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I am a writer and want to understand a concept so that I can portray elements of injury realistically.

There are areas of the body (such as within the GI tract or urinary tract) where an internal hemorrhage would be able to exit the body (mouth, anus, urethra, etc). This happens in bleeding ulcers, diverticular bleeding, bleeding from kidneys, etc.

However, there are other body areas (such as the chest cavity, abdominal cavity) where there is no natural "outlet" for a hemorrhage to exit. Therefore, in the case of massive internal hemorrhages within those cavities, it seems an enormous amount of pressure would build up. Is the pressure ever sufficient to erupt through the skin or another body orifice? If not, what happens to the blood as it builds up?

  • What has your research revealed? – Carey Gregory Apr 20 '19 at 4:38
  • This is actually a first step (well, second step after using Google searches) because I'm far from a medical professional (mechanical engineering). I'm trying to treat a disease semi-realistically for an RPG I'm running and was hoping for some resources that can at least point me in the right direction for future research. My initial inkling is that it is not possible, that it would fill the chest cavity and the pressure would equalize long before it generated enough pressure to come through the skin. But I'm not well-versed in the tissue strength or partitions that could hold it in. – Sawyer Apr 20 '19 at 4:44
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    Welcome @Sawyer, I checked your profile to see where you were coming from since it seemed like a q someone would ask from Writing Worldbuilding or RPGs. Site guidelines ask that you provide some background and foundation to your questions here. It's not intended as the primary but to answer more professional level questions. I will rewrite it so it can be answered if you're okay with that? – DoctorWhom Apr 20 '19 at 4:46
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    I'm going to be interested to see this. – Carey Gregory Apr 20 '19 at 4:55
  • Absolutely. That edit looks perfect to provide a clearer scope to the question and achieve better answers. And if an answer proves helpful to a professional at some point, all the better. – Sawyer Apr 20 '19 at 4:57
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It is very unlikely that the skin would rupture due to internal bleeding.

Adults have about 5.5 liters of blood inside the circulatory system (arteries/veins/heart/pulmonary circulation) or "intravascular space." When about 40% of blood is lost from the intravascular space (so about 2 liters), the circulatory system collapses, and you die.

Clinical Review: Hemorrhagic Shock (PubMed, 2004):

Intrathoracic injuries, especially to the lung, heart, or the great vessels, can result in the loss of several liters of blood into the thorax without external evidence of hemorrhage. Intra-abdominal injuries to solid organs (spleen and liver) and great vessels (ruptured aneurysm, penetrating injury to intra-abdominal vessels) can cause rapid loss of the entire blood volume into the abdomen.

From these examples you can see that internal bleeding does not break the skin.

During deep breathing, your chest volume can increase by 5 liters and nothing breaks. When gas builds in your intestine, the volume of your abdomen can increase by more than 5 liters, which results in obvious abdominal distension, and the skin does not break.

Let's say that a systolic (upper) arterial blood pressure in a healthy adult is about 120 mm Hg. When an artery breaks and the blood escapes into the chest or abdominal cavity, it instantly loses most of the pressure. If the blood accumulates in a cavity and the pressure within it rises to 120 mm Hg, the blood will no longer escape from the arteries and the pressure in a cavity will no longer increase. But the pressure in the chest or abdominal cavity is very unlikely to increase so much just from few liters of blood, because these cavities are quite expandable, mostly due to the diaphragm muscle that can move up or down a lot. I don't know exact pressures in internal bleeding, but, in one case, removal of 4.5 liters of fluid in a patient with ascites, decreased intraabdominal pressure by only 15 mm Hg (from 45 to 30 mm Hg) (ajemjournal.com).

Another comparison: Average see-level atmospheric pressure is 760 mm Hg.

In compartment syndrome (due to bleeding or muscle swelling), the pressure in a limb can increase to as high as 240 mm Hg, but I have never read this would result in skin rupture. Google search for "compartment syndrome" "skin rupture" also does not give any meaningful results.

Somewhat injured skin could break due to a hematoma buildup beneath it, but this is probably not what you are asking.

What happens with the blood in the chest or abdominal cavity? It is slowly decomposed and reabsorbed within weeks/months. Some internal scars (adhesions) may develop as a complication.

  • I think this answer is missing the simplest explanation, which is that blood pressure even in extreme circumstances isn't going to go over 200 mmHg (and especially not while bleeding out internally). The only tissue that would ever be at risk of rupture is tissue that cannot handle that pressure. "Enormous" pressure can't really build up in compartment syndrome, it will never be as high as what is normally experienced inside the arteries, but that's kind of the problem, because if you equalize pressure inside and outside an artery you cut off the flow. – Bryan Krause Apr 20 '19 at 15:10
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    I didn't think explaining pressures would be convincing. Stomach, gallbladder, intestine and pericardium can all rupture and they are all seemingly stronger than the skin. The simplest explanation (backed up by doctors' experience) is that the body cavities are elastic enough to hold several liters of blood without skin rupture. – Jan Apr 20 '19 at 15:26
  • Actually, I find pressures a more compelling explanation. – Carey Gregory Apr 20 '19 at 22:14
  • I have now mentioned some pressures. – Jan Apr 23 '19 at 11:16
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    Great answer! Compartment syndrome occurs only in specific regions where the fascia lining the compartment lacks the flexibility to expand, unlike the abdomen and chest can expand. I've drained up to12L of ascites fluid out of the abdominal cavity, basically double the intravascular blood volume, and while the patient's abdomen prior to paracentesis was certainly tense and distended it was not near rupturing. He felt like it was going to, but the elasticity is impressive. – DoctorWhom Apr 24 '19 at 6:03

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