Hydrogen sulfide toxicity: Difference between revisions

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HYDROGEN SULFIDE
==Background==
*Hydrogen sulfide (H₂S) is an extremely toxic, colorless, flammable gas that inhibits mitochondrial cytochrome C oxidase — a mechanism nearly identical to [[Cyanide poisoning|cyanide]].
*It is the '''most common cause of fatal toxic gas exposure''' in the workplace.<ref name="Tintinalli">Tintinalli et al.
*Hydrogen Sulfide.
*In: Tintinalli et al.
*Emergency Medicine A Comprehensive Study Guide.
*New York, NY: McGraw Hill. 2011. 1320.</ref>
*The classic toxidrome is knockdown (rapid loss of consciousness), pulmonary edema, conjunctivitis, and olfactory paralysis.<ref name="StatPearls">Hydrogen Sulfide Toxicity. ''StatPearls''. 2024.
*PMID: 32119270</ref>


n pathophys identicle to cn except bond of h2s to cytochrome more rapidly reversible than cn.  Therefore, just need to remove pt from source and use standard resus measures to reverse h2s toxicity.


===General information===
*Colorless, highly flammable, heavier-than-air gas
*"Rotten egg" odor at low concentrations (detectable at ~0.5 ppb)<ref name="ATSDR">Hydrogen Sulfide Medical Management Guidelines. Agency for Toxic Substances and Disease Registry (ATSDR). CDC.</ref>
*WARNING: Odor is NOT a reliable safety indicator — olfactory nerve fatigue occurs at ≥100 ppm (within 2-15 minutes), causing complete loss of smell at the very concentrations that are dangerous<ref name="StatPearls"/>
*Heavier than air → accumulates in enclosed, low-lying, and poorly ventilated spaces (sewers, manure pits, tanks)
*Encountered in:
**Oil and gas industry (primary chemical hazard of natural gas production)
**Sewers, wastewater treatment
**Manure pits, animal confinement facilities
**Paper/pulp mills, tanneries
**Roofing/asphalt operations
**Mining, smelting
**Hot springs, volcanic areas
*Suicide method ("detergent suicide"): mixing acidic household cleaners (toilet bowl cleaner) with sulfur-containing products (bath salts, lime sulfur pesticide) to generate H₂S in an enclosed space — increasing in prevalence<ref name="Tintinalli"/>
*Most fatalities occur in '''confined spaces'''; rescuers entering without SCBA frequently become secondary victims<ref name="ATSDR"/>
*Children are at higher risk at the same ambient concentration due to higher minute volume:weight ratios and shorter stature (gas settles near the ground)<ref name="ATSDR"/>


HYDROGEN SULFIDE (septic tank)
===Concentration-dependent effects===
{| class="wikitable"
|-
! Concentration (ppm) !! Effects
|-
| 0.01-0.03 || Rotten egg odor detectable
|-
| 2-5 || Nausea, headache, tearing with prolonged exposure
|-
| 10-20 || Eye irritation ("gas eye"), mild respiratory irritation
|-
| 50-100 || Conjunctivitis, respiratory tract irritation; '''olfactory fatigue begins at 100 ppm'''
|-
| 100-200 || Olfactory paralysis (loss of smell); cough, eye irritation, drowsiness; potentially fatal after 4-48 hours
|-
| 200-300 || Marked conjunctivitis, respiratory irritation after 1 hour; pulmonary edema risk
|-
| 500-700 || Staggering, collapse within 5 minutes; serious eye damage; fatal in 30-60 minutes
|-
| 700-1000 || '''Rapid "knockdown"''' — LOC within 1-2 breaths; respiratory paralysis; death within minutes
|-
| >1000 || Immediate collapse, cardiac arrest, death after single breath
|}


remove pt from source and use standard resus measures
===Mechanism of toxicity===
*Rapidly absorbed through the lungs
*Inhibits mitochondrial cytochrome C oxidase (complex IV) by binding to the ferric (Fe³⁺) moiety → blocks aerobic metabolism → cellular asphyxia<ref name="StatPearls"/>
**Identical mechanism to [[Cyanide poisoning|cyanide]]
**Tissues with high oxygen demand (brain, heart) are most sensitive
*Causes lactate accumulation and metabolic acidosis from impaired oxidative phosphorylation
*Causes hyperpolarization of potassium-mediated neuronal channels → CNS depression<ref name="Tintinalli"/>
*Potentiates neuronal inhibitory mechanisms; alters brain neurotransmitter content
*Direct mucosal irritant → conjunctivitis, pulmonary edema
*At very high concentrations, stimulates carotid/aortic chemosensors → initial hyperpnea, then central respiratory arrest


