Jackie Quint, Dani Deyette,

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• Jackie Quint, Dani Deyette,
• Ed Evanson, and Jordan Getz

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The Question

• A 59-year old carpenter is seen in the emergency
  room complaining of shortness of breath.
• The objective evaluation reveals
• HR 112,
• BP 138/88,
• Resp. 35/min (rapid shallow).
• Patients skin ashen,
• nail beds are cyanotic
• Predict deviations from a normal blood gas
  analysis using the given information

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Arterial P O2 (mmHg)Partial Pressure of Oxygen
in the Arteries

• Reflects amount of O2 gas dissolved in blood
• Measures effectiveness of lungs pulling O2 into
  the blood from the atmosphere
• There is a decrease in PO2 with the increase of
  PCO2.
• Rapid shallow breathing suggests a high amount of
  CO2 and low O2
• Probably due to inadequate ventilation

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Decreased PO2 levels Caused by

• Decreased Oxygen levels in the inhaled air
• Anemia
• Heart decompensation
• Chronic obstructive pulmonary disease
• Restrictive pulmonary disease
• Hypoventillation

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Arterial PCO2 (mmHg)Partial Pressure of CO2 in
Arteries

• Reflects the amount of CO2 dissolved in the
  blood.
• High levels of CO2 leads to rapid breathing to
  get rid of the gas.
• The more CO2, the more acidic the plasma pH will
  probably be

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Increased CO2 levels cause by

• Holding your breath
• Pulmonary Edema
• Acute asthmatic attack
• Obstructive lung disease

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Arterial HCO3- Content Will Increase

• As the partial pressure of CO2 builds up in the
  blood the HCO3- content will increase as well.
• 70 of CO2 in the body is converted to HCO3- in
  red blood cells with the aid of the enzyme
  carbonic anhydrase and is then transported back
  to the lungs for diffusion out of the body.
• This happens because
• A) It is a means to more easily transport CO2
  from the tissue
• where it is a byproduct of cellular
  respiration to the lungs where it is
• expelled from the body.
• B) It increases the amount of HCO3- available
  to act as a buffer for
• metabolic acids.

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How?

• CO2 is generated from cellular respiration in
  peripheral tissues. It then dissolves into the
  plasma (7 of CO2) or diffuses quickly into the
  RBC (93 of CO2).
• Inside the RBC the CO2 will either bind with
  Hemoglobin (23 of CO2) or it will react with
  water in the presence of carbonic anhydrase to
  produce carbonic acid (70 of CO2).
• Because carbonic acid is unstable it readily
  dissociates into HCO3- and H.
• CO2 H2O ? H2CO3 ? H HCO3-
• Or
• CO2 H20 ? H HCO3-
• HCO3- leaves the cell through an antiporter which
  brings in one Cl- ion for each bicarbonate ion
  that leaves. This maintains the electrical
  neutrality. One negative charge in for an equal
  negative charge out.
• The H leaves the RBC by binding to hemoglobin
  which acts as a buffer.

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pH Will Decrease

• pH decreases as a result of increased partial
  pressure of CO2 in the blood.
• Remember that most CO2 in the body (70) is
  converted to HCO3- in RBCs.
• Along with HCO3-, H is also produced from the
  reaction
• CO2 H2O ? H2CO3 ? H HCO3-
• When CO2 is at normal levels, the H produced can
  be effectively buffered by hemoglobin.
• When CO2 is very high, so much H is produced in
  RBCs that there isnt enough hemoglobin available
  to soak it all up. H then accumulates in the
  plasma. This is called respiratory acidosis.

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Total Arterial O2 content

• Richards O2 level is low. That is why there is
  evidence of cyanotic nail beds.
• Nails are out on the periphery so, without an
  adequate amount of oxygen in the body, by the
  time hemoglobin on the RBCs reaches the nails,
  O2 has already been given up elsewhere.
  Consequently, the hemoglobin is blue making the
  nail beds blue.

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Hypoxia and Hypercapnia
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Causes of Mr. Carpenters Hypoxia and Hypercapnia

• There is likely a disruption of the exchange of
  gases between alveoli and the pulmonary
  capillaries.
• This could be caused by one or a combination of
  the following conditions
• 1) Decrease in alveolar surface area
• 2) Increase in the thickness of the
• alveolar membrane (example
• emphysema)
• 3) Increase in the diffusion distance
• between the alveoli and the blood
• (example pulmonary edema which
• usually affects O2 content more
• than CO2 because O2 is less
• soluble in tissue fluids than CO2)

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Analogy

• Hypoxia is like basketball camp without enough
  basketballs.
• The kids are like RBCs, and the basketballs are
  oxygen.
• To efficiently run the camp, each kid should have
  at least one basketball. If there arent enough
  balls, then you have kids not participating.
• Just like if you have RBCs that dont have
  enough oxygen, you cant support the whole body.