Persistent Vagal Activation Caused by a Large Mesenteric Hematoma After Blunt Abdominal Trauma: A Case Report

In patients with trauma, decreased circulating blood volume and pain increase sympathetic nerve activation, which increases the heart rate (HR) and vasoconstriction. When this compensatory mechanism is disrupted, the effects of trauma are more severe. Stimulation via the afferent vagal nerves from the gastrointestinal tract causes vagal activation, inducing a cardioinhibitory response that sometimes causes shock and bradycardia. A 51-year-old man sustained an abdominal injury while playing baseball. His blood pressure was normal; however, examination revealed persistent sinus bradycardia (HR: 38-42 bpm). Focused assessment with sonography for trauma (FAST) examination revealed fluid accumulation in the hepatorenal space, suggesting intraperitoneal hemorrhage, which was subsequently confirmed by contrast-enhanced CT. After arrival at the hospital, the patient's HR suddenly decreased to 32 bpm, and his blood pressure dropped to 58/40 mmHg, consistent with shock. He was diagnosed with a vasovagal reaction and recovered after receiving two doses of atropine. Contrast-enhanced CT revealed a large mesenteric hematoma without extravasation of contrast media. After the CT examination, the patient's HR again suddenly decreased to 36 bpm, and his blood pressure dropped to 83/42 mmHg with peripheral coldness, indicating recurrent shock. After the administration of atropine and continuous dopamine, his vital signs stabilized. A laparotomy revealed that the mesentery of the descending colon was filled with a large hematoma (820 g), with an estimated blood loss of 1100 mL. The descending colon was partially resected. The bradycardia did not recur after surgery. Vagal afferent fibers terminate in the mesentery and monitor tension. In our patient, the mesentery was stretched by a large hematoma, which induced persistent vagal activation and sinus bradycardia. Owing to vagal activation, the compensatory mechanism was not fully functional. Repeated vasovagal reactions combined with blood volume loss can cause shock. Therefore, when a patient presents with persistent bradycardia following trauma, the possibility of a vasovagal reaction should be considered.