===Healthcare worker safety===
*'''Rescuers entering confined spaces without SCBA frequently become fatalities themselves'''<ref name="ATSDR"/>
*SCBA is mandatory for any responder entering the hot zone
*Chemical-protective clothing is generally NOT needed (H₂S is not significantly absorbed through skin)
*In detergent suicide scenarios:
**Approach with extreme caution; do not enter enclosed space (car, bathroom) without respiratory protection
**Look for warning signs posted by the patient
**Ventilate the space before entry
*Patients exposed only to H₂S gas do not generally require decontamination
*H₂S burns to produce sulfur dioxide (SO₂) — a secondary hazard if ignited


==Clinical features==
*The classic toxidrome: '''"knockdown + pulmonary edema + conjunctivitis + olfactory paralysis"'''<ref name="StatPearls"/>


===Respiratory===
*Dyspnea, cough, chest tightness
*Hemoptysis
*Bronchospasm, wheezing
*Rales, rhonchi
*Pulmonary edema — may be immediate or delayed up to 72 hours<ref name="ATSDR"/>
*[[ARDS]]
*Central respiratory arrest at high concentrations


[[Category:Tox]]
===Ophthalmic ("gas eye")===
*Conjunctivitis (often the earliest sign at low concentrations)
*Corneal ulceration, corneal scarring
*Photophobia, tearing
*Blepharospasm
 
===Central nervous system===
*Headache, dizziness, weakness (early)
*"Knockdown" — sudden loss of consciousness within 1-2 breaths at ≥500 ppm; may be followed by apparent rapid recovery, but can leave lasting neurologic injury<ref name="StatPearls"/>
*Disequilibrium, ataxia
*Intention tremor, muscle rigidity
*Seizures
*Coma
 
===Neuropsychiatric (may be delayed/persistent)===
*Amnesia (particularly surrounding the event)
*Lack of insight, disorientation
*Delirium
*Cognitive impairment, dementia
*Depression, personality changes
*Peripheral neuropathy
*Persistent neurologic deficits may follow '''"knockdown"''' events even with apparent recovery<ref name="StatPearls"/>
 
===Cardiovascular===
*[[Chest pain]]
*[[Bradycardia]]
*Tachycardia (early sympathetic stimulation)
*Hypotension
*Myocardial injury (elevated troponin/CK reported)<ref name="Chou2013">Chou S, et al. Hydrogen sulfide exposure in an adult male. ''Ann Saudi Med''. 2010;30(1):76-80. doi:10.4103/0256-4947.59379</ref>
*ECG: T-wave changes, P-wave abnormalities, QTc prolongation
*Cardiac arrest (PEA, asystole)
 
===Gastrointestinal===
*Green-gray line on gingiva (characteristic but not always present)
*Nausea, vomiting, diarrhea
 
===Other===
*Cyanosis (from respiratory failure, not methemoglobinemia in most cases)
*Metabolic acidosis with elevated lactate
*Gray-green discoloration of skin/blood on autopsy (sulfhemoglobin formation — a postmortem finding)
 
==Differential diagnosis==
===Toxic gas exposures===
*[[Cyanide poisoning]] (virtually identical mechanism; distinguish by exposure context)
*[[Carbon monoxide poisoning]]
*[[Arsine gas exposure]]
*[[Phosphine poisoning]] ([[Aluminum phosphide poisoning]], [[Zinc phosphide poisoning]])
*[[Methane]] / simple asphyxiant exposure
*[[Chlorine gas exposure]]
*Sulfur dioxide exposure
{{Toxic gas exposure DDX}}
 
==Evaluation==
*No single rapid bedside test exists to confirm H₂S exposure<ref name="StatPearls"/>
*Diagnosis is clinical: exposure history (confined space, rotten egg odor, industrial setting, detergent suicide setup) + compatible symptoms
 
