Tetralogy of Fallot

Jennifer de la Cruz
Mar 27
2 min read

Updated: Apr 6

Aim:

To enhance understanding of Tetralogy of Fallot (TOF), enabling accurate interpretation of haemodynamic changes and timely, physiology-driven interventions in perioperative care.

Background

Tetralogy of Fallot (TOF) is a congenital cyanotic heart defect consisting of four abnormalities: A hole between the lower heart chambers (ventricular septal defect)

A narrow path from the right ventricle to the lungs (right ventricular outflow obstruction)
The main artery (aorta) sits over the hole instead of the left ventricle (overriding aorta)
The muscle of the right ventricle is thickened

The defects create a right-to-left shunt, where deoxygenated blood bypasses the lungs and enters systemic circulation—resulting in low oxygen levels that may not respond to oxygen therapy, low blood pressure, high heart rate (when compensating), low heart rate (when not compensating = deteriorating, or when under sedation).

Patients with TOF often adapt to this physiology over time, meaning their baseline oxygen saturation and clinical presentation may appear abnormal but are “normal” for them. However, this balance is fragile and can deteriorate rapidly under perioperative stress.

Perioperative Triggers for Deterioration

Perianaesthesia nurses should observe closely as these perioperative factors worsen right-to-left shunting:

Low systemic vascular resistance (e.g. anaesthetic agents, vasodilation)
Hypovolaemia (fasting, blood loss)
Pain, agitation, or crying
Hypoxia or hypercarbia
Increased intrathoracic pressure

These factors reduce pulmonary blood flow and can precipitate a "tet spell"—an acute hypoxic event requiring rapid intervention.

Implications for Perianaesthesia Nursing

Recognise physiology, not just numbers: Hypoxia in TOF is due to shunting—not simply oxygen deficiency.
Avoid hypotension to prevent worsening shunt.
Support preload: Ensure adequate fluid status to optimise cardiac output.
Minimise stress response: Pain and agitation can precipitate deterioration.
Identify late signs early: Bradycardia and hypotension indicate severe decompensation and require urgent escalation.

Key Clinical Insight

In Tetralogy of Fallot: Oxygenation is determined by circulation, not just ventilation

Understanding this distinction enables perianaesthesia nurses to anticipate deterioration, interpret vital signs accurately, and deliver targeted, life-saving care.