Respiratory (Arterial Blood Gas)

Front 1

what are the normal arterial blood values of:

-pH
-PaCO2 (arterial pressure)
-PaO2
-HCO3

Back 1

pH=7.35-7.45
PaCO2 = 35-45 (~40)
PaO2 = >70 mmHg (age-dependent)
HCO3 = 22-26 (~24)

Front 2

what's the difference b/w alveolar ventilation (VA) and dead space ventilation (VD)?

Back 2

VA = amt of air that reaches the alveoli and takes part in gas exchange

VD = amt of air that DOESN'T take part in gas exchange

(Out of one breath about 150 mL is dead space ventilation, and 350 mL is for alveolar ventilation. Disorders of the lung change this ratio…)

Front 3

a LOW/HIGH PaCO2 (<35) signifies hyperventilation

Back 3

low; bc all the CO2 is getting breathed out of the arterial circulatory system faster than normal

Front 4

a LOW/HIGH PaCO2 (>35) signifies hypoventilation

Back 4

high; bc all the CO2 is not getting the chance to be breathed out of the arterial circulatory system as normal

Front 5

the lower the ventilation (VA), the LOWER/HIGHER that CO2 is found in the arterial blood circulation (PaCO2)

Back 5

higher; REMEMBER that PaCO2 is inversely related to alveolar ventilation

Front 6

name some factors that cause increased PaCO2

Back 6

most of the time, it's alveolar hypoventilation due to increased dead space (VD). most of the time, this is seen in COPD

you can also have decreased minute volume (VE) via CNS depression (brain problem leading to respiratory rate decreasing)

Front 7

name some common causes of decreased PaCO2

Back 7

of course, it's due to alveolar hyperventilation (PALEPAM):

- pain
- anxiety
- liver failure
- early sepsis
- pulmonary embolism
-acute asthma
-metabolic acidosis

Front 8

what does the alveolar gas equation help you do clinically?

Back 8

by measuring the PaCO2, you can plug in this # into the EQ and find out the estimated PAO2 (alveolar O2). then you can take this number and subtract the measured PaO2 (arterial O2) to give you the A-a difference. now the A-a difference basically tells you how much air is actually getting into the arterial supply from the alveoli and can signal potential ventilation/perfusion mismatching (normal A-a difference = 10-12). so if A-a difference is 18, then you've got ventilation/perfusion (V/Q) mismatch!!! COOL...!!!

Front 9

explain when V/Q = infinity. what could be the underlying cause?

Back 9

Where V/Q = infinity, this is pulmonary embolism, so there is no blood perfusing the lung

Front 10

explain when V/Q = 0. what could be the underlying cause?

Back 10

shunting due to anything that blocks the alveoli. this could occur with severe pneumonia, for example.

Front 11

T or F. the part of the lung that receives the best ventilation are the upper lobes.

Back 11

False!! The lower lobes get the best ventilation. However the ratio (V/Q) is highest in the upper lungs bc there’s more ventilation there than perfusion. The lower lobes have more ventilation and perfusion absolutely.

Front 12

where is V/Q the highest in the lungs?

Back 12

upper lungs, near the apex (since ventilation is highest there)

Front 13

T or F. the older you get, the A-a difference gets bigger.

Back 13

T, arterial pressure O2 gradually goes down as you age

Front 14

the most accurate estimation of A-a difference is when pt is breathing:

a. tank oxygen
b. room air

Back 14

B. basically, check blood gases of the pt when they are breathing room air in order to properly calculate alveolar gas EQ to find out A-a difference

Front 15

arterial blood gases tell us information about which 3 processes?

Back 15

alveolar ventilation
oxygenation
acid-base balance

Front 16

partial pressure of oxygen (PaO2) is:

a. oxygen molecules found in alveolar spaces
b. oxygen molecules dissolved in plasma AND bound to Hb
c. oxygen molecules dissolved in plasma and NOT bound to Hb
d. none of the above

Back 16

C.

Front 17

arterial oxygen saturation (SaO2) is:

a. % heme binding sites saturated with oxygen
b. number of oxygen molecules found in plasma AND bound to Hb
c. number of oxygen molecules foudn in plasma NOT bound to Hb
d. none of the above

Back 17

A

Front 18

arterial oxygen content (CaO2) is:

a. amount of free oxygen dissolved in plasma
b. amount of oxygen bound to Hb AND oxygen dissolved in plasma
c. amount of oxygen bound to Hb only
d. none of the above

Back 18

B

Front 19

partial pressure of oxygen (PaO2) is:

a. oxygen molecules found in alveolar spaces
b. oxygen molecules dissolved in plasma AND bound to Hb
c. oxygen molecules dissolved in plasma and NOT bound to Hb
d. none of the above

Back 19

C.