===Labs===
*ABG/VBG: metabolic acidosis with elevated lactate + normal or elevated PaO₂/SaO₂ (cellular asphyxiant — oxygen delivery is adequate but cells cannot use it)
**Classic finding: lactic acidosis with normal oxygen saturation (unless concurrent pulmonary edema reduces oxygenation)
*Serum lactate: elevated (reflects impaired oxidative phosphorylation)
*BMP: electrolytes, renal function
*CBC: leukopenia, neutropenia reported
*Hepatic function panel (hepatic injury reported in severe cases)
*Troponin, CK — myocardial and skeletal muscle injury
*Methemoglobin level — obtained if nitrite therapy administered (target <30%)
*Whole blood sulfide: >0.05 mg/L is abnormal; must be obtained '''within 2 hours''' of exposure and analyzed immediately; not available in most hospitals and will not affect acute management<ref name="StatPearls"/>
*Urine thiosulfate: reflects H₂S exposure in acute setting; useful for workplace monitoring but rarely available acutely
 
===Imaging===
*Chest radiograph: pulmonary edema (may be delayed 24-72 hours)
*CT head: consider if persistent altered mental status; basal ganglia necrosis has been reported after severe exposure
 
===Other===
*ECG: ST-T changes, QTc prolongation, dysrhythmias
*Discolored copper coins found on the patient may turn dark/black (copper sulfide formation) — can serve as a supportive diagnostic clue<ref name="Tintinalli"/>
 
==Management==
===Immediate===
*Remove from exposure — ensure scene safety; do not enter confined space without SCBA
*100% high-flow oxygen via NRB mask — cornerstone of treatment
**Competes with H₂S for cytochrome oxidase binding
**Administer to all patients regardless of SpO₂
*Airway management: intubate early for altered mental status, respiratory failure, or airway compromise
*IV access, continuous cardiac monitoring
 
===Antidotal therapy===
 
====Hydroxocobalamin (preferred)====
*[[Hydroxocobalamin]] (Cyanokit): 5 g IV over 15 minutes; second dose may be given PRN<ref name="Haouzi2015">Haouzi P et al. High-dose hydroxocobalamin administered after H₂S exposure counteracts sulfide-poisoning-induced cardiac depression in sheep. ''Clin Toxicol (Phila)''. 2015;53(1):28-36.</ref>
*Mechanism: binds sulfide directly, forming sulfhydroxocobalamin
*Animal models demonstrate prevention of PEA cardiac arrest when given early<ref name="Haouzi2015"/>
*Emerging as the preferred antidote over nitrites due to safer side-effect profile (does not induce methemoglobinemia) and efficacy against both H₂S and cyanide
*[[Cobinamide]] (vitamin B₁₂ analog) shows promise in animal studies as a potentially superior antidote with greater sulfide-binding capacity<ref name="Jiang2016">Jiang J et al. Hydrogen Sulfide — Mechanisms of Toxicity and Development of an Antidote. ''Sci Rep''. 2016;6:20831.</ref><ref name="Brenner2014">Brenner M et al. The vitamin B₁₂ analog cobinamide is an effective hydrogen sulfide antidote in a lethal rabbit model. ''Clin Toxicol (Phila)''. 2014;52(5):490-497.</ref>
 
====Nitrite therapy (alternative)====
*May use the nitrite component of the cyanide antidote kit — do NOT give the thiosulfate portion (thiosulfate is the product of H₂S detoxification and does not help)<ref name="Goldfrank">Goldfrank et al. Hydrogen Sulfide Poisoning. In: Goldfrank et al. Goldfrank's Toxicologic Emergencies. New York, NY: McGraw Hill. 2002. 1504-1507.</ref>
*Mechanism: nitrites induce methemoglobinemia; methemoglobin (Fe³⁺) has high affinity for sulfide → converts it to the less toxic sulfmethemoglobin
*[[Amyl nitrite]] inhaled (pearls crushed and inhaled) — may be used as a bridge
*[[Sodium nitrite]] (3% NaNO₂): 10 mL (300 mg) IV over 2-4 minutes in adults; pediatric dose 0.33 mL/kg (max 10 mL)
*Obtain methemoglobin level 30 minutes after dose — desired level <30%
*Caution: nitrite-induced methemoglobinemia can worsen oxygen-carrying capacity in already hypoxic patients; not first-line if hydroxocobalamin is available
 
