Chapter 12- Oxygen Transport, Calculations, and CO2

What is the primary goal of every breath taken?

To deliver O₂ to tissues and remove CO₂.

How much O2 do the tissue consume and how much CO2 do they produce per minute?

Oxygen Consumption (O2): Approximately 250 mL per minute

Carbon Dioxide Production (CO2): Approximately 200 mL per minute

What are the 2 methods for O2 transportation in the blood?

• Dissolved in plasma (~1-2%)

• Chemically bound to hemoglobin (Hb) (~98-99%)

What does Henry's Law state regarding gas dissolution?

The amount of gas that dissolves in a liquid is directly proportional to its partial pressure.

How much oxygen is dissolved in plasma at a PaO₂ of 100 mmHg?

0.3 mL/dL.

What is the formula to calculate dissolved oxygen in blood?

PaO₂ x 0.003 = Dissolved Oxygen (mL O₂/dL blood).

What is hemoglobin's role in oxygen transport?

Hemoglobin carries oxygen inside red blood cells and can bind up to 4 oxygen molecules.

At normal body temperature (37°C):

_____ mL O2 / _____ mL blood per mmHg (PaO2)

.003/100

Describe the structure of each hemoglobin molecule and its contents

1 Hemoglobin molecule contains:

• 4 heme groups → each with an iron (Fe²⁺) atom that binds to 1 O₂ molecule

• 4 globin chains → 2 alpha (α) + 2 beta (β) chains

Each Hemoglobin molecule can carry up to __ O2 molecules.

4

What is the difference between adult hemoglobin (HbA) and fetal hemoglobin (HbF)?

HbF has a higher affinity for oxygen than HbA, allowing it to extract oxygen from maternal blood.

What is HbS?

Sickle cell mutation (β-chain defect)

Low O₂ → HbS sticks together → sickled RBC shape

Results in poor O₂ delivery, clots, pain crises

How does sickle cell hemoglobin (HbS) affect oxygen delivery?

It causes red blood cells to sickle under low oxygen conditions, leading to poor oxygen delivery and pain crises.

What is methemoglobin (MetHb)?

Hemoglobin with oxidized iron (Fe³⁺) that cannot bind oxygen, leading to functional anemia.

*Iron changes from Fe²⁺ → Fe³⁺ (oxidized)

What is the formula to calculate the total amount of oxygen bound to hemoglobin?

O₂ bound to Hb = Hb x 1.34 x SaO₂

How do you calculate total oxygen content of arterial blood? (CaO2)

CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)

Normal CaO2 value

~20 mL O₂ per 100 mL blood

What is oxyhemoglobin?

Hemoglobin that is bound to oxygen.

What is deoxyhemoglobin?

Hemoglobin that is not bound to oxygen.

What is the significance of the oxyhemoglobin dissociation curve?

It shows the relationship between PaO₂ and SaO₂, illustrating how hemoglobin loads and unloads oxygen.

What do the x-axis and y-axis represent on the oxyhemoglobin dissociation curve?

• PaO₂ (x-axis) → the pressure driving O₂ into blood

• SaO₂ (y-axis) → the percentage of hemoglobin saturated with O₂

What is P50?

The partial pressure of O2 at which Hb is 50% saturated

What is the normal P50 value for hemoglobin?

Approximately 27 mmHg.

What causes the sigmoid (S-shape) of the oxyhemoglobin dissociation curve?

The sigmoid (S-shape) is due to cooperative binding.

What is cooperative binding?

The increasing ease with which hemoglobin binds its second and third oxygen molecules, as the conformation of the hemoglobin molecule changes.

What does the steep portion of the OHDC represent? What is the significance?

(PaO2 0-60 mmHg)

• O₂ unloading zone

• Allows efficient O₂ delivery to tissues

What does the flat portion of the OHDC represent? What is the significance?

• O₂ loading zone (PaO₂ 60-100 mmHg = SaO₂ 90-100%)

• Protects against mild hypoxemia -> saturation stays high

What is the significance of the steep and flattened portions of the oxyhemoglobin dissociation curve?

The steep portion allows for efficient oxygen unloading at low pressures, while the flattened portion protects against mild hypoxemia.

P50 greater than 27 mmHg indicates.....

Right shift

P50 less than 27 mmHg indicates.....

Left shift

How is the affinity for oxygen effected in a left shift? What does this result in?

Increased affinity for oxygen→ O₂ binds tightly, less release to tissues.

What are the causes for a left shift?

• ↓ CO₂

• ↓ Temperature (hypothermia)

• ↑ pH (alkalosis)

• ↓ 2,3-BPG

• Fetal Hb, COHb, MetHb

How is the affinity for oxygen effected in a right shift? What does this result in?

Decreased affinity for O2 → O₂ unloads more easily to tissues

What are the causes for a right shift?

• ↑ CO₂ (hypercapnia)

• ↑ Temperature (fever, exercise)

• ↓ pH (acidosis → Bohr Effect)

• ↑ 2,3-BPG (from hypoxia or anemia)

CADET

What is the relationship between oxygen saturation (SaO₂) and partial pressure of oxygen (PaO₂)?

SaO₂ increases with PaO₂, but the relationship is not linear due to the sigmoid shape of the oxyhemoglobin dissociation curve.

How does the body adjust oxygen affinity in response to hypoxia?

By shifting the oxyhemoglobin dissociation curve to the right, enhancing oxygen unloading to tissues.

