The most common cause is bowel ischemia.
Decreased blood flow to the bowel causes damage to the mucosal barrier, as well as over-distension of the bowel loops and proliferation of gas-forming bacteria. This results in the migration of gas from the bowel lumen into the mesenteric veins, which then flows to the portal system . For this reason, pneumatosis intestinalis is sometimes concurrent in these cases.
When HPVG is associated with bowel ischemia, there is usually transmural necrosis and a high mortality rate (85 percent) . There have been case reports describing pneumatosis intestinalis and HPVG after CPR. The pathophysiology is thought to be due to bowel ischemia resulting from poor mesenteric perfusion during CPR. This may be exacerbated by high doses of epinephrine during CPR, causing severe vasoconstriction .
Another proposed mechanism is over-distension of the stomach during bag-mask ventilation, resulting in mucosal tears and translocation of intraluminal air . Lien et al. found that HPVG was more likely in older patients, unwitnessed arrest, prolonged resuscitation, and also in patients who received more epinephrine . These patients were also less likely to have return of spontaneous circulation, survival to hospital admission, and survival to hospital discharge.