===Supportive care===
*Aggressive IV fluid resuscitation
*Bronchospasm: inhaled beta-2 agonists (albuterol), consider racemic epinephrine for stridor in children
*Seizures: [[Benzodiazepines|benzodiazepines]] first-line
*Pulmonary edema: positive-pressure ventilation (CPAP/BiPAP or mechanical ventilation); diuretics generally not effective for noncardiogenic pulmonary edema
*Metabolic acidosis: treat with oxygen and supportive care; IV sodium bicarbonate if severe
*Cardiac arrest: standard ACLS protocols; prolonged resuscitation may be warranted (potentially reversible etiology)
*Hyperbaric oxygen therapy: has been used; no proven benefit; consider on a case-by-case basis for severe neurologic injury<ref name="Goldfrank"/>
 
===Things to avoid===
*'''Do NOT give thiosulfate''' (the third component of the traditional cyanide antidote kit) — thiosulfate is the end product of endogenous H₂S detoxification and provides no benefit
*'''Do NOT rely on odor''' as a gauge of ongoing exposure — olfactory nerve fatigue renders it unreliable at dangerous concentrations
 
==Disposition==
*Asymptomatic patients with possible low-level exposure: observe for minimum 4-6 hours; if asymptomatic with normal labs and CXR, may discharge with return precautions for delayed pulmonary edema (up to 72 hours)<ref name="ATSDR"/>
*Any symptomatic patient or significant exposure: admit, likely to ICU
**Continuous cardiac and pulse oximetry monitoring
**Serial ABGs, lactate, CXR
**Watch for delayed pulmonary edema (may develop up to 72 hours after exposure)<ref name="ATSDR"/>
*"Knockdown" patients (even with apparent rapid recovery): admit for observation — high risk for persistent or delayed neurologic sequelae<ref name="StatPearls"/>
*Outpatient follow-up:
**Neuropsychiatric evaluation — cognitive impairment, amnesia, personality changes, and peripheral neuropathy may develop or persist weeks to months after exposure
**Pulmonary function testing if respiratory symptoms persist
**Ophthalmologic evaluation for corneal injury
*Toxicology consultation for all significant exposures
*Contact [[Poison control]] (1-800-222-1222 in the US) for all cases
 
==Medication Dosing==
{{MedicationDose
| drug = Hydroxocobalamin
| dose = 5g IV over 15 min, may repeat x1 PRN
| route = IV
| context = Preferred antidote
| indication = Hydrogen sulfide toxicity
| population = Adult
}}
 
==See Also==
*[[Cyanide poisoning]]
*[[Carbon monoxide poisoning]]
*[[Arsine gas exposure]]
*[[Aluminum phosphide poisoning]]
*[[Zinc phosphide poisoning]]
*[[Methemoglobinemia]]
 
==External Links==
*[https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=385&toxid=67 ATSDR — Hydrogen Sulfide Medical Management Guidelines]
*[https://www.ncbi.nlm.nih.gov/books/NBK559264/ StatPearls — Hydrogen Sulfide Toxicity]
*[https://www.cdc.gov/niosh/idlh/7783064.html NIOSH — Hydrogen Sulfide IDLH Documentation]
*[https://www.osha.gov/hydrogen-sulfide OSHA — Hydrogen Sulfide Hazards]
 
==References==
<references/>
 
[[Category:Toxicology]]

Latest revision as of 09:30, 22 March 2026

Background

  • Hydrogen sulfide (H₂S) is an extremely toxic, colorless, flammable gas that inhibits mitochondrial cytochrome C oxidase — a mechanism nearly identical to cyanide.
  • It is the most common cause of fatal toxic gas exposure in the workplace.[1]
  • The classic toxidrome is knockdown (rapid loss of consciousness), pulmonary edema, conjunctivitis, and olfactory paralysis.[2]


