What is the treatment for a patient with suspected cyanide poisoning?

Treatment for Cyanide Poisoning

Administer hydroxocobalamin 5 g IV (10 g for cardiac arrest) as the first-line antidote for suspected cyanide poisoning, as it does not cause hypotension or impair oxygen-carrying capacity—critical advantages when carbon monoxide co-poisoning is possible. 1, 2

Immediate Supportive Care

• Administer 100% oxygen immediately via non-rebreather mask or endotracheal tube to all patients with suspected cyanide poisoning, as this counteracts cyanide's mitochondrial effects and accelerates carboxyhemoglobin elimination if carbon monoxide is also present 1, 3
• Secure the airway, provide ventilatory support, and ensure circulatory stability—do not delay these interventions to administer antidotes 4
• Obtain arterial blood gas, lactate level, carboxyhemoglobin, and complete blood count 3

Clinical Recognition

Suspect cyanide poisoning when patients present with: 1, 4

• Fire or smoke exposure in enclosed spaces with soot around mouth/nose/oropharynx
• Altered mental status (confusion, disorientation, depressed consciousness)
• Cardiovascular collapse or shock despite adequate oxygenation
• Metabolic acidosis with elevated lactate: ≥10 mmol/L in fire victims without severe burns, or ≥8 mmol/L in pure cyanide poisoning 2, 5
• Seizures, coma, or mydriasis 1, 4

Do not delay treatment for laboratory confirmation—clinical suspicion warrants empiric hydroxocobalamin administration 2

First-Line Antidote: Hydroxocobalamin

Adult Dosing

• Standard dose: 5 g IV over 15 minutes for suspected cyanide poisoning with severe manifestations 2
• Cardiac arrest dose: 10 g IV when the patient is in cardiac arrest from cyanide toxicity 2

Pediatric Dosing

• 70 mg/kg IV (maximum 5 g) for children with moderate to severe cyanide poisoning 2

Key Advantages

• Does not cause methemoglobinemia or impair oxygen-carrying capacity, making it safe in smoke inhalation victims with concurrent carbon monoxide poisoning 1
• Acts immediately by binding cyanide to form non-toxic cyanocobalamin that is renally excreted 6

Important Consideration

• Monitor renal function as hydroxocobalamin can cause oxalate nephropathy 2
• May interfere with hemodialysis machines due to red discoloration—alert nephrology if dialysis is needed 7

Second-Line Antidote: Sodium Nitrite

Use sodium nitrite only when hydroxocobalamin is unavailable, particularly when carbon monoxide poisoning is not a concern 1, 8

Critical Safety Warnings

• Causes methemoglobinemia and severe hypotension, which can worsen hypoxia in smoke inhalation victims with carbon monoxide co-poisoning 4
• Requires precise weight-based and hemoglobin-adjusted dosing in children and anemic patients to avoid excessive methemoglobin formation 1, 4
• Use with extreme caution in patients with anemia, G6PD deficiency, smoke inhalation injury, or diminished cardiovascular reserve 4

Monitoring Requirements

• Monitor methemoglobin levels closely and keep below 30% 4
• Monitor hemodynamics and slow infusion if hypotension occurs 4
• Standard pulse oximetry is unreliable in the presence of methemoglobinemia—use co-oximetry 4

Adjunctive Therapy: Sodium Thiosulfate

Add sodium thiosulfate following hydroxocobalamin or sodium nitrite to enhance cyanide elimination: 1, 2

• Adult dose: 12.5 g IV 2
• Pediatric dose: 250 mg/kg 2
• Acts by serving as a substrate for enzymatic conversion of cyanide to thiocyanate, but mechanism is too slow for monotherapy in life-threatening poisoning 1
• May potentiate or synergize with hydroxocobalamin effects—hydroxocobalamin acts immediately while sodium thiosulfate provides delayed but persistent effect 9

Administration Compatibility

Do not administer hydroxocobalamin and sodium nitrite simultaneously through the same IV line due to chemical incompatibility 4

• Sodium thiosulfate and sodium nitrite can be administered sequentially through the same line 4
• Blood products and sodium nitrite should use separate IV lines 4

Monitoring and Follow-up

• Monitor patients for 24-48 hours after antidote administration for adequacy of oxygenation, perfusion, and recurrent signs of cyanide toxicity 4
• Continue 100% oxygen until carboxyhemoglobin levels normalize in smoke inhalation victims 3
• Consider hyperbaric oxygen therapy for patients with loss of consciousness, neurological deficits, significant metabolic acidosis, or carboxyhemoglobin >25% 3
• Clinical follow-up at 1-2 months to assess for delayed neurological sequelae 3

Common Pitfalls to Avoid

• Never delay hydroxocobalamin administration in smoke inhalation victims with cardiovascular collapse, shock, or coma while waiting for laboratory confirmation 2, 4
• Avoid sodium nitrite in smoke inhalation victims unless hydroxocobalamin is truly unavailable, as methemoglobin formation worsens hypoxia from concurrent carbon monoxide poisoning 8, 4
• Do not use sodium thiosulfate as monotherapy in life-threatening poisoning due to its delayed mechanism of action 1
• Do not target arbitrary methemoglobin levels when using sodium nitrite—therapeutic effects do not correlate directly with methemoglobin formation, and clinical response should guide dosing 4