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Respiratory Ax > Martin ABG > Flashcards

Martin ABG Flashcards

1
Q

Blood gas (def)

A

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

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2
Q

Inert gases in blood

A

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

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

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3
Q

Carbon Monoxide

A

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

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4
Q

T/F: not all blood gases are routinely measured

A

True

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5
Q

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

A

True

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6
Q

Co-oximeter

A

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

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7
Q

Co-oximetry

A

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

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8
Q

What do you expect PaO2 in CO and MetHb?

A

NORMAL! (unless patient has lung disease)

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9
Q

What do you expect the SaO2 in CO and MetHb?

A

Will be artificially high

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10
Q

What does blood gas analysis entail?

A

Measurements of:

  1. Blood gases
  2. Hgb content/binding
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11
Q

SaO2

A

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%
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12
Q

Methemoglobin

A

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

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13
Q

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

A

Incorporating special electrodes into the blood gas machine

–Na, K, Cl, bicarb, +/- Ca, Mg

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14
Q

Important considerations when interpreting ABG

A
  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
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15
Q

Isolated PaO2

A

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

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16
Q

What is normal PaO2?

A

IT DEPENDS!!!

Depends on FiO2, Pb, patient’s age

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17
Q

Air composition

A

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

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18
Q

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

A

True

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19
Q

Barometric Pressure

A
  • -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
20
Q

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

A

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

21
Q

What is the Pb on Everest?

A

253 mm Hg

22
Q

How does altitude affect Pb?

A

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

23
Q

Pressure of a gas in dry air

A

= percentage of a gas x barometric pressure

24
Q

Water vapor in ambient air

A
  • -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
25
Q

Water vapor in the upper airway

A

Becomes fully saturated

Pressure = 47mm Hg

26
Q

How to maintain acceptable oxygen levels at extreme altitude?

A 
Change the environment 
1. Increase FiO2
2. Increase Pb 
Adapt physiologically 
1. Lower PaCO2 by hyperventilating
27
Q

What is the average airway pressure in the lungs?

A

= 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)

28
Q

What happens when breathe 100% O2?

A

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

29
Q

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

A

Alveolar Ventilation
Oxygenation
Acid-Base Balance

30
Q

Equation for alveolar ventilation?

A

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

31
Q

Alveolar ventilation

A

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

32
Q

Minute/total ventilation

A

VE = RR x Tv

33
Q

Dead space ventilation

A

VD = RR x Dead space volume

34
Q

PCO2 Equation

A

PaCO2 = (VCo2 x 0.863)/VA

Evaluates PaCO2 based on patient’s RR and breathing effort

35
Q

What is PaCO2 directly proportional to?

A

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

36
Q

What is PaCO2 inversely proportional to?

A

Alveolar ventilation

37
Q

What equations assess oxygenation?

A

Alveolar gas, oxygen content

38
Q

What equation(s) assess acid-base balance?

A

Henderson-Hasselbalch

39
Q

Short form alveolar gas equation

A

PAO2 = PIO2 - 1.2PaCO2

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

40
Q

Longer form of the alveolar gas equation

A

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

41
Q

Oxygen content

A

Oxygen = gas –> exerts a pressure

Also has a content: CaO2 (mL O2/dL blood)

42
Q

Oxygen content equation

A

CaO2 = amt of O2 bound to hgb + amt dissolved in plasma

= (SaO2xHbx1.34) + 0.003PaO2

43
Q

CaO2

A

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

44
Q

SaO2

A

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

45
Q

Hb

A

Hemoglobin content (g/dL blood)

Respiratory Ax (5 decks)

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