Arterial Blood Gases

Question 1

facts about ABG

Answer 1

• it’s serious - only get if needed
• remember Allen’s test
• cost is ~ $75
• apply pressure for 5 min. after
• pt is usually being given chest compressions - complicates finding pulse

Question 2

oxygen tension

Answer 2

measure of molecular oxygen dissolved in blood

Question 3

hgb saturation

Answer 3

oxygen bound to hgb

Question 4

what drives oxygen into the tissues?

Answer 4

oxygen tension

Question 5

when do you get a Hgb saturation of 95-99%?

Answer 5

when PaO2 is 80-90 mmHg (measured w ABG)

Question 6

During resuscitation, if PaO2 is less than 80 mmHG, what pulmonary causes would you consider?

Answer 6

1. 100% oxygen is not being delivered
2. incorrect intubation
3. aspiration of gastric contents/solids
4. pulmonary edema and/or
5. pneumothorax

Question 7

During resuscitation, if PaO2 is less than 80 mmHG, what cardiac causes would you consider?

Answer 7

1. poor chest compressions
2. dysrhythmias
3. pump failure

Question 8

What determines gas exchange?

Answer 8

CO2 - if there is no blood flow through the lungs, won’t have gas exchange

Question 9

what is the result of too much O2?

Answer 9

• partial pressure will increase causing free radical formation
• ARDA; IRDS; neuro issues
• maintain O2 sat between 94-99% - not 100%

Question 10

what percent of hgb is normally saturated at any given time?

Answer 10

-94-99%

Question 11

What is the relationship between % saturation of hgb and PO2?

Answer 11

• a small drop in hgb saturation will cause a significant drop in pO2
• ex: 80% saturation of hgb = 50% PO2

Question 12

reading a CO2 detector

Answer 12

• purple = problem
• tan = think
• yellow = yes

-it’s purple to start out, CO2 changes it yellow; if intubated incorrectly like in the right mainstem bronchus, it will be tan

Question 13

waveform capnography

Answer 13

quantitative measure of CO2

Question 14

PetCO2

Answer 14

• PCO2 right before you breathe in

- if it drops below 10 mmHg, need to push harder on chest compressions

Question 15

what is the product of normal metabolism?

Answer 15

• 2 forms of acid:
• respiratory
• metabolic

Question 16

respiratory acid formed in normal metabolism

Answer 16

-volatile: carbonic

H2CO3 H2O +CO2

Question 17

metabolic acid formed in normal metabolism

Answer 17

-larger molecular size:
from amino acids, fats, carbs, phosphoric, sulfuric: excreted by kidneys

H+ + HCO3

Question 18

normal metabolism total equation

Answer 18

H+ + HCO3- H2CO3 H2O + CO2

Question 19

what happens during anaerobic metabolism?

Answer 19

• ex: cardiac arrest/DKA
• production of lactic acid accumulates, hence metabolic acidosis
• strong acids combine w/ sodium bicarb resulting in a weak acid and neutral salt
• the weak carbonic acid is blown off by the lungs as CO2

Question 20

anaerobic metabolism equation

Answer 20

HAcid + NcHCO3 –> H2CO3 + NaA NaA + H2O + CO2

Question 21

CO2 and water forms ________, which can then be broken down into _____ and ___.

Answer 21

CO2 and water forms carbonic acid, which can then be broken down into bicarb and H+.

Question 22

what are the 2 ways in which you can get rid of acid?

Answer 22

• get rid of H+

- get rid of CO2

Question 23

how to effect pH through respiratory rate

Answer 23

• getting rid of CO2 leads to no formation of carbonic acid

- retaining CO2 leads to formation of more acid and more H+

Question 24

buffer systems consist of what?

Answer 24

• a weak acid

- the salf of the weak acid

Question 25

purpose of buffering systems

Answer 25

to prevent the accumulation of carbonic and metabolic acids that produce marked changes in acidity of the body

Question 26

What is the most important buffering system in the body?

Answer 26

sodium bicarbonate and carbonic acid system

Question 27

what is the weak acid in the sodium bicarb/carbonic acid buffer?

Answer 27

carbonic acid

Question 28

what is another example of a buffer system in the body?

Answer 28

- hgb | - if it dumps all O2 in the periphery and takes nothing but CO2, it's serving as a buffer for the RBC

Question 29

pH

Answer 29

- hydrogen ion concentration | - ration of base:acid

Question 30

what is the ratio in pH

Answer 30

- NaHCO3:H2CO3 - Base:Acid - 20:1

Question 31

changes in PaCO2 result in changes of what?

Answer 31

H2CO3 (NOT NaHCO3) | because an acid cannot react w/ its own salt, so only the ratio b/w the two changes

Question 32

as [H+] double or halves, what is the result?

Answer 32

- pH change of 0.3 | - therefore, small pH changes signify marked accumulation/depletion of acid

Question 33

normal ABG values

Answer 33

- pH: 7.35-7.45 (use 7.4 as reference) - PaO2: 80-90 mmHg - PaCO2: 35-45 mmHg (use 40 as reference) - HCO3: 21-28 mEq/l

Question 34

golden rule #1

Answer 34

A change in PaCO2 of 10 mmHg = up/down pH change of 0.08 units

Question 35

golden rule #2

Answer 35

A change in HCO3 of 10 mEql = up/down pH change of 0.15 units

Question 36

if the calculated pH approximates the real pH, what is the mechanism?

Answer 36

pure respiratory

Question 37

if the calculation pH do not approximate the real pH, what is the mechanism?

Answer 37

it must have a metabolic component

Question 38

how do you treat respiratory and metabolic acidosis?

Answer 38

by increasing ventilations and giving a base (ex: NaHCO3) | driving the equation to the right

Question 39

base deficit is d/t what?

Answer 39

loss of sodium bicarb from ECF

Question 40

base deficit expresses...

Answer 40

the deficit of sodium bicarb in mEq for a L of ECF

Question 41

golden rule #3

Answer 41

base deficit X pt. weight in kg / 4

Question 42

metabolic acidosis is treated with ...

Answer 42

IV sodium bicarb

Question 43

if the ABG is out of whack, but the pH is normal, what is going on?

Answer 43

compensation

Question 44

compensation

Answer 44

- in chronic disease, lungs/kidneys may compensate for disease in the other - if pH has returned to 7.35 - 7.45, the compensated - if not, uncompensated

Question 45

in COPD, what do the kidneys do?

Answer 45

retain base

Question 46

in hyperaldosteronism, what do the lungs do?

Answer 46

retain CO2 (increased renal absorption of bicarb)

Question 47

if pH is increased...

Answer 47

= alkalosis - if PaCO2 is in same direction = metabolic - if PaCO2 is in opposite direction = respiratory

Question 48

if pH is decreased...

Answer 48

= acidosis - if PaCO2 is in same direction = metabolic - if PaCO2 is in opposite direction = respiratory