Congenital heart disease

 

List:

·        Clinical pathways

·        Left to right shunt

·        Right to left shunt (TOF)

·        Univentricular heart (HLHS)

·        Fontan surgery

·        Fontan circulation

 

Pathways for congenital heart disease:

 

Left to right shunt:

Problem:

·      Not perfusing the tissues = heart failure

Examples

·      ASD, VSD

·      AP window

·      Truncus arteriosus

Goals

↑PVR:

·      Physical: ↑PEEP (7-8)

·      Physiological: ↓SaO2 (90%), ↑PaCO2 (45-50)

↓SVR:

·      Occurs by default under GA

Causes of hypoxaemia

·      Airway: ETT endobronchial, dislodged, occluded

·      Breathing: de-recruitment

·      Circulation: rarely

 

Right to left shunt:

Problem:

·      Not oxygenating the blood = hypoxaemia

Examples

·      Tetralogy of Fallot

·      Transposition of the great arteries

Goals

↑SVR:

·      Physical: flex the hips

·      Pharmacological: alpha agonist, minimize anaesthetic

↓PVR:

·        Physical: lung volume at FRC, ↓airway pressure

·        Physiological: ↑PaO2, ↓↔PaCO2, ↔temp, ↔pH

·        Pharm: anaesthetics, vasodilators

Cause of hypoxaemia

·        Airway: as before

·        Breathing: as before

·        Circulation: often
Solution: ↑SVR i.e. flex the hips, alpha agonist

 

Tetralogy of Fallot:

Problem

·        Not oxygenating the blood = hypoxaemia

·        RVOTO

Features

·        RVOT obstruction -> RVH

·        AVSD with aorta overriding it

Goals

↑SVR:

·        Physical: flex the hips

·        Pharmacological: alpha agonist

↓PVR:

·        Physical: ↓PEEP

·        Physiological: ↑PaO2, ↓PaCO2

·        Pharm: anaesthetics, vasodilators

Prevent RVOTO: (like right-sided HOCM)

·        Full

·        Tight

·        Slow

 

Hypoplastic left heart syndrome:

Problem

·        Only one pump for both pulmonary and systemic circulations

Severity

·        Patency of ductus (if not, then dead)

·        Patency of foramen ovale (if not, then dead)

·        Function of remaining ventricle

·        Balance of Qp (oxygenation of blood) and Qs (perfusion of tissues)

Management

·        Deliver near a tertiary children’s hospital

Keep the ductus arteriosus open:

·        PGE1 for DA (side effects: apnoea, ↓plt)

Goldilocks flow allocation:

·        PVR high enough to allow systemic flow (incl heart and brain)

·        PVR low enough to allow pulmonary flow

·        Ideal SaO2 85%

·        May require ETT + IPPV

·        May require FiO2 <0.21

Strong ventricle:

·        RV is not designed for high afterload

·        Low-normal SVR

·        ±Inotrope

 

Surgery for hypoplastic left heart syndrome

 

Stage 1: Norwood procedure (1-3 days)

Picture

Aims

·        Supply both lungs and body

·        Allow the child to grow

Operation

·        Atrial septectomy

·        Fashion the main PA into an aorta

·        Close the ductus arteriosus

·        Create a new systemic-to-pulmonary shunt

o    e.g. Blalock-Taussig shunt: right subclavian to right PA

o    Small hole to avoid stealing too much

 

Stage 2: Bi-directional cavo-pulmonary shunt (2-6 months)

Picture

Aims

·        Partially separate the systemic and pulmonary circulations

o  Improve cyanosis a bit

o  Offload the ventricle a bit

Operation

·        Create a systemic-venous-to-pulmonary-arterial shunt

o  i.e. SVC to right pulmonary artery

o  Big hole is ok now because venous pressure is lower

·        Close the systemic-arterial-to-pulmonary-arterial shunt

 

Stage 3: Fontan procedure (2-6 years)

Picture

Aims

·        Separate the systemic and pulmonary circulations completely

·        Hence improve cyanosis even more (SaO2 ~90% is the new normal)

·        Hence offload the ventricle even more

Operations

·        Complete the systemic-venous-to-pulmonary-arterial shunt

o  i.e. IVC to right pulmonary artery via Dacron graft

·        Create a pop-off valve

o  Communication between the Dacron graft the common atrium

Problems

·        Many complications

·        Causes: incl high CVP, disrupted lymphatics

·        e.g. chylothorax, ascites, oedema, protein-losing enteropathy

 

Fontan circulation:

Problem:

·        No accessory pump to fill the main pump

Goal:

·        Maintain venous return (“trans-pulmonary gradient”)

   ↑Pressure1

i.e. CVP (~10-12mmHg)

·        Euvolaemia

·        Jack-knife position

   ↓Resistance

i.e. PVR

 

Physiology:

·        ↑PaO2

·        ↓PaCO2

·        ↔pH

·        ↔Temp

Pharmacology:

·        General anaesthetics

·        Vasodilators

·        Avoid histaminergic drugs (atrac, sux, morph)

Ventilation:

·        ↔Lung volume

·        ↔Airway pressure

·        Spont vent if possible

·        ↓PEEP

·        ↑Expiratory time

   ↓Pressure2

i.e. atrial pressure ~7-8mmHg

·        Sinus rhythm

·        ↔Contractility

·        ↓Afterload

·        A-V valve functioning

 

Other Fontan issues:

·        Complications of ↑CVP

·        Thromboembolism

·        Infections

·        Valvular regurgitation

 

 

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