Cyanotic heart disease in acute paediatrics is a nightmare. How much oxygen to give? How much fluid to give? How quickly can google explain a Stage II Fontan?
Elizabeth Weinstein gave an amazing talk at the AAEM Scientific Assembly about managing cyanotic heart disease in the acute setting. Here’s my summary.
If in doubt – aim for sats of 80-85% – this may not be ideal but it is unlikely to cause a big problem and the patient won’t be too hypoxic.
Give fluid in lots of 10ml/kg and go slowly.
Fontans like fluid to maintain their passive pulmonary blood flow
A six-month-old presents to ED looking unwell. He has a HR of 170, Sats of 60%, and RR 70. He is distressed but his chest sounds are clear. Mum says he has ‘some sort of heart condition’ but doesn’t know the details.
Essentially all patients with cyanotic heart conditions have some derrangement in pulmonary or systemic blood flow. We mean one of four things when we talk about congenital heart disease:
- Not enough pulmonary blood flow
- Too much pulmonary blood flow
- Not enough systemic blood flow
- Not enough coronary artery blood flow
Once you know which of these it is, it helps to manage and troubleshoot.
If the child is blue – there is not enough pulmonary blood flow
If the child is pink – they may have too much pulmonary blood flow
if the child is grey – there is not enough systemic flow
You realise that your patient is having a Tet Spell.
What is Tetralogy of Fallot?
Tetralogy of Fallot accounts for 10% of cyanotic heart disease – it is the most common cause of cyanosis in children over eight months. It comprises the well known four elements:
- Ventricular septal defect
- Right ventricular hypertrophy
- Overriding aorta
- Pulmonary stenosis
How sick is a patient with Tetralogy of Fallot?
The baseline status of a patient with Tetralogy of Fallot depends on the degree of pulmonary stenosis (or pulmonary outflow obstruction).
If there is only mild pulmonary stenosis, there will be normal pulmonary blood flow. These are often called ‘pink tets‘ – they have normal sats and for that reason, they may be much older before diagnosis.
But if there is a significant outflow tract obstruction, then the patient is hypoxic, usually with sats in the 70s. Normal sats in children with TOF may range from 70-100% on room air, depending on the degree of the outflow tract obstruction.
What happens in a Tet Spell?
The patient’s baseline status will change if the systemic vascular resistance drops. This change causes oxygenated blood to be preferentially shunted from the right side of the heart, through the ventricular septal defect, to the left side of the heart (rather than going through outflow obstruction).
A Tet Spell can be preceded by an innocuous event (e.g. crying). The event results in dropping the systemic vascular resistance, so there is increased shunting from the right side of the heart to the left side. This results in falling pO2, rising CO2, and a falling pH. All of these increase pulmonary vascular resistance and stimulate the respiratory centre (and consequently increase venous return).
The increased venous return results in more shunting and the whole cycle gets worse.
We need to break the cycle!
How should we manage a Tet Spell?
We need to increase the systemic vascular resistance, decrease the venous return, or drop the pulmonary vascular resistance. The best management plan is:
- Knees to chest
- Calm the patient
- High flow oxygen
- Morphine and IV fluids
- If you are still having trouble – go to ketamine (IM or IV)
How is Tetralogy of Fallot repaired?
By six months, the outflow tract obstruction will be definitively repaired in most children. However, some children need a staged repair if the outflow is so tight that they cannot maintain adequate pulmonary blood flow while waiting for a full repair.
The staged repair involves a Blalock-Taussig shunt (essentially a man-made ductus arteriosus). This involves a subclavian artery and pulmonary artery tube graft and allows the pulmonary blood flow to be maintained (in an obstructive lesion) until the patient is big enough for a definitive repair.
What’s the survival rate and what are the complications?
Survival is 86% at 30 years, but the patients do have complications along the way.
There is a right bundle ECG pattern in the vast majority of post-op patients; some have pulmonary regurgitation or recurrent stenosis. Right ventricular dysfunction is common (so bear in mind that it is easy to volume overload these patients as they get older).
Sudden cardiac death is a real risk (4% at 25 years post-op) – and this risk is thought to increase if the QRS is >180ms so watch out for a wide QRS.
Arrhythmias happen too – many patients have complex ventricular ectopics but we rarely see ventricular tachycardia. Atrial arrhythmias are very common – specifically intra-atrial re-entrant tachycardia (a fibrillation/flutter hybrid). In Tetralogy of Fallot in particular, we see a wide complex tachyarrhythmia which is often difficult to distinguish from ventricular tachycardia
A six-year-old presents to ED with vomiting and diarrhoea. Grandma says she had a ‘fountain’ operation when she was younger. She takes aspirin every day and needs antibiotics for dental procedures Her sats are 70%, RR 30 and she has eyes sunken, poor capillary refill and tachycardia.
