Management of the Polycythaemic Newborn

• Background
• Causes of polycythaemia
• Clinical features
• Management
• Parital exchange transfusion

Background:

Neonatal Polycythaemia affects 2-5% of newborns. It is defined as a haematocrit/Haemoglobin concentration > two standard deviation above the normal value for gestational and postnatal age (1). A term baby is considered to be polycythaemia if haematocrit from a peripheral venous sample is above >65% or Haemoglobin >22 g/dL (2-5).

• The haematocrit typically peaks at 4-6 hours after birth and the declines over the next 12-18 hours so that by 24 hours of age it is equivalent to that at birth.7 the postnatal age at which newborns are screened is very relevant as the incidence may increase up to 20% when screened at two hours whereas may be as low as 2% when screened at 12-18 hours postnatally. (6)

• Capillary samples have been proven to over-estimate PCV and the gold standard for diagnosis is arterial or umbilical venous sample. In the clinical setting a free flowing sample from a large vein is sufficient for diagnostic criteria (7).

Most of the clinical significance of polycythaemia is related to associated increase in blood viscosity (3 - Medscape). The relationship between haematocrit and viscosity is linear below haematocrit levels of 60% whereas progressive increases over 65% show a logarithmic relationship (8,9). This means even a small increase in haematocrit after that leads to exponential increase in the viscosity. Although several factors determine blood viscosity like blood pH, plasma protein concentration, Platelet and WBC volume as well as endothelial factors. In the newborn the principle determinant of blood viscosity is the haematocrit.(7) Hyperviscosity occurs in about 47% of infants with polycythaemia(10).

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Causes of Polycythaemia:

(Table 1)

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Clinical Features:

Most of the newborns with polycythaemia (74-90%) are asymptomatic (11,12). In symptomatic newborns, hyperviscosity, decrease in tissue perfusion, and metabolic complications such as hypoglycaemia and hypocalcaemia are responsible for most clinical signs (13).
 In severely symptomatic newborns with polycythaemia, central nervous system disorders are commonly seen (14) which is attributed to both physiological reduction in cerebral blood flow and hypoglycaemia. Of the metabolic problems, the most commonly encountered is  hypoglycaemia (12-40%) and Hypocalcaemia is the next most common metabolic derangement and is found in 1-11% of neonates with polycythaemia.  At least one third of infants with polycythaemia develop Hyperbilirubinemia(3).
 Although polycythaemia and hyperviscosity have been suggested responsible for the pathogenesis of necrotizing enterocolitis in term and near-term newborns (15,16), partial exchange transfusion itself, performed to lower the hematocrit, has been reported to cause necrotizing enterocolitis(17).
Renal problems encountered in polycythaemia are decrease in glomerular filtration rate, oliguria, haematuria, proteinuria and renal vein thrombosis (16,39).
Thrombocytopenia, low antithrombin III levels, and more rarely development of thrombosis are haematological problems encountered in polycythaemia [9,11]. As the density of the erythrocytes increases they accumulate in the center of blood flow, and thrombocytes, which are lighter, migrate to periphery of the vascular wall (thrombocyte margination). This causes the number of thrombocytes to be counted lower than the actual count (relative thrombocytopenia) (14).

Table 2

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Management:

Current Recommendations:

• At present there is no evidence to support the treatment of asymptomatic babies (or those babies with only mild symptoms) with partial exchange transfusion (PET) regardless of their PCV(17) hence there is no indication to check a PCV in an asymptomatic baby who is plethoric without any risk factors.
• There is no evidence of long term benefit from partial exchange transfusion in polycythaemia infants, and the incidence of gastrointestinal injury is increased (e.g. NEC). The long term outcome is more likely to be related to the underlying cause of polycythaemia or associated conditions like hypoglycaemia etc (17, 18, 19).
• Babies with significant neurological symptoms or progressive symptoms can be treated with PET (19).
• Crystalloid solutions are as effective as colloid solutions for partial exchange transfusion, with no risk of transmission of blood-borne diseases and anaphylaxis. The use of crystalloid should be the standard practice for partial exchange transfusion (20,21)unless indicated otherwise.

Please refer to Flow Chart 1.

Flow Chart 1:

Laboratory tests to consider in symptomatic babies with polycythaemia:

• Serum Glucose and Calcium levels (as most common metabolic derangements).
• Serum Bilirubin: likely to have hyperbilirubinaemia due to increased red cell mass
• FBC - to monitor Haemoglobin, haematocrit and sometimes they can have thrombocytopenia.
• Electrolytes and kidney function tests especially in oliguric/anuric babies.

Imaging:

• Consider cranial USS, MRI, Renal USS and Doppler’s if clinically indicated.

If in doubt, please discuss with your senior.

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Partial Exchange Transfusion:

This should always be discussed with the consultant.
This is a procedure to correct polycythaemia without hypovolaemia. The desired PCV is 50-55% and to achieve this 20ml/kg of blood is exchanged for normal saline.

Prior to procedure:

• Informed written consent to be taken from parents as procedure is with significant risks.
• Place baby nil by mouth, insert NGT and empty the stomach and put on free drainage.
• It is important to stabilise baby hence to treat hypoxia, hypoglycaemia, acidosis etc before commencing the procedure
• Cannulate umbilical vein, ensure tip of line is not in the liver (can also be done via peripheral arterial line/peripheral vein if no umbilical lines).
• Record baseline observations before commencing the procedure.
• Prescribe 0.9% Sodium chloride and calculate how much blood to be withdrawn in total and divide it by 4 (this will be equivalent to 20 mls/kg divided by 4).
• Investigations
• FBC, U+E LFT, Calcium, glucose, gas

Procedure:     

• Full aseptic precautions to be taken.
• Procedure should be in ICU, baby to be on continuous monitoring including temperature and with BP monitoring every 15 minutes.
• Set infusion of normal Saline 20ml/kg running over 1 hour via peripheral cannula.
• In same hour remove 4 aliquots of 5ml/kg of blood. (every 15 minutes, each cycle to take at least 5 minutes)

Post- procedure care:

• Continue to monitor for at least 2 hours.
• Check FBC, U&Es, Calcium, blood gas, blood sugar at the end of procedure.
• Repeat FBC after 4 hours
• Restart feeds 4 hours after exchange unless clinical concerns raised. (i.e abdominal distension/discolouration, abnormal NG aspirate, abnormal stools.)
• Ensure clear documentation of procedure.

Complications

• Hypothermia-ensure fluids are warmed
• Respiratory distress.
• Fluid overload/fluid loss
• Electrolyte disturbance
• Infection
• Line complications- haemorrhage, embolism, infection etc
• Necrotising Enterocolitis.

(Please refer to local guidelines for Exchange transfusion for more details)