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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Cyanotic versus acyanotic congenital heart disease

Paediatrics and child health · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Cyanosed or shocked newborn

Persistent central cyanosis, profound hypoxaemia, weak pulses, acidosis or collapse in the first days of life may reflect duct-dependent pulmonary or systemic flow or inadequate mixing and can deteriorate as the arterial duct constricts.

Action: Call neonatal and paediatric cardiac help and use ABCDE resuscitation. Warm the baby, support ventilation, use right-hand preductal and foot postductal oximetry, obtain blood gas, lactate, glucose and cultures, and treat sepsis when plausible. Arrange urgent echocardiography and network transfer; start titrated alprostadil only through the neonatal duct-dependent-lesion protocol because apnoea and hypotension require airway-ready monitoring.

Overview

Classify congenital heart disease by physiology rather than colour alone, recognise duct-dependent and mixing emergencies, and organise investigation, stabilisation and specialist transfer safely across neonatal and childhood presentations.

Congenital heart disease is present from cardiac development, but symptoms depend on postnatal physiology. The abrupt loss of placental gas exchange, fall in pulmonary vascular resistance and closure of fetal communications can expose lesions at different times.

Left-to-right shunts initially send oxygenated systemic blood back to the lungs. Systemic saturation remains normal, but pulmonary overcirculation and chamber volume loading can cause heart failure as pulmonary resistance falls during the first weeks.

Obstructive acyanotic lesions reduce forward flow. Coarctation or critical aortic stenosis can depend on the arterial duct for systemic perfusion, so shock rather than cyanosis may dominate after discharge.

Right-to-left shunts bypass the lungs or allow desaturated venous blood into the aorta. In tetralogy, right-ventricular outflow obstruction controls shunt direction; worsening obstruction deepens cyanosis.

Practice

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Paediatrics and child healthOriginal SBA

Ductal closure presentation

A 4-day-old who fed normally after birth is now grey, acidotic and oliguric with weak femoral pulses. Saturation is only mildly reduced. Which physiology is most concerning?

Choose one answer, then submit
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NHS congenital heart diseaseUK overview of congenital lesion symptoms, diagnosis and treatment.
  • British Heart Foundation congenital diseaseUK explanation of congenital heart physiology and ongoing care.
  • Resuscitation Council UK paediatric basic life supportCurrent UK recognition and initial resuscitation principles for a critically ill child.
  • NHS England paediatric cardiac servicesNational specialised congenital cardiac network context.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
In transposition, pulmonary and systemic circuits run in parallel. Survival depends on mixing across an atrial communication, VSD or duct until balloon atrial septostomy or definitive surgery can restore effective circulation.

Duct-dependent pulmonary lesions use a patent arterial duct to deliver blood from the aorta to pulmonary arteries. Duct-dependent systemic lesions use it to bypass left-sided obstruction and perfuse the descending aorta.

History includes antenatal diagnosis, gestation, maternal diabetes or infection, neonatal screening, onset relative to feeding and ductal closure, weight gain and syndromic or family features. Ask whether an existing cardiac plan specifies baseline saturation.

Central cyanosis involves the tongue and oral mucosa; peripheral blue hands or feet can occur with cold or low flow. Pulse oximetry confirms hypoxaemia but technical artefact, skin perfusion and haemoglobin species affect interpretation.

A quiet precordium or absent murmur does not reassure. Very low pulmonary flow creates little turbulence, and a large unrestrictive communication may have only a soft sound because pressure is equalised.

Respiratory disease, sepsis, persistent pulmonary hypertension, haemoglobin abnormality, hypoglycaemia and metabolic disease can mimic cardiac cyanosis or shock and may coexist. Parallel assessment and empirical sepsis treatment are often appropriate while anatomy is defined.

Treatment aims to preserve the circulation needed before repair: keep the duct open when necessary, improve mixing, balance pulmonary and systemic flow, correct acidosis and avoid interventions that destabilise vascular resistance.

After intervention, congenital anatomy is not erased. Residual shunts, valve dysfunction, arrhythmia, ventricular failure, pulmonary hypertension, endocarditis and neurodevelopmental needs determine continuing follow-up and transition.

