The disorder is usually contracted but, in rare cases, it can be inherited. It is typically characterized by an increase in the production of red blood cells erythrocytes. Patients with PV are often symptom-free at the time of diagnosis. At the onset of the disorder, the signs and symptoms tend to be unspecific. A noticeable reddening of the face can give the impression that the affected person is actually very healthy.
When the red blood cell count reaches a critical number, the flowability of the blood decreases leading to restricted blood circulation. This causes a blue coloration of the skin cyanosis. The most common complications are a result of the high viscosity resistance to flow of the blood, which can lead to blood clots thrombosis.
Hyperviscosity is the decrease of blood fluidity, and defined as a viscosity above the 2 standard deviation of the mean. Hyperviscosity syndrome, on the other hand, is a syndrome of circulatory disorder developing secondary to increase in resistance against blood flow [ 9 , 11 ]. Except for the hematocrit level, there are a lot of factors affecting whole blood viscosity.
Leukocytes, platelets, plasma proteins, immunoglobulins and coagulation factors are the other cellular elements which affect the whole blood viscosity. It is not easy to measure viscosity, and Wells-Brookfield viscometer is used with this aim. However most of the neonatal intensive care units do not have this device, and high hematocrit level and the presence of polycythemia-associated symptoms are taken into account as the determinator of hyperviscosity [ 9 , 11 ].
Tissue hypoxia, acidosis and hypoglycemia develop secondarily to regional effects of hyperviscosity. Tissue blood supply and oxygenation are disrupted. Oxygen carrying capacity is determined by the hemoglobin level and blood flow, it is optimal at the normal hematocrit levels, and oxygen transport is decreased at low hematocrit levels as the oxygen binding capacity decreases [ 17 ].
Increase of blood volume, while the hematocrit is the same, increases blood flow and oxygen transport by decreasing peripheral vascular resistance with vasodilatation.
This mechanism constitutes the basis of treatment of polycythemia [ 7 ]. Decreased microcirculation has been deemed responsible for the morbidity associated with polycythemia. Thrombi ocurring in microcirculation may cause symptoms in central nervous system, kidneys, surrenal glands, cardiopulmonary and gastrointestinal systems [ 19 ]. Drew, et al. As a conclusion perfusion and tissue oxygenation are disturbed, plasma glucose concentration decreases, cerebral glucose uptake is disturbed and risk of cerebral morbidity is increased with microthrombi formation as the viscosity increases [ 7 , 17 , 21 ].
In neonatal polycythemia increased destruction of increased erythrocyte mass with a relatively shorter erythrocyte life span primarily contributes to hyperbilirubinemia. Hypervolemia may lead to congestive heart failure, pulmonary edema and cardiopulmonary failure, and hypovolemia may cause hypoxic-ischemic organ injury [ 12 ]. Although the etiology of polycythemia is multifactorial, there are two primary mechanisms: passive erythrocyte transfusion and active increased intrauterine erythropoiesis Table 1 [ 22 ].
Polycythemia secondary to excess erythrocyte transfusion to the fetus Passive polycythemia may occur due to delayed clamping of the cord, acute fetal distress and intrapartum hypoxia, twin-to-twin transfusion syndrome, materno-fetal transfusion and holding the baby below the level of introitus [ 9 , 11 ].
Table 1: Etiology of neonatal polycythemia [ 22 ]. View Table 1. In acute fetal distress and peripartum hypoxia transcapillary leakage of plasma occurs and blood flow from placenta to fetus increases, and all these result in increased plasma volume and erythrocyte mass in the fetus [ 9 ].
Clamping of the umbilical cord later than 3 minutes after delivery of the baby is defined as "delayed cord clamping" [ 11 ]. Carpasso, et al. Therefore, early cord clamping and holding the baby at the level of introitus at the time of delivery could play a role in prevention from polycythemia by minimizing materno-fetal transfusion. On the other hand, however, no statistically significant differences were reported in the hematocrit values of newborns whose umbilical cord was clamped early or late [ 24 ].
