Hydrogen Sulfide Poisoning

Hydrogen sulfide is a colorless, flammable gas with a rotten-egg smell. It is heavier than air and accumulates in confined spaces. It inhibits cytochrome c oxidase in mitochondria (as cyanide does) and irritates mucous membranes, which causes both systemic and local toxicity. Gas is produced by bacterial decomposition of sulfur-containing organic matter.

Sources

• Sewers, manure and slurry pits, septic tanks and drains
• Oil and gas extraction and refining, and geothermal energy plants
• Pulp and paper mills, tanneries and fishing vessel holds
• Natural springs and volcanic areas

Exposure effects by concentration

• 10 to 50 parts per million: eye and respiratory irritation
• 100 parts per million: olfactory fatigue (the smell is lost, so the warning disappears), and cough
• 250 to 500 parts per million: pulmonary edema
• Over 500 to 1000 parts per million: "knockdown" with sudden collapse, apnea and death within minutes

Most deaths occur in confined spaces, and rescuers are commonly killed. Complications: pulmonary edema, anoxic brain injury, persistent cognitive and parkinsonian deficits, keratoconjunctivitis ("gas eye") and cardiomyopathy.

• Low concentrations: eye pain, lacrimation, photophobia, cough, sore throat, headache, nausea
• Moderate concentrations: dyspnea, wheeze, delayed noncardiogenic pulmonary edema (up to 24 hours), confusion
• High concentrations: sudden loss of consciousness (knockdown), seizures, apnea, cardiac arrhythmia, and death
• Metabolic acidosis with raised lactate
• Greenish-black discoloration of the body at autopsy and darkening of silver or copper items
• Red flags: collapse in a confined space, loss of consciousness, severe dyspnea and apnea

1. Clinical diagnosis from the history of exposure (setting, smell, group collapse).
2. Oxygen saturation, arterial blood gas and lactate: metabolic acidosis and a raised lactate.
3. Co-oximetry: sulfhemoglobin and methemoglobin (when present), and carboxyhemoglobin to exclude carbon monoxide.
4. Chest radiograph at presentation and repeated at 12 to 24 hours for delayed pulmonary edema.
5. ECG, troponin, creatinine, and slit-lamp examination of the eyes with fluorescein.
6. Exposure measurements by gas monitors at the scene. Blood and urine sulfide or thiosulfate tests are not useful for management.

Differentials: cyanide poisoning, carbon monoxide poisoning, methane or other asphyxiants, chlorine inhalation, organophosphate poisoning, other causes of collapse.

1. Scene safety: only rescuers with self-contained breathing apparatus should enter. Remove the patient to fresh air and begin resuscitation immediately.
2. Oxygen: 100% by high-flow mask, or intubate and ventilate with positive end-expiratory pressure for pulmonary edema or depressed consciousness.
3. Decontamination: remove and bag clothing, and wash the skin. Irrigate the eyes with 0.9% saline for at least 15 minutes, then apply erythromycin 0.5% ointment four times daily for keratoconjunctivitis, with cycloplegic drops (cyclopentolate 1% twice daily) for pain.
4. Sodium nitrite (controversial, only in the first minutes after severe exposure with coma or apnea, when the patient is hemodynamically stable and carbon monoxide is excluded): 300 mg (10 mL of 3%) IV over 5 minutes (children 4.5 to 10 mg/kg, maximum 300 mg). It forms methemoglobin that binds sulfide. Avoid in hypotension and smoke inhalation. Do not give sodium thiosulfate.
5. Hydroxocobalamin 5 g IV over 15 minutes (children 70 mg/kg, maximum 5 g) may be given when available, though evidence is limited.
6. Hyperbaric oxygen is used in some centers for coma, without proven benefit.
7. Supportive care: IV crystalloid and norepinephrine 0.05 to 0.5 micrograms/kg/min for hypotension, lorazepam 4 mg IV for seizures (children 0.1 mg/kg), bronchodilators (salbutamol 2.5 to 5 mg nebulized) for bronchospasm, and sodium bicarbonate 1 to 2 mmol/kg IV for pH under 7.1.
8. Observation: at least 24 hours after any significant exposure, since pulmonary edema may be delayed.

Follow-up: neurologic and cognitive review for survivors of collapse, and workplace investigation with gas detectors, ventilation, confined space entry procedures and rescue plans. Counsel workers that loss of smell does not mean the gas has gone.