General information

  • Colorless, highly flammable, heavier-than-air gas
  • "Rotten egg" odor at low concentrations (detectable at ~0.5 ppb)[3]
  • WARNING: Odor is NOT a reliable safety indicator — olfactory nerve fatigue occurs at ≥100 ppm (within 2-15 minutes), causing complete loss of smell at the very concentrations that are dangerous[2]
  • Heavier than air → accumulates in enclosed, low-lying, and poorly ventilated spaces (sewers, manure pits, tanks)
  • Encountered in:
    • Oil and gas industry (primary chemical hazard of natural gas production)
    • Sewers, wastewater treatment
    • Manure pits, animal confinement facilities
    • Paper/pulp mills, tanneries
    • Roofing/asphalt operations
    • Mining, smelting
    • Hot springs, volcanic areas
  • Suicide method ("detergent suicide"): mixing acidic household cleaners (toilet bowl cleaner) with sulfur-containing products (bath salts, lime sulfur pesticide) to generate H₂S in an enclosed space — increasing in prevalence[1]
  • Most fatalities occur in confined spaces; rescuers entering without SCBA frequently become secondary victims[3]
  • Children are at higher risk at the same ambient concentration due to higher minute volume:weight ratios and shorter stature (gas settles near the ground)[3]

Concentration-dependent effects

Concentration (ppm) Effects
0.01-0.03 Rotten egg odor detectable
2-5 Nausea, headache, tearing with prolonged exposure
10-20 Eye irritation ("gas eye"), mild respiratory irritation
50-100 Conjunctivitis, respiratory tract irritation; olfactory fatigue begins at 100 ppm
100-200 Olfactory paralysis (loss of smell); cough, eye irritation, drowsiness; potentially fatal after 4-48 hours
200-300 Marked conjunctivitis, respiratory irritation after 1 hour; pulmonary edema risk
500-700 Staggering, collapse within 5 minutes; serious eye damage; fatal in 30-60 minutes
700-1000 Rapid "knockdown" — LOC within 1-2 breaths; respiratory paralysis; death within minutes
>1000 Immediate collapse, cardiac arrest, death after single breath

Mechanism of toxicity

  • Rapidly absorbed through the lungs
  • Inhibits mitochondrial cytochrome C oxidase (complex IV) by binding to the ferric (Fe³⁺) moiety → blocks aerobic metabolism → cellular asphyxia[2]
    • Identical mechanism to cyanide
    • Tissues with high oxygen demand (brain, heart) are most sensitive
  • Causes lactate accumulation and metabolic acidosis from impaired oxidative phosphorylation
  • Causes hyperpolarization of potassium-mediated neuronal channels → CNS depression[1]
  • Potentiates neuronal inhibitory mechanisms; alters brain neurotransmitter content
  • Direct mucosal irritant → conjunctivitis, pulmonary edema
  • At very high concentrations, stimulates carotid/aortic chemosensors → initial hyperpnea, then central respiratory arrest

Healthcare worker safety

  • Rescuers entering confined spaces without SCBA frequently become fatalities themselves[3]
  • SCBA is mandatory for any responder entering the hot zone
  • Chemical-protective clothing is generally NOT needed (H₂S is not significantly absorbed through skin)
  • In detergent suicide scenarios:
    • Approach with extreme caution; do not enter enclosed space (car, bathroom) without respiratory protection
    • Look for warning signs posted by the patient
    • Ventilate the space before entry
  • Patients exposed only to H₂S gas do not generally require decontamination
  • H₂S burns to produce sulfur dioxide (SO₂) — a secondary hazard if ignited

Clinical features

  • The classic toxidrome: "knockdown + pulmonary edema + conjunctivitis + olfactory paralysis"[2]

Respiratory

  • Dyspnea, cough, chest tightness
  • Hemoptysis
  • Bronchospasm, wheezing
  • Rales, rhonchi
  • Pulmonary edema — may be immediate or delayed up to 72 hours[3]
  • ARDS
  • Central respiratory arrest at high concentrations

Ophthalmic ("gas eye")

  • Conjunctivitis (often the earliest sign at low concentrations)
  • Corneal ulceration, corneal scarring
  • Photophobia, tearing
  • Blepharospasm

Central nervous system

  • Headache, dizziness, weakness (early)
  • "Knockdown" — sudden loss of consciousness within 1-2 breaths at ≥500 ppm; may be followed by apparent rapid recovery, but can leave lasting neurologic injury[2]
  • Disequilibrium, ataxia
  • Intention tremor, muscle rigidity
  • Seizures
  • Coma

