Blood Gases: O2 & CO2 Flashcards Preview

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Flashcards in Blood Gases: O2 & CO2 Deck (59)
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1

How can you estimate PA02 from % inspired 02? Estimate PA02 when % inspired 02 is 50%. 100%.

PA02 can be estimated by multiplying % inspired 02 by 6 (PA02 = % inspired O2 x 6). When FiO2 = 50%, PA02 = 50 x 6 = 300 mmHg. When Fi02 = 100%, PA02 = 100 x 6 = 600 mmHg.

2

How can you estimate Pa02 from % inspired 02? Estimate the Pa02 if the patient is breathing 50% 02. 100% 02.

Pa02 can be estimated by multiplying % inspired 02 by 5 (PaO2 = % inspired 02 x 5). When Fi02 is 50%, PaO2 = 50 x 5 = 250 mmHg. When Fi02 is 100%, Pa02 = 100 x 5 = 500 mmHg.

3

Estimate the PA02-Pa02 gradient if the normal, healthy patient has an FiO2 of 0.4.

PA02-Pa02 = 40 x 6 - 40 x 5 = 240 - 200 = 40 mmHg.

4

What is the maximal Pa02 achievable in a young healthy adult breathing room air?

The maximal Pa02 for a young person breathing room air is 104 mm Hg (Guyton). The best achievable Pa02 is 100-105 mm Hg.

5

What is normal Pa02 in the adult breathing room air?

Normal Pa02 ranges from about 78 mmHg in elderly persons to 105 mmHg in young individuals (Pa02 = 102- Age/3).

6

In a young, normal healthy adult, what is the difference between Pa02 and Pv02: 20,40,60,80, or 100 mm Hg?

The difference between Pa02 and PvO2 is 60 mm Hg. The partial pressure of oxygen in mixed venous blood (PvO2) is 40 mm Hg. Pa02 ranges from 60 mm Hg (lower limit of normal) to about 100 mm Hg. The typical PaO2 shown in textbooks is 95 mm Hg. Hence, the difference between PaO2 and PvO2 is 95 40 = 55 mm Hg, which is close to 60 mm Hg.

7

What is the normal Sa02?

Normal SaO2 is 90-97%.

8

If the oxygen saturation is 90%, what will the P02 be? Where is blood with this P02 found?

When oxygen saturation is 90%, PO2 is 60 mmHg. This is arterial blood.

9

What is the P02 if the 02 saturation of hemoglobin is 70%?
Where in the circulation is blood with this PO2 found?

When oxygen saturation is 70%, PO2 is 40 mmHg. This is mixed venous blood.

10

What is the hemoglobin oxygen saturation when the PO2 is 60 mmHg? When the PO2 is 40 mm Hg?

When the P02 is 60 mm Hg, oxygen saturation is 90%. When the PO2 is 40 mm Hg, oxygen saturation is 70%.

11

What is the normal arteriovenous oxygen content difference (CaO2 - CvO2)?

5 ml O2/100 ml blood. This says that 5 ml O2 are extracted from each 100 ml of blood by tissues as blood flows from the arterial to the venous side of the systemic circulation.

12

What two changes can cause SaO2 to remain normal and Sv02 to decrease?

decrease in SvO2 can occur if there is: (1) a decrease in oxygen delivery (decreased cardiac output, decreased hemoglobin concentration, abnormal hemoglobin) with a resulting increased extraction of O2 from the blood, or (2) an increase in 02 consumption (fever, shivering, malignant hyperthermia, thyroid storm).

13

How can you calculate how much oxygen is dissolved in the blood? What law applies?

Multiply PO2 x 0.003, and your answer will be the amount of oxygen dissolved in blood. The units are ml O2/100 ml blood. Henry's law permits this calculation to be made.

14

When the Pa02 is 200 mmHg at normal body temperature, how many ml of oxygen will dissolve in 100 ml of blood plasma?

0.003x200= 0.6 ml 02/l00 ml blood.

15

Calculate how much oxygen is dissolved in blood when the patient is breathing 50% 02. When the patient is breathing 100% 02.

PaO2s while breathing 50% O2 and 100% O2 are estimated to be 250 (50 x 5) and 500 (100 x 5) mmHg, respectively. The amounts of O2 dissolved are 0.75 (250 x 0.003) and 1.5 (500 x 0.003) ml O2/I00 ml blood when breathing 50% O2 and 100% O2, respectively.

16

If the PaO2 increases from 100 to 400 mmHg, how much
does the amount of dissolved oxygen increase? Explain how you arrived at this answer.

The amount of dissolved O2 increases 0.9 ml O2/100 ml blood. When PO2 is 100 mmHg, dissolved O2 = 0.003 x 100 mmHg = 0.3 ml O2/IOO ml blood. When PO2 is 400 mmHg, dissolved O2 = 0.003 x 400 mmHg = 1.2 ml O2/l00 ml blood. Therefore, the dissolved oxygen increased by 0.9 ml O2/I00 ml blood (1.2 - 0.3 = 0.9).

