[Pulmonary hypertension in pediatric heart surgery]

Congenital heart disease can increase or decrease pulmonary blood flow, pulmonary vascular resistance (PVR) or pulmonary artery pressure (PAP). PAP is the product of PVR and pulmonary minute volume (Qp), such that pulmonary hypertension (PHT) may develop as a result of an increase in either PVR or Qp or both. Given that the pulmonary vascular bed is a low pressure system with high flow, any increase in resistance would generate PHT. The normal value of PVR is 2 Woods units (mm Hg/l/min). Increased PAP is due to hypoxic lesions of the endothelium, which release proteolytic enzymes that alter the balance of metabolites of arachidonic acid, regulators of pulmonary vasomotor tone. Hypoxia and acidosis cause intense pulmonary vasoconstriction (hypoxic vasoconstrictor reflex). An increase of PVR is due to a combination of vasoconstrictive processes and remodeling, with hypertrophy of the pulmonary artery. Structural lesions are related to hypertrophy of the endothelium, the transformation of fibroblasts to myocytes and the decrease of the alveolar/arteriolar ratio with the formation of new vessels.PHT may be primary or secondary to another disease. Primary PHT is a rare genetic disease. The most common secondary forms of PHT in pediatrics are due to persistence of neonatal anatomy (neonatal PHT), to heart diseases with left-right shunt (CIV, DAP, etc.), to diseases of the pulmonary parenchyma (interstitial viral infection, mucoviscidosis), and complications of heart surgery. All congenital heart diseases can lead to PHT if not treated promptly. Clinical signs of PHT are highly non-specific: dyspnea, fatigue, syncopes, exercise intolerance, precordialgia, cyanosis and edema. The best approaches to diagnosis and prognosis are echocardiography and cardiac catheterization with vasodilators. Anesthetics that do not alter PVR should be used in such patients, who are sensitive to changes in pulmonary ventilation, to changes in cardiac output and to anesthetics. The treatment of PHT during intra and postoperative pediatric surgery is based on the use of high inspirated oxygen concentration (100%), an adequate sedation and the use of vasodilators (prostaglandin I2, nitric oxide, sodium nitroprusiate and milrinone).