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Oxygen and Carbon Dioxide Transport in the Blood

Final Exam - Dr. Carter
STUDY
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In what 2 ways is oxygen transported in the blood?
dissolved and bound to Hb
What percent of the total oxygen is dissolved in the blood?
3%; for every mmHg of O2, the blood contains 0.003mL O2/100mL of blood
What form of oxygen is PaO2 a measure of?
dissolved O2
What is the importance of the dissolved O2?
it drives the concentration gradient of O2 across the respiratory membrane
What is a normal PaO2?
100mmHg
What is positive cooperativity?
the binding of each successive molecule of O2 induces a conformational change in the Hb and making it easier for the next molecule to bind
Approximately how much of the RBCs is Hb?
1/3; if a PCV = 45, the Hb = 15g/dL
What is the shape of the oxyhemoglobin dissociation curve?
sigmoidal
What is oxyhemoglobin?
Hb bound to O2
What is reduced Hb?
unbound Hb
At what PO2 is Hb 97% saturated? 75% saturated? 50% saturated?
100mmHg; 40mmHg; 28mmHg
Where is Hb normally 97% saturated?
arterial blood
Where is Hb normally 75% saturated?
venous blood
What will PO2 be if SpO2 is 85%?
estimate! between 40 and 100 (75% and 97% SpO2) so probably about 70mmHg
Approximately how much O2 can a normal gram of Hb carry?
1.34mL
What is the Oxygen Concentration equation?
CaO2 = (1.34 x Hb x (%sat/100)) + (0.003 x PO2) where:
CaO2 = concentration of oxygen in mL/dL
Hb = hemoglobin concentration in g/dL
PO2 = partial pressure of O2 in blood in mmHg
Which part of the oxygen concentration equation denotes the O2 bound to Hb? Which part denotes the dissolved O2?
(1.34 x Hb x (%sat/100)); (0.003 x PO2)
What will anemia do to Hb concentration?
decrease it
What will polycythemia do to Hb concentration?
increase it
What does an SpO2 <95% denote?
hypoxemia
What 5 things causes a shift to the right of the O2 Hb dissociation curve?
1) decrease in pH
2) increase in temp
3) increase in RBC 2,3 DPG
4) increase in H+
5) increase in CO2
What is the Bohr Effect?
a decrease in Hb's affinity for O2; a shift to the right of the O2 Hb dissociation curve
What does the Bohr effect do to a patient's P50 value?
increases it
How does the Bohr Effect effect tissue offloading?
it increases it
What 5 things cause a shift to the left of the O2 Hb dissociation curve?
1) increase in pH
2) decrease in temp
3) decrease in RBC 2,3 DPG
4) decrease in H+
5) decrease in CO2
What is 2,3 DPG?
glycolysis intermediate
What does a left shift of the O2 Hb dissociation curve indicate? How does this effect tissue offloading?
it indicates an increase in Hb's affinity for O2; this decreases offloading at the tissues
What does a left shift do to a patient's P50 value?
decreases it
What is carboxyhemoglobin?
carbon monoxide bound to hemoglobin
Why is CO so toxic?
Hb's affinity for CO is 240x greater than its affinity for O2, therefore with a CO partial pressure of only 0.16mmHg 75% of Hb is bound to CO
Which way does CO toxicity shift the O2 Hb dissociation curve?
left which means that there isn't much offloading at the tissues
What is a non-invasive way to measure oxygenation? When is this method not recommended?
pulse oximetry; it can't distinguish between oxyhemoglobin and carboxyhemoglobin, and therefore is not recommended for CO toxicity patients
What are the 5 main causes of hypoxemia?
1) decreased inspired O2 partial pressure
2) hypoventilation
3) V/Q mismatch
4) right to left shunts
5) diffusion impairment
True or False: A left to right anatomic shunt will cause hypoxemia.
False! A right to left shunt will!
In what 3 ways is CO2 transported in the blood?
1) dissolved (10%)
2) carbamino compounds (30%)
3) bicarbonate (60%)
What is carbaminohemoglobin?
CO2 bound to Hb
Hb will more readily bind CO2 than O2. How is this helpful?
the unloading of O2 at the tissues supports the binding of CO2 and the unloading of CO2 at the respiratory membrane (via diffusion gradient) supports the binding of O2
How is bicarbonate formed?
CO2 + H2O <-CA-> H2CO3 <--> H+ + HCO3-
where CA = carbonic anhydrase
Where is CA found?
in the RBCs, not the plasma
What is the chloride shift?
When bicarb is made, the bicarb ion diffuses out of the cell, but H+ remains in the cell, so Cl- diffuses in to maintain electrical neutrality
How does bicarbonate benefit the plasma?
it acts as a buffer
Why is it important that the bicarbonate equation is reversible?
at the level of the respiratory membrane so CO2 can form and diffuse across the membrane into the alveoli
What is bicarbonate a marker of?
metabolic function in acid-base balance
What is the Haldane effect?
deoxygenation of the blood increases its ability to carry carbon dioxide and oxygenated blood has a reduced capacity for carbon dioxide; this doubles the amount of CO2 picked up at the tissues and doubles the CO2 released at the lungs
What is respiratory acidosis and what is it a consequence of?
blood pH <7.4 and pCO2 >40mmHg; hypoventilation
What does hypoventilation do to the carbonic acid equation?
pushes it towards the left producing more HCO3- and H+
How does the body compensate for chronic respiratory acidosis?
the kidneys preserve more HCO3- and excrete more H+
In what 2 instances might you see respiratory acidosis?
anesthesia and brain stem injuries
What is respiratory alkalosis and what is it a consequence of?
blood pH >7.4 and pCO2 <40mmHg; hyperventilation
How does the body compensate for chronic respiratory alkalosis?
the kidneys preserve more H+ and excrete more HCO3-
What can respiratory alkalosis occur secondary to?
pain or hypoxemia
Which of the following is the major transport form of CO2 in the blood?
a) Bicarbonate
b) CO2 is not transported in the lungs
c) Bound to Hb
d) dissolved
a
Which of the following best describes the Bohr effect?
a) Deceased P50
b) Increased O2 offloading at the tissues
c) Left shift in the oxyhemoglobin dissociation curve
d) Increased Hb affinity for O2
b
Which of the following is false regarding the consequences of exposure to carbon monoxide?
a) Left shift of the oxyHb dissociation curve
b) Decreased CaO2
c) Decreased Hb affinity for O2
d) Decreased offloading of O2 at the peripheral tissues
c
Which of the following best describes a respiratory acidosis?
a) PCO2 = 40mmHg; pH = 7.4
b) PCO2 = 60mmHg; pH = 7.4
c) PCO2 = 60mmHg; pH = 7.3
d) PCO2 = 40mmHg; pH = 7.3
c