16-Irrespirable_gases

Irrespirable Gases

Carbon Monoxide (CO)

  • Formation:

    • Produced by incomplete combustion of carbon-based materials.

  • Properties:

    • Colorless, odorless, tasteless, non-irritating, and lighter than air.

  • Chemical Reactions:

    • Combines with chlorine to form carbonyl chloride (phosgene, CoCl2).

Sources:

  • Automobile exhaust

  • Industrial smoke

  • Tobacco smoke

  • Coal gas

Signs and Symptoms:

  • Commonly occur after mine explosions (damp, choke damp).

  • Safety Limit: 0.01% (100 ppm) upper limit in air.

Mechanism of Action:

  • Combines with hemoglobin to form carboxyhemoglobin, causing anemic hypoxia.

  • Has 200-300 times more affinity for hemoglobin than oxygen, inhibiting Cytochrome A3 oxidase and Cytochrome P450, affecting intracellular respiration.

  • 15% of CO bonds with myoglobin.

Symptoms Progression:

  • Symptoms correlate with CO saturation in blood:

    • Common acute symptoms include headache, dizziness, nausea, confusion.

    • Recovery depends on the clearance of CO from the blood.

  • Effects Mimic Hypoxia:

    • Liver: Enlarged liver, bleeding tendency.

    • CNS: Spastic paraplegia, intellectual impairment, personality changes, retrograde amnesia, parkinsonism.

    • CVS: Dysrhythmias, myocardial infarction.

    • Skin: Bullous lesions due to hypoxia.

Signs & Symptoms by Carboxyhemoglobin Levels (% in blood):

COHb %

Symptoms

0-10%

No symptoms

10-20%

Mild headache, lassitude, breathlessness on moderate exertion

20-30%

Throbbing headache, breathlessness, muscular weakness, incoordination

30-40%

Severe headache, nausea, vomiting, dim vision, confusion

40-50%

All symptoms intensified

50-60%

Syncope or coma, convulsions, rapid respiration, rapid weak pulse

60-70%

Deep coma, incontinence of urine and feces

70-80%

Respiratory paralysis and death

Notes:

  • Victims may exhibit erratic movements, potentially mistaken for assault.

  • Children saturate CO more rapidly than adults.

  • Severity varies by blood concentration:

    • 10-30%: Mild

    • 30-40%: Moderate-Severe

    • 40%: Very severe

Differential Diagnosis:

  • Alcohol intoxication

  • Uremia

  • Hypoglycemic coma

  • Head injury >20%

Diagnosis:

  • Often misinterpreted due to vague symptoms.

  • Methods for Diagnosis:

    • Patient history and clinical signs.

  • Lab Findings:

    • COHb Analysis: Spectroscopy identifies carboxyhemoglobin (COHb).

    • Kunkel's Test: Shows crimson red coagulum with diluted blood and tannic acid.

    • Hoppe-Seyler's Test: Produces pink/red color with blood and 10% NaOH if COHb is present.

Treatment Options:

  1. Immediate Care:

    • Remove patient to fresh air.

  2. Specific Treatments:

    • Blood transfusion if required.

    • Hyperbaric oxygen for COHb above 25%: PO2 at 2-3 atmospheric pressure.

    • Gastric lavage to prevent aspiration pneumonia.

    • Supportive measures for cerebral edema (20% mannitol solution IV).

Postmortem Findings:

  • External Findings:

    • Cherry-red color in hypostasis and mucous membranes.

    • Fine froth at mouth/nasal areas.

    • Blisters over bony pressure points (buttocks, calves, wrists, knees).

  • Internal Findings:

    • Lungs: Congested and edematous.

    • Heart: Possible petechial hemorrhages.

    • Brain: Congested and edematous, bilateral necrosis in basal ganglia.

Circumstances of Poisoning:

  • Suicidal: Starting car in neutral in a closed garage.

  • Accidental: Exposure to exhaust gases from burning buildings or gas mines.

  • Safety Note: Safe CO level in air is 0.1%. Inhalation risks in confined spaces during explosions.

  • Homicidal Cases: Rare unless the victim is incapacitated or a child.

Carbon Dioxide (CO2)

Properties:

  • Heavy, colorless, odorless, slightly irritating gas.

  • Solid form: Dry ice.

Sources:

  • Unused wells, putrefied organic matter.

Actions:

  • Pure CO2 may cause glottic spasm due to vagal inhibition, potentially leading to sudden death.

  • Symptoms of CO2 poisoning arise from lack of oxygen.

Signs and Symptoms by Blood Concentration:

CO2 %

Symptoms

2-10%

Throbbing headache, tachypnea, tinnitus, mental confusion, muscle tremors

10-20%

Slow respiration, blood pressure drops

20-40%

Dyspnea, muscular weakness

40-60%

Drowsiness, coma, convulsions, and death

Postmortem Findings:

  • Asphyxia symptoms:

    • Froth at nostrils.

    • Cyanosis.

    • Blue hypostasis.

    • Petechiae on face and in pleural/pericardial surfaces.

    • All internal organs congested; brain congested and edematous.

Circumstances of Poisoning:

  • Rare in suicides and homicides, common in accidents (e.g., mining).

  • Historical context: "Ghost wells" due to certain beliefs about deaths in abandoned wells.

  • Testing CO2 concentration: Use soda lime in a bottle lowered into the well; a milky white indicates calcium carbonate formation.

Hydrogen Sulphide (H2S)

Properties:

  • Colorless gas with a rotten egg smell.

  • Dissolves in water & burns with a pale blue flame.

Sources:

  • Sewage, putrefying bodies, petroleum, silk, rayon, paper industries.