17

What two factors determine the amount of oxygen carried by hemoglobin?

PO2 and the amount of hemoglobin are the two factors that determine the amount of oxygen carried by hemoglobin.

18

How much 02 is carried by each gram of hemoglobin when saturated?

1.34 ml of O2 is carried by each gram of saturated hemoglobin.

19

What is the maximum oxygen carrying capacity (100% saturation) of blood in a patient with 15 gm Hgb/100 ml blood? Hint: You need to calculate both hemoglobin- bound O2 and dissolved O2. Assume Pa02 = 100 mm Hg.

Hemoglobin (Hgb)-bound 02 = (1.34 ml 02/gm Hgb) (15 gm Hgb/100 ml blood) = 20.1 ml O2/100 ml blood. Dissolved O2 = (100 mmHg) (.003) = 0.3 ml O2/100 ml blood. Total O2 = Hgb-bound O2 + dissolved O2 = 20.1 + 0.3 = 20.4 ml O2/100 ml blood.

20

What is the significance of the flat portion of the oxyhemoglobin dissociation curve?

The flat portion of the oxyhemoglobin dissociation curve facilitates the loading of oxygen by the blood because, in the flat portion of this curve, large changes in the partial pressure of oxygen in arterial blood (Pa02) produce only small changes in oxygen saturation (SaO2).

21

What is the significance of the steep portion of the oxyhemoglobin dissociation curve?

The steep portion of the oxyhemoglobin dissociation curve facilitates unloading of oxygen at tissues because large amounts of oxygen are unloaded from hemoglobin (large decrease in oxygen saturation) in response to a small change in the partial pressure of oxygen.

22

Below what Pa02 are there substantial reductions in arterial blood O2 saturation (SaO2) for a small decrease in PaO2?

When Pa02 falls below 60 mmHg, large reductions in Sa02 occur with small decreases in PaO2.

23

Define P50. The normal P50 is how many mmHg?

The P50 is the 02 partial pressure at which hemoglobin (Hgb) is 50% saturated. The normal P50 = 26-27 mmHg.

24

**What happens to the P50 when the oxyhemoglobin
dissociation curve shifts rightward? Leftward?

The P50 increases when the oxyhemoglobin dissociation curve shifts to the right and decreases when the oxyhemoglobin dissociation curve shifts to the left.

25

List five conditions that cause the oxyhemoglobin dissociation curve to shift rightward.

(1) Increased temperature, (2) increased H+ concentration (decreased pH), (3) increased partial pressure of CO2, (4) increased 2,3-DPG, and (5) sickle cell disease.

26

List seven conditions that shift the oxyhemoglobin dissociation curve to the left.

(1) Decreased temperature, (2) decreased H+ concentration (increased pH), (3) decreased partial pressure of C02, (4) decreased 2,3-DPG, (5) presence of fetal hemoglobin, (6) presence of carboxyhemoglobin, and (7) presence of methemoglobin.

27

With an increase in C02, does the oxyhemoglobin
dissociation curve shift to the right or to the left? Where in the circulation does this shift normally occur? Why is this important?

The oxyhemoglobin curve shifts to the right when PCO2 increases; this rightward shift, which occurs as blood flows through capillaries of the tissues, is important because more 02 is released from Hgb; unloading of 02 is favored with a rightward shift in the oxyhemoglobin dissociation curve, so the tissues get more 02.

28

With a decrease in C02, does the oxyhemoglobin
dissociation curve shift to the left or to the right? Where in the circulation does this shift normally occur? Why is it important?

The oxyhemoglobin curve shifts to the left when PC02 decreases; this leftward shift occurs in pulmonary capillaries as C02 is blown off; 02 loading by hemoglobin is favored in pulmonary capillaries when the oxyhemoglobin dissociation curve shifts left.

29

What is the Bohr effect?

The shift in the oxyhemoglobin dissociation curve caused by carbon dioxide entering or leaving the blood is the Bohr effect. As you know, the increase in PC02 in systemic capillaries is partly responsible for shifting the oxyhemoglobin dissociation curve rightward, which facilitates the unloading of oxygen from hemoglobin. The decrease in PC02 in pulmonary capillaries, on the other hand, helps shift the oxyhemoglobin curve to the left, which facilitates the loading of oxygen onto hemoglobin.

30

Iron is in what state in methemoglobinemia? What is the significance of this?

Normal hemoglobin (Hgb) has iron in the ferrous (Fe2+) state. Oxygen carriage by normal Hgb is excellent. Met- Hgb has iron in the ferric (Fe3+) state. The oxygen carrying capacity in patients with methemoglobinemia is poor.