Table 2 Open in new tab Potential...

Mode of desaturation

Mechanism

Notes

Mixed venous desaturation

Reduced oxygen delivery (DO₂): causes of cardiogenic shock (arrhythmia, ischaemia, and tamponade)
Increased oxygen extraction (VO₂): fever and raised sympathetic drive (anxiety and pain)
Anaemia (decreased oxygen carrying capacity)

Only contributing if there is a source of shunting (i.e. patent fenestration, baffle leak, or intrapulmonary shunting)

Pulmonary venous desaturation

Pulmonary oedema
Atelectasis
Pleural effusion
Pneumothorax
Pneumonia/respiratory infection

Typical causes of hypoxaemia in non-congenital patients

Venovenous collaterals

Collateral vessels from systemic veins to pulmonary veins can form secondary to long-standing systemic venous hypertension

Fenestration in the Fontan circulation

Typically created at the time of the Fontan completion with the aim of reducing the systemic venous pressures

Pulmonary arteriovenous malformations

Can develop in the setting of:

Absent ‘hepatic factor’
Long-standing hepatic congestion leading to portopulmonary syndrome
Most notable in patients palliated with ‘classic’ Glenn

Impaired pulmonary blood flow

Thrombus in pulmonary artery or Fontan pathway
Acidosis
Haemolysis (via free radical scavenging)
Hypercarbic respiratory failure
Dehydration

Elevated PVR leads to reduction in pulmonary blood flow relative to systemic blood flow

Hepatic veins not incorporated into Fontan

Source of right-to-left shunting at atrial level

Drainage of coronary sinus into pulmonary venous atrium

Increased desaturation with exercise

Drainage of embryologic structures (levo-atrial cardinal vein) into coronary sinus draining into pulmonary venous atrium

Long-standing systemic venous hypertension can lead to ‘re-opening’ of embryologic venous structures

Patency of a previously unrecognized severely hypoplastic AV valve in atrio-pulmonary Fontan

Not applicable to patients with extracardiac or lateral tunnel style Fontan palliations

Table 2

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Potential sources of arterial oxygen desaturation in Fontan patients

Mode of desaturation	Mechanism	Notes
Mixed venous desaturation	Reduced oxygen delivery (DO₂): causes of cardiogenic shock (arrhythmia, ischaemia, and tamponade) Increased oxygen extraction (VO₂): fever and raised sympathetic drive (anxiety and pain) Anaemia (decreased oxygen carrying capacity)	Only contributing if there is a source of shunting (i.e. patent fenestration, baffle leak, or intrapulmonary shunting)
Pulmonary venous desaturation	Pulmonary oedema Atelectasis Pleural effusion Pneumothorax Pneumonia/respiratory infection	Typical causes of hypoxaemia in non-congenital patients
Venovenous collaterals		Collateral vessels from systemic veins to pulmonary veins can form secondary to long-standing systemic venous hypertension
Fenestration in the Fontan circulation		Typically created at the time of the Fontan completion with the aim of reducing the systemic venous pressures
Pulmonary arteriovenous malformations		Can develop in the setting of: Absent ‘hepatic factor’ Long-standing hepatic congestion leading to portopulmonary syndrome Most notable in patients palliated with ‘classic’ Glenn
Impaired pulmonary blood flow	Thrombus in pulmonary artery or Fontan pathway Acidosis Haemolysis (via free radical scavenging) Hypercarbic respiratory failure Dehydration	Elevated PVR leads to reduction in pulmonary blood flow relative to systemic blood flow
Hepatic veins not incorporated into Fontan		Source of right-to-left shunting at atrial level
Drainage of coronary sinus into pulmonary venous atrium		Increased desaturation with exercise
Drainage of embryologic structures (levo-atrial cardinal vein) into coronary sinus draining into pulmonary venous atrium		Long-standing systemic venous hypertension can lead to ‘re-opening’ of embryologic venous structures
Patency of a previously unrecognized severely hypoplastic AV valve in atrio-pulmonary Fontan		Not applicable to patients with extracardiac or lateral tunnel style Fontan palliations

Mode of desaturation	Mechanism	Notes
Mixed venous desaturation	Reduced oxygen delivery (DO₂): causes of cardiogenic shock (arrhythmia, ischaemia, and tamponade) Increased oxygen extraction (VO₂): fever and raised sympathetic drive (anxiety and pain) Anaemia (decreased oxygen carrying capacity)	Only contributing if there is a source of shunting (i.e. patent fenestration, baffle leak, or intrapulmonary shunting)
Pulmonary venous desaturation	Pulmonary oedema Atelectasis Pleural effusion Pneumothorax Pneumonia/respiratory infection	Typical causes of hypoxaemia in non-congenital patients
Venovenous collaterals		Collateral vessels from systemic veins to pulmonary veins can form secondary to long-standing systemic venous hypertension
Fenestration in the Fontan circulation		Typically created at the time of the Fontan completion with the aim of reducing the systemic venous pressures
Pulmonary arteriovenous malformations		Can develop in the setting of: Absent ‘hepatic factor’ Long-standing hepatic congestion leading to portopulmonary syndrome Most notable in patients palliated with ‘classic’ Glenn
Impaired pulmonary blood flow	Thrombus in pulmonary artery or Fontan pathway Acidosis Haemolysis (via free radical scavenging) Hypercarbic respiratory failure Dehydration	Elevated PVR leads to reduction in pulmonary blood flow relative to systemic blood flow
Hepatic veins not incorporated into Fontan		Source of right-to-left shunting at atrial level
Drainage of coronary sinus into pulmonary venous atrium		Increased desaturation with exercise
Drainage of embryologic structures (levo-atrial cardinal vein) into coronary sinus draining into pulmonary venous atrium		Long-standing systemic venous hypertension can lead to ‘re-opening’ of embryologic venous structures
Patency of a previously unrecognized severely hypoplastic AV valve in atrio-pulmonary Fontan		Not applicable to patients with extracardiac or lateral tunnel style Fontan palliations

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