Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Tetralogy of Fallot and hypercyanotic spells
Paediatrics and child health · UK scope · Sources checked 27 Aug 2026 · Clinical review pending
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Hypercyanotic spell
Sudden deepening blue, grey or pale colour with tachypnoea, distress, limpness or reduced consciousness in unrepaired tetralogy reflects acutely reduced pulmonary blood flow and increased right-to-left shunting; the outflow murmur may shorten or disappear.
Action: Call the paediatric emergency team, keep the child calm with a caregiver, give high-flow oxygen as tolerated and bring the knees firmly to the chest. Obtain IV or IO access, monitor ECG and saturation, give IV morphine 50 micrograms/kg and repeat once after 3 minutes if needed, then 0.9% sodium chloride 10 mL/kg if the spell persists. Contact paediatric cardiology and critical care early for propranolol, esmolol, phenylephrine, ventilation or urgent intervention.
Overview
Recognise tetralogy anatomy and age-dependent cyanosis, treat a hypercyanotic spell in the correct physiological sequence with complete weight-based rescue regimens, and anticipate repair and lifelong complications.
Anterior and cephalad malalignment of the outlet septum narrows the right-ventricular outflow tract, leaves a malalignment VSD and positions the aortic root over both ventricles. Right-ventricular hypertrophy develops from ejecting against obstruction.
The VSD is usually large and nonrestrictive, so ventricular pressures are similar. The balance between pulmonary and systemic vascular resistance and the severity of fixed and dynamic outflow obstruction determine which way blood crosses.
Infundibular muscle can contract during catecholamine surges. Crying, pain or dehydration reduces preload and systemic resistance or increases contractility, narrowing the outflow tract further and accelerating a self-reinforcing right-to-left shunt.
Children may be pink with a systolic ejection murmur when obstruction is modest, cyanosed from early infancy when severe, or duct dependent when pulmonary flow is critically restricted. Squatting in an older unrepaired child is an adaptive way to raise systemic vascular resistance.
Practice
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Paediatrics and child healthOriginal SBA
First response to a tet spell
An unrepaired 6-month-old with tetralogy suddenly becomes deeply blue and tachypnoeic while crying. The outflow murmur is now difficult to hear. What should be done first?
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. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
During a spell, rapid deep breathing increases venous return but can intensify the cycle. Hypoxaemia and acidosis further alter vascular tone, so prompt physical and pharmacological interruption is important.
Knees-to-chest compresses femoral arteries and increases systemic resistance, reducing the pressure advantage for right-to-left flow. Calming lowers catecholamine-driven infundibular spasm; oxygen lowers pulmonary resistance even though an intracardiac shunt limits saturation response.
Morphine or fentanyl reduces distress and hyperpnoea, while a cautious saline bolus restores preload. Beta blockade reduces infundibular contraction, and phenylephrine raises systemic vascular resistance. These potent steps require monitoring and specialist support.
History should record baseline saturation, spell onset and duration, precipitant, feeding, growth, medicines and previous procedures. Ask whether caregivers have a written spell plan and whether cardiac surgery timing has changed.
Examination between spells may show central cyanosis, clubbing later, right-ventricular impulse and a harsh ejection systolic murmur at the upper left sternal edge. Murmur intensity reflects flow across obstruction, not simply obstruction severity.
Echocardiography defines pulmonary annulus and arteries, coronary anatomy, VSD and aortic override, associated arch anatomy and ventricular function. CT, MRI or catheterisation is used selectively for surgical planning.
Repair generally closes the VSD so the aorta receives left-ventricular output and enlarges the obstructed pathway to the pulmonary arteries. A transannular patch may relieve obstruction but often leaves important pulmonary regurgitation.
Late care evaluates right-ventricular volume and scar. Pulmonary valve replacement, catheter intervention, electrophysiology treatment or reoperation may be needed before symptoms become advanced, so apparently well children should not be lost to surveillance.
Key points
Tetralogy consists of a VSD, overriding aorta, right-ventricular outflow tract obstruction and secondary right-ventricular hypertrophy; one developmental malalignment creates the first three and pressure load creates hypertrophy.
Severity is governed mainly by outflow obstruction. Mild obstruction permits left-to-right flow and little cyanosis; severe obstruction drives venous blood through the VSD into the aorta.
A hypercyanotic spell is sudden dynamic reduction in pulmonary flow with increased right-to-left shunting, often during crying, feeding, defecation, fever or dehydration.