What is the P50 in relation to hemoglobin?

The P50 is the point at which hemoglobin is 50% saturated with oxygen.

What factors should be assessed when oxygenation is low?

Ventilation/perfusion, hemoglobin levels, and hemoglobin's willingness to release oxygen.

What is CaO2?

total amount of oxygen in 100ml of arterial blood

Venous Oxygen Content (CvO₂)

CvO2 = (Hb x 1.34 x SvO2) + (PvO2 x.003)

• SvO₂ = mixed venous O₂ saturation (normal ≈ 75%)

• PvO₂ = partial pressure of O₂ in venous blood

(normal ≈ 40 mmHg)

Arteriovenous Oxygen Content Difference (C(a-v)O₂):

1. What does it indicate?

2. Formula

3. Normal values

1. Indicates how much oxygen the tissues extract

2. (C(a-v)O₂)= CaO2 - CvO2

3. Normal: ≈ 4-5 mL O₂ per 100 mL of blood

What does high vs low C(a-v)O₂ indicate?

• High= tissues are working harder or not getting enough O₂ delivered

• Low = tissues aren't using oxygen (e.g., sepsis, cyanide toxicity)

What is DO₂?

DO₂ is the oxygen delivery, indicating how much oxygen reaches the tissues per minute.

Give the formula for DO₂

DO₂ = CaO2 × cardiac output × 10

What is normal DO₂

≈ 1000 mL O₂/min

What 3 factors does DO₂ depend on?

• Hemoglobin (Hb) → how much oxygen can be carried

• SaO₂ / PaO₂ → how full the hemoglobin is

• Cardiac Output (CO) → how fast the blood moves it

What is O₂ER?

O₂ER is the oxygen extraction ratio, indicating the percentage of delivered oxygen that tissues actually use.

O₂ER Formula

What is normal O₂ER

≈ 25% → tissues extract about ¼ of the oxygen delivered

What does increased O₂ER indicate?

- Tissues pulling out more O₂ because delivery decrease or demand increase.

- Seen in shock, anemia, hypoxia, low cardiac output.

What does decreased O₂ER indicate?

- Tissues not using O₂ effectively (delivery adequate but uptake impaired).

- Seen in sepsis, cyanide poisoning, shunting

Oxygen calculations

• CaO₂ → How much O₂ leaves the lungs

• CvO₂ → How much returns unused

• C(a-v)O₂ → How much tissues extracted

• DO₂ → How much was delivered per minute

• O₂ER → What percent of that delivery was use

What is carbon monoxide poisoning's effect on hemoglobin?

CO binds to hemoglobin more strongly than oxygen, forming carboxyhemoglobin, which prevents oxygen release to tissues. Causes a left shift in the oxyhemoglobin curve.

What are the 3 ways CO₂ is transported in the blood?

• Dissolved in plasma (~5%)

• As carbamino compounds (~20%)

• As bicarbonate (HCO₃⁻) (~75%)

Which method of CO2 transport is most common? Why?

Most CO₂ is carried as bicarbonate because it's a safe, soluble way to transport acid without changing blood pH too quickly.

Carbonic acid equation

CO2 + water ↔ carbonic acid ↔ H+ ions + HCO3-

*reaction aided by the enzyme carbonic anhydrase

What is the role of carbonic anhydrase in CO₂ transport?

It catalyzes the conversion of CO₂ and water into carbonic acid, which dissociates into bicarbonate and hydrogen ions.

What is the carbonic acid-bicarbonate system's function?

It maintains acid-base balance by regulating CO₂, H⁺, and HCO₃⁻ levels in the blood.

What is the chloride shift?

The chloride shift is the exchange of bicarbonate leaving red blood cells and chloride entering to maintain electrical neutrality.

What does the Bohr Effect describe?

The Bohr Effect explains how increased CO₂ and H⁺ (lower pH) decrease hemoglobin's affinity for oxygen, facilitating oxygen release.

What is the key takeaway for the Bohr Effect?

The Bohr Effect ensures oxygen is unloaded where metabolism is high (tissues) and loaded where CO₂ is low (lungs).

What does the Haldane Effect describe?

The Haldane Effect describes how oxygenation of hemoglobin promotes CO₂ unloading in the lungs.

__________ : ↑ CO₂ / ↓ pH → helps unload O₂ in tissues.

Bohr Effect

__________ : ↑ O₂ → helps unload CO₂ in lungs

Haldane Effect

What happens during hypoventilation in relation to CO₂ and pH?

Hypoventilation leads to increased CO₂ levels, causing acidosis (lower pH).

___________ directly controls CO₂ — it's the fastest way the body adjusts acid levels

Ventilation

What are the common causes of carbon monoxide poisoning?

Smoke inhalation, faulty heaters, and running engines in enclosed areas.

How does the body adjust acid levels quickly?

By regulating ventilation, which directly controls CO₂ levels.

When oxygen binds to hemoglobin in the lungs, what happens to CO2 transport?

Hemoglobin releases CO2 to allow exhalation

What do you call CO2 when it is bound to the alpha and beta chains of hemoglobin?

Carbaminohemoglobin

How saturated is Hemoglobin at a pressure of 60 mmHg?

about 90%

Which of the following is true about methemoglobin ( MetHb )?

A. Has the highest affinity for O2

B. Is normal in healthy adults

C. Iron changes from Fe2+ to Fe3+ ( oxidized )

D. Causes poor O2 delivery, clots, pain crises

C