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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

Polycythemia and Hyperviscosity

Kirsten E. Crowley, MD

June, 2005

definitions
Definitions
  • 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
Incidence
  • 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
Pathophysiology
  • 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
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
conditions that alter incidence
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
perinatal processes
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)
hypertransfusion
Hypertransfusion
  • 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
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
Diagnosis
  • 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
Management
  • 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
Management
  • 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
other labs to check
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
Prognosis
  • 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