Recognise deeper cyanosis or pallor, rapid deep breathing, irritability, limpness or syncope and a softer or absent outflow murmur; do not wait for a numeric saturation threshold.
Immediate sequence: call help, minimise distress, high-flow oxygen as tolerated and knees-to-chest to raise systemic resistance and venous return.
If persistent, obtain IV or IO access and give morphine 50 micrograms/kg IV, repeat once after 3 minutes if required; without IV access use intranasal fentanyl 1–2 micrograms/kg or IM morphine 100 micrograms/kg under the emergency pathway.
Give 0.9% sodium chloride 10 mL/kg and repeat only after reassessment when dehydration or low preload contributes; provide respiratory support if opioid or spell physiology depresses breathing.
Aetiology
01
Conotruncal maldevelopment
Malalignment of the developing outlet septum produces the VSD, overriding aorta and right-ventricular outflow narrowing that define tetralogy.
02
Genetic associations
A 22q11.2 deletion and other chromosomal or single-gene conditions occur more often, particularly when arch or pulmonary artery anatomy is complex.
03
Sporadic multifactorial origin
Many children have no single identified cause, reflecting combined developmental and genetic influences rather than an acquired postnatal disease.
Pathophysiology
1
Nonrestrictive septal route
The large VSD permits pressure equalisation, allowing right-ventricular blood to reach the overriding aorta when pulmonary ejection is obstructed.
2
Outflow-controlled cyanosis
Fixed valvar and infundibular narrowing determines pulmonary flow and therefore the magnitude of right-to-left shunting and systemic desaturation.
3
Dynamic spell cycle
Catecholamine-driven infundibular contraction, reduced preload and low systemic resistance abruptly divert more blood away from lungs and worsen acidosis.
4
Post-repair volume loading
Relieving the outflow with a patch can leave chronic pulmonary regurgitation, progressively enlarging the right ventricle and creating arrhythmic substrate.
Clinical features and red flags
Baseline tetralogy
Variable central cyanosis, right-ventricular impulse and an upper-left ejection systolic murmur occur with otherwise defined congenital anatomy.
Mild spell
The infant becomes clammy, pale, grey or bluer than baseline with tachypnoea and irritability, often during feeding or crying.
Severe spell
Limpness, reduced consciousness, seizure, bradycardia or shock indicates critically reduced pulmonary flow and cerebral oxygen delivery.
Murmur attenuation
A shorter or absent outflow murmur during deeper cyanosis reflects reduced forward pulmonary flow and is an ominous dynamic sign.
Chronic hypoxaemia
Clubbing, exercise squatting, polycythaemia symptoms and reduced growth can appear when repair is delayed or palliation remains cyanotic.
Late repaired phenotype
Declining exercise, palpitations, syncope, right-heart signs or changing murmur suggests pulmonary regurgitation, obstruction or arrhythmia.
Red flags requiring action
A spell with reduced consciousness, limpness, seizure, persistent severe cyanosis, bradycardia or shock is immediately life-threatening and requires resuscitation-team and intensive-care support.
Investigations
01Immediate monitored clinical diagnosis of a spellFirst step
Why
Recognise the emergency and begin treatment without waiting for imaging.
Interpretation and limitations
A fall from baseline saturation with hyperpnoea, distress and murmur attenuation in susceptible anatomy is sufficient to act.
02Blood gas, lactate, glucose and electrolytes
Why
Quantify acidosis and perfusion and identify reversible metabolic precipitants.
Interpretation and limitations
Worsening metabolic acidosis or lactate marks severe low pulmonary and systemic oxygen delivery and accelerates intensive-care escalation.
03Full blood count and iron status
Why
Identify anaemia, iron deficiency or excessive erythrocytosis affecting oxygen carriage and viscosity.
Interpretation and limitations
A haemoglobin normal for an acyanotic child may be inappropriately low for chronic cyanosis; specialist interpretation is needed.
Anatomy and physiological severity determine repair timing; imaging must not delay treatment of an active spell.
05
Differential diagnosis
01
Pulmonary atresia with VSD
No effective forward pulmonary outlet creates profound duct-dependent neonatal cyanosis and different surgical anatomy despite related conotruncal development.
02
Transposition of great arteries
Parallel circulation causes severe early hypoxaemia that depends on mixing rather than a dynamic outflow murmur and classic tetralogy anatomy.
