Carbon monoxide (CO) poisoning is a common, potentially fatal toxicological emergency caused by inhalation of a colorless, odorless, non-irritant gas produced by incomplete combustion of carbon-containing materials.

Sources include:

• Charcoal stoves used indoors

• Firewood burning in poorly ventilated rooms

• Gas heaters and boilers

• Motor vehicle exhaust in enclosed spaces

• Petrol/diesel generators in homes

• House fires

Because CO cannot be detected by smell or sight, exposure frequently occurs unknowingly during sleep, making it a leading cause of accidental poisoning worldwide.

2. Pathophysiology

Carbon monoxide toxicity occurs through tissue hypoxia and cellular poisoning.

Mechanisms

1. Carboxyhemoglobin formation

   • CO binds hemoglobin with affinity 200–250× greater than oxygen

   • Forms carboxyhemoglobin (COHb)

   • Prevents oxygen delivery to tissues

2. Left shift of oxygen dissociation curve

   • Remaining oxygen cannot be released to tissues

3. Cellular respiration inhibition

   • Binds cytochrome oxidase

   • Blocks mitochondrial oxidative phosphorylation

   • Causes anaerobic metabolism → lactic acidosis

4. Inflammatory neuronal injury

   • Delayed neurologic syndrome (days–weeks later)

3. Risk Factors

• Indoor charcoal cooking/heating

• Poor ventilation housing

• Generator use indoors or near windows

• Sleeping in parked car with engine running

• House fires

• Gas heater malfunction

• Cold weather seasons

• Infants and elderly

• Pregnant women (fetal Hb binds CO more strongly)

• Chronic heart disease or anemia

4. Clinical Features

Symptoms correlate poorly with COHb level — patients may appear “normal”.

Mild Poisoning (COHb ~10–20%)

• Dull frontal headache

• Dizziness

• Fatigue

• Weakness

• Nausea

• Vomiting

Moderate Poisoning (COHb ~20–40%)

• Severe headache

• Shortness of breath

• Blurred vision

• Confusion

• Ataxia

• Chest pain

• Syncope

Severe Poisoning (COHb >40%)

• Altered consciousness

• Seizures

• Coma

• Hypotension

• Arrhythmias

• Respiratory failure

• Death

Important Clinical Clues

• Multiple people in same house affected

• Symptoms improve outdoors

• “Flu-like illness” without fever

• Patient may look pink/cherry colored (rare and late sign)

5. Diagnostic Criteria

Suspect CO poisoning in any patient with:

• Headache + dizziness in enclosed environment

• Unexplained altered mental status

• Exposure to combustion source

• Family members with similar symptoms

Diagnosis confirmed by elevated carboxyhemoglobin level.

6. Investigations

Essential

• Arterial or venous blood gas

• Carboxyhemoglobin level (CO-oximetry)

Pulse oximetry is unreliable (reads falsely normal)

Additional Tests

• Serum electrolytes

• Lactate (elevated in severe poisoning)

• ECG (ischemia/arrhythmia)

• Troponin (myocardial injury)

• CT brain (persistent coma)

• Fetal monitoring in pregnancy

7. Management

Treat immediately — do not wait for lab confirmation

7.1 Initial Stabilization (ABCDE)

Airway

• Clear airway

• Intubate if GCS ≤8

Breathing

• High-flow oxygen immediately

Circulation

• IV access

• Cardiac monitoring

• Treat hypotension

7.2 Oxygen Therapy (Primary Treatment)

Give 100% oxygen via non-rebreather mask

Effects:

• Reduces COHb half-life from 5 hours → 60 minutes

Continue until:

• Symptoms resolved

• COHb <5% (<3% in pregnancy/children)

7.3 Hyperbaric Oxygen Therapy (HBOT)

Indications:

• COHb ≥25% (≥15% in pregnancy)

• Loss of consciousness

• Neurological deficits

• Severe metabolic acidosis

• Ischemic ECG changes

• Pregnancy with symptoms

Benefits:

• Reduces delayed neurologic syndrome

• Faster CO elimination

• Protects fetal brain

7.4 Supportive Treatment

• IV fluids

• Treat seizures (benzodiazepines)

• Manage arrhythmias

• Correct acidosis

• ICU admission if severe

8. Complications

Early

• Myocardial ischemia

• Pulmonary edema

• Shock

Delayed (days–weeks later)

Delayed Neuropsychiatric Syndrome

• Memory loss

• Personality change

• Parkinsonism

• Gait disturbance

• Dementia

9. Special Populations

Pregnancy

Fetus is highly vulnerable:

• Fetal COHb > maternal levels

• Requires aggressive oxygen ± HBOT

Children

Develop neurologic injury at lower exposures.

10. Prognosis

11. Prevention

Home Safety Measures

• Install carbon monoxide detectors

• Ventilate cooking areas

• Never use charcoal indoors

• Do not run generators inside house

• Service gas appliances regularly

• Avoid sleeping in running vehicle

Do’s

• Keep hazardous materials safely

• Read safety labels

Don’ts

• Indoor charcoal burning

• Generator use in enclosed space

• Sealed room heating fires