A 2-year-old girl from Delhi with known Tetralogy of Fallot presents to the emergency department with acute onset severe cyanosis, syncope, and rapid shallow breathing. Her parents report she was playing when she suddenly became more blue and unresponsive for a few seconds. On examination, she is deeply cyanosed, tachypneic (RR 50/min), and has a loud single S2. Her oxygen saturation is 65% on room air. What is the immediate management priority for this acute hypercyanotic spell?

Explanation

## Management of Hypercyanotic (Tet) Spells in Tetralogy of Fallot **Key Point:** Hypercyanotic spells are acute episodes of severe cyanosis caused by a sudden increase in right-to-left shunting. First-line management is non-invasive and focuses on reducing the R→L shunt gradient. ### Pathophysiology of a Hypercyanotic Spell ```mermaid flowchart TD A[Hypercyanotic Spell Triggered]:::urgent --> B[RV outflow obstruction worsens<br/>or systemic vasodilatation occurs]:::outcome B --> C[RV pressure rises further<br/>or LV pressure drops]:::outcome C --> D[R→L shunt increases dramatically]:::outcome D --> E[Severe hypoxemia & syncope]:::urgent E --> F{Immediate Management}:::decision F -->|First-line| G[Knee-chest position<br/>+ O2 + Morphine]:::action F -->|If no response| H[IV Propranolol<br/>or IV Esmolol]:::action H --> I[Reduce RV contractility<br/>& RVOT obstruction]:::outcome G --> J[Increase SVR<br/>Reduce R→L shunt]:::outcome ``` ### First-Line Management Steps | Intervention | Mechanism | Rationale | |--------------|-----------|----------| | **Knee-chest position** | Increases systemic vascular resistance | Raises LV pressure → decreases R→L shunt gradient | | **Supplemental oxygen** | Improves pulmonary vascular dilation | Reduces PVR, increases pulmonary blood flow | | **Morphine (0.1–0.2 mg/kg IV)** | Reduces anxiety, decreases catecholamines, reduces RV contractility | Decreases RVOT obstruction severity | | **IV Propranolol (0.01–0.1 mg/kg)** | Beta-blocker; reduces RV contractility & outflow obstruction | Used if morphine fails; reduces dynamic RVOT obstruction | **High-Yield:** The knee-chest position is the single most important immediate maneuver — it can terminate a spell within minutes by increasing SVR and reducing the R→L shunt. **Clinical Pearl:** Hypercyanotic spells typically occur in infants and young children with TOF. They are self-limited but carry risk of syncope, stroke, and death if untreated. Chronic propranolol prophylaxis is often used to prevent spells in symptomatic children awaiting surgery. **Mnemonic:** **KSOM** = **K**nee-chest position, **S**upplemental O₂, **O**pioid (morphine), **M**orphine/Medications (propranolol if needed). ### Why NOT Intubation or Diuretics? ~~Intubation~~ is reserved for respiratory failure or inability to protect airway — not first-line for a spell. ~~Diuretics~~ worsen hypercyanotic spells by reducing preload and SVR, exacerbating the R→L shunt.