16.Irrespirable gases

Carbon Monoxide (CO) (UQ)

• Formed by incomplete combustion of carbonaceous materials

• Colorless, odorless, tasteless, non-irritating gas, lighter than air

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

• Sources:

  • Automobile exhaust

  • Industrial smoke

  • Tobacco smoke

  • Coal gas

Signs and Symptoms

• Common after mine explosions (after damp, choke damp)

• Upper limit of safety in air: 0.01% (100 ppm)

Mechanism of Action

• Combines with hemoglobin to form carboxyhemoglobin, producing anemic hypoxia

• Has 200 to 300 times more affinity for hemoglobin than oxygen

• Inhibits Cytochrome A3 oxidase and Cytochrome P450, hindering intracellular respiration

• 15% of CO combines with myoglobin

Symptoms Progression

• Development of symptoms correlates with CO saturation in the blood

• Common acute symptoms: headache, dizziness, nausea, confusion

• Regression of symptoms depends on clearance of CO from blood

• Effects mimic hypoxia:

  • Liver: Enlarged liver, bleeding tendency

  • CNS: Most sensitive; potential spastic paraplegia, impairment of intellectual functions, personality changes, retrograde amnesia, parkinsonism

  • CVS: Dysrhythmias, myocardial infarction

  • Skin: Bullous lesions due to skin hypoxia

Signs & Symptoms by Carboxyhemoglobin Levels (% in blood)

• Victims may exhibit erratic movements, which can be mistaken for assault

• Children saturate their blood more rapidly than adults

• Severity of symptoms 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

• Diagnosis often misinterpreted due to vague symptoms.

• Methods for diagnosis:

  • History, signs, and symptoms

• Lab findings:

  • COHb Analysis

    • Spectroscopy can identify carboxyhemoglobin (COHb) by showing two absorption bands between Fraunhoffer's lines D & E, similar to oxyhemoglobin.

    • With a reducing agent, bands remain unchanged unlike oxyhemoglobin.

  • Kunkel's Test

    • Diluted blood (1:10) + few drops of tannic acid; a crimson red coagulum indicates COHb presence.

  • Hoppe-Seyler's Test

    • Blood + 10% NaOH; results in pink/red color 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 of 2-3 atmospheric pressure

   • Gastric lavage to prevent aspiration pneumonia

   • Supportive measures

   • Treat cerebral edema with 20% mannitol solution (500 ml 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: may contain petechial hemorrhages

  • Brain: congested and edematous

    • Bilateral symmetrical necrosis in basal ganglia (putamen and globus pallidus)

    • Punctiform ring hemorrhage in white matter (common)

Circumstances of Poisoning

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

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

• Inhalation Risks: CO with CO2 in confined spaces during explosions.

• Safety Note: Safe CO level in air is 0.1%.

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

Carbon Dioxide (CO₂)

Properties

• Heavy, colorless, odorless, slightly irritating gas.

• Solid form: Dry ice.

Source

• Unused wells, putrefied organic matter.

Action

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

• Symptoms of CO₂ poisoning result from lack of oxygen.

Signs and Symptoms by Blood Concentration

• 2-10%: Throbbing headache, tachypnea, tinnitus, mental confusion, muscle tremors.

• 10-20%: Slow respiration, blood pressure falls

• 20-40%: Dyspnea, Muscular weakness

• 40-60%: Drowsiness, Coma, convulsions, and death.

Postmortem Findings

• Features of asphyxia

• Froth at nostrils

• Cyanosis

• Blue tint to hypostasis

• Petechiae on face, in pleural and pericardial surfaces.

• All internal organs congested; brain congested and edematous.

Circumstances of Poisoning

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

• "Ghost wells" named due to historical beliefs about deaths in unused wells.

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

Hydrogen Sulphide (H₂S)

Properties

• Colorless gas with a smell of rotten eggs.

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

Sources

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

Action

• H₂S does not combine with hemoglobin but with methemoglobin, causing asphyxiation by disrupting oxygen use in the cytochrome oxidase system.

