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Simply stated, Gastric Distention, is "air in the stomach." A question that is asked of every class, when discussing this subject is, "Has anyone ever experienced gastric distention?" Because the reality is that everyone, at one point or another, has had the experience to some degree. Recall for a moment the last big meal that you had, and that "bloated" feeling that, as you walked away from the table, resulted in the loudest burp you have ever heard. That was, to a minor extent, some gastric distention.
This "condition," called gastric distention is "created" by emergency care providers through the use of an improper ventilation technique, during rescue breathing or CPR.
At the distal end of the esophagus is the lower esophageal sphincter (LES), an area of high pressure which occupies the distal 2-3 centimeters of the esophagus. During the swallowing process, muscle action conducts solid and liquid particles down the esophagus, through the area of high pressure and into the stomach. Once there, that area of high pressure keeps stomach contents in the stomach.
When a rescuer attempts to ventilate a patient, but has failed to position the head correctly, and the opening to the trachea is blocked by the anatomy, the rescuer will continue to increase the pressure of his/her effort (thinking that the lungs are not compliant.) Once the pressure developed by the rescuer exceeds the pressure in the LES, an air bolus enters the stomach and gastric distention begins. A single bolus of air is not going to cause problems, but it is a cumulative process, and after several repetitions the patient begins to look "pregnant," because of all the air in the stomach.
If the position of the patient's head is correct, but the rescuer attempts to ventilate the patient too quickly, the resistance to the flow of air in the trachea causes a pressure increase in the oropharynx. When the pressure caused by the rescuer is greater than that in the LES, a small portion of the air enters the stomach. Again, this single bolus of air is not a problem. If, however, the rescuer continues to use an inappropriate ventilation technique, the additional boluses of air will combine to create gastric distention.
If the position is correct, the rate of ventilation is appropriate, but the amount of air is greater than the size of the lungs, the additional air will increase the pressure in the oropharynx and when the pressure exceeds that in the LES, air enters the stomach.
Now, we can understand the first two ventilation technique errors (improper head position and excessive ventilation rate,) what the heck, these rescuers are excited, but the last error (too much air) is hard for us to understand. You see, we believe that when the lungs are full, the attentive rescuer (excited or not) will realize it and stop blowing. But all too often, we've seen the "error" is the case and the attentive "end point" is the exception. After some careful scrutiny and discussion, we believe that we have found the answer. It seems that instructors everywhere are telling students everywhere that the lungs need to be filled until the anterior chest wall is seen moving. Well, listen to us for a minute, while we explain why we disagree with the concept that the rescuer has to "see" chest wall movement in order to be sure that the lungs are filled.
We start by explaining inspiration and why the chest wall moves at all.
A question. Does the chest wall move during inspiration because the lungs are filling with air? Or, do the lungs fill with air because the chest wall moves? .............☺............ Had enough time to think? ............. Hopefully, you came to the conclusion the the lungs fill with air because the chest wall moves. Muscles in the shoulders move the superior aspect of the lungs upward, intercostal muscles move the anterior aspect of the lungs forward and the diaphragm moves the inferior aspect of the lungs downward. This muscle action causes a negative pressure inside the lungs. It creates a pressure on the exterior surface of each alveolus that is lower than atmospheric pressure. Consequently air is "sucked" into the alveolus. Bear with us while we attempt to explain just how inefficient this process is. We're certain that you've had the opportunity to blow up a balloon. Normally, one would hold the neck of the balloon and blow into the small opening to inflate the body of the balloon. This time, however, we would like you to imagine turning the balloon around, placing the body of the balloon in your mouth and attempting to suck the balloon into your mouth while holding the neck of the balloon and the small opening outside your mouth (Please don't try this, just imagine it.) If your imagination is as active as ours, then you will have no problem picturing the balloon "inflating" inside your mouth. You should also have no problem imagining just how difficult it would be to actually inflate a balloon using this technique (utilizing negative pressure to cause air to flow.) This negative pressure technique