Key points

  • Acyanotic lesions usually create left-to-right shunting or obstruction without systemic desaturation; examples include ASD, VSD, PDA, aortic stenosis and coarctation before shunt reversal.
  • Cyanotic lesions deliver desaturated blood to the systemic circulation through right-to-left shunting, parallel circulations or inadequate mixing; examples include tetralogy, transposition, pulmonary atresia and truncus arteriosus.
  • Colour is an imperfect classifier. Acyanotic shunts can eventually become cyanotic through pulmonary vascular disease, and a critically obstructed newborn may look grey from shock rather than visibly blue.
  • Initial priorities are physiology: oxygenation and ventilation, systemic perfusion, pulmonary blood flow, mixing, ductal dependency and heart failure. Name the lesion only after echocardiographic definition.
  • Measure preductal and postductal saturation, brachial and femoral pulses, four-limb blood pressure when feasible, perfusion, liver size and response to carefully delivered oxygen.
  • Blood gas and lactate quantify acidosis and perfusion but cannot distinguish pulmonary from cardiac disease alone. Hyperoxia response is not a substitute for echocardiography.
  • Urgent paediatric echocardiography is the diagnostic reference test for anatomy, connections, shunt direction, obstruction and ventricular function.
  • Suspected duct-dependent circulation requires immediate cardiac-network discussion and specialist-directed alprostadil. Prepare for apnoea, hypotension, fever and the need for ventilation during infusion and transfer.
  • Do not chase a normal saturation target in a child with a known palliated or mixing circulation; use the child's documented target and assess perfusion and lactate alongside saturation.
  • Long-term care is lesion-specific and may involve observation, catheter intervention, surgery, staged palliation, medicines and lifelong congenital cardiac surveillance.

Aetiology

01

Sporadic cardiac development

Most defects arise through multifactorial disruption of embryonic septation, looping, valves or great-vessel development without a single identifiable cause.

02

Chromosomal and genetic disease

Trisomy 21, Turner syndrome, 22q11 deletion and numerous single-gene conditions carry characteristic lesion patterns and extracardiac needs.

03

Maternal and fetal exposures

Pre-existing diabetes, selected infections, teratogenic medicines, alcohol and fetal haemodynamic conditions increase risk, although association does not prove causation in one child.

04

Prematurity-related persistence

An arterial duct is more likely to remain haemodynamically important in a preterm infant because ductal muscle and oxygen responsiveness are immature.

Pathophysiology

  1. 1
    Left-to-right flow

    A pressure or compliance difference moves oxygenated blood back to pulmonary circulation, producing volume loading without early systemic desaturation.

  2. 2
    Right-to-left flow

    Obstruction or high right-sided pressure directs venous blood across a communication into systemic output, lowering arterial oxygen content.

  3. 3
    Parallel circulation

    When great arteries connect to the wrong ventricles, effective oxygen delivery depends on blood mixing between otherwise separate loops.

  4. 4
    Ductal dependency

    The fetal arterial connection temporarily bypasses critical obstruction; constriction removes pulmonary or systemic flow and precipitates rapid instability.

  5. 5
    Pulmonary vascular transition

    Postnatal resistance falls over weeks, increasing left-to-right shunting and explaining delayed heart-failure symptoms in large communications.

Clinical features and red flags

Cyanotic circulation

Central mucosal blue colour, persistently low saturation, single S2, clubbing later or episodic deeper cyanosis points to systemic desaturation.

Pulmonary overcirculation

Tachypnoea without wheeze, feeding diaphoresis, prolonged feeds, hepatomegaly and poor growth emerge as pulmonary resistance falls.

Systemic outflow obstruction

Weak femoral pulses, upper-lower perfusion difference, acidosis, renal impairment and shock suggest arch or left-heart obstruction.

Ductal timing

Deterioration during days two to seven after initial wellbeing is a key clue because the arterial duct is constricting.

Mixing failure

Severe stable hypoxaemia with limited lung signs in a newborn may reflect transposition with an inadequate atrial communication.

Syndromic context

Dysmorphism, palatal, renal, limb or growth abnormalities can indicate a genetic diagnosis requiring coordinated testing and counselling.

