Its 3 am and you are called by a midwife on the postnatal ward to review a ‘jittery baby’ with a respiratory rate of 70. The midwife informs you that Alice is a term baby born via Cat 2 LSCS (failure to progress, Apgar 9,9) following an uncomplicated pregnancy (although she does note that mum has admitted to smoking cannabis occasionally during pregnancy). She is currently establishing breastfeeding.
On examination, Alice is settled but does have some mild tremors on handling. They settle on containment and don’t appear to be rhythmic or jerking in nature. She is centrally pink, with a red face and purple hands and feet. All observations, other than the respiratory rate are within normal limits.
You decide its likely Transient Tachypnoea of the Newborn but as part of your assessment, you obtain a capillary blood gas.
The decision is made to give the baby a full top-up of formula feed (with mum’s consent) and to do formal, free-flowing venous bloods in an hour’s time to re-assess, but what is the next step?
The term polycythemia refers to a raised red cell concentration >2 standard deviations above the expected normal values. It can either be defined as a haematocrit from a peripheral venous sample being >65 percent or the haemoglobin is >22 g/dL however the former is more commonly used in clinical settings.
Haematocrit peaks maximally at the mean age of 2.8hrs. Although capillary blood gas samples are a helpful guide to the diagnosis, the sample on which treatment should be based must be from a peripheral venous sample. Studies have shown that the haematocrit from true venous samples (depending on capillary gas sample technique) can be up to 15% lower than the capillary sample.
Most cases of polycythaemia occur in normal healthy infants and may result from a variety of reasons, which can be broadly categorised into:
Increased red cell volume from increased transfusion, causes include:
- Twin to twin transfusion
- Delayed cord clamping*
- Maternal hypertension
Placental insufficiency with increased foetal erythropoiesis secondary to intra-uterine hypoxia. This may occur in association with:
- small for gestational age infants
- post-term infants.
Other causes of polycythaemia include:
- maternal substance use such as smoking
- maternal diabetes
- large for gestational age infant
- chromosomal abnormality (such as Down syndrome).
* A note on delayed cord clamping:
Interestingly, although delayed cord clamping in IUGR babies has been shown to double the likelihood of polycythemia, a recent study found there was no increase in babies with symptomatic polycythemia and nor was there any increase in the need for partial exchange transfusion. Delayed cord clamping as also been found not to have an effect on hyperbilirubinemia.
An increased red cell mass results in an increased blood viscosity and reduced blood flow, impaired tissue oxygenation and a tendency to microthrombus formation. This is exacerbated by hypoxia, acidosis and/or poor perfusion.
Thrombosis may result in:
- renal venous thrombosis
- adrenal insufficiency
- necrotising enterocolitis (NEC)
- cerebral infarction that may affect long-term neurological outcome
Hyperviscosity of blood results in increased resistance to blood flow and decreased oxygen delivery. Viscosity exponentially increases when an infant has polycythemia. In the neonate, this can lead to abnormalities of central nervous system function, hypoglycemia, decreased renal function, cardiorespiratory distress, and coagulation disorders. Hyperviscosity has been reported to be associated with long-term motor and cognitive neurodevelopmental disorders.
Signs and symptoms
The majority of newborns with polycythemia as asymptomatic (74-90%). In symptomatic infants, the hyperviscosity causes a decrease in tissue perfusion and metabolic complications such as hypoglycemia and hypocalcemia. They are responsible for clinical signs and symptoms including:
- feeding problems
- respiratory distress
The most commonly encountered problems in severely symptomatic newborns with polycythemia are central nervous system disorders.
In addition to cerebral blood flow, glucose carrying capacity also decreases in polycythemia. As a result, plasma glucose concentration, especially venous is lower than normal. Hypocalcemia and hyperbilirubinemia may also be seen in polycythemic newborns. The level of calcitonin gene-related peptide (CGRP) has been shown to be high in polycythemic newborns. This peptide regulates vascular tone, stimulates vasodilatation, and leads to hypocalcemia. High levels of CGRP suggest a role in response to polycythemia.
A 2010 cochrane review found there to be:
‘No proven clinically significant short or long‐term benefits of PET (Partial Exchange Transfusion) in polycythemic newborn infants who are clinically well or who have minor symptoms related to hyperviscosity. PET may lead to an increase in the risk of NEC. The data regarding developmental follow‐up are extremely imprecise due to the large number of surviving infants who were not assessed and, therefore, the true risks and benefits of PET are unclear.’
With this in mind, it is broadly accepted that PET should only be undertaken if it is thought to be the primary cause of the symptoms, rather than a byproduct of dehydration from other causes e.g. feeding difficulties or metabolic disorders.
The formal bloods reported as Hb 215 g/L with a Hct of 69% and a repeat gas shows a glucose of 3.2 mmol/L. The midwifery staff report she seems less ‘jittery’ and a plan is made for full formula top-ups and daytime review to ensure resolution of symptoms.
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