Hypercyanotic spell (Tetralogy of Fallot)

Publication: 01/02/2019  --
Last review: 01/02/2019  
Next review: 01/02/2022  
Clinical Guideline
ID: 5883 
Approved By: Trust Clinical Guidelines Group 
Copyright© Leeds Teaching Hospitals NHS Trust 2019  


This Clinical Guideline is intended for use by healthcare professionals within Leeds unless otherwise stated.
For healthcare professionals in other trusts, please ensure that you consult relevant local and national guidance.

Management of a hypercyanotic spell (Tetralogy of Fallot)

Summary of Guideline

Pertinent aspects of history - patient with diagnosis of tetralogy of fallot prior to repair. May have a history from parents of blue/agitated/listless episodes at home.
Key diagnostic criteria - profound desaturation, agitated or listless, quiet or absent murmur.
Investigations required - nil
Treatment - see flow chart in appendix 1

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To improve the diagnosis and management of a hypercyanotic spell.

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Approximately 3-5% of neonates born with congenital heart disease have tetralogy of fallot, this equates to 1 in every 3600 live births1. Prior to repair these patients are at risk of hypercyanotic spells. Hypercyanotic spells are episodes of severe cyanosis due to decreased pulmonary blood flow secondary to increased right ventricular outflow tract obstruction. The exact aetiology is unknown2. Hypercyanotic spells can be self-limiting however if ongoing can be serious and life threatening2. Therefore they are a medical emergency and need immediate intervention.

Hypercyanotic spells are relatively infrequent and therefore the exact management, in particular drug doses, during a high pressure environment can be easily forgotten. We have developed this guideline with a flow chart of the emergency management.

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A diagnosis of tetralogy of fallot can be made during fetal life and will be confirmed on echocardiography after the baby is born. Postnatal diagnoses are also made by echocardiography following clinical suspicion e.g. cyanosis, episodes suspicious of hypercyanotic spells.

Diagnosis of a hypercyanotic spell is clinical. The infant will become profoundly desaturated (often with oxygen saturations less than 50%) and either agitated or floppy and lethargic2. On auscultation of their heart you will notice that their murmur will be quiet or may even be absent2 due to reduced pulmonary blood flow. Prompt diagnosis is essential to ensure prompt treatment and good outcome.

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A hypercyanotic spell is a clinical diagnosis and does not require any investigations.

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Treatment / Management

Appendix 1 shows a flow chart detailing the emergency medical management of a hypercyanotic spell including information on how to prepare and administer the medications. This flow chart has been reviewed and agreed in the congenital cardiology governance meeting on 16/01/2018.

Once a hypercyanotic spell is identified, this is a medical emergency and needs prompt treatment. It is important that you feel comfortable dealing with this and call for immediate help if required. Inform the paediatric cardiology team.

The first stage of management is supportive and involves trying to calm the child and provide supplemental oxygen. Not all children tolerate the oxygen, it is important not to cause increased distress trying to give this. The child should be placed in a ‘knees to chest’ position; this is often easiest by sitting them on a parent’s knee and bringing their knees to their chest. The aim of this is to increase venous return to the heart and also increase systemic vascular resistance2. This may result in more pulmonary blood flow.

If the hypercyanotic spell is ongoing give intravenous or intramuscular (if no cannula) morphine. This helps calm the child down, reduces tachypnea and decreases pulmonary vascular resistance. Obtain intravenous access. If unable to secure access over the next 3 minutes then insert an intraosseous needle. The intravenous/intraosseous morphine should be repeated once after 3 minutes if the hypercyanotic spell is ongoing. Be prepared for respiratory depression post morphine dose and have the ability to provide ventilatory support via a bag if required, do not give naloxone.

If there is no improvement at this stage, give intravenous fluid resuscitation. This assists as a hypercyanotic spell can be exacerbated by dehydration. Giving intravenous fluids will increase circulating volume and therefore pulmonary blood flow.