Red flags requiring action

  • Blue or grey tongue and mucosa, persistent low saturation or poor response to oxygen indicates central cyanosis and requires urgent hospital assessment.
  • Shock, weak or absent femoral pulses, metabolic acidosis, oliguria or differential upper- and lower-body perfusion suggests duct-dependent systemic obstruction.
  • Severe hypoxaemia with little respiratory distress, a single second sound or an abnormal cardiac silhouette raises cyanotic congenital heart disease even without a murmur.
  • Tachypnoea, sweating with feeds, hepatomegaly and faltering growth emerging after pulmonary resistance falls suggests a large left-to-right shunt or obstructed pulmonary venous return.
  • A newborn can pass pulse-oximetry screening and still have coarctation or another lesion that is not substantially hypoxaemic before ductal closure.
  • Sudden deeper cyanosis with irritability in tetralogy, or collapse with fever or dehydration in a child with known congenital disease, needs immediate specialist-led resuscitation.

Investigations

  1. 01
    Initial preductal and postductal pulse oximetryFirst step
    Why
    Confirm hypoxaemia and identify differential ductal shunting patterns.
    Interpretation and limitations
    Direction and size of a difference can guide physiology but neither equality nor a normal screen excludes congenital heart disease.
  2. 02
    Blood gas, lactate and glucose
    Why
    Measure ventilation, acid-base disturbance, tissue hypoperfusion and a reversible metabolic contributor.
    Interpretation and limitations
    Metabolic acidosis and rising lactate indicate inadequate oxygen delivery; values support urgency but are not lesion-specific.
  3. 03
    Four-limb pulses and blood pressure
    Why
    Assess systemic output and possible aortic arch obstruction.
    Interpretation and limitations
    Weak femoral pulses or a reproducible arm-leg gradient is concerning, but shock and cuff error can distort measured pressures.
  4. 04
    Twelve-lead ECG
    Why
    Describe rhythm, axis, hypertrophy, conduction and baseline before intervention.
    Interpretation and limitations
    Age-specific normal patterns are essential; ECG supports but rarely defines neonatal anatomy.
  5. 05
    Chest radiograph
    Why
    Assess pulmonary blood flow, oedema, lung disease and cardiac silhouette when the child is stable enough.
    Interpretation and limitations
    Patterns such as reduced vascularity or cardiomegaly can guide the differential but must not delay echocardiography or transfer.
  6. 06
    Urgent paediatric echocardiography
    Why
    Establish connections, obstruction, mixing, shunt direction, ductal flow and ventricular function.
    Interpretation and limitations
    This anatomical and physiological study directs prostaglandin, septostomy, catheter or surgical planning and is the diagnostic reference assessment.

Differential diagnosis

01

Respiratory parenchymal disease

Grunting, asymmetric breath sounds and radiographic lung disease support a pulmonary cause, although cardiac disease can also create oedema.

02

Persistent pulmonary hypertension

High pulmonary resistance drives extrapulmonary right-to-left shunting after birth and requires echocardiographic distinction from structural disease.

03

Sepsis and shock

Temperature instability, poor perfusion, respiratory distress and acidosis overlap substantially, so cultures and timely antibiotics may be needed alongside cardiac evaluation.

04

Haemoglobin disorder

Methaemoglobinaemia causes saturation that responds poorly to oxygen despite a relatively normal arterial oxygen tension and no structural explanation.

05

Metabolic decompensation

Hypoglycaemia, inborn errors and adrenal or electrolyte emergencies can produce tachypnoea, shock and acidosis without primary congenital cardiac anatomy.