Action:

  • H2S combines with methemoglobin instead of hemoglobin, asphyxiating by disrupting oxygen use in the cytochrome oxidase system.

  • Comparable toxicity to cyanide and rapid onset.

Signs and Symptoms of H2S Poisoning:

  • Respiratory: Rhinitis, breathlessness, cyanosis, pulmonary edema, pneumonia.

  • Cardiovascular: Arrhythmia, myocardial depression.

  • CNS: Giddiness, headache, nystagmus, muscular weakness, poor concentration, delirium, coma, convulsions.

  • Ocular: Lachrymation, photophobia, conjunctivitis.

  • Death: Results from respiratory center paralysis.

Treatment Options:

  1. Remove victim to fresh air.

  2. Provide artificial respiration & 100% oxygen.

  3. Administer amyl nitrite inhalation and sodium nitrite infusion to form sulfmethemoglobin.

    • Break amyl nitrite ampoules and hold over the nose for 30 seconds.

    • Infuse sodium nitrite in 10cc of sterile water slowly IV.

  4. Supportive measures for electrolyte imbalances and pulmonary edema.

Postmortem Appearances:

  • Signs of asphyxia: cyanosis, froth at nostrils, petechial hemorrhages, pulmonary edema.

  • Greenish discoloration of postmortem stains, blood, and visceral organs.

  • Rotten egg smell at the mouth and nostrils.

Circumstances of Poisoning:

  • Accidental Poisoning: Common in industrial workers and sewage cleaners.

  • Detergent Suicide/Chemical Suicide: Involves household items (bath sulfur + toilet cleaner), resulting in toxicity via inhalation.

Chronic Exposure to H2S:

  • Symptoms include:

    • Headache, nausea, weakness, weight loss, ataxia, tremors, nasal mucosa anesthesia, conjunctivitis, pharyngitis.

    • Green Line on Gingiva and allergic bronchitis.

War Gases

Categories of War Gases:

  1. Vesicants/Blistering Gases

  2. Asphyxiants/Lung Irritants

  3. Lachrymators/Tear Gases

  4. Sternutators/Nasal Irritants

  5. Paralysants

  6. Nerve Gases

i) Vesicants or Blistering Gases:

  • Examples: Mustard Gas, Lewisite.

  • Symptoms: Irritation of eyes, nose, throat; nausea, abdominal pain; skin irritation and vesication.

  • Treatment:

    • Wash affected area with soap and water.

    • Eye wash with sodium bicarbonate.

    • BAL (British Anti-Lewisite) for systemic treatment.

ii) Asphyxiants or Lung Irritants:

  • Examples: Carbon Monoxide, Carbon Dioxide, Chlorine, Phosgene, Diphosgene.

  • Properties: Phosgene is 4x more toxic than chlorine, acts primarily on pulmonary alveoli.

  • Symptoms: Watering eyes, nausea, vomiting, cough, dyspnea, cyanosis, collapse.

  • Treatment:

    • Eye wash with saline.

    • Oxygen therapy.

    • Antibiotics to prevent infection.

iii) Lachrymators or Tear Gases:

  • Examples: Chloracetophenone, Ethyliodoacetate.

  • Symptoms: Severe eye irritation, temporary blindness, nausea, skin blistering.

  • Treatment:

    • Remove patient to fresh air.

    • Wash eyes with normal saline.

    • Antibiotics to prevent infection.

iv) Sternutators or Nasal Irritants:

  • Examples: Diphenyl chlorarsine, Diphenylamine chlorarsine.

  • Symptoms: Intense nasal/sinus irritation, rhinitis, sneezing, chest tightness.

  • Treatment:

    • Removal to fresh air.

    • Nose irrigation with sodium bicarbonate.

    • Antibiotics to prevent infection.

v) Paralysants:

  • Types of Paralysants:

    1. Hydrogen sulphide (H2S)

    2. Hydrocyanic acid (HCN)

    3. Carbon monoxide (CO)

    4. Methyl isocyanate (MIC)

Methyl Isocyanate (MIC):

  • Bhopal Gas Tragedy:

    • Occurred in 1984; over 2000 deaths, 200,000 injuries, 50,000 blindness cases. Phosgene was released, which is 10 times more toxic than MIC.

  • Physical Properties:

    • State: Liquid.

    • Boiling Point: 31°C.

    • Reactivity: Violently reacts with water; requires inert storage conditions.

  • Usage: Intermediate product in carbamate pesticide production.

Mechanism of Action:

  • Local Effects: Irritant to eyes and respiratory system.

  • Systemic Action: Carbamylation of enzymes.

  • Fatal Dose: >21 ppm for 1-5 minutes. Fatal Period: 5 minutes to 2 days.

Clinical Features:

  • Symptoms include irritation, blindness, pulmonary edema (common complication), bronchopneumonia, uremia, hypotension, hypothermia, psychological disturbances in ~10% cases.

Treatment:

  • Decontamination of skin/eyes; oxygen therapy; bronchodilators; antibiotics to prevent pneumonia.

vi) Nerve Gases:

  • Types: Tabun (GA), Sarin (GB), Soman (GD), Cyclosarin (GF), VX.

  • Chemical Nature: Derivatives of phosphoric acid, functioning like organophosphates.

  • Properties: Colorless, odorless, absorbed through lungs, skin, GIT, conjunctiva.

  • Mechanism: Inhibit acetylcholinesterase.

Signs and Symptoms:

  • Similar to organophosphate (OP) poisoning; loss of consciousness within seconds from large doses; convulsions; respiratory paralysis leading to death.

  • Treatment: Similar to OP poisoning.