An intravenous/intraosseous morphine infusion should be commenced if there is failure to improve after the fluid bolus.

Ongoing spells after these steps are unusual. If you do not have paediatric intensive care and/or paediatric anaesthetic support present at this stage you need to call them urgently to attend and provide support. Consideration should be given to administer either an intravenous propranolol or intravenous phenylephrine bolus.

Evidence is limited with differing expert opinion regarding whether propranolol or phenylephrine should be the next choice. The majority of paediatric cardiology consultants in this trust recommend phenylephrine as their first choice. However if you are able to get intravenous propranolol before phenylephrine then the propranolol should be given whilst the phenylephrine is being obtained.

Phenylepherine is a potent systemic vasoconstrictor and works by increasing the systemic venous resistance by stimulation of peripheral alphaadrenergic receptors2. If the systemic venous resistance is raised above the right ventricular outflow tract resistance then the blood from the right ventricle will return to flowing through the pulmonary artery2. The exact mechanism of propranolol is unclear; it is thought to work by relaxing the infundibulum and slowing the heart rate. This allows more time for right ventricular filling and increases pulmonary blood flow2.

The final medical stage of managing a hypercyanotic spell is to commence a phenylephrine infusion. This should only be given either with intensive care support prior to transfer to the paediatric intensive care unit or in the paediatric intensive care unit. Patients are likely to require intubating and ventilation.

If the patient is still having a hypercyanotic spell after all this management there are emergency interventional/surgical procedures that can be carried out (right ventricular outflow tract stent or blalock-taussig shunt).

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Appendix 1

Emergency Treatment of Hypercyanotic Spell  

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Appendix 2

Advice for drawing up medications
IV/IM morphine - Bolus administer the preparation neat over 2mins
Morphine infusion:- Preferred diluent: sodium chloride 0.9%  (Other diluents: glucose 5%, glucose 10%)

  • Weight less than 5kg - Add 5mg of morphine to 50ml of 0.9% sodium chloride. Concentration 100 micrograms/mL
  • Weight 5 - 20kg - Add 10mg of morphine to 50mL of 0.9% sodium chloride. Concentration 200 micrograms/mL

IV propranolol - For slow intravenous injection, give neat over at least 3–5 minutes; rate of administration should not exceed 1 mg/minute. May be diluted with Sodium Chloride 0.9% or Glucose 5% if easier to give.
Phenylepherine (100micrograms/mL) - Please double check monograph if changes in concentration: -
Bolus :-  Administer the preparation neat (if stronger than 100micrograms/mL cannot be given neat), slowly preferably via a central line. Only give via a peripheral line in an emergency situation.
Infusion: - Preferred diluent: Glucose 5% (Other diluents: Sodium chloride 0.9%, glucose 10%)

  • To prepare a solution for infusion: Draw up 10mL (1mg) of 1mg/10mL phenylephrine injection and add to 40mL of glucose 5% and mix well, this creates 1mg in 50mL solution (20microgram/mL)


Record: 5883

To provide evidence-based recommendations for appropriate diagnosis and management of a hypercyanotic spell.

Clinical condition:

Hypercyanotic spell

Target patient group: Children with a diagnosis of Tetralogy of Fallot
Target professional group(s): Secondary Care Doctors
Secondary Care Nurses
Registered Nurses Working in Critical Care
Tertiary care teams
Adapted from:

Evidence base


  1. Christian Apitz, Gary D Webb, Andrew N Redington. Seminar Tetralogy of Fallot. The Lancet. Volume 374, Issue 9699, 24–30 October 2009, Pages 1462-1471
  2. BMJ best practice. Tetralogy of Fallot. http://bestpractice.bmj.com/topics/en-gb/701/pdf/701.pdf. Accessed 22/2/18

Approved By

Trust Clinical Guidelines Group

Document history

LHP version 1.0

Related information

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