Tet Spell Management
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Direct answer
A hypercyanotic spell is infundibular spasm meeting falling systemic vascular resistance, and its management is a fixed ladder every NEET-SS candidate must recite: knee-to-chest positioning, high-flow oxygen, morphine 0.1 mg/kg, an intravenous fluid bolus of 10 to 20 mL/kg, then phenylephrine to raise systemic resistance and intravenous propranolol 0.05 to 0.1 mg/kg to break the spasm, with sodium bicarbonate for the acidosis that itself perpetuates the spell. Spells peak between two and six months of age, announce themselves with hyperpnoea and deepening cyanosis, and end in limpness, seizures or death if untreated. Chronic oral propranolol, iron correction of deficiency anaemia and early surgical repair are the preventives.
What you must remember
- Recognition precedes the ladder: a crying infant who suddenly develops rapid deep breathing, increasing cyanosis and a softening murmur, then becomes limp — the falling murmur is the bedside clue that infundibular spasm is worsening.
- Knee-chest position works by trapping blood in the lower limbs, raising systemic vascular resistance and reducing right-to-left shunting; in an older child, squatting is the child's own version of the same manoeuvre.
- Morphine 0.1 mg/kg subcutaneously or intravenously calms the infant and reduces infundibular spasm; ketamine is a useful alternative that preserves systemic pressure while sedating.
- Phenylephrine, in carefully titrated boluses or an infusion, is the pure alpha option: it raises systemic vascular resistance without increasing contractility, which matters because inotropes worsen infundibular spasm — this is why adrenaline is wrong in a spell.
- Propranolol 0.05 to 0.1 mg/kg intravenously slow, or esmolol infusion in the ventilated child, directly relaxes the infundibulum and slows the heart, improving filling.
- Acidosis drives a vicious cycle — acidotic pulmonary vasoconstriction and hyperpnoea deepen the spell — so sodium bicarbonate is part of the ladder, not an afterthought.
- Chronic prophylaxis: oral propranolol 1 to 4 mg/kg per day in divided doses, iron supplementation when ferritin is low (iron deficiency anaemia is the commonest correctable spell trigger in Indian clinics), avoidance of dehydration, and expedited surgical repair.
- A spell refractory to the full ladder needs intubation, complete beta-blockade, and an emergency surgical decision — a modified Blalock-Taussig shunt or complete repair, depending on anatomy and centre.
The spell ladder, step by step
Rehearse it as a timed sequence on a real five-month-old in the emergency department. Minute zero: recognise the pattern, stop examinations and procedures that involve crying, and put the baby on the mother's shoulder with the knees held to the chest — calming and positioning alone abort many early spells. Give 100 per cent oxygen by mask; its contribution is modest because pulmonary flow is the bottleneck, but it is never omitted. Minute two to five: morphine 0.1 mg/kg subcutaneously if the baby is struggling, and a 10 to 20 mL/kg isotonic bolus to raise preload, since an underfilled right ventricle ejects more across the infundibulum relative to the VSD. If cyanosis persists, draw the phenylephrine: titrated boluses or an infusion to lift systemic systolic pressure, watching for reflex bradycardia; simultaneously prepare propranolol 0.05 to 0.1 mg/kg intravenously over several minutes with monitoring. Check the gas: a pH below about 7.2 gets sodium bicarbonate, because the acidotic infant hyperventilates, drops systemic resistance further and spirals. Fifteen to twenty minutes: a baby still blue and obtunded is intubated, sedated and paralysed, started on an esmolol infusion, and the cardiac surgeon is woken — the definitive treatment of recurrent or refractory spells is surgical, and the exam answer to "spell not settling on full medical ladder" is never a second fluid bolus but a shunt or repair.
The viva trap
Two traps recur. First, the drug-selection trap: candidates reach for adrenaline or dopamine in the blue, hypotensive infant — both increase contractility, worsen infundibular spasm and kill the baby in the question; the vasopressor of a spell is phenylephrine, deliberately chosen because it lacks inotropy. Second, the anaemia paradox: a tetalogy child with haemoglobin of 9 g/dL is not "protected" from spells by thinner blood — iron deficiency is a spell trigger, and the correct move is iron therapy, with transfusion only for severe deficiency, because a rising haematocrit too fast raises viscosity. A third favourite asks why the child squats and the answer must include all three mechanisms, not merely "increases return".
Frequently asked questions
What is the first manoeuvre in a hypercyanotic spell?
Knee-to-chest positioning with calming and high-flow oxygen, before any drug is drawn up.
Why is phenylephrine preferred over adrenaline in a spell?
It raises systemic vascular resistance by pure alpha action without increasing contractility, so it does not aggravate infundibular spasm.
What dose of morphine is used?
0.1 mg/kg subcutaneously or intravenously, sedating the infant and reducing infundibular spasm.
Which haematological condition triggers spells and how is it treated?
Iron deficiency anaemia, treated with oral iron — a classic correctable precipitant in Indian outpatient practice.
What is the definitive treatment of recurrent tet spells?
Early complete surgical repair, or a modified Blalock-Taussig shunt as palliation when anatomy or condition does not permit immediate repair.