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Pulse oximetry screening in the newborn

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Background

Congenital heart defects are the most common group of congenital malformations, with a reported incidence of between 4 and 10 per thousand live-born infants(1, 2). The term congenital heart disease (CHD) encompasses a variety of lesions with a wide range of clinical importance, ranging from those with no functional or clinical significance to potentially life-threatening lesions. If critical defects are not detected early, they can result in cardiovascular compromise resulting in death or significant long-term effects on neurodevelopment. Critical CHD refers to heart defects that require intervention or lead to death in the first 28 days after birth. Timely recognition of these conditions allows the possibility of early intervention that may influence the natural history of the condition and subsequent outcome.

Current screening strategies to detect CHD in New Zealand include antenatal ultrasound ('anatomy scan') and physical examination of the newborn. Both these investigations have only modest sensitivity. Nearly 20% of infants born in New Zealand with a critical heart defect are diagnosed after initial discharge from hospital. Pulse oximetry screening will detect hypoxaemic infants and has been shown to improve the early diagnosis of CHD in newborn infants.

Pulse oximetry screening does not replace the newborn clinical assessment for congenital heart disease. Auscultating for murmurs, detection of clinically visible cyanosis and palpation of pulses (femoral pulses in particular) remain an important part of the newborn and 6 week examination. Clinical concerns warrant an immediate referral to the paediatric team.

Eligibility criteria

  • All newborn infants with a gestational age ≥ 35 weeks
  • Screening should be performed between 2 and 24 hours of age

Contraindications

  • Parental refusal
  • Infants for palliative care
  • Infants with an antenatal diagnosis of congenital heart disease
  • Unwell infants admitted to the newborn unit

Special considerations

Infants that are < 35 weeks' gestation at birth will generally be admitted to a newborn unit where they will be monitored as part of standard care provided to premature infants. On the rare occasion that such an infant is admitted to the postnatal ward, pulse oximetry screening should be performed.

Unwell infants ≥ 35 weeks' gestational age admitted to a newborn unit are often haemodynamically unstable and will have routine on-going monitoring of oxygen saturations. It is the responsibility of the attending paediatric team to ensure that all infants have reached saturation targets prior to discharge from the unit. It should be documented in the patient's discharge letter that saturations ≥ 95% have been achieved.

Echocardiograms are routinely performed on infants with Trisomy 21 and some other chromosomal anomalies. If a previously undiagnosed cardiac anomaly is identified, the findings should be recorded on the 'Hypoxaemia report'.

If screening did not take place in the first 24 hours in an otherwise healthy infant, the test should be performed at the earliest possible opportunity.

Screening before 2 hours of age is associated with higher false-positive rates. Early screening can therefore potentially delay discharge or transfer from hospital. Infants should remain in hospital until they have reached saturations of ≥ 95%.

Nearly 4% of New Zealand's babies are born at home. Midwives will usually stay with a mum and baby for 2 to 3 hours following a home birth and will return for a follow-up visit within the next 24 hours. Pulse oximetry screening should ideally be performed prior to the midwife's departure, but may have to be deferred until the return visit if an oximeter is not available at the time of the birth.

Screening pathway

  • Obtain consent from parents or caregivers to perform the screening test.Foot
  • Ensure that the infant is calm and warm. Movement and crying can affect test accuracy. The test may be performed while the baby is feeding or sleeping.
  • Obtain a saturation reading from one foot. 
  • Document the results on the 'Screening record'. 
  • Refer to the screening algorithm to establish if further action is required.

What to do if there is an infant that does not reach oxygen saturation targets 

  • Refer the infant for a same-day paediatric assessment. 
  • A thorough clinical examination is indicated.
  • Further investigations should be performed at the discretion of the paediatric team. 
  • Consideration should be given to respiratory, infective and metabolic conditions. Refer to the 'diagnostic approach to the hypoxaemic newborn infant'. 
  • An echocardiogram should only be requested via the children's heart specialist after consultation with the responsible neonatologist/paediatrician.
  • The paediatric team should complete the 'Hypoxaemia report' if an infant failed to reach saturation targets.

Differential diagnosis

  • Be aware that pulse oximetry screening has a false-positive rate of 0.14%(3) and so the baby may not have CHD. 
  • Screening before 2 hours of age is associated with higher false-positive rates.
  • Approximately two thirds of positive tests will not be attributed to congenital heart disease but may reveal alternative diagnoses.

Documentation 

  • Screening algorithm
  • Screening record
    • to be completed by midwives or nurses performing pulse oximetry screening on well infants with a gestational age ≥ 35 weeks'.
  • Hypoxaemia report
    • to be completed by paediatric/neonatal health care providers if an infant is diagnosed with CHD in the first few days of life, or
    • any infant undergoing assessment and investigations as a result of low oxygen saturations that were detected by pulse oximetry screening. 
  • Late presentation report
    • to be completed by cardiology health care providers if an infant presents to the service in the first year of life with previously undiagnosed major CHD.

Information

Diagnostic approach to the hypoxaemic newborn infant

Definitions

Hypoxaemia is a failure of normal blood oxygenation and is defined as low partial pressure of oxygen in the arterial blood (PaO2). Causes of hypoxaemia include: hypoventilation; low inspired oxygen; right to left shunting, and ventilation-perfusion mismatch.

Hypoxia is a failure of normal tissue oxygenation.

SpO2 refers to the oxygen saturation of arterial blood as measured by a pulse oximeter.

