Martin ABG

Question 1

Blood gas (def)

Answer 1

Any element or compound that is gas under ordinary conditions
Also dissolved got some extent in our blood

Question 2

Inert gases in blood

Answer 2

Nitrogen, krypton, helium (last two in trace amounts)

Cause no clinical problems –> not measured as part of ABG

Question 3

Carbon Monoxide

Answer 3

Gas, measured in its combined form with hgb as % carboxyhgb (%COhgb)
Measurement is only an indirect guide to %COHb

Question 4

T/F: not all blood gases are routinely measured

Answer 4

True

Question 5

T/F: not all blood gas measurements are of true blood gases

Answer 5

True

Question 6

Co-oximeter

Answer 6

Can measure, on a small portion of the arterial blood sample, hgb content (in grams per deciliter) and values related to the hgb binding: SaO2, %COHb, percent methemoglobin (%MetHb)
–> can calculate arterial oxygen content

Question 7

Co-oximetry

Answer 7

Distinct test that may not be available - must ensure able to run
Can miss life-threatening conditions: methemoglobinemia, carbon monoxide poisoning

Question 8

What do you expect PaO2 in CO and MetHb?

Answer 8

NORMAL! (unless patient has lung disease)

Question 9

What do you expect the SaO2 in CO and MetHb?

Answer 9

Will be artificially high

Question 10

What does blood gas analysis entail?

Answer 10

Measurements of:

1. Blood gases
2. Hgb content/binding

Question 11

SaO2

Answer 11

Percentage of hgb sites chemically combined (saturated) with oxygen

• -Hgb binding site cannot contain more than one gas molecule at a time
• • Percentages (%O2Hb, %COHb, %MetHb) = additive –> cannot be greater than 100%

Question 12

Methemoglobin

Answer 12

Hgb that has iron in its ferric or oxidized state (Fe+++) as opposed to the normal ferrous state (Fe++)
–Hgb w Fe3+ can bind neither oxygen nor carbon monoxide

Question 13

Basics: how measure electrolytes in the arterial sample? Which electrolytes do we measure?

Answer 13

Incorporating special electrodes into the blood gas machine

–Na, K, Cl, bicarb, +/- Ca, Mg

Question 14

Important considerations when interpreting ABG

Answer 14

1. Patient’s environment –> FiO2, barometric pressure
2. Other lab data –> prior BGs, ELs, gluc, BUN, hct, CXR
3. Clinical picture –> RR/effort, other vitals, mentation, tissue perfusion

Question 15

Isolated PaO2

Answer 15

Reveals little useful information without reference to the patient’s mental status and resp effort
Low PaO2 may mean one thing if patient inhaling supplemental air vs room air

Question 16

What is normal PaO2?

Answer 16

IT DEPENDS!!!

Depends on FiO2, Pb, patient’s age

Question 17

Air composition

Answer 17

78% nitrogen, 21% oxygen, 1% other inert gases, negligible amount of CO2

Question 18

T/F: At any altitude the fraction of inspired O2 is 0.21

Answer 18

True

Question 19

Barometric Pressure

Answer 19

• -Fxn of wght of atms above the point of measurement
• -Sum of all of the pressures of the constituent gases
• -Each gas exerts its own partial pressure, which is the pressure it would exert if no other gases were present

Question 20

What does it mean that the Pb is 760mmHg at sea level?

Answer 20

Air pressure at sea level will sustain a closed column of mercury 760mmHg high

Question 21

What is the Pb on Everest?

Answer 21

253 mm Hg

Question 22

How does altitude affect Pb?

Answer 22

Higher the altitude, lower the weight of the air at that point and lower the Pb

Question 23

Pressure of a gas in dry air

Answer 23

= percentage of a gas x barometric pressure

Question 24

Water vapor in ambient air

Answer 24

• -Exerts own partial pressure
• -Must be subtracted from the barometric pressure since dilutes out all of the dry gases
• -Depends on climate: amp of water vapor in ambient air varies from 0 to >50 mm Hg

Question 25

Water vapor in the upper airway

Answer 25

Becomes fully saturated | Pressure = 47mm Hg

Question 26

How to maintain acceptable oxygen levels at extreme altitude?

Answer 26

``` Change the environment 1. Increase FiO2 2. Increase Pb Adapt physiologically 1. Lower PaCO2 by hyperventilating ```

Question 27

What is the average airway pressure in the lungs?

Answer 27

= ambient/barometric pressure (with mechanical ventilation, avg airway pressure will be slightly higher than ambient - difference depends on art of positive pressure being delivered by the ventilator)

Question 28

What happens when breathe 100% O2?

Answer 28

Extra oxygen displaces nitrogen from the body's tissues Amount of N2 displaced depends on the FiO2 and how long supplemental oxygen has been inhaled --> oxygen pressure merely replaces the N2 pressure

Question 29

What physiological processes are assessed by pH, PaO2, and PaCO2?

Answer 29

Alveolar Ventilation Oxygenation Acid-Base Balance

Question 30

Equation for alveolar ventilation?

Answer 30

PaCo2 = (VCo2 x 0.863)/VA Alveolar PCo2 = amount of CO2 produced by metabolism and delivered to the lungs x constant divided by alveolar ventilation

Question 31

Alveolar ventilation

Answer 31

VA = VE - VD --> minute/total ventilation - dead space ventilation

Question 32

Minute/total ventilation

Answer 32

VE = RR x Tv

Question 33

Dead space ventilation

Answer 33

VD = RR x Dead space volume

Question 34

PCO2 Equation

Answer 34

PaCO2 = (VCo2 x 0.863)/VA | Evaluates PaCO2 based on patient's RR and breathing effort

Question 35

What is PaCO2 directly proportional to?

Answer 35

VCO2 --> amount of CO2 produced by metabolism and delivered to the lungs

Question 36

What is PaCO2 inversely proportional to?

Answer 36

Alveolar ventilation

Question 37

What equations assess oxygenation?

Answer 37

Alveolar gas, oxygen content

Question 38

What equation(s) assess acid-base balance?

Answer 38

Henderson-Hasselbalch

Question 39

Short form alveolar gas equation

Answer 39

PAO2 = PIO2 - 1.2PaCO2 | Where PIO2 = partial pressure of inspired/tracheal oxygen in mm Hg --> FIO2 (Barometric pressure - water vapor pressure)

Question 40

Longer form of the alveolar gas equation

Answer 40

PAO2 = FIO2(Pb-PH20)-PACO2 x [FiO2+(1-FiO2)/R) R = respiratory quotient PACO2 assumed to equal PaCO2

Question 41

Oxygen content

Answer 41

Oxygen = gas --> exerts a pressure | Also has a content: CaO2 (mL O2/dL blood)

Question 42

Oxygen content equation

Answer 42

CaO2 = amt of O2 bound to hgb + amt dissolved in plasma | = (SaO2xHbx1.34) + 0.003PaO2

Question 43

CaO2

Answer 43

Oxygen content of arterial blood - mL O2/dL arterial blood

Question 44

SaO2

Answer 44

Percent saturation of arterial hgb with oxygen, expressed as decimal fraction

Question 45

Hb

Answer 45

Hemoglobin content (g/dL blood)