A hemoperitoneum is a potentially life threatening situation. The peritoneal or abdominal cavity is a potentially large space that could contain a significant amount of blood. If a large amount of blood is lost into this space, the abdominal wall musculature is stretched and abdominal distension will be noted. Abdominal distension also may cause discomfort and pain, leading to increased agitation and stress. The rapid expansion of the abdomen may also cause pressure on the diaphragm, and thus, a decreased ability to breath comfortably.
Rapid blood loss into the abdomen will also lead to a decrease in blood pressure and tissue perfusion. This may lead to shock. As continued blood is lost, the decrease in circulating red blood cells may lead to acute (sudden) anemia. Pale mucus membranes are commonly observed. If veterinary care is not immediately available, rapid blood loss may lead to death. A slower blood loss is more common and will allow for more time to seek veterinary care.
Chronic (long standing) or intermittent blood loss generally occurs more slowly, and more subtle clinical signs might be present. If the blood loss is slow, the body can reabsorb (auto transfuse) the free blood in the abdomen. Thus, animals may only have a small amount of blood present in the abdominal cavity. These animals may not present as an emergency, but they still may have a serious underling disease process. Making the diagnosis of a hemoperitoneum is critical in establishing an underling cause.
If the animal has normal clotting parameters the bleeding into the abdomen will, many times, stop on it's own. Blood clots form that stop the bleeding. Sometimes, an animal will collapse due to the acute blood loss, and then slowly recover due to clot formation, and the body's own compensatory mechanisms. These animals will appear pale and weak initially, but with time, slowly become stronger and their mucus membranes will again become pink. Owners may describe intermitted episodes of weakness followed by spontaneous recovery. Blood clots can, however, be dislodged especially with increased movement or manipulations. If blood clots are dislodged, the bleeding may start again. In many cases of hemoperitoneum due to abdominal trauma, the bleeding will stop on its own.
There are several main causes of a hemoperitoneum. Probably the most common cause is trauma. A lacerated blood vessel within the abdomen or internal organ trauma may lead to rapid or slow bleeding depending on the amount of organ or tissue damage. Outdoor animals are at significantly greater risk then indoor animals. Younger animals are more likely to be injured as well. Trauma. The most common traumatic injury causing a hemoperitoneum occurs when a car has hit an animal. Severe abdominal trauma may cause a rapid death if the bleeding is significant. Most of the time, bleeding occurs more slowly and there is time to seek emergency care. The spleen and liver are common internal organs that may be traumatized, and cause a hemoperitoneum. Less commonly, the bladder or kidneys may bleed into the abdomen, but this is generally also associated with an uroabdomen (urine within the peritoneal cavity). The bleeding may be mild or severe, but most of the time will stop without intervention. Other cause of trauma include gun and knife wounds.
In young animals with a hemoperitoneum and no history of trauma, a coagulopathy (bleeding disorder) should be suspected. In these animals, the bleeding usually does not stop on its own, unless vitamin K and other appropriate therapy is administered.
In older animals with a hemoperitoneum and no history of trauma, a bleeding tumor within the abdomen is often the cause. Bleeding tumors may cause a rapid blood loss or be chronic, having intermittent smaller bleeding events.
Specific causes of hemoperitoneum include:
Tumors. Tumors in the abdomen may erode a blood vessel or simply rupture causing an acute bleed. Tumors located on the peritoneal surface of the abdomen, or more commonly associated with abdominal organs, may cause bleeding into the abdomen. The most common tumor to cause intra-abdominal bleeding is a hemangiosarcoma (a tumor of blood vessels). These tumors are aggressive and malignant. They are commonly found on the spleen or liver. Golden retrievers and German shepherd dogs are two breeds at increased risk of getting this tumor. A hemangioma is the benign form, but it is not as commonly seen. Hemangiosarcoma is a very common tumor in dogs.
Hematomas. Hematomas are formed by broken blood vessels that cause blood to accumulate in a tissue, organ or space. They are a common cause of hemoperitoneum, and usually are associated with the spleen. They may be caused by previous trauma, or more commonly nodular regeneration (excessive production of splenic tissue). Hematomas may be quite large and are indistinguishable from hemangiosarcomas at surgery.
Coagulopathies. Rodenticide poisoning with products containing anticoagulants is a very common cause of bleeding disorders in animals. The bleeding may be exclusively within the abdomen, or may involve other sites (e.g. under the skin). Products containing the following active ingredients may cause a hemoperitoneum: warfarin, fumarin, chlorophacinone, diphacinone, pindone, bromadiolone, or brodaficoum.