Polycythemia secondary to increased intrauterine erythropoiesis active polycythemia is usually observed in cases of placental insufficiency, intrauterine hypoxia and situations associated with the fetus. Maternal hypertension [ 26 ], preeclampsia, maternal diabetes mellitus type 1 diabetes mellitus and gestational diabetes [ 27 ], maternal cyanotic heart disease, intrauterine growth retardation, postmaturity, living at high altitude and maternal smoking are all associated with this mechanism.
Situations associated with fetus may develop secondarily to problems either in fetus or maternal diseases Table 1. There is an increased risk of polycythemia in diseases with a genetic inheritance such as trisomy 18 and trisomy 13 [ 28 ], trisomy 21 [ 29 ], and Beckwith-Wiedemann syndrome.
Congenital hypothyroidsm, neonatal thyrotoxicosis and congenital adrenal hyperplasia are the other causes of polycythemia associated with the fetus [ 9 , 11 ]. Another etiologic classification of polycythemia is the one based on the volume status of plasma: normovolemic, hypervolemic and hypovolemic [ 12 ].
There is an increase in erythrocyte mass while intravascular volume is normal. There is an increase in plasma volume in association with an increased erythrocyte mass. It is usually seen in cases of acute transfusion such as maternofetal transfusion and twin-to-twin transfusion. It is due to the relative increase of erythrocyte mass in comparison to plasma volume.
This situation usually develops due to intravascular dehydration [ 12 ]. In symptomatic newborns polycythemia may affect many organs and systems. Hyperviscosity, decrease of tissue perfusion, and metabolic complications such as hypoglycemia and hypocalcemia are responsible for clinical signs [ 10 , 32 ].
Nonspecific signs and symptoms such as apnea, cyanosis, feeding problems, vomiting, irritability, jitteriness, tremor, lethargy, respiratory distress and seizures may be seen [ 16 ]. The most commonly encountered problems in severely symptomatic newborns with polycythemia are central nervous system disorders [ 11 , 32 , 33 ]. Cardiopulmonary complications Cardiomegaly, increase in pulmonary vascular resistance and decrease in cardiac output with tachycardia and tachypnea may develop [ 32 ].
Although polycythemia and hyperviscosity have been suggested responsible for the pathogenesis of necrotizing enterocolitis in term and near-term newborns [ 34 , 35 ], partial exchange transfusion itself, performed to lower the hematocrit, has been reported to cause necrotizing enterocolitis [ 36 - 38 ].
Renal problems encountered in polycythemia are decrease in glomerular filtration rate, oliguria, hematuria, proteinuria and renal vein thrombosis [ 16 , 39 ]. In addition to cerebral blood flow, glucose carrying capacity also decreases in polycythemia. As a result plasma glucose concentration, especially venous one is lower than normal [ 9 ]. You may find one of our health articles more useful.
NICE has issued rapid update guidelines in relation to many of these. This guidance is changing frequently. Patients with anaemia do not develop cyanosis until the oxygen saturation SaO 2 has fallen to lower levels than for patients with normal haemoglobin levels and patients with polycythaemia develop cyanosis at higher oxygen saturation levels.
Cyanosis can be divided into either central or peripheral [ 1 ]. Unless the cause is already established, episodes of central cyanosis require urgent assessment, especially infants and young children, who require urgent admission. Curr Opin Pediatr. Adeyinka A et al ; Cyanosis. In: StatPearls, When present over the pinna, it disappears with pressure. Peripheral cyanosis is a manifestation of excessive deoxygenation increased oxygen extraction of hemoglobin in peripheral tissues. Normal arterial oxygen saturation SaO 2 is usually observed.
Pseudocyanosis : As opposed to central and peripheral cyanosis, this does not disappear with the application of pressure to the skin. It is a rare phenomenon. Causes: abnormal pigmentation of the skin drugs: chlorpromazine, amiodarone, minocycline; exposure to heavy metals, eg, to silver [argyria] or gold [chrysiasis].
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