is, however, the only mechanism that the body has for "getting" air into the lungs. And the body accomplishes this inflation (inspiration) by changing the chest geometry (as explained above) and causing that negative pressure inside the lungs. Knowing how inefficient this technique is, we believe that the body, at times, exaggerates the chest movement in order to insure that the lungs inflate as intended. Positive pressure ventilation, where air is actually forced into the lungs is a very effective inflation technique, and in reality, the rescuer does not necessarily have to see a lot of chest movement in order to be able to insure that the lungs are full of air. Imagine, again, that you have two brown paper bags (the kind, into which, mothers pack lunch for their school children.) Take a soda straw and place one end of the straw into one of the two bags. Place it so the end of the straw (inside the bag) is located in the center of the bag. Once accomplished, tape the bag to the straw, then crumple the bag around the straw. Place this straw/bag combination, with the "crumpled" bag into the center of the second bag, and tape the second bag to the same straw (The resulting "structure" is a crumpled bag inside a "square" bag with a soda straw that inflates the inner bag.) Now blow air into the straw. At some point when the inside bag is completely inflated, the outside bag will move. Do you agree with us that, the outside bag moves only if the inside bag is full or nearly full? And that there doesn't have to be a whole heck of a lot of movement to be sure that the inside bag is full or nearly full? Well, the "outside bag" is the chest wall, and the inside bag is the alveolus, and the chest movement necessary to insure that the alveolus is full doesn't have to be any greater than what was just seen in these bags. If the rescuer is intent on recreating the amount of chest movement that a breathing individual displays, there is a very good possibility that the rescuer will attempt to blow too much air into the lungs and subsequently cause gastric distention.
So. Why all the excitement about gastric distention? It is, after all, only air in the stomach.
Well, let's return to that big meal from earlier. This time instead of walking away from the table, we would like you to lay down on the floor, right next to your chair, on your back, and wait for that "loud burp." We'll ask you to employ your imagination one more time, here, and imagine just how this "burp" is going to play out. Because, this time, it probably will not be the loudest burp that you've ever heard, but more likely will be an event that will "remind" you just how good the meal tasted. This time, the stomach content will be laying up against the lower esophageal sphincter and the pressure in the stomach will force the stomach content back into the esophagus and up into your mouth. And this, with just a little bit of air in the stomach. Let's move back to our patient, who has enough air in his/her stomach to actually look pregnant. In addition to the fact that all that air will interfere with the effectiveness of chest compressions, there should be no doubt that our patient, with all this gastric distention, will definitely expel stomach content. The only question is how violently the event will occur. It could be as gentle as regurgitation (like a glass of soda, filled too quickly, that overflows it's brim,) or it could be as violent as projectile vomit (no explanation necessary.) The degree of "violence" is dictated only by the amount of gastric distention. In either case, the rescuer is instructed to sweep out the mouth, remove as much of the vomit as possible and continue ventilating. If you don't mind, we would like to take a few seconds to think about what was actually in the vomit. (Yuk!) Stomach content (partially digested food) and all the "juices" that the stomach uses to start the digestive process. One of the major "players" in that lineup of "juices" is Hydrochloric Acid. And so, after sweeping the mouth and removing as much vomit as possible, there will still be a film of "juices" left on the inside of the mouth. As mentioned, the rescuer has been instructed to continue ventilating and when the next ventilation takes place, microscopic droplets of hydrochloric acid will be blown (aspirated) into the patient's lungs. Did you ever have one of those bubble pipes, as a child? You know, the one that had three or four bowls on top, and when you blew the bubbles, it would create a whole "mountain" of connected bubbles (20 or 30 bubbles at a time.) Well, lung tissue is really as delicate as those bubbles. If someone were to throw a hand full of sand at those bubbles, the bubbles would burst and disappear almost instantly. If hydrochloric acid is aspirated into the lungs, human lung tissue will react much the same way as all those bubbles, and a whole section of the lungs could be destroyed in a matter of seconds. The FIX? Avoid the gastric distention. Be aware of what causes it and avoid the causes.
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