Arterial blood gases section 1

Question 1

standard arterial blood gases

Answer 1

pH / PaCO2 / PaO2 / HCO3-

SaO2 / BE

Question 2

PaO2

Answer 2

partial pressure of arterial oxygen. amount of pressure given off by the free oxygen dissolved within the aqueous phase of the blood
PaO2 is dependent on PAO2 (partial pressure of alveolar oxygen, or space between lungs). the alveolar capillary interphase - body diffuses oxygen from alveolar space into the capillary eventually converting to arterial space.

PaO2 80 to 100 mmHg

PAO2 = (713 x FiO2 [atmosphere]) – (1.25 x PaCO2 [from patient]) at sea level

A-a gradient = PAO2 – PaO2
Normal value increases with age
Normal value roughly estimated as (age / 4) + 4
widened A-a gradient means the oxygen is not appropriately diffusing from alveolar space to arterial space.

Question 3

SaO2

Answer 3

hemoglobin saturation of arterial oxygen, >95%
for a given Pa02 (x axis), you should have relatively expected level of Sa02. if something affects pa02, then it will affect SaO2.
right shift in graph –> reduced Hb-O2 affinity
-higher CO2
-lower pH
-higher temperature
-in left shift in graph, it will be opposite

Question 4

CaO2

Answer 4

total content of arterial oxygen
CaO2 18 to 22 mL O2 / dL blood

Sum of PaO2 contribution and SaO2 contribution

 - > PaO2 x 0.003 +
 - > SaO2 (% binding to hemoglobin) x Hgb x 1.34

Question 5

small a indicates

Answer 5

in arterial blood space

Question 6

examples SvO2 can indicate

Answer 6

hemoglobin saturation in VENOUS blood

Question 7

the oxygen dissociation curve is the steepest or increases most rapidly

Answer 7

bw PaO2 of app 20-60 mm Hg. for every incremental increase in this range, you will achieve much greater increase in % saturation.

Question 8

carbon monoxide poisoning

Answer 8

something that can affect the amount of hemoglobin oxygen binding without necessarily affecting the dissociation curve bc its not related to affinity. it will bind to hemoglobins binding sites and wont change affinity of the remainding oxygen sites for the oxygen.

Question 9

vast majority of oxygen is carried

Answer 9

within the hemoglobin and the aqueous portion contributes very little

Question 10

Hemolytic anemia is most likely to affect

Answer 10

CaO2

bc of reduced hemoglobin we will likely have reduced CaO2

Question 11

hypoxemia

Answer 11

low levels of oxygen within blood, <80 mm Hg (depends on PaO2)
Low PAO2
Poor diffusion (A-a gradient)
V/Q mismatch (ventilation-perfusion). maybe alveolar capillary is not the problem, but larger problem with where and how the lung and vascular system are matching up
Shunting - shunting blood from one side to another

Question 12

hypoxia

Answer 12

low levels of oxygen within tissues
can be caused by hypoxemia (if theres low levels of oxygen in blood, then its not getting into tissues)
anemia - low levels of hemoglobin. if you cant carry oxygen effectively, can cause hypoxia
vascular insufficiency - if blood flow is not getting to tissue correctly
Histotoxia - disorder within tissue itself that leads to hypoxia

Question 13

PvO2 represents a vein

Answer 13

coming in and encircling at the alveolar capillary interphase and and exiting and the right bottom side in the artery. when V/Q ratio is 1, the alveolus has available oxygen to give off to the vascular system. the vascular system is appropriately perfusing that area in order to accept the oxygen. when the blue/unoxygenated blood comes in, picks up oxygen from alveolar capillary interphase, and exits oxygenated.

Question 14

when V/Q is lower than 1

Answer 14

you might have shunt like situation. its causing vascularized areas to not pick up oxygen where its supposed to. It comes in deoxygenated and exit deoxygenated.

Question 15

when V/Q is infinity or greater than 1,

Answer 15

dead space. not perfusing right areas.

Question 16

if A-a oxygen gradient is normal,

Answer 16

then one explanation is hypoventilation (not having sufficient alveolar pressure of oxygen transferred over to the arterial.)

Question 17

if there is a widened gradient, then

Answer 17

theres a V/Q mismatch, shunting, or a diffusion limitation which could be something like copd or a chronic abnormality within lung structures.
in order to deferentiate between all 3 options, you can see, is response to oxygen good?
if response to oxygen is good: V/Q mismatch or diffusion limitation
if its poor: shunt