Gas Transport-Scharf

Question 1

Which is the ferric form of hemoglobin?

Answer 1

Methemoglobin. Can’t carry O2.

Question 2

How much O2 can each gram of hemoglobin hold?

Answer 2

1.39mL. 15g/mL of Hgb total so capacity is 20.8g O2

Question 3

O2 content vs saturation

Answer 3

Content is the total amount of O2 in blood. Saturation is the proportion of Hgb bound to oxygen.

Question 4

How is the O2 carrying capacity calculated?

Answer 4

O2 saturation (1.39) x Hgb concentration

Question 5

How is the O2 bound to Hgb calculated

Answer 5

O2 carrying capacity x O2 saturation

Question 6

How is total O2 content of blood calculated?

Answer 6

O2 dissolved + O2 bound to Hgb

Question 7

How do you decrease the amount of O2 bound to Hgb?

Answer 7

Decrease Hgb (by anemia or bleeding) or bind with CO

Question 8

What shifts the Hgb dissociation curve to the right (more release of O2)?

Answer 8

Increased PCO2, increased acidity, increased temperature, increased DPG

Question 9

How is CO2 transported in body?

Answer 9

1. Dissolved CO2, about 10%, 2. Bicarbonate converted by carbonic anhydrase from CO2 and H2O, equilibrating CO2 and bicarbonate in RBCs. 90% majority of transport, 3. Carbamino compounds, most importantly Hgb, 5%.

Question 10

Events when CO2 diffuses from tissues into capillary blood

Answer 10

1) As HCO3 increases, leaves rbc, H+ can’t (not permeable) 2) To maintain electroneutrality CL- diffuses into RBC (Gibbs-Donnen equilibrium) 3) Some H+ bound to reduced Hgb. Thus deO2 Hgb helps load CO2 by soaking up H+ 4) Haldane effect: deO2 Hgb helps carry CO+2+

Question 11

What is normal VCO2 production at rest?

Answer 11

250mL/min

Question 12

Henderson-Hasselbach equation

Answer 12

pH=pKA+log(HCO3/.03pCO2) in blood: pH=6.1+log(24/.03x40)=7.4

Question 13

What is normal pH of the blood?

Answer 13

7.35-7.45

Question 14

What are the consequences and compensation of primary hypoventilation?

Answer 14

PCO2 goes up more than HCO3, leads to respiratory acidosis. Compensation through renal retention of bicarbonate and raising pH. If you see high HCO3 and normal pH: assume respiratory acidosis.

Question 15

What are the consequences and compensation of primary hyperventilation?

Answer 15

PCO2 goes down more than HCO3, leads to respiratory alkalosis and increased pH. Compensation through renal HCO3 exretion and acid retention. Patient will have low PCO2, low bicarbonate and normal pH.

Question 16

What are the consequences and compensation of primary metabolic acidosis?

Answer 16

HCO3 goes down more than PCO2. Compensate by increased ventilation to blow off CO2. Patient shows normal pH and low HCO3. Occurs in Kausmall’s respirations in DKA.

Question 17

What are the consequences and compensation of primary metabolic alkalosis?

Answer 17

HCO3 goes up more than PCO2. Compensation by hypoventilation but not clinically. Could happen because of vomiting of acid. So may present as high pH and high HCO3.

Question 18

Bicarbonate lab values

Answer 18

Calculated HCO3 (from HH), Standard HCO3 (mathematically if PCO2 were 40), Base excess.

Question 19

Mechanisms leading to inadequate oxygenation

Answer 19

-dec pO2 – hypoxic hypoxia -Dec O2 content of blood – e.g. anemia, CO, methemoglobin: “anemic hypoxic) – dec O2 flow to dtissues – circulatory hypoxia – shock , O2 delivery, CN poisoning or toxic interference to O2 use at cell level.

Question 20

How is O2 delivery calculated?

Answer 20

TO2=CaO2xCO =content x cardiac output =TO2