Hemoperitoneum  (also haemoperitoneum, sometimes also hematoperitoneum) is the presence of blood in the peritoneal cavity. The blood accumulates in the space between the inner lining of the abdominal wall and the internal abdominal organs. Hemoperitoneum is generally classified as a surgical emergency; in most cases, urgent laparotomy is needed to identify and control the source of the bleeding. In selected cases, careful observation may be permissible. The abdominal cavity is highly distensible and may easily hold greater than five liters of blood, or more than the entire circulating blood volume for an average-sized individual. Therefore, large-scale or rapid blood loss into the abdomen will reliably induce hemorrhagic shock and, if untreated, may rapidly lead to death. Causes
Causes of hemoperitoneum include:
Penetrating trauma
Blunt trauma, most commonly injuries to solid organs such as the liver and spleen. Vascular accidents, such as rupture of an abdominal aortic aneurysm, iliac aneurysm, or splenic aneurysm. Bleeding due to a ruptured ectopic pregnancy or uterine rupture. Rupture of corpus luteum in some cases. Less commonly, bleeding due to a perforated gastric ulcer. Bleeding due to rupture of an intra-abdominal neoplasm, (e.g., Hepatoblastoma)
Disseminated intravascular coagulation
People on high dose of anticoagulants (blood thinners)
Perforation of the colon

Diagnosis
Hemoperitoneum can be reliably diagnosed with the following examinations:
Focused assessment with sonography for trauma (FAST)
Paracentesis or diagnostic peritoneal lavage
Computed tomography
Diagnostic laparoscopy or exploratory laparotomy

Treatment
Initial management consists of immediate blood transfusion if the patient is in hemorrhagic shock.
There are features of malignant catatonia (posturing, impulsivity, etc.) that are absent from NSM and the lab results are not as consistent in malignant catatonia as they are in NMS. Some experts consider NMS to be a drug-induced condition associated with antipsychotics, particularly, first generation antipsychotics, but it has not been established as a subtype. Therefore, discontinuing antipsychotics and starting benzodiazepines is a treatment for this condition, and similarly it is helpful in catatonia as well. Anti-NMDA receptor encephalitis is an autoimmune disorder characterized by neuropsychiatric features and the presence of IgG antibodies. The presentation of anti-NMDAR encephalitis has been categorized into 5 phases: prodromal phase, psychotic phase, unresponsive phase, hyperkinetic phase, and recovery phase. The psychotic phase progresses into the unresponsive phase characterized by mutism, decreased motor activity, and catatonia. Both Serotonin syndrome and malignant catatonia may present with signs and symptoms of delirium, autonomic instability, hyperthermia, and rigidity. Again, similar to the presentation in NSM. However, patients with Serotonin syndrome have a history of ingestion of serotonergic drugs (Ex: SSRI). These patients will also present with hyperreflexia, myoclonus, nausea, vomiting, and diarrhea. Malignant hyperthermia and malignant catatonia share features of autonomic instability, hyperthermia, and rigidity. However, malignant hyperthermia is a hereditary disorder of skeletal muscle that makes these patients susceptible to exposure to halogenated anesthetics and/or depolarizing muscle relaxants like succinylcholine. Malignant hyperthermia most commonly occurs in the intraoperative or postoperative periods. Other signs and symptoms of malignant hyperthermia include metabolic and respiratory acidosis, hyperkalemia, and cardiac arrhythmias.