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Scenario
40 years old Ahmed returned to his apartment in the cold winter
night. He turned on his heater and shut all the windows. After
sleeping for 2 hours, he woke up and noticed that his vision
became progressively blurred. When he got up he became
disoriented and fell down. His friend found him unconscious and
hyperventilating with a reddish complexion. He immediately took
him out of the house and called for an ambulance. The doctor
made a diagnosis of “CO poisoning” based upon history and
examination. Ahmed was treated with hyperbaric oxygen therapy.

Learning Objectives
1. Dynamics of oxygen transport by the blood.
2. Understanding the oxygen-Hb dissociation curve and effect of CO on
this curve.
3. Forms of transport of respiratory gases in blood including O2, CO2,
CO and Nitrogen.
4. Learning the physiological basis of treatment with hyperbaric oxygen.
5. Compare the skin color of the patient in cyanosis, CO poisoning and
methemoglobinemia
6. Pathophysiology of CO poisoning.
7. Relate the symptoms to CO poisoning. (Clinical)
8. Which complex protein of electron transport chain is inhibited by
carbon monoxide?
9. why is oxygen carrying capacity is reduced in carbon monoxide
poising?

Symptoms of CO Poisoning
• Blurred vision
• Disorientation dizziness
• Unconsciousness
• Hyperventilation
• Reddish complexion

Physiological
• CO is toxic because it reacts with Hb to form
CARBOXY Hb( bright red colour)
• Hb affinity for CO is 250 times > O2
• It competes with O2 to react with Hb
• Once carboxyHb is formed ,it librates CO very
slowly
• Dissociation curve of remaining HbO2 shifts to
left.

Although the oxygen content of blood is greatly
reduced , P02 remains normal so cherry red
colour of COHb is visible in the skin. It is
dangerous because the brain is one of the ﬁrst
organs affected by lack of oxygen, the person
may become disoriented and unconscious
before becoming aware of the danger.

Carbon monoxide Poisoning imp on respiratory systemacts.pptx

Effect of CO on O2 – Hb dissociation curve curve
curve

Treatment
• Administer hyperbaric oxygen.
• Oxygen at high alveolar pressure can displace carbon
monoxide rapidly from its combination with
hemoglobin.
• The patient can also beneﬁt from simultaneous
administration of 5 % CO2 which strongly stimulates
the respiratory center, which increases alveolar
ventilation and reduces the alveolar CO.
• With intensive O2 and CO2 therapy, CO can be
removed from the blood

Compare skin colour
• Cyanosis:- bluish
• CO poisoning:- cherry red
• Methemoglobinemia :- bluish
Here Hb contain Ferric form of iron.

Transport of oxygen from alveoli to
pulmonary capillaries
• Alveolar PO2 104mmHg  Pulmonary capillary PO2
40mmHg
• This great difference of pressure allows rapid
uptake of oxygen by the pulmonary blood.
• PO2 becomes equal before blood has passed more
than one third of the distance through the
capillary.

Transport of Oxygen in the
Arterial blood
• 98% of blood entering the left atrium  PO2 104
mmHg
• 2% has passed from the aorta through the
bronchial circulation and is not exposed to lung air,
this is called “shunt flow” (it is shunted past the gas
exchange area)
• Shunt flow PO2 is 40mmHg as that of normal venous
blood
• This “venous admixture of blood” causes the PO2 of
aortic blood to fall to 95mmHg

Diffusion of Oxygen from the Peripheral
Capillaries into the Tissue Fluid
• When the arterial blood reaches the
peripheral tissues, its PO2 in the capillaries is
still 95 mm Hg while the PO2 in the interstitial
fluid that surrounds the tissue cells averages
only 40 mm Hg
• Thus, there is a tremendous initial pressure
difference that causes oxygen to diffuse
rapidly.

Diffusion of oxygen from the peripheral
capillaries
into the tissue cells
• The normal intracellular PO2 ranges from as
low as 5 mm Hg to as high as 40 mm Hg,
averaging 23 mm Hg.
• Because only 1 to 3 mm Hg of oxygen
pressure is normally required, even this low
intracellular PO2 of 23 mm Hg is more than
adequate and provides a large safety factor.

Diffusion of oxygen from the peripheral capillaries
into the tissue fluid and cells

Forms of transport
• O2 97 % bound to Hb in RBCs
3 % dissolved in water of blood and
cells
• N2  At sea level, 1 litre of N2 is dissolved in
the entire body. Slightly less than one half is
dissolved in H2O of the body and rest is
dissloved in the fat. N2 is 5 times more soluble
in fat.

Forms of transport
• CO2a) 70 % transported from tissues to the
lungs in reversible combination of CO2 with H2O
in RBCs
b) 30 % carbaminoHb in combination with
amino radicals of Hb molecule loose bond
c) Plasma proteins in tissue capillaries also
carry little amount of CO2.

Physiological basis for hyperbaric O2
• Breathing 100% oxygen while under increased
atmospheric pressure.
• Although only a fractional increase in
oxyhaemoglobin occurs, there is a many-fold
increase in oxygen dissolved in the plasma. This
provides extra available oxygen for the tissues
and because of the high partial pressure at
which the oxygen is dissolved, causes a
diffusion gradient from plasma to tissues.

• Allows oxygen to cross the blood brain barrier
effortlessly
• Stimulates the growth of new capillaries (tiny
blood vessels) which allows circulation to be
restored or improved, and this reduces or
eliminates hypoxia in affected areas.
• Stimulates the immune response
• Has potent anti-inflammatory effects

Q. which complex protein of electron transport chain is
inhibited by carbon monoxide?
A.Complex 4 of cytochrome oxidase enzyme gets
inhibited by carbon monoxide leading to formation of
reactive oxygen species and lack of production of ATP.
Q.Why is oxygen carrying capacity is reduced in carbon
monoxide poising?
A. Carbon monoxide has got greater affinity of binding
with hemoglobin than oxygen which further prevents
the RBC from carrying oxygen around the body leading
to hypoxia of body cells.

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Carbon monoxide Poisoning imp on respiratory systemacts.pptx

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