This patient is blue, so there is not enough pulmonary blood flow. There are also signs of systemic hypoperfusion.
What is a Fontan procedure?
A Fontan repair is for children with a functionally univentricular heart (this could be TA, hypoplastic right/left heart, but it doesn’t matter – the point is there is just one ventricle working). This accounts for 10% of complex congenital heart disease.
Fontan knew that one ventricle wasn’t enough. So he developed a repair so that one ventricle only needs to provide the systemic blood flow (by making the pulmonary blood flow passive).
The IVC and SVC connect directly to the pulmonary artery (bypassing the right heart completely). Therefore, pulmonary blood flow is passive, and the ventricle is only responsible for systemic flow.
This is done as a staged repair:
Stage I (hemi-fontan or bidrectional Glenn). This is carried out at four to nine months. The SVC is connected to the pulmonary artery.
Stage II is carried out 12-24 months later (a full Fontan). This connects the IVC to the pulmonary artery.
Depending on their individual physiology, some children may not be candidates for the full Fontan, and so may only have a hemi-fontan. Therefore, by two to three years of age, it’s all completed.
The pulmonary blood flow is passive; the systemic blood flow is by the one ventricle.
Survival post-Fontan is excellent – 85% at 20 years post-op.
Some patients need a Blalock-Taussig shunt before Stage I. And those with only a right ventricle need surgery to make it a ‘left ventricle’ before they proceed with the staged Fontan (this is a Norwood procedure).
What’s a Norwood procedure and what happens afterwards?
The Norwood procedure essentially connects the single ventricle to the systemic circulation.
Patients following a Norwood procedure are unstable and at risk of sudden death (15%). They are very sensitive to fluid and oxygen (it’s easy to kill them) – so BE CAREFUL!
Back to Fontan – should we give fluids or not?
In a Fontan, if the pulmonary blood flow is passive, then it is clearly volume and pressure-dependent (to maintain pulmonary flow).
So – dehydration is bad. A dry Fontan is a dead Fontan as they cannot maintain the pulmonary blood flow or the cardiac output. This patient will become increasingly hypoxic, but if we rehydrate them the hypoxia resolves.
Low blood pressure and intrathoracic pressures are a problem too. Routine respiratory illnesses can cause huge problems (due to intrathoracic pressures) so have a low threshold for admission.
If intubating a patient post-Fontan repair (although generally try to avoid this), remember – intrathoracic pressure is bad. Therefore when ventilating: use a low PEEP (<5); low volume; and low rate (to allow PBF). Ketamine is good for induction as it maintains haemodynamic status.
In this case – a dehydrated Fontan – we need to give fluids and oxygen (a fully repaired Fontan likes oxygen).
The patient comes back again a few months later as he is tired.
In Fontan’s, arrhythmias occur at slower heart rates (usually low 100s) than in Tetralogy of Fallot – so it can be difficult to distinguish an arrhythmia from sinus rhythm. These patients do not tolerate arrhythmias for long. We just need to work out if it’s not sinus rhythm as the patient will therefore need other interventions. Tachy- and brady-arrhythmias are common and patients can deteriorate quickly if not they are not managed promptly. Look out for junctional rhythms and atrial rhythms.
But, there is the same management as for normal arrhythmias. If the patient is unstable, shock them.
Thromboemobilic disease (3-20%) is a real problem too so think of this.
Most will develop some degree of myocardial depression as they get older (not clinically seen) so it is easy to volume overload them. Give fluid, but don’t go nuts. 20ml/kg is too much – give 10ml/kg and go slowly but continue until you reach your goal.
How can we know sats to aim for?
In cyanotic congenital heart disease, there are usually mixing lesions. How much goes to the lungs and how much goes to the body is a tight balance (and easy to unbalance).
Vasodilating the pulmonary vasculature can tip the balance i.e. lots of pulmonary blood flow at the expense of the systolic blood flow. Be careful of pulmonary over circulation and cardiovascular collapse.
If a child has a shunt or a partially repaired complex lesion, then sats are likely to be 75-85% (e.g. BT shunts; Norwood; Stage I Fontan).
Tetralogy of Fallot patients have sats of 70-100% on room air depending on the degree of outflow obstruction.
A child who has had a Fontan completion, the sats will be 95-100% (but they can drop as the patient gets older).
The best tip is to ask the family what the normal sats are – if they are normally 70%, then there is no point trying to get them to 75%.
Fully repaired Fontans like oxygen; but in Norwood and central shunts it is easy to get pulmonary overcirculation.
Be careful in children with newly diagnosed cyanotic heart disease, i.e. neonates starting on PGE. Oxygen will hasten closing the duct (so aim for 85% sats)