Carbon monoxide (CO) poisoning

Question 1

The silent killer is characterized by

Answer 1

1. It is the most common cause of fatal gas poisoning in many countries
2. Colorless
3. Odorless
4. Tasteless
5. Non irritating (not detected by victim)
6. Easy to disperse in the room

Question 2

Sources of CO

Answer 2

Endogenous Normally the body produces small amount of CO during catabolism of protoporphyrin ring of Hb.

•(COHb) normally does not exceed 4-6%.

Exogenous: it is produced due to incomplete combustion of any carbon containing materials in poorly ventilated places.

Examples:

1. Motor vehicle exhaust
2. At home, defective oil and gas heaters, kerosene heaters, and charcoal grills
3. Tobacco cigarette smoking
4. Fires: CO is the most common hazard to smoke inhalation victims.

Question 3

Factors affecting toxicity

Answer 3

1. Duration of exposure
2. Concentration of the gas during exposure
3. Muscular activity of the victim
4. Previous disease: cardiac, pulmonary, anemia
5. Neonates and foetuses are more vulnerable: fetal Hb has increased affinity to CO, and has oxygen Hb dissociation curve shifted to the left
6. Cigarette Smoking.

Question 4

Mechanism of toxicity

Answer 4

Question 5

As consequence of CO toxicity

Answer 5

1. Since CO produces toxicity by additional mechanisms and not only due to Carboxy-Hb, manifestations may not correlate with its level in the blood.
2. Poor prognostic signs:

Altered mental status, hypotension and abnormal findings in the MRI and CT brain.

Question 6

Clinical manifestations of CO toxicity

Answer 6

1. Early symptoms: headache, dizziness (confused in diagnosis with influenza).
2. CNS: headache, ataxia, confusion , convulsion , coma
3. CVS: Hypotension, tachycardia, arrhythmia, chest pain (angina- infarction)
4. Pulmonary: Tachypnea, Cardiogenic and non- cardiogenic pulmonary edema.
5. Skin color is uncommonly cherry red due to carboxy Hb color(rarely seen)
6. EYE: Blurred vision, decreased adaptation to light retinal affection
7. Rhabdomyolysis

Question 7

Delayed neurological sequels

Answer 7

• May occur after 2-40 days of acute exposure
• C/P:

1. Parkinsonism, chorea
2. Memory loss, emotional labiality, psychosis and personality changes
3. Paralysis
4. Behavioural changes, learning difficulty in children

Question 8

INVESTIGATIONS of CO Poisoning

Answer 8

I.Laboratory

1. Carboxyhemoglobin Level (CO-Hb): for diagnosis but not correlated with severity( normal range 0-5%, smokers may have range up to 10%).
2. ABG: may reveal metabolic acidosis, which is more reliable index for severity than COHb. PO2 is usually normal.
3. CPK: to detect rhabdomyolysis
4. Cardiac markers: CK-MB and troponin
5. Others: renal function, serum electrolytes, glucose level.

II.ECG and cardiac monitoring to rule out ischemia and dysrhythmia.

III.Imaging

1. Chest x-ray: (pulmonary edema)
2. Brain CT and MRI: specially when there is altered mental status

Question 9

TREATMENT of CO Poisoning

Answer 9

I. First aid:

• Immediate removal from exposure.
• CPR if needed

II. Emergency measures:

1. ABC Airway, Breathing, Circulation support
2. 100% Oxygen (is the antidote): by non-rebreathable mask (increase rate of dissociation of CO from Hb, its half life is decreased from 6 h to 1 hour).
3. Hyperbaric O2:

INDICATIONS

1. Loss of consciousness, seizures
2. Significant metabolic acidosis
3. MI or arrhythmias
4. CO-HB>25%
5. Pregnancy

•

Question 10

III. Supportive treatment for:

Answer 10

1. Acidosis
2. Hypotension
3. Myocardial ischemia
4. Arrhythmias
5. Pulmonary oedema
6. Brain edema