Secondary polycythemia in children

May 29, 2018 15:45 | Disease Treatment
In secondary polycythemia, the total volume of circulating erythrocytes is increased secondary to any known cause. In pediatric practice, the most common cause is certainly congenital blue heart defects, accompanied by a discharge of blood from right to left. Other causes of chronic reduction in arterial oxygen saturation with oxygen, including high altitude and chronic lung diseases, also lead to polycythemia. It is assumed that the pathogenetic mechanism is the stimulation of erythropoietin due to anoxia.

Recently, Slitton and Lee published an article on this topic. A number of authors emphasized that in all patients with polycythemia it is necessary to investigate pulmonary function.

Congenital blue heart defects

In newborns with severe congenital heart defects, there is no normal postnatal decline in hemoglobin, but there is a tendency for relative anemia, beginning at 3 and 4 months and later. The appointment of treatment with iron leads to an increase in hematocrit up to 75% or more, and the symptoms sometimes become more severe. The increase in hematocrit with blue congenital heart defects is accompanied by a progressive and inconsistently large increase in the mass of circulating red blood cells, according to the following formula: the mass of red blood cells per 1 kg of body weight = 26 + 0.056.

When the volume of circulating red blood cells increases, the total volume of blood increases. The increase in blood volume is beneficial in two respects: a) the ability of the blood to carry oxygen increases;b) the cardiac output of the heart rises.

With any given hematocrit, the minute volume of the heart is greater with hypervolemia than with normovolemia. However, these benefits lose their importance due to the increasing viscosity of the blood as the hematocrit rises. Contras and co-authors have shown that with a hematocrit above 60% its further, at least a slight increase, causes a sharp increase in viscosity. Thus, with a hematocrit greater than 70%, the fluidity of blood in small blood vessels becomes critical. Above this level, hypervolemia loses its favorable value due to increased viscosity. In view of this, the relationship between the degree of polycythemia and the operational mortality among patients during the correction of the tetralogy of Fallot becomes understandable.

Creation of system-pulmonary anastomosis before radical correction, successfully reducing hemoglobin to below 18 g%, significantly reduces the risk of surgery.

If, with blue congenital heart disease, an attempt is made to reduce the hematocrit by phlebotomy or erythrophoresis, it is important to maintain hypervolemia by the exchange infusion of an appropriate volume of plasma or 5% albumin. Rosenthal and co-authors showed that an acute decrease in the volume of red blood cells without a significant change in blood volume leads to a decrease in peripheral vascular resistance, an increase in the stroke volume of the heart, an increase in systemic blood flow, and an increase in oxygen transport in severe cases. In the opinion of these authors, these changes are explained by a decrease: the viscosity of the blood and the associated "shearing force".If the blood volume were reduced, as is the case with simple phlebotomy, then the same beneficial effect could not be expected.

Disturbed oxygen supply to tissues due to hemoglobinopathy with a modified oxygen dissociation curve and increased oxygen affinity can also lead to polycythemia through tissue anemia( renal).Polycithemia cases among patients with hemoglobinopathies, although rare, indicate the need to examine the families of all patients polycythemia and hemoglobin analysis in case of suspected family erythrocytosis.

The first anomalous hemoglobin in which this bond was found was the hemoglobin Chesapeake, named after the name of the bay in the US, where Columbus first landed.

Tumors and kidney diseases

A number of tumors in some patients are combined with polycythemia. In cerebellar hemangioblastoma, the polycythemia rate is less than 10%.With tumors of the kidneys, the appearance of polycythemia is easier to understand. It was shown the formation of erythropoietin in a Wilms tumor with an increase in the level of this hormone in the blood and urine. In the literature it is indicated that polycythemia may be caused by benign renal diseases, including polycystosis and unilateral hydronephrosis. Usually the level of hemoglobin normalizes after the elimination of a local tumor or pathological process.

Endogenous and exogenous endocrine effects can also increase the total volume of red blood cells. These include the chronic use of testosterone or related steroid, the introduction of somatotropic hormone to experimental animals, adrenal adrenal glands with primary aldosteronism, congenital adrenal hyperplasia and pheochromocytoma. The clinical impression of the presence of polycythaemia in Cushing's syndrome is almost always deceptive. In fact, polycythaemia was detected only in one of the 36 patients described recently. With congenital adrenal hyperplasia, polycythemia develops in the neonatal period.

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