Surgical Timing and Management of Tetralogy of Fallot in Children Aged 4 Years and Older

Indications for Immediate Repair

Children who have reached 4 years of age should undergo complete surgical correction without further delay, as this exceeds the optimal repair window of 3–6 months. 1
Reaching 4 years without prior intervention generally reflects a milder anatomic variant with relatively balanced pulmonary blood flow, but definitive repair remains indicated. 3

Complete repair should be performed via a trans‑atrial, trans‑ventricular, or combined approach selected according to individual anatomy, with the primary goals of closing the ventricular septal defect and relieving right‑ventricular outflow tract (RVOT) obstruction at all levels. 2
Whenever feasible, the size of the ventriculotomy should be minimized to reduce scar formation, thereby preserving right‑ventricular function, exercise tolerance, and lowering long‑term arrhythmia risk. 2

Contemporary series report 25‑year survival rates of 94–95 % and 36‑year survival rates of 85–96 % after complete repair, indicating excellent durability of the procedure. 1

Baseline mixed‑venous oxygen saturation (SvO₂) in stable Tetralogy of Fallot typically ranges from 60 % to 75 % because of chronic right‑to‑left shunting. 3
A pH < 7.35 together with a base deficit > ‑5 mmol/L denotes metabolic acidosis, signaling inadequate tissue oxygen delivery and possible progression toward a hypercyanotic crisis. 3
Lactate concentrations exceeding 2 mmol/L indicate tissue hypoxia from insufficient pulmonary blood flow and warrant urgent therapeutic intervention. 3
A venous CO₂ tension (PvCO₂) > 50 mmHg suggests hypoventilation or respiratory fatigue, which can increase pulmonary vascular resistance and precipitate hypercyanotic spells. 3

Serial VBG analyses during the peri‑operative period are recommended to assess systemic oxygen delivery and to guide fluid resuscitation, inotropic support, and ventilator management in children undergoing repair. 4

VBG results should not be interpreted in isolation; they must be correlated with clinical indicators such as cyanosis severity, mental status, and capillary refill to accurately assess perfusion. 3
Chronic hypoxemia in Tetralogy of Fallot leads to compensatory erythrocytosis, which shifts the oxygen‑hemoglobin dissociation curve and can impair oxygen delivery despite similar arterial PO₂ values. 3