03
Seizure or breath holding
Motor activity or crying-related colour change may mimic a spell, but rhythm, saturation, murmur change and known anatomy distinguish causes.
04
Respiratory deterioration
Bronchiolitis, pneumonia or airway obstruction causes hypoxaemia with lung findings; infection can also trigger a genuine cardiac spell.
05
Post-repair ventricular arrhythmia
Abrupt palpitations or syncope years after surgery requires ECG-based assessment for scar-related tachycardia, not infant spell management alone.
Management
01ImmediateBreak the spell physicallyFirst stepA child with susceptible anatomy develops sudden deeper cyanosis, hyperpnoea or reduced responsiveness.+
1Call emergency help, minimise handling and keep the child calm with the caregiver.
2Give high-flow oxygen as tolerated and position knees firmly against the chest.
3Attach continuous ECG and saturation monitoring and obtain IV or IO access without prolonging distress.
02Rescue medicineSedate and restore preloadThe spell persists after calming, oxygen and knee-to-chest positioning.+
1AlternativeGive morphine 50 micrograms/kg IV and repeat once after 3 minutes if needed; use the guideline non-IV alternative when access is unavailable.
2Prepare to support ventilation and give 0.9% sodium chloride 10 mL/kg, repeating only after reassessment.
Complications
01
Hypoxic neurological injury
A prolonged severe spell can cause seizure, loss of consciousness, stroke or permanent injury through profound cerebral oxygen deprivation.
02
Secondary erythrocytosis
Chronic hypoxaemia increases red-cell mass; iron deficiency can paradoxically worsen viscosity and oxygen delivery despite a lower cell size.
03
Pulmonary regurgitation
Outflow repair may leave chronic valve incompetence, right-ventricular dilatation and important eventual exercise or rhythm consequences.
04
Residual structural disease
Residual VSD, outflow obstruction, branch pulmonary stenosis, tricuspid regurgitation and aortic root dilatation may persist or progress.
05
Atrial and ventricular arrhythmia
Chamber enlargement and surgical scar can cause late tachyarrhythmia, syncope and sudden cardiac death risk requiring specialist surveillance.
Monitoring and follow-up
During a spell, continuously record rhythm, saturation, respiratory effort, consciousness, pulses and blood pressure and reassess after every physical, fluid or medicine step.
Observe for opioid-related respiratory depression and have bag-mask ventilation and advanced airway personnel immediately available.
After resolution, monitor for recurrence and investigate hydration, fever, anaemia, iron deficiency, arrhythmia and missed doses or procedures that triggered the event.
Before repair, track baseline saturation, spell frequency, feeding and growth and move the surgical plan forward when episodes or hypoxaemia worsen.
After repair, use serial echocardiography and ECG plus cardiac MRI and ambulatory rhythm monitoring according to anatomy and symptoms.
Ensure adolescents understand operations, residual lesions, exercise advice, endocarditis prevention, reproductive counselling and their adult congenital service.
Special situations
A quieter murmur is worse
When dynamic obstruction nearly stops pulmonary flow, less blood crosses the outflow tract and its murmur fades while cyanosis deepens.
Knees change resistance
Knee-to-chest positioning raises systemic vascular resistance and venous return, reducing the pressure drive for right-to-left shunting.
Oxygen is not the whole answer
Oxygen lowers pulmonary resistance, but blood cannot reach the lungs through severe obstruction; the shunt cycle must also be reversed.
Iron deficiency is harmful
Microcytic rigid cells can increase viscosity symptoms in a cyanotic child, so indiscriminate venesection without specialist assessment may worsen delivery.
Repair creates new physiology
Relieving obstruction saves pulmonary flow but chronic pulmonary regurgitation and scar explain why lifelong imaging and rhythm surveillance remain necessary.
Common pitfalls
01
Do not separate a distressed child from the caregiver or prolong painful procedures before positioning.
02
Do not interpret a fading murmur during deeper cyanosis as resolution.
03
Do not wait for echocardiography before treating a clinically recognised spell.
04
Do not forget microgram-to-milligram conversion and independent checking for opioid and vasoactive doses.
05
Do not give repeated fluid boluses without reassessing perfusion and ventricular function.
06
Do not use beta blocker or phenylephrine without continuous monitoring and senior specialist support.
