returning from the lungs with the deoxygenated blood returning from systemic circulation. This decreased saturation is sensed by the kidneys, resulting in a compensatory increase in erythropoietin production and an increased production of red blood cells in an attempt to increase oxygen delivery. As the bone marrow increases erythropoiesis, the systemic reticulocyte count and the risk for hyperviscosity syndrome increases. Reticulocytes are less efficient at carrying oxygen as mature red cells, and they are less deformable, causing impaired transit through capillary beds. This contributes to the death of pulmonary capillary beds. A person with Eisenmenger syndrome is paradoxically subject to the possibility of both uncontrolled bleeding due to damaged capillaries and high pressure, as well as spontaneous clots due to hyperviscosity and stasis of blood. Diagnosis Diagnosis of Eisenmenger syndrome is typically conducted via transthoracic echocardiography, which facilitates the identification and evaluation of shunts, anatomical defects, and ventricular function. Following diagnosis, or in some cases of inconclusive diagnosis, a cardiac catheter may be used to both confirm the diagnosis and to assess the patient's pulmonary arterial pressure, an important predictive value for prognosis and treatment. Treatment If the inciting defect in the heart is identified before it causes significant pulmonary hypertension, it can normally be repaired through surgery, preventing the disease. After pulmonary hypertension is sufficient to reverse the blood flow through the defect, however, the maladaptation is considered irreversible, and a heart–lung transplant or a lung transplant with repair of the heart is the only curative option. Transplantation is the final therapeutic option and only for patients with poor prognosis and quality of life. Timing and appropriateness of transplantation remain difficult decisions. 5-year and 10-year survival ranges between 70% and 80%, 50% and 70%, 30% and 50%, respectively. Since the average life expectancy of patients after lung transplantation is as low as 30% at 5 years, patients with reasonable functional status related to Eisenmenger syndrome have improved survival with conservative medical care compared with transplantation. Various medicines and therapies for pulmonary hypertension are under investigation for treatment of the symptoms. Air filters for intravenous lines are recommended for persons with Eisenmenger syndrome who have been hospitalized to reduce the risk of accidental introduction of air into the veins due to the increased risk for paradoxical air embolism. If air is introduced into the veins and travels through the ventricular septal defect into the arterial circulation, a stroke may occur.