  • Comparable toxicity and rapidity of action to cyanide.

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 occurs due to paralysis of respiratory centre leading to respiratory failure.

Treatment

1. Remove the victim to fresh air.

2. Artificial respiration & 100% oxygen.

3. Amyl nitrite inhalation and sodium nitrite infusion to form sulfmethemoglobin.

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

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

4. Supportive measures for electrolyte imbalance and pulmonary edema.

Postmortem Appearances

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

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

• Rotten egg smell at the mouth and nostrils.

Circumstances of Poisoning

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

• Detergent Suicide/Chemical Suicide: A method using household items (bath sulfur + toilet cleaner) resulting in toxicity through inhalation, notably in Japan due to internet influence.

Chronic Exposure to H2S

• Symptoms include:

  • Headache

  • Nausea

  • Weakness

  • Weight Loss

  • Ataxia and Tremors

  • Anesthesia of the nasal mucosa

  • Conjunctivitis, Pharyngitis

  • Green Line on Gingiva

  • 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

• Irritation of eyes, nose, throat and respiratory passages.

• Nausea, vomiting, and abdominal pain.

• Passes through the clothes into the skin producing itching, redness, vesication and ulceration

• 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

• Phosgene: 4x more toxic than Chlorine, produced by oxidation of chlorinated hydrocarbons.

• Their action is mainly on pulmonary alveoli.

• Phosgene and diphosgene are known as green cross gases.

• Signs and Symptoms:

  • Watering Eyes

  • Nausea and Vomiting

  • Cough and Dyspnea

  • Stertorous Breathing

  • Cyanosis and Collapse

• Treatment:

  • Eye wash with saline

  • Oxygen therapy

  • Antibiotics to prevent infection.

iii) Lachrymators or Tear Gases

• Examples: Chloracetophenone, Ethyliodoacetate, Bromobenzyl cyanide

• Symptoms: Severe eye irritation, temporary blindness, irritation of air passages, nausea, and vomiting with 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, Diphenylcyanoarsine

• Symptoms: Intense nasal and sinus irritation, rhinitis, sneezing, chest tightness, headache, nausea, vomiting.

• 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 - C₂H₃NO)

• Bhopal Gas Tragedy:

  • Occurred in 1984

  • Death toll: over 2000

  • Injuries: more than 200,000 people affected

  • Blindness: over 50,000 people affected

  • Alleged gas released: Phosgene (10 times more toxic than MIC)

Physical Properties of MIC

• State: Liquid

• Boiling Point: 31°C

• Reactivity: Violently reacts with water and moisture, necessitating storage under inert conditions.

• Usage: Intermediate product in the production of carbamate pesticide.

Mechanism of Action

• Local Effects:

  • Irritant to eyes and respiratory system

• Systemic Action:

  • Carbamylation of enzymes

• Fatal Dose: >21 ppm concentration for 1-5 minutes

• Fatal Period: 5 minutes to 2 days

Clinical Features

• Irritation of eyes, nose, and throat

• Blindness

• Pulmonary edema: most common complication

• Bronchopneumonia

• Uremia

• Hypotension

• Hypothermia

• Psychological disturbances in 10% of cases

Treatment

• Decontamination of skin and eyes

• Oxygen therapy

• Bronchodilators

• Antibiotics to prevent pneumonia

vi) Nerve Gases

• Types of Nerve Gases:

  1. Tabun (GA)

  2. Sarin (GB)

  3. Soman (GD)

  4. Cyclosarin (GF)

  5. VX (Ethyl-methyl phosphonothioate)

• Chemical Nature: Derivatives of phosphoric acid, act identically to organophosphates

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

• Mechanism: Inhibitors of acetylcholinesterase

Signs and Symptoms

• Similar to organophosphate (OP) poisoning

• Loss of consciousness within seconds with large doses

• Convulsions following shortly after

• Death due to respiratory paralysis

Treatment

• Similar to that of OP poisoning