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Polycythemia

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About polycythemia and hyperviscosity

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Polycythemia

  1. 1.  Polycythemia is increased total RBC mass • Central venous hematocrit > 65%  Above 65% blood viscosity rises exponentially  Polycythemic hyperviscosity is increased viscosity of the blood resulting from increased numbers of RBCs • Not all polycythemic infants have symptoms of hyperviscosity
  2. 2.  Polycythemia occurs in 2-4% of newborns • Half of these are symptomatic  Hyperviscosity occurs in 25% of infants with hematocrit 60-64% • Hyperviscosity without polycythmia occurs in 1% (nonpolycythemic hyperviscosity)
  3. 3.  Clinical signs result from regional effects of hyperviscosity and from the formation of microthrombi • Tissue hypoxia • Acidosis • Hypoglycemia  Organs affected: CNS, kidneys, adrenals, cardiopulmonary system, GI tract
  4. 4.  Hematocrit • Increased hct is the most important single factor • Results from increase in circulating RBCs or decreased plasma volume (dehydration)  Plasma viscosity • Higher plasma proteins = increased viscosity  Especially fibrinogen (typically low in neonates) • Not usually an issue in neonates  RBC aggregation • Occurs in areas of low blood flow = venous microcirculation • Not a large factor in neonates  Deformability of RBC membrane: usually normal
  5. 5.  Altitude: increased RBC mass  Neonatal age • Physiologic increase in hematocrit due to fluid shifts away from intravascular compartment with maximum at 2-4 hours of age  Obstetric factors: delayed cord clamping or “stripping” of the umbilical cord  High-risk delivery, especially if precipitous
  6. 6.  Enhanced fetal erythropoiesis usually related to fetal hypoxia • Placental insufficiency  Maternal hypertension, abruption, post-dates, IUGR, maternal smoking • Endocrine disorders: due to increased oxygen consumption  IDM (>40% incidence), congenital thyrotoxicosis, CAH, Beckwith-Wiedemann syndrome (hyperinsulinism)
  7. 7.  Delayed cord clamping  Placental vessels contain 1/3 of the fetal blood volume, half of which will be returned within 1 minute  Gravity: positioning below the placenta will increase placental transfusion  Meds: oxytocin can increase contractions and thus transfusion  Decreased in c-section b/c no contractions  Twin-twin transfusion  Maternal-fetal transfusion  Intrapartum asphyxia  Enhances net umbilical flow toward the infant, while acidosis increases capillary leak leading to reduced plasma volume
  8. 8.  Symptoms are non-specific!  CNS: lethargy, hyperirritability, proximal muscle hypotonia, vasomotor instability, vomiting, seizures, cerebral infarction (rare)  Cardiopulmonary: respiratory distress, tachycardia, CHF, pulmonary hypertension  GI: feeding intolerance, sometimes NEC  GU: oliguria, ARF, renal vein thrombosis, priapism  Metabolic: hypo-glycemia/-calcemia/- magnesemia  Heme: hyperbili, thrombocytopenia  Skin: ruddiness
  9. 9.  Central venous hematocrit > 65%  ALWAYS draw a central venous sample if the capillary hematocrit is > 65% • Warmed capillary hematrocrit > 65% only suggestive of polycythemia
  10. 10.  Asymptomatic infants • Expectant observation unless central venous hematocrit >75% (consider partial exchange transfusion) • Can do a trial of rehydration over 6-8 hr if dehydrated  Usually at > 48 hours of age and weight loss > 8-10%  Give 130-150 ml/kg/d • Check central hematocrit q6 hours  Normal peak is at 2-4 hours of age for acute polycythemia
  11. 11.  Symptomatic infants with central hct > 65% • Partial exchange transfusion is advisable but debatable • For exchange can use normal saline, Plasmanate, 5% albumin, or FFP • Volume exchanged =  (Weight (kg) x blood volume) x (hct - desired hct) / hct  Blood volume is 80 ml/kg • Exchange can be done via UVC that is not in the liver, low UAC, or PIV
  12. 12.  Serum glucose • Hypoglycemia is common with polycythemia  Serum bilirubin • Increased bili due to increased RBC turnover  Serum sodium, BUN, urine specific gravity • Usually high if baby is deyhdrated  Blood gas to rule-out inadequate oxygenation as cause of symptoms  Platelets, as thyrombocytopenia can be present  Serum calcium b/c hypocalcemia can be seen
  13. 13.  Increased risk of GI disorders and NEC with partial exchange transfusion (PET)  Older trials show decreased neurologic complications from hyperviscosity with PET, but newer trials show no real benefit • PET is controversial!  Infants with asymptomatic polycythemia have an increased risk for neurologic sequelae • Normocythemic controls with the same perinatal history have a similarly increased risk

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