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Polycythemia and Hyperviscosity. Kirsten E. Crowley, MD June, 2005. Definitions. Polycythemia is increased total RBC mass Central venous hematocrit > 65% Above 65% blood viscosity rises exponentially

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Polycythemia and hyperviscosity l.jpg

Polycythemia and Hyperviscosity

Kirsten E. Crowley, MD

June, 2005

Definitions l.jpg

  • 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

Incidence l.jpg

  • 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)

Pathophysiology l.jpg

  • 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

What affects hyperviscosity l.jpg
What affects hyperviscosity?

  • 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

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Conditions that alter incidence

  • 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

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Perinatal processes

  • 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)

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  • 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

  • Clinical presentation l.jpg
    Clinical presentation

    • 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

    Diagnosis l.jpg

    • Central venous hematocrit > 65%

    • ALWAYS draw a central venous sample if the capillary hematocrit is > 65%

      • Warmed capillary hematrocrit > 65% only suggestive of polycythemia

    Management l.jpg

    • 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

    Management12 l.jpg

    • 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

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    Other labs to check

    • 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

    Prognosis l.jpg

    • 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