Neuropsychiatric (may be delayed/persistent)

  • Amnesia (particularly surrounding the event)
  • Lack of insight, disorientation
  • Delirium
  • Cognitive impairment, dementia
  • Depression, personality changes
  • Peripheral neuropathy
  • Persistent neurologic deficits may follow "knockdown" events even with apparent recovery[2]

Cardiovascular

  • Chest pain
  • Bradycardia
  • Tachycardia (early sympathetic stimulation)
  • Hypotension
  • Myocardial injury (elevated troponin/CK reported)[4]
  • ECG: T-wave changes, P-wave abnormalities, QTc prolongation
  • Cardiac arrest (PEA, asystole)

Gastrointestinal

  • Green-gray line on gingiva (characteristic but not always present)
  • Nausea, vomiting, diarrhea

Other

  • Cyanosis (from respiratory failure, not methemoglobinemia in most cases)
  • Metabolic acidosis with elevated lactate
  • Gray-green discoloration of skin/blood on autopsy (sulfhemoglobin formation — a postmortem finding)

Differential diagnosis

Toxic gas exposures

Toxic gas exposure

Evaluation

  • No single rapid bedside test exists to confirm H₂S exposure[2]
  • Diagnosis is clinical: exposure history (confined space, rotten egg odor, industrial setting, detergent suicide setup) + compatible symptoms

Labs

  • ABG/VBG: metabolic acidosis with elevated lactate + normal or elevated PaO₂/SaO₂ (cellular asphyxiant — oxygen delivery is adequate but cells cannot use it)
    • Classic finding: lactic acidosis with normal oxygen saturation (unless concurrent pulmonary edema reduces oxygenation)
  • Serum lactate: elevated (reflects impaired oxidative phosphorylation)
  • BMP: electrolytes, renal function
  • CBC: leukopenia, neutropenia reported
  • Hepatic function panel (hepatic injury reported in severe cases)
  • Troponin, CK — myocardial and skeletal muscle injury
  • Methemoglobin level — obtained if nitrite therapy administered (target <30%)
  • Whole blood sulfide: >0.05 mg/L is abnormal; must be obtained within 2 hours of exposure and analyzed immediately; not available in most hospitals and will not affect acute management[2]
  • Urine thiosulfate: reflects H₂S exposure in acute setting; useful for workplace monitoring but rarely available acutely

Imaging

  • Chest radiograph: pulmonary edema (may be delayed 24-72 hours)
  • CT head: consider if persistent altered mental status; basal ganglia necrosis has been reported after severe exposure

Other

  • ECG: ST-T changes, QTc prolongation, dysrhythmias
  • Discolored copper coins found on the patient may turn dark/black (copper sulfide formation) — can serve as a supportive diagnostic clue[1]

Management

Immediate

  • Remove from exposure — ensure scene safety; do not enter confined space without SCBA
  • 100% high-flow oxygen via NRB mask — cornerstone of treatment
    • Competes with H₂S for cytochrome oxidase binding
    • Administer to all patients regardless of SpO₂
  • Airway management: intubate early for altered mental status, respiratory failure, or airway compromise
  • IV access, continuous cardiac monitoring

Antidotal therapy

Hydroxocobalamin (preferred)

  • Hydroxocobalamin (Cyanokit): 5 g IV over 15 minutes; second dose may be given PRN[5]
  • Mechanism: binds sulfide directly, forming sulfhydroxocobalamin
  • Animal models demonstrate prevention of PEA cardiac arrest when given early[5]
  • Emerging as the preferred antidote over nitrites due to safer side-effect profile (does not induce methemoglobinemia) and efficacy against both H₂S and cyanide
  • Cobinamide (vitamin B₁₂ analog) shows promise in animal studies as a potentially superior antidote with greater sulfide-binding capacity[6][7]

Nitrite therapy (alternative)

