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:

                                                Curative procedure

 

Problem                               Staged procedure

 

                                                Palliative procedure

 

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

↓PVR:

·      Physical: ↓PEEP

·      Physiological: ↑PaO2, ↓PaCO2

·      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:

·      Euvolaemia

·      Sympatholysis (beta blocker, opioid)

 

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

Open channels:

·      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 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 right heart to fill the left heart

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. RAP ~7-8mmHg

·      Sinus rhythm

·      ↔Contractility

·      ↓Afterload

·      A-V valve functioning

 

Feedback welcome at ketaminenightmares@gmail.com