, the comfort level is of prime importance and what may be an ideal point for a person might be very uncomfortable level for another.
The 90% Debate
Whenever any discussion happens with regards to CPAP pressures, the 90% number shoots into prominence. So what is this 90%? The term 90% refers to the percentage of time spent at a certain number on the CPAP machine. In other words, a user spends 10% of the time above the desired number. This is calculated by noting the time and pressure (lowest to peak) and finding a point where 90% of time and pressure are reported.
Some people recommend setting the low pressure at 90% number so that the pressure range can be narrowed for a more quick response. Many sleep studies have reported an increased number of events compared to those during treatment when the setting is set at lowest level, thereby indicating treatment just prevented events and did not clear them. Higher constant pressure results in the splint keeping the airway open and as a result, lesser events being reported and lower events lead to lower AHI.
Certain users, on the other hand do not take 90% as the gold standard. They take the average pressure and set the threshold limit. This can help them in setting a limit even lower than the desired level, which may prove effective.
Many people consider having 0 AHI as the ultimate achievement. Though 0 AHI is most desirable, there are many skeptics in this regard, the simple reason being even normal people without OSA can also have events like snoring which can be a result of some physical deformity or some infection. It should never mean the patient should spend the entire life on CPAP and masks.
One has to also keep in mind the fact that the tools for determining an event are not perfect and there can be false positives also. A classic example in this case is that of a person, who is prone to shallow breathing compared to others, without having any symptoms of apneas, being diagnosed as having hypopneas and another set of studies on same person revealing him to be perfectly alright.[/h2]