Front 20

SaO2 > ___% is usually ok!

Back 20

90%

Front 21

arterial oxygen saturation (SaO2) is:

a. % heme binding sites saturated with oxygen
b. number of oxygen molecules found in plasma AND bound to Hb
c. number of oxygen molecules foudn in plasma NOT bound to Hb
d. none of the above

Back 21

A

Front 22

what is the cut off for O2 sat, where below it, you need to calculate the blood gas (measure PaCO2 and PaO2)

Back 22

below 90%

Front 23

arterial oxygen content (CaO2) is:

a. amount of free oxygen dissolved in plasma
b. amount of oxygen bound to Hb AND oxygen dissolved in plasma
c. amount of oxygen bound to Hb only
d. none of the above

Back 23

B

Front 24

SaO2 > ___% is usually ok!

Back 24

90%

Front 25

what is the cut off for O2 sat, where below it, you need to calculate the blood gas (measure PaCO2 and PaO2)

Back 25

below 90%

Front 26

which of the following shift the oxygen dissociation curve to the RIGHT:

a. low temperature
b. high pH
c. high pCO2
d. low PaO2

Back 26

C. (right = think "muscles")

Front 27

which of the following shifts the oxygen dissociation curve to the LEFT:

a. low temperature
b. high pH
c. high pCO2
d. two of the above (name 'em!)

Back 27

A, B (left = think "lungs)

Front 28

define hypoxemia vs. hypoxia

Back 28

hypoxemia = low oxygen in blood and plasma (low CaO2, PaO2, SaO2)

hypoxia = decreased OXYGEN DELIVERY to the tissues

Front 29

in cyanide poisoning, are you hypoxic, hypoxemic, or both?

Back 29

only hypoxic. you'll have normal oxygen in blood and plasma, but hypoxic at the level of the tissues

Front 30

what two underlying causes could give you hypoxemia but normal A-a difference?

Back 30

- low oxygen content in atmosphere (aka. low barometric pressure)
- hypoventilation

Front 31

most common cause of hypoxemia

Back 31

V/Q mismatch

Front 32

what are 3 main causes of hypoxia?

Back 32

- hypoxemia (severe anemia, CO intoxication)
- reduced oxygen delivery to tissues (reduced cardiac output)
- reduced tissue oxygen uptake (mitochondrial poisoning, left shift of oxygen dissociation curve)

Front 33

name the conditions for metabolic acidosis in terms of pH, HCO3, and PaCO2.

Back 33

dec pH
dec HCO3 (primary)
dec PaCO2 (compensatory)

Front 34

name the conditions for respiratory alkalosis in terms of pH, HCO3, and PaCO2

Back 34

inc pH
dec PaCO2 (primary)
dec HCO3 (compensatory)

Front 35

which acid/base disorder would give you hyperventilation?

Back 35

metabolic acidosis (to try to decrease PaCO2 as fast as possible to compensate the loss of HCO3 in the blood. this is all, of course, in response to the acidemia that is at the underlying cause)

Front 36

a pt who is hypoventilating is likely to have which acid/base disorder?

Back 36

metabolic alkalosis

Front 37

what two causes can give you metabolic acidosis with a normal anion gap?

Back 37

diarrhea
renal tubular acidosis

these both willl causes concentration of Cl to be increased to replace HCO3

Front 38

how do you calculate serum anion gap?

what is its normal value?

Back 38

Na - (Cl + HCO3)

nl = 12 +/- 4

Front 39

what does an increased serum anion gap mean?

Back 39

that the conc of an unmeasured anion (ie. phophate, lactate, etc) is increased to replace HCO3 (as opposed to Cl)

Front 40

pt with diarrhea will most likely have what kind of acid/base disorder and why? would they have anion gap increased and why?

Back 40

metabolic acidosis (bc you're losing a lot of bicarb through pooping it all out)

no increase in AG (bc you're compensating this loss with increased conc of Cl)

Front 41

you find out a pt has metabolic acidosis, whatsyour next step?

Back 41

calculate anion gap