07
Do not assume a repaired child cannot have dangerous arrhythmia or ventricular dysfunction.
08
Do not discharge after a first spell without cardiac review, trigger assessment and a family emergency plan.
Refractory spells need paediatric cardiology and critical-care direction for IV propranolol 100 micrograms/kg or esmolol 600 micrograms/kg, and phenylephrine infusion starting 500 nanograms/kg/min within the guideline range.
Echocardiography confirms anatomy and severity; ECG and chest radiography support baseline assessment, while blood count identifies anaemia or harmful hyperviscosity.
Definitive treatment is surgical repair, usually closing the VSD and relieving outflow obstruction; timing depends on anatomy, saturation, growth and spells, with palliation when complete repair is not immediately feasible.
Every repaired child needs congenital cardiac surveillance for pulmonary regurgitation, residual obstruction or VSD, right-ventricular dilatation, aortic root disease and atrial or ventricular arrhythmia.
The obstruction murmur becoming shorter or absent during worsening cyanosis indicates falling pulmonary flow, not improvement.
A first suspected spell needs hospital assessment even if colour recovers, because the diagnosis, trigger, anaemia, hydration and need for earlier repair require review.
Fever, dehydration, feeding, crying, defecation, tachypnoea or procedures can precipitate dynamic outflow obstruction and should be corrected alongside rescue measures.
Cyanosis from birth or profound neonatal hypoxaemia may represent severe pulmonary obstruction or pulmonary atresia with duct-dependent flow and needs neonatal cardiac transfer.
After repair, syncope, sustained palpitations, exertional decline, heart-failure signs or haemoptysis suggests arrhythmia, pulmonary regurgitation, ventricular dysfunction or another late complication rather than a simple infant spell.
ECG and rhythm monitoring
Why
Establish baseline hypertrophy and detect acute or late arrhythmia.
Interpretation and limitations
After repair, QRS change and documented tachyarrhythmia contribute to risk assessment but require congenital electrophysiology context.
06Cardiac MRI in repaired tetralogy
Why
Measure right-ventricular volumes, function and pulmonary regurgitation accurately.
Interpretation and limitations
Serial changes help time pulmonary valve or other reintervention before irreversible right-ventricular decline.
3
Treat fever, dehydration, pain and anaemia while paediatric cardiology and critical care guide ongoing care.
03RefractoryManipulate outflow and vascular resistanceSevere cyanosis continues after initial positioning, opioid and volume treatment.+
1Use IV propranolol 100 micrograms/kg or esmolol 600 micrograms/kg only with specialist and resuscitation support.
2Use a phenylephrine infusion within the current specialist protocol when raising systemic resistance is required.
3EscalationEscalate airway and ventilation support and arrange urgent catheter, shunt or complete surgical intervention.
04DefinitiveRepair and surveilDefinitiveTetralogy anatomy is confirmed or spells recur.+
1Plan complete repair or interim palliation based on outflow and pulmonary artery anatomy, age, weight, saturation and symptoms.
2Teach caregivers the emergency position and provide a written pathway while awaiting intervention.
3After repair, maintain lifelong congenital follow-up with echocardiography, ECG, rhythm assessment and cardiac MRI when appropriate.
Key medicines and prescribing safety2 treatments · regimens, roles and cautions+
Reduces distress and catecholamine-driven hyperpnoea during a persistent hypercyanotic spell after oxygen, calming and knee-to-chest positioning.
Morphine for hypercyanotic spell
Give 50 micrograms/kg IV as a bolus and repeat once after 3 minutes if needed; when IV access is unavailable, the Sheffield pathway uses 100 micrograms/kg IM while IV or IO access is obtained.
Continuous cardiorespiratory monitoring and immediate airway support are essential because respiratory depression and hypotension can worsen oxygen delivery; calculate in micrograms, reassess after each dose and involve critical care early.
Provides a rapid non-IV calming and analgesic option to interrupt catecholamine-driven worsening when the child cannot tolerate prolonged cannulation attempts.
Intranasal fentanyl alternative
When vascular access is unavailable, give 1–2 micrograms/kg intranasally under the current hypercyanotic-spell pathway while obtaining IV or IO access and monitoring breathing continuously.
Use only within an airway-capable resuscitation setting; check prior opioid exposure and exact concentration, monitor for apnoea, rigidity or hypotension, and do not delay definitive vascular access and cardiology escalation.