☠️ Carbon Monoxide (CO) Poisoning

🔷 1. What is Carbon Monoxide?

• Colorless, odorless, tasteless gas
• Produced by incomplete combustion of carbon-containing fuels (e.g., gas stoves, car exhausts, fires, generators)
• A major cause of accidental poisoning worldwide

🔷 2. Sources of Exposure

🔷 3. Pathophysiology of CO Poisoning

Carbon monoxide is toxic via multiple mechanisms:

🩸 1. Carboxyhemoglobin Formation

• CO has ~200–250× affinity for Hb vs oxygen
• Forms Carboxyhemoglobin (COHb) → reduces O₂ carrying capacity

⛔ 2. Leftward Shift of Oxy-Hb Curve

• Decreases oxygen unloading at tissues → tissue hypoxia

🧠 3. Direct Cellular Toxicity

• CO binds cytochrome oxidase in mitochondria → impairs oxidative phosphorylation 
• CO induces lipid peroxidation, leukocyte activation, and nitric oxide (NO) release, causing vasodilation, hypotension, and CNS damage.
• Causes lactic acidosis, free radical injury

🧠 4. Delayed Neurotoxicity

• Neuroinflammation, demyelination → delayed encephalopathy

🔷 4. Clinical Features

⏱️ Acute Presentation (dose-dependent)

🧠 Key Signs

• Cherry red skin/mucosa (rare, late finding)
• Tachycardia, hypotension
• Confusion, seizures, coma
• Metabolic acidosis with raised lactate

🔷 5. Diagnosis

🧪 Arterial Blood Gas (ABG):

• Normal PaO₂ despite hypoxia!,  cyanosis absent
• May show metabolic acidosis (↑ lactate)

🩸 COHb Level:

• Gold standard
• Detected via CO-oximetry
• Normal: <2% (nonsmokers), <10% (smokers)
• Toxic: >10–15%

🛑 Pulse oximetry is unreliable: It overestimates SpO₂ (can’t distinguish oxy-Hb vs COHb)

🔷 6. Management

🧯 A – Immediate Removal

• Remove from source
• Ensure patient & responder safety

💨 B – 100% Oxygen Therapy

• High-flow O₂ via non-rebreather mask
• Increases CO elimination (reduces half-life of COHb):

💊 C – Hyperbaric Oxygen (HBO) Therapy

• Indications:
• COHb >25% (>15% in pregnancy)
• Loss of consciousness
• Severe acidosis (pH <7.1)
• Neurologic deficits, cardiac ischemia
• Benefits:
• Faster CO clearance
• Prevents delayed neurological sequelae

🔴 Why HBOT in Pregnancy?

• Fetal hemoglobin has higher affinity for CO, leading to fetal hypoxia.

🔷 7. Investigations

🔷 8. Complications

🔷 9. Delayed Neurological Sequelae (DNS)

• Seen in ~15–40% of survivors
• Develops 3–21 days post exposure
• Symptoms: memory loss, mood changes, psychosis, Parkinsonism
• MRI Brain: demyelination, basal ganglia changes
• Prevention: Early HBO therapy

✅ Avoid Succinylcholine for Intubation

• Risk of hyperkalemia in CO-induced muscle damage

✅ ECG & Cardiac Monitoring

• Myocardial ischemia is common (CO-induced hypoxia & vasodilation)

• Check troponins in high-risk patients

✅ Seizure Control

• Benzodiazepines for seizures (avoid phenytoin due to CO-induced cardiac effects)

🔷 10. Prognosis

• Good with early recognition and treatment
• Poor in delayed diagnosis, prolonged exposure, CNS involvement

🔷 11. Prevention

• CO detectors in homes
• Regular maintenance of appliances
• Educate about safe heating/cooking practices

🔑 Summary Mnemonic: “CO-POISON”

• C – Carboxyhemoglobin formed
• O – Oxygen affinity ↑, tissue delivery ↓
• P – Pulse ox unreliable
• O – Oxygen therapy (100% O₂, HBO)
• I – Investigation = COHb levels
• S – Sequelae (neuro, cardiac)
• O – Occupational/environmental exposure
• N – Neurological signs: headache → coma

 MCQs on Carbon Monoxide Poisoning

Q1. What is the most reliable test for diagnosing carbon monoxide poisoning?

A) Pulse oximetry

B) Serum lactate

C) Carboxyhemoglobin level

D) Arterial blood gas

✅ Answer: C) Carboxyhemoglobin level

Q2. Which of the following is a classic MRI finding in delayed CO poisoning?

A) Diffuse white matter lesions

B) Bilateral globus pallidus lesions

C) Unilateral temporal lobe hyperintensity

D) Pontine hemorrhage

✅ Answer: B) Bilateral globus pallidus lesions

Q3. Which of the following is the best treatment for severe carbon monoxide poisoning?

A) 100% oxygen via nasal cannula

B) Hyperbaric oxygen therapy

C) High-dose steroids

D) Alkalinization with sodium bicarbonate

✅ Answer: B) Hyperbaric oxygen therapy