Management of Cyanotic (Hypoxic / "Tet") Spells in Tetralogy of Fallot

What is a Cyanotic Spell?

• Intense cyanosis
• Hyperpnea (deep, rapid breathing)
• Restlessness and crying
• Limpness / loss of consciousness (in severe cases)
• Disappearance or softening of the ejection systolic murmur (the RVOT murmur reduces as flow through it decreases)

• Harriet Lane Handbook, p. 47

Pathophysiology (The Vicious Cycle)

1. A trigger (crying, exertion, dehydration, fever, anemia) causes infundibular spasm → increased RVOTO
2. Pulmonary blood flow falls → right-to-left shunting increases through the VSD
3. Systemic hypoxia worsens → metabolic acidosis develops
4. Acidosis → peripheral vasodilation → fall in SVR → more R→L shunting
5. This worsens hypoxia and hyperpnea further → vicious cycle

• Break the infundibular spasm
• Increase SVR (reduces R→L shunt)
• Decrease PVR
• Correct acidosis
• Increase preload

Management - Stepwise Approach (Op Ghai)

STEP 1 - Non-Pharmacological (Immediate, First Response)

STEP 2 - Pharmacological (Escalating)

A. Morphine Sulfate (First-line drug - Op Ghai)

• Dose: 0.1-0.2 mg/kg SC/IM (do NOT wait for IV access)
• Mechanism:
  • Suppresses the hyperpnea (breaks the respiratory drive)
  • Sedates and calms the child (reduces agitation)
  • Reduces spasm of the infundibulum (RVOT)
• Monitor for respiratory depression
• Harriet Lane: 0.05-0.2 mg/kg IM/SUBQ/IV

B. Sodium Bicarbonate

• Dose: 1 mEq/kg IV
• Corrects metabolic acidosis → reduces the acidosis-driven peripheral vasodilation → helps restore SVR
• Acidosis also impairs myocardial function; correction improves cardiac output

C. Propranolol

• Dose: 0.1 mg/kg IV (slow push, over 10 minutes); max 1 mg
• Oral dose for prevention: 1-4 mg/kg/day in 4 divided doses
• Mechanism:
  • Beta-blockade reduces infundibular spasm (negative inotrope on the dynamic RVOT obstruction)
  • Slows heart rate → improves ventricular filling time
  • Reduces oxygen demand
• Monitor for hypotension and bradycardia
• Harriet Lane: 0.15-0.25 mg/kg slow IV push, max initial dose 1 mg

D. IV Fluids

• 10-20 mL/kg isotonic crystalloid (Normal saline)
• Increases preload → improves RV filling → increases forward flow across RVOT

E. Phenylephrine (Alpha-agonist) - for refractory spells

• Dose: 5-20 mcg/kg IV bolus
• Mechanism: Pure alpha-agonist → increases SVR → reduces R→L shunt
• Directly addresses the SVR component of the vicious cycle
• Harriet Lane: max single dose 200 mcg

F. Ketamine - for refractory/severe spells

• Dose: 1-2 mg/kg IM or IV (give IV dose over 60 seconds)
• Mechanism:
  • Increases SVR
  • Provides sedation and analgesia
  • Reduces O₂ consumption
• Has the advantage of maintaining airway reflexes

STEP 3 - For Refractory Spells

• General anesthesia with intubation and ventilation (reduces muscle O₂ demand, enables controlled hyperventilation to correct acidosis)
• Emergent surgical intervention:
  • Modified Blalock-Taussig (BT) Shunt - systemic-to-pulmonary shunt as palliation
  • Total corrective repair - if the child is suitable

Quick Reference Summary Table (Op Ghai Algorithm)

Spell occurs
     ↓
1. Calm child + knee-chest position + O₂
     ↓ (if not relieved)
2. Morphine 0.1-0.2 mg/kg SC/IM
     ↓ (if not relieved)
3. NaHCO₃ 1 mEq/kg IV + IV fluids 10 mL/kg
     ↓ (if not relieved)
4. Propranolol 0.1 mg/kg IV slow push
     ↓ (if not relieved)
5. Phenylephrine / Ketamine
     ↓ (refractory)
6. Intubation + emergent surgery (BT shunt / repair)

Long-Term Prevention of Spells (Op Ghai)

• Oral Propranolol: 1-4 mg/kg/day in 3-4 divided doses
  • Given to children who have had spells while awaiting surgery
  • Reduces infundibular spasm chronically
• Correct anemia: Hemoglobin should be maintained > 10 g/dL (iron deficiency worsens spells by increasing blood viscosity at low Hb and reducing O₂ carrying capacity)
• Adequate hydration especially in hot weather / fever / gastroenteritis
• Early surgical correction is the definitive management - primary repair is now done at 4-6 months of age at most centers; earlier if spells are recurrent or severe

Indicators for Urgent/Early Surgery

• Recurrent cyanotic spells despite propranolol
• Progressive hypoxia (SpO₂ < 75% baseline)
• Growth faltering and hypoxic symptoms
• Polycythemia with hematocrit > 65%

1. Morphine is the first-line drug for an acute spell - give IM even without IV access
2. Knee-chest position increases SVR - this is the same reason older children with TOF instinctively squat after exercise
3. Propranolol works on the dynamic infundibular component - it does NOT relieve fixed valvular stenosis
4. The murmur gets softer or disappears during a spell (less blood flowing through the RVOT = less turbulence)
5. Avoid giving digoxin in TOF with spells - it can worsen infundibular spasm
6. Do NOT use pure oxygen as the sole treatment and falsely reassure - it has limited effect when pulmonary blood flow itself is severely compromised

• Harriet Lane Handbook (23rd ed.), p. 47, Table 1.9 - Hypercyanotic Crisis Management
• PMC review on TOF management in PICU (PMCID 10285149)