Background

Pulse oximetry is a biomarker for the detection of hypoxaemia, which would not necessarily produce visible cyanosis, in apparently healthy newborns. It has been shown to improve the early diagnosis of congenital heart disease (CHD) in newborn infants(4, 5), as a degree of hypoxaemia is present in the majority of infants with CHD. Pulse oximetry screening will also detect other significant pathologies which produce hypoxaemia that may otherwise have gone undetected prior to discharge, for instance: sepsis; respiratory compromise, and metabolic disease. It has been reported that approximately two thirds of positive pulse oximetry screening results will be related to conditions other than CHD(6). Pulse oximetry has a false-positive rate of 0.14% (95% CI 0.06 - 0.33)(3). We have adopted an early screening strategy that can potentiate the diagnosis of CHD prior to cardiovascular compromise and collapse; however, earlier screening is associated with higher false-positive rates.

The hypoxaemic newborn

An infant who has failed to reach oxygen saturation targets during pulse oximetry screening requires a paediatric assessment and, potentially, further investigations. A low SpO2 reading can be normal in newborns adjusting to the extra-uterine environment.

Consideration should be given to the following diagnoses when assessing a hypoxaemic newborn infant:

  1. Transient tachypnoea of the newborn (TTN)
    TTN is a self-limiting disease commonly seen in newborn infants. It is the result of delayed clearance of fetal lung fluid. 

  2. Persistent pulmonary hypertension (PPHN)
    PPHN is failure of normal circulatory transition after birth and is characterised by elevated pulmonary vascular resistance, right-to-left extrapulmonary shunting and severe hypoxaemia. Severe PPHN occurs in 2 per 1000 live born term infants and some degree of pulmonary hypertension complicates the course of approximately 10% of newborn infants with respiratory failure(7). Right-to-left shunting will produce a gradient between pre- and post-ductal saturations (pre-ductal saturations will be higher). 
  3. Respiratory distress syndrome (RDS)
    RDS is a result of inadequate surfactant production and release. The incidence of surfactant deficiency is inversely related to gestational age. 

  4. Pneumonia
    Pneumonia can be congenital, intrapartum or nosocomial. The onset of congenital pneumonia will usually be within 6 h after birth and intrapartum acquired pneumonia within 48 h after birth. 

  5. Meconium aspiration syndrome (MAS)
  6. Pulmonary air leak
    Pneumothoraces occur in up to 1% of otherwise healthy term infants(8). It is more common in surfactant deficiency, MAS, pneumonia and pulmonary hypoplasia.

  7. Sepsis
  8. Congenital heart disease
    These infants are often asymptomatic in the first 24-48 hours when the ductus arteriosus is still patent. Hypoxaemia may be the only sign suggestive of underlying cardiac disease.

  9. Other less common causes for hypoxaemia include: pulmonary hypoplasia; trachea-oesophageal fistula; obstruction of the upper respiratory tract; metabolic disorders, and seizures.

Investigations

Investigations should be guided by the history and findings on clinical examination. Consideration can be given to the following investigations:

  1. Chest X-ray
  2. Blood gas
  3. Full blood count, CRP, blood culture
  4. Electrolytes and glucose
  5. Lumbar puncture
  6. Echocardiogram
  7. ECG

The majority of hypoxaemic infants will have an underlying respiratory cause. Chest X-rays are inexpensive and easy to obtain and should therefore be considered as a first line investigation in hypoxaemic infants.

Blood tests and CSF can be particularly useful to identify infective or metabolic causes for hypoxaemia.

Echocardiography is indicated if congenital heart disease is suspected or if no other cause for hypoxaemia can be identified. This test has to be performed by a skilled operator in consultation with the children's heart specialist. This may result in referral to a regional centre with echocardiography services.

References

  1. Prudhoe S, Abu-Harb M, Richmond S, Wren C. Neonatal screening for critical cardiovascular anomalies using pulse oximetry. Arch Dis Child Fetal Neonatal Ed. 2013;98(4):F346-50.
  2. Ewer AK. Pulse oximetry screening for critical congenital heart defects in newborn infants: should it be routine? Arch Dis Child Fetal Neonatal Ed. 2014;99(1):F93-5.
  3. Thangaratinam S, Brown K, Zamora J, Khan KS, Ewer AK. Pulse oximetry screening for critical congenital heart defects in asymptomatic newborn babies: a systematic review and meta-analysis. Lancet. 2012;379(9835):2459-64.
  4. Ewer AK. Evidence for CCHD screening and its practical application using pulse oximetry. Early Hum Dev. 2014;90 Suppl 2:S19-21.
  5. de-Wahl Granelli A, Wennergren M, Sandberg K, Mellander M, Bejlum C, Inganas L, et al. Impact of pulse oximetry screening on the detection of duct dependent congenital heart disease: a Swedish prospective screening study in 39,821 newborns. BMJ. 2009;338:a3037.
  6. Bhola K, Kluckow M, Evans N. Post-implementation review of pulse oximetry screening of well newborns in an Australian tertiary maternity hospital. J Paediatr Child Health. 2014;50(11):920-5.
  7. Konduri GG, Solimano A, Sokol GM, Singer J, Ehrenkranz RA, Singhal N, et al. A randomized trial of early versus standard inhaled nitric oxide therapy in term and near-term newborn infants with hypoxic respiratory failure. Pediatrics. 2004;113(3 Pt 1):559-64.
  8. Shaireen H, Rabi Y, Metcalfe A, Kamaluddeen M, Amin H, Akierman A, et al. Impact of oxygen concentration on time to resolution of spontaneous pneumothorax in term infants: a population based cohort study. BMC Pediatr. 2014;14:208.

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Document Control

  • Date last published: 19 February 2016
  • Document type: Clinical Guideline
  • Services responsible: Neonatology, Paediatric Cardiology
  • Author(s): Elza Cloete, Tom Gentles, Jane Alsweiler, Frank Bloomfield
  • Owner: Elza Cloete
  • Review frequency: 2 years

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