Management

01ResuscitateTreat physiology before naming anatomyFirst stepA newborn or child has central cyanosis, shock, acidosis or severe cardiorespiratory distress.+
  1. 1Provide warmth, airway and ventilation support, monitor continuously and obtain IV or IO access, glucose, gas, lactate and cultures.
  2. 2Give antibiotics promptly when sepsis is plausible and correct hypoglycaemia while arranging urgent echocardiography.
  3. 3Call neonatal, cardiac and retrieval teams early; avoid unmonitored transfer or delay for nonessential imaging.
02Preserve ductUse the network prostaglandin pathwayDuct-dependent pulmonary or systemic flow is suspected clinically or confirmed.+
  1. 1Discuss immediately with paediatric cardiology and start alprostadil at the network-specified weight-based infusion rate.
  2. 2Monitor breathing, blood pressure, temperature, glucose and perfusion with personnel able to intubate because apnoea can occur.
  3. 3DefinitiveTitrate to physiological effect and transfer to the cardiac centre for definitive anatomical intervention.
03Balance flowRespect individual saturation targetsA known mixing or palliated circulation has abnormal saturation but preserved or changing perfusion.+
  1. 1Confirm the child's documented baseline and assess work of breathing, pulses, urine output, lactate and mental state.
  2. 2Correct dehydration, infection, anaemia or arrhythmia with congenital-cardiology advice rather than targeting a generic saturation in isolation.
  3. 3EscalationEscalate any departure from baseline, rising lactate or falling systemic perfusion to the specialist team.
04Definitive careMatch intervention to lesionDefinitiveEchocardiography defines a haemodynamically important congenital defect.+
  1. 1Use catheter septostomy when emergency mixing is inadequate and anatomy supports it.
  2. 2Plan catheter, surgical repair or staged palliation according to anatomy, size, physiology and comorbidity.
  3. 3Provide genetic, feeding, neurodevelopmental and lifelong congenital surveillance alongside cardiac procedures.

Complications

01

Heart failure and growth failure

Pulmonary overcirculation or ventricular pressure loading increases respiratory and feeding work, limiting energy available for growth.

02

Pulmonary vascular disease

Sustained high-pressure pulmonary flow remodels arterioles and can reverse a previously acyanotic shunt into irreversible cyanotic Eisenmenger physiology.

03

Neurological injury

Hypoxaemia, shock, embolism, bypass exposure and associated genetic disease can affect brain injury risk and neurodevelopment.

04

Arrhythmia and ventricular dysfunction

Native chamber load, surgical scars and valve abnormalities create lifelong risks even after technically successful repair.

05

Infective endocarditis

Abnormal endocardial surfaces and prosthetic material can support infection; fever with unexplained deterioration requires prompt cultures and specialist assessment.

Monitoring and follow-up

  • During acute instability, trend saturation at the appropriate site, heart rate, blood pressure, capillary refill, urine output, blood gas and lactate rather than one isolated value.
  • During alprostadil treatment, continuously monitor respiration and circulation and have an airway plan because apnoea and hypotension are clinically important adverse effects.
  • Plot weight, length and head circumference and observe feeding; caloric intake and route may need dietetic and speech-and-language support.
  • Follow lesion-specific echocardiography, ECG, rhythm, blood pressure and exercise surveillance after repair or palliation.
  • Monitor developmental, hearing, renal and genetic needs when the congenital lesion forms part of a wider syndrome.
  • Begin transition preparation before adolescence so the young person understands anatomy, operations, medicines, exercise, pregnancy implications and the adult congenital team.

Special situations

Cyanotic is physiology

The label describes systemic desaturation, not a fixed list: a left-to-right lesion can become cyanotic after pulmonary vascular remodelling.

Oxygen response is limited

A poor response raises cardiac shunting but also occurs in severe lung disease or pulmonary hypertension; modern echocardiography replaces a formal hyperoxia test.

Ducts support either circuit

The arterial duct may supply lungs in pulmonary obstruction or the body in left-heart obstruction, so the same medicine preserves very different physiology.

Saturation is not output

A child can have an acceptable saturation with critically low systemic blood flow, or a low planned saturation with adequate delivery in a balanced circulation.

Repair is not discharge

Residual lesions, valve disease, arrhythmia and ventricular adaptation make structured lifelong congenital follow-up essential.

Common pitfalls

  1. 01

    Do not call peripheral blue hands central cyanosis without inspecting the tongue and measuring a reliable saturation.

  2. 02

    Do not exclude cardiac disease because lungs appear abnormal; heart failure can cause pulmonary oedema and both diseases can coexist.

  3. 03

    Do not rely on a murmur, because critical lesions may be quiet.

  4. 04

    Do not let a negative newborn screen exclude later coarctation or ductal closure deterioration.

  5. 05

    Do not start or transfer a child on alprostadil without continuous monitoring and airway capability.

  6. 06

    Do not apply a healthy-child saturation target to a documented mixing or palliated circulation.

  7. 07

    Do not delay antibiotics when sepsis remains plausible while cardiac investigations proceed.

  8. 08

    Do not lose repaired congenital disease to general follow-up without planned transition.