Nursing care
Tetralogy of Fallot nursing care: what to assess and what to do first
Written and reviewed by Dana Whitfield, RN, MSN · 6 min read · Updated September 2026
Short answer
Tetralogy of Fallot combines four structural defects that together cause cyanotic spells, or tet spells, when pulmonary blood flow drops sharply. An older child having a spell will instinctively squat, drawing the knees to the chest, because it raises systemic vascular resistance and pushes more blood to the lungs. Recognising that posture as a compensatory reflex, not a behaviour to correct, is central to nursing this condition.
The pathophysiology in one pass
Tetralogy of Fallot is four defects occurring together: a ventricular septal defect, pulmonary stenosis, an overriding aorta, and right ventricular hypertrophy. The pulmonary stenosis is the defect that drives most of the clinical picture, because it restricts blood flow to the lungs and, combined with the VSD, allows deoxygenated blood to shunt right to left into the systemic circulation.
A tet spell happens when something further narrows the right ventricular outflow tract or drops systemic vascular resistance, both of which increase the right-to-left shunt and send more deoxygenated blood into the body. Crying, straining on a bowel movement, feeding, or waking from sleep can all trigger one. The child becomes acutely more cyanotic, tachypnoeic, and irritable, and in severe spells, loses consciousness. Understanding that the spell is a sudden worsening of an existing shunt, not a new event, explains why every intervention for it is aimed at reversing the shunt direction rather than simply giving oxygen.
Assessment findings that matter
Baseline findings include a harsh systolic ejection murmur at the left sternal border, clubbing of fingers and toes in the older, unrepaired child, and a history of cyanosis that worsens with exertion or crying. Some infants are only mildly cyanotic at rest, so ask specifically about episodes with feeding or crying rather than relying on the resting colour alone.
During a spell, the findings escalate quickly: cyanosis deepens, respiratory rate and effort increase, and the child becomes agitated then lethargic as oxygenation falls further. The murmur often becomes softer or disappears during a severe spell, which is counterintuitive but reflects reduced flow across the stenotic valve, not improvement. In the toddler or older child, watch for the spontaneous squat, which precedes or accompanies these spells and is one of the most specific findings in paediatric cardiology. A caregiver reporting that their child suddenly stops playing and squats down is describing a tet spell until proven otherwise.
What the exam asks about this
The NCLEX consistently tests the squatting or knee-chest response as a compensatory mechanism the nurse should recognise and support, not discourage. Expect a scenario where a child squats during play, and the correct interpretation is that the child is self-treating a hypercyanotic spell by increasing systemic vascular resistance, which reduces the right-to-left shunt and improves pulmonary blood flow.
You will also see items asking you to select the first nursing action during a spell, where placing the infant or child in the knee-chest position is typically the correct or leading answer, ahead of oxygen administration, because it is immediate and nurse-initiated. Distractor options often include placing the child supine or encouraging ambulation, both of which worsen a spell by lowering systemic vascular resistance. Questions may also test your understanding of why crying and straining are dangerous in this condition, connecting the trigger to the underlying shunt physiology rather than presenting it as an isolated fact to memorise.
Nursing interventions in priority order
The first action in a tet spell is positioning: knee-chest for an infant, or allowing an older child to squat if that is what they are already doing. This is immediate, requires no equipment, and directly addresses the physiology by raising systemic vascular resistance and reducing the right-to-left shunt. Do not force a child out of a squat to reposition them for a different reason; let the posture stand.
Once positioned, calm the child, since crying worsens the spell by increasing oxygen demand and further dropping systemic vascular resistance. Administer supplemental oxygen, though its benefit in this specific spell is more limited than in simple hypoxaemia, because the core problem is a shunt, not primarily a diffusion or ventilation issue. If the spell does not resolve, morphine is used to reduce hyperpnoea and calm the child, and further pharmacological escalation follows medical protocol. For an infant, tucking the knees to the chest while holding them against the caregiver's shoulder achieves the same effect as the older child's squat and is a technique worth teaching directly.
Medications and monitoring
Beta blockers such as propranolol are sometimes used prophylactically to reduce the frequency and severity of spells by relaxing the infundibular spasm that narrows the right ventricular outflow tract. Monitor heart rate and blood pressure with these, and hold and report a heart rate below the parameter set for the child's age.
IV fluids may be given during a spell to increase preload and venous return, since a well-filled right ventricle pushes more blood across the pulmonary valve. Continuous pulse oximetry is standard for a hospitalised child with unrepaired tetralogy, and a saturation drop from the child's own baseline is more meaningful than any single absolute number, since baseline saturations vary between children with this defect. Iron studies are checked periodically in chronically cyanotic children, since chronic hypoxaemia drives compensatory polycythaemia, which in turn raises the risk of stroke if the child becomes dehydrated.
When to escalate
Escalate immediately if a spell does not resolve within a few minutes of positioning and calming, if the child loses consciousness, or if cyanosis deepens despite intervention. These spells can progress to seizure, cerebral hypoxic injury, or death if prolonged, so a spell that persists past initial first-line measures is a medical emergency, not a wait-and-see situation.
Also escalate for a first-time spell in a child not yet diagnosed with a cardiac defect, for any spell accompanied by chest pain or a new murmur change reported by the family, and for signs of a hypercyanotic spell in an infant too young to squat, since these infants rely entirely on caregiver recognition and the knee-chest manoeuvre performed for them. Document the trigger, the duration, the intervention used, and the response, since this pattern informs the surgical team's decision on timing for corrective repair.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our pediatrics practice questions are the closest set to what this page covers.
Common questions
Why does squatting help during a tet spell?
Squatting kinks the femoral arteries and increases systemic vascular resistance, which reduces the right-to-left shunt across the ventricular septal defect and pushes more blood toward the lungs. It is a compensatory reflex the child performs instinctively, not a habit to discourage.
What should a nurse do first when an infant with tetralogy of Fallot has a hypercyanotic spell?
Place the infant in the knee-chest position immediately. It is the fastest, nurse-initiated action that addresses the underlying shunt, and it is typically prioritised ahead of oxygen administration in exam scenarios and in practice.
Is oxygen enough to treat a tet spell?
No. Oxygen helps but does not correct the underlying right-to-left shunt, so positioning, calming the child, and sometimes morphine or IV fluids are needed alongside it.
Why are beta blockers used in children with tetralogy of Fallot?
Propranolol reduces spasm in the right ventricular outflow tract, which lowers the frequency and severity of hypercyanotic spells. Heart rate is monitored closely while a child is on this therapy.
What triggers a tet spell?
Crying, straining during a bowel movement, feeding, and waking from sleep are common triggers, because each can lower systemic vascular resistance or increase oxygen demand and worsen the existing right-to-left shunt.