A 32-year-old male worker in a jewelry manufacturing unit is brought to the emergency department unconscious after exposure to cyanide fumes. His arterial blood gas shows pH 7.20, HCO₃⁻ 12 mEq/L, and PaO₂ 95 mmHg with SaO₂ 98%. All of the following are true regarding his management EXCEPT:

Question

Accepted Answer

D. Sodium nitrite should be administered first to induce methemoglobinemia, which has higher affinity for cyanide than cytochrome c oxidase. ## Cyanide Poisoning Management Algorithm

**Key Point:** Modern management prioritizes hydroxocobalamin over sodium nitrite due to superior safety profile. Sodium nitrite is NOT the first-line agent in contemporary toxicology practice.

### Why Option 1 (Correct Answer) is Wrong

While sodium nitrite does induce methemoglobinemia (which binds cyanide), it is **NOT** the preferred first-line antidote anymore. The statement is outdated:

- **Sodium nitrite** causes methemoglobinemia, which can lead to hypotension, reflex tachycardia, and tissue hypoxia
- **Hydroxocobalamin** is now preferred because:
  - Directly binds cyanide to form cyanocobalamin (excreted in urine)
  - Does NOT cause methemoglobinemia
  - Does NOT cause hypotension
  - Safer in patients with unknown toxin exposure
  - Can be given in higher doses without toxicity

**High-Yield:** In modern NEET PG exams, hydroxocobalamin is the DOC for cyanide poisoning; sodium nitrite is considered second-line or for use only if hydroxocobalamin is unavailable.

### Treatment Algorithm

```mermaid
flowchart TD
  A[Suspected cyanide poisoning]:::outcome --> B[High-flow O₂ + supportive care]:::action
  B --> C{Hydroxocobalamin available?}:::decision
  C -->|Yes| D[Hydroxocobalamin IV 5g over 15 min]:::action
  D --> E[Add sodium thiosulfate 12.5g IV]:::action
  C -->|No| F[Sodium nitrite 300mg IV over 5-20 min]:::action
  F --> G[Sodium thiosulfate 12.5g IV]:::action
  E --> H[Monitor ABG, lactate, vital signs]:::action
  G --> H
  H --> I[Repeat doses if symptoms persist]:::action
```

### Why Options 0, 2, and 3 are Correct

| Option | Accuracy | Rationale |
|--------|----------|----------|
| **Hydroxocobalamin preferred** | ✓ Correct | Superior safety; no methemoglobinemia or hypotension risk |
| **Thiosulfate concurrently** | ✓ Correct | Enhances conversion via rhodanese; given with or after hydroxocobalamin |
| **Supportive care** | ✓ Correct | O₂, IV fluids, acid-base correction, seizure prophylaxis all essential |

**Clinical Pearl:** The combination of metabolic acidosis + normal PaO₂ with high SaO₂ (as in this case) is classic for cyanide poisoning and demands immediate antidote administration.

Answer

A. Sodium thiosulfate should be given concurrently or immediately after hydroxocobalamin to enhance conversion of cyanide to thiocyanate

Answer

B. Hydroxocobalamin is preferred over sodium nitrite because it does not cause methemoglobinemia and has no risk of hypotension

Answer

C. Supportive care including high-flow oxygen and correction of metabolic acidosis are essential adjuncts to antidote therapy

A 32-year-old male worker in a jewelry manufacturing unit is brought to the emergency department unconscious after exposure to cyanide fumes. His arterial blood gas shows pH 7.20, HCO₃⁻ 12 mEq/L, and PaO₂ 95 mmHg with SaO₂ 98%. All of the following are true regarding his management EXCEPT:

Explanation

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