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Flashcards in Arterial blood gases Deck (31):
1

Describe the importance of oxygen “off-loading” from hemoglobin

Off loading is the dynamics of O2 unbinding from hemoglobin. Tissues can only use freely-dissolved oxygen, and fast unbinding makes O2 available to the tissues. Without fast unbinding, total oxygen levels might be high, but most oxygen molecules would stay bound to
hemoglobin and be unavailable for use.Off loading is the dynamics of O2 unbinding from hemoglobin. Tissues can only use freely-dissolved oxygen, and fast unbinding makes O2 available to the tissues. Without fast unbinding, total oxygen levels might be high, but most oxygen molecules would stay bound to
hemoglobin and be unavailable for use.

2

How does decreased pH affect oxygn dissociation

Rightward shift in oxygen dissociation curve: O2 binds less tightly to hemoglobin. This is the Bohr effect

3

How does increased temperature affect oxygn dissociation

rightward shift in oxygen dissociation curve: O2 dissociates from hemoglobin easier

4

How does increased 2,3-BPG affect oxygn dissociation

rightward shift in O2 dissociation curve: happens during chronic hypoxia at altitude

5

Calculate oxygen delivery to tissues

Oxygen delivery (DO2) per minute: Q X CaO2. Where Q is cardiac output, CaO2 is total concentration of oxygen in arterial blood (hemoglobin bound and freely dissolved)

6

Calculate CaO2 (concentration of arterial O2)

CaO2 = (SaO2 × [Hb] X 1.39) + (0.003 × PaO2) (in ml O2 / 100 ml blood)

7

How is O2 delivery decreased in diseases that cause hypoxemia

Reduced saturation of hemoglobin or reduced free O2 content

8

Calculate oxygen consumption

Oxygen consumption (VO2)= Q x (SaO2 - SvO2) x [Hb] x 1.39. Where Q is cardiac output, SaO2 is arterial O2 saturation, SvO2 is venous O2 saturation, [Hb] is Hb concentration. Normal VO2 is 240ml O2/minute

9

What factors determine amount of O2 in inspired air

Barometric pressure and FIO2.

10

What factors determine amount of O2 in the alveoli

Water vapor dilutes inspired oxygen then gas exchange with blood further dilutes the oxygen. Oxygen tension in alveoli depends on alveolar ventilation (Va) and oxygen uptake (VO2)

11

What factors determine amount of O2 in the arterial blood

venous admixture drops the tension: shunted venous blood and VQ mismatch

12

What factors determine amount of O2 in the capillary/ cell

Hemoglobin conc., blood flow (Q), oxygen-hemoglobin binding dynamics. There is a further drop btw capillaries and mitochondria in cell b/ of limits of O2 diffusion and utilization of O2 in mitochondria. O2 is lowest in mitochondria.

13

Pasteur point

The point at which oxidative phosphorylation drops significantly due to low PO2

14

Which ABG component is the best reflection of oxygen content?

hemoglobin oxygen saturation- nearly all oxygen in blood exists as oxy-hemoglobin

15

Hypoxemia vs desaturation

NOT the same thing: hypoxemia indicates low PaO2, while desaturation indicates low SaO2. You can have low saturation with normal PaO2 in cases such as CO poisoning where CO competes with O2 for hemoglobin binding

16

Define hypoxia and hypoxemia.

Hypoxemia: PaO2 <1-2 Torr)whereas hypoxemia is low arterial oxygen supply

17

Causes of hypoxemia

(1). Low ambient PO2 in inspired air (altitude).(2) Hypoventilation (reduced VA ). This reduces alveolar oxygen indirectly by increasing alveolar PACO2 (recall the alveolar gas equation). (3) Diffusion limitations between alveoli and pulmonary capillaries. (4) V/Q mismatch. (5) Shunt.

18

Causes of hypoxia

low Q (blood flow), low SaO2 due to low PaO2 (Hypoxemia), and deliver problems such as anemia or carbon monoxide

19

Describe how different causes of hypoxia/hypoxemia can be determined from alveolar arterial gradient

An A-a gradient of < or = 10 Torr is normal. Hypoxemia due to altitude and hypoventilation gives a normal A-a gradient. In these cases, the hypoxemia is due to problems in oxygen delivery to all alveoli. Hypoxemia due to shunt, V/Q mismatch, and diffusion problems gives a widened A-a gradient.

20

Describe CO2 and O2 in mild/moderate and severe resistance/compliance problems

Mild to moderat disease: Normal CO2, Low O2 due to VQ mismatch. Severe disease: high CO2 due to hypoventilation and low O2 due to hypoventilation and VQ mismatch

21

What does CO poisoning do to oxygen-hemoglobin dissociation curve, PaO2, PaCO2 and SaO2 and A-a gradient

Curve shifts to the left (decreases oxygen-hemoglobin dissociation) thus it prevents oxygen from being delivered to tissues, PaO2 stays the same, PaCO2 is normal, SaO2 decreases. A-a gradient is normal

22

Triple threat of CO poisoning

Reduces arterial oxygen content, decreases oxygen off loading from hemoglobin and poisons the electron transport chain resulting in cellular anaerobic metabolism

23

How does low hemoglobin affect ABG

PaO2, SaO2, PaCO2 and A- a gradient are all normal

24

Describe the ways in which CO2 is carried in blood.

Dissolved gas (more soluble than O2), as bicarbonate ion, and as carbamino compounds which are bound to proteins then bound to hemoglobin.

25

Haldane effect

De-oxygenated hemoglobin in venous blood binds to carbamino compounds better than oxygenated, and this contributes to the higher levels of CO2 in venous blood compared to arterial blood.

26

High altitude ABG

Low PIO2: Low PaO2, low SaO2, and low PaCO2 (hyperventilation), with normal A-a gradient

27

Severe COPD ABG

Low PAO2: low PaO2, low SaO2, high PaCO2, normal A-a gradient

28

Interstitial disease ABG

Diffusion problem: low PaO2, low SaO2, normal PaCO2, elevated A-a gradient. Order a CO single breath test

29

Moderate COPD ABG

VQ mismatch problem: low PaO2, low SaO2, normal PaCO2, elevated A-a gradient. Use 100% O2 to distinguish btw moderate COPD and pneumonia

30

Pneumonia ABG

Shunt problem: low PaO2, low SaO2, normal PaCO2, elevated A-a gradient. Use 100% O2 to differentiate btw moderate COPD ad pneumonia

31

How does 100% O2 differentiate btw V/Q mismatch and shunt

Will coreect arterial oxygenation in V/Q mismatch but not shunt