“Blowing Up” the CPAP Belly Myth

 

I started training in pediatrics in the early 90’s. Back then, an infant born less than 1500 grams had a very high chance of experiencing an endotracheal tube (ETT) in the delivery room.

My colleagues and I had lots of intubation practice those days, even as pediatric residents. We would have NICU infants to intubate each day because they developed respiratory failure or self-extubated.

The colossal shift to non-invasive respiratory support over the last few decades (and embracing the concept of “less is more”) has done our collective preterm infants a huge favor. It is now much less common that infants die from consequences of immature lung disease, although they may still suffer and deal with a protracted period of respiratory support from chronic lung disease (which needs a better name because CLD is not a winning favorite amongst parents).

Quality improvement science

Each time we seek to implement better neonatal care strategies, we also need to consider if we have inadvertently caused harm somewhere else from this change.

Considered as balancing measures, these metrics are just as important as the improvements we see. We have been humbled in the past by implementations in neonatology where we bulldozed forward with treatments with abandon, only to pick up the pieces many years later (remember postnatal corticosteroids?).

As such, I have been growing increasingly concerned that our zeal for noninvasive modes of respiratory support has resulted in some unintended consequences. One such concern is something the literature and our NICU colloquialism has termed “CPAP belly”.1

Why CPAP belly happens

The noninvasive movement has led to quite prolonged periods of noninvasive positive pressure exposure for preterm infants.

The problem with noninvasive positive pressure is that there is not one, but two primary internal pathways for gas to flow: the trachea and the esophagus. Gas generally finds its way down the path of least resistance. For example, if the mouth is open, that is where the air will flow out and circumvent the internal routes. That’s why many of us favor using a chin strap or some other means to keep the mouth shut.

Once the mouth is shut, however, and if the lungs are well aerated and compliant, gas will find itself traveling to the lung. But when there is lung disease or when lung disease is progressively getting worse, lung compliance decreases and the esophagus becomes far more attractive for gas to travel down.

While the top half of the esophagus maintains basal tone with both voluntary and involuntary muscles, the placement of an enteral feeding tube provides an unwanted wedge to the closed esophagus. That enables air to travel down, and also gastric contents to travel up, as seen with gastroesophageal reflux.

The entry of gas into the stomach may at first seem innocuous, since we have an enteral feeding tube in practically all of these infants, and this should make gastric gas readily accessible. Unfortunately, that is not to be the case.

How many times have you seen a chest or abdominal radiograph where there is a large, gas-filled stomach with lots of gas in the rest of the intestine… and yet there is clearly a well-placed enteral feeding tube sitting in the stomach? How can this be? Why doesn’t the air come out of the stomach through the enteral tube sitting there, even with frequent venting? The answer, which generally stumps our housestaff for many minutes, can be deciphered by examining the three-dimensional orientation of the stomach.

Despite having several open ports at the end of the enteral feeding tube, air trapped in the stomach often does not exit. Remember that the stomach is not completely dry and empty. Therefore, the placement of an enteral feeding tube in the stomach falls through gravity and sinks to the bottom of the stomach in the midst of gastric content and tissue opposed to the ports of the tube.

On an anterior-posterior radiograph, the tube appears to be in the gas-filled stomach, but is actually behind the gas in whatever fluid is in the stomach. This frequently prevents passive exhausting of air from the stomach, even when enough high pressure inflates the stomach to fill half of the abdomen. The small lumen and length of enteral feeding tube also adds further airway resistance too.

Clinical implications

Is CPAP belly a clinical problem?

The medical literature is silent in identifying this as a problem. Seeing a baby blow up their belly with gas is a routine sight in the NICU, and I worry that we have normalized the condition.

What is wrong with an inflated belly? I have witnessed a handful of infants who have had to undergo laparotomy shortly after an extubation to CPAP or noninvasive positive pressure ventilation (NIPPV). In some cases, we found spontaneous intestinal perforations (SIP), and in other cases the bowel was obstructed with inspissated meconium that may or may not have caused bowel perforation.

The timing of these surgical events shortly after extubation may not be coincidental, and may corroborate the concern that air in the intestine could be dangerous in the face of poor dysmotility or partial obstruction from such meconium plugs. Furthermore, it is well recognized that distended bowel can lead to disruption of the gut mucosal barrier, allowing for bacterial translocation into the blood stream. No one has really looked carefully at the possibilities of sepsis in relationship to CPAP belly, since it seems many discount the seriousness of it.

Most of us have the experience that it takes very little bowel distension to restrict the lungs’ capacity to expand in a preterm infant. When the diaphragm gets pushed up the lung readily gets restricted in volume in the confined chest.

The further growth and clinical implementation of NIPPV has introduced additional, routine spikes of higher positive pressure that may divert even more gas into the stomach. I can think of no reason to believe we will move away from noninvasive ventilation anytime soon, although the artificial womb certainly has taken a leap this year.2

The trapping of gas in the intestines once it exits from the stomach remains mostly a silent problem. The consequences of poor evacuation of intestinal gas is an unclear but present danger. Creative solutions are required to improve our ability to keep the gas out. In the meantime, here are other suggestions:

1. Optimize PEEP and lung compliance since that will permit the path of least resistance for gas into the lung
2. Feed the gut early and help move the “poo poo train” below so an alternate route of gas exhaust is available
3. Support vigilance in nursing observation and gastric suctioning when distension occurs, especially during transitions in respiratory support
4. Take timely radiographs to evaluate observed marked distension when they occur

Most of us have personally felt the discomfort of bloating or overeating. Experiencing a distended stomach and gut is uncomfortable and stressful. For the preterm infant, however, this bloating might just be more dangerous than we have previously thought.

It may be time to say goodbye to the jolly old CPAP belly.

 

REFERENCES

1. Jaile JC, Levin T, Wung JT, Abramson SJ, Ruzal-Shapiro C, Berdon WE. Benign gaseous distension of the bowel in premature infants treated with nasal continuous airway pressure: a study of contributing factors. AJR Am J Roentgenol. 1992 Jan;158(1):125-7. PubMed PMID: 1727337.
2. Partridge EA, Davey MG, Hornick MA, McGovern PE, Mejaddam AY, Vrecenak JD, Mesas-Burgos C, Olive A, Caskey RC, Weiland TR, Han J, Schupper AJ, Connelly JT, Dysart KC, Rychik J, Hedrick HL, Peranteau WH, Flake AW. An extra-uterine system to physiologically support the extreme premature lamb. Nat Commun. 2017 Apr 25;8:15112. doi: 10.1038/ncomms15112. PubMed PMID: 28440792; PubMed Central PMCID: PMC5414058.