toxicology

1. Carbon monoxide poisoning

2. Introduction
• This deadly gas is one of the major causes of toxin-related
deaths, amounting to at least 5000 deaths
per year. Approximately 70% of these deaths are
suicides.
• CO is very common in the environment and usually
arises from incomplete oxidation of reduced
carbon.
• An example is the automobile engine burning
hydrocarbons.
• Also, inadequate venting of devices that burn fossil
fuels leads to the transfer of the gas to areas where
people are sleeping, resulting in their deaths.
• Cigarette smoke contains 5% CO.
• Heaters
• Fire fighters and fire victims

3. Pathophysiology
CO has multiple toxic properties:
• The major one is the displacement of O2 from
hemoglobin, the O2 carrier protein, forming
carboxyhemglobin (HbCO). Hemoglobin has a much
stronger affinity for CO than it does for oxygen (200
times). CO imparts a cherry pink discoloration to the
skin (the inherent color of HBCO).
• CO can also bind to myoglobin, another O2 carrier
protein. Myoglobin (affinity is 40 times greater than
oxygen) causing myocardial inhibition, hypotension
(the degree of CNS toxicity depends on the degree of
hypotension), ventricular arrhythmia, and cardiac
arrest.

4. • CO has the capacity to inhibit cytochrome
oxidase and cytochrome P450.
All of these will diminish the overall level of
oxidative respiration within the body.

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6. • CO has many effects on the heart. CO is
known to cause gradual deterioration of
myocardial function. It may produce
ventricular arrhythmias and ECG
abnormalities. When death occurs from CO,
the immediate cause is believed to be
myocardial ischemia (in case of high doses).
• Neurological damages may occur.

7. Metabolism of CO
• Pulmonary absorption depends on the duration of
exposure, the concentration of CO in the
environment and the alveolar ventilation rate.
•
• Approximately 1% of an inspired dose of CO is
metabolized to CO2.
• Pulmonary exhalation is the major pathway of CO
elimination.
• The half life of CO is about 4.5 hrs. The elimination
of CO from the body depends greatly on the
concentration of O2 because the 2 gases are
competing for Hb. 80-90 min using oxygen therapy
and 30 min using hyperbaric oxygen.

8. Signs and symptoms
According to the measured carboxyhemoglobin level:
• 10-20% Headache, dyspnea & weakness
• 20-30% Severe headache & nausea may appear
• 30-40% Severe headache, nausea & vomiting, ataxia,
visual & auditory abnormalities & impaired judgment
may be seen
• 50-60% Confusion, syncope, seizures & coma
Neurological complications: The degree of brain damage
depends on the degree of hypoxia and hypotension.
Headache is typically throbbing due to reflex
vasodilation according to CNS hypoxia.

9. • CVS complications: Atrial and ventricular
arrhythmia and ventricular fibrillation in severe
cases.
• Pulmonary complications: Shortness in breath
and dyspnea, pulmonary edema and
haemorrhage.
• Kidney: Acute tubular necrosis and renal failure
• Blood: Hemolytic anemia
• Ophthalmic complications: Blurred vision and
blindness
• Skin: Pale or cyanosis skin

10. Chronic toxicity:
- It is uncommon because CO does not
accumulate. However, repeated exposure will
cause accumulation of damage e.g. higher
attitude, heavy smokers and pregnant
woman.
- The fetus is particularly vulnerable to CO
poisoning. CO exposure leads to fetal death,
anatomical malformation or decrease weight
birth.

11. Treatment
• Immediate removal from the contaminated
area.
• The goal of CO therapy is to improve
oxygenation especially to the vital organs,
the heart and brain. Hyperbaric O2 is used
where; the amount of oxygen is 30 times
greater than normal. Hyperbaric O2 shortens
the half-life of the HbCO reaching 1 hr.
•

13. • A blood sample for COHb assay should be
obtained as early as possible and oxygen
therapy continued while awaiting result.
• In case of smoke inhalation, one must always
alert for the possibility of toxicity from
poisonous gases other than CO.
• Hyperbaric oxygen has several disadvantages:
- Most hospitals has no hyperbaric chamber, so
the decision for patient traveling is important. It
depends on severity of symptoms, patient's
stability, and time for traveling.
- Complications: emesis, seizures, agitation, &
rupture of tympanic membrane.

14. Criteria for using hyperbaric oxygen:
• Unconsciousness
• Any acute or chronic neurological symptoms
• Myocardial ischemia or arrhythmia
• COHb > 40%
• Pregnant woman with COHb > 8%
• Metabolic acidosis with pH < 7.2