  • May use the nitrite component of the cyanide antidote kit — do NOT give the thiosulfate portion (thiosulfate is the product of H₂S detoxification and does not help)[8]
  • Mechanism: nitrites induce methemoglobinemia; methemoglobin (Fe³⁺) has high affinity for sulfide → converts it to the less toxic sulfmethemoglobin
  • Amyl nitrite inhaled (pearls crushed and inhaled) — may be used as a bridge
  • Sodium nitrite (3% NaNO₂): 10 mL (300 mg) IV over 2-4 minutes in adults; pediatric dose 0.33 mL/kg (max 10 mL)
  • Obtain methemoglobin level 30 minutes after dose — desired level <30%
  • Caution: nitrite-induced methemoglobinemia can worsen oxygen-carrying capacity in already hypoxic patients; not first-line if hydroxocobalamin is available

Supportive care

  • Aggressive IV fluid resuscitation
  • Bronchospasm: inhaled beta-2 agonists (albuterol), consider racemic epinephrine for stridor in children
  • Seizures: benzodiazepines first-line
  • Pulmonary edema: positive-pressure ventilation (CPAP/BiPAP or mechanical ventilation); diuretics generally not effective for noncardiogenic pulmonary edema
  • Metabolic acidosis: treat with oxygen and supportive care; IV sodium bicarbonate if severe
  • Cardiac arrest: standard ACLS protocols; prolonged resuscitation may be warranted (potentially reversible etiology)
  • Hyperbaric oxygen therapy: has been used; no proven benefit; consider on a case-by-case basis for severe neurologic injury[8]

Things to avoid

  • Do NOT give thiosulfate (the third component of the traditional cyanide antidote kit) — thiosulfate is the end product of endogenous H₂S detoxification and provides no benefit
  • Do NOT rely on odor as a gauge of ongoing exposure — olfactory nerve fatigue renders it unreliable at dangerous concentrations

Disposition

  • Asymptomatic patients with possible low-level exposure: observe for minimum 4-6 hours; if asymptomatic with normal labs and CXR, may discharge with return precautions for delayed pulmonary edema (up to 72 hours)[3]
  • Any symptomatic patient or significant exposure: admit, likely to ICU
    • Continuous cardiac and pulse oximetry monitoring
    • Serial ABGs, lactate, CXR
    • Watch for delayed pulmonary edema (may develop up to 72 hours after exposure)[3]
  • "Knockdown" patients (even with apparent rapid recovery): admit for observation — high risk for persistent or delayed neurologic sequelae[2]
  • Outpatient follow-up:
    • Neuropsychiatric evaluation — cognitive impairment, amnesia, personality changes, and peripheral neuropathy may develop or persist weeks to months after exposure
    • Pulmonary function testing if respiratory symptoms persist
    • Ophthalmologic evaluation for corneal injury
  • Toxicology consultation for all significant exposures
  • Contact Poison control (1-800-222-1222 in the US) for all cases

Medication Dosing

Hydroxocobalamin 5g IV over 15 min, may repeat x1 PRN IV

See Also

External Links

References

  1. ↑ 1.0 1.1 1.2 1.3 Tintinalli et al.
    • Hydrogen Sulfide.
    • In: Tintinalli et al.
    • Emergency Medicine A Comprehensive Study Guide.
    • New York, NY: McGraw Hill. 2011. 1320.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Hydrogen Sulfide Toxicity. StatPearls. 2024.
    • PMID: 32119270
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Hydrogen Sulfide Medical Management Guidelines. Agency for Toxic Substances and Disease Registry (ATSDR). CDC.
  4. ↑ Chou S, et al. Hydrogen sulfide exposure in an adult male. Ann Saudi Med. 2010;30(1):76-80. doi:10.4103/0256-4947.59379
  5. ↑ 5.0 5.1 Haouzi P et al. High-dose hydroxocobalamin administered after H₂S exposure counteracts sulfide-poisoning-induced cardiac depression in sheep. Clin Toxicol (Phila). 2015;53(1):28-36.
  6. ↑ Jiang J et al. Hydrogen Sulfide — Mechanisms of Toxicity and Development of an Antidote. Sci Rep. 2016;6:20831.
  7. ↑ Brenner M et al. The vitamin B₁₂ analog cobinamide is an effective hydrogen sulfide antidote in a lethal rabbit model. Clin Toxicol (Phila). 2014;52(5):490-497.
  8. ↑ 8.0 8.1 Goldfrank et al. Hydrogen Sulfide Poisoning. In: Goldfrank et al. Goldfrank's Toxicologic Emergencies. New York, NY: McGraw Hill. 2002. 1504-1507.
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