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Clinical Medicine - Pulmonary > Diagnosis - ABG > Flashcards

Diagnosis - ABG Flashcards

1
Q

What important values are obtained via ABG?

A

pH
PaCO2
PaO2

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2
Q

What is an Allen’s test?

A

Compression of ulnar and radial arteries
–release each, one at a time, to check for reperfusion

Demonstrates the blood supply to the hand

Used to check that the hard is still well supplied if a thrombus were to occur

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3
Q

What is the normal pH?

A

7.4

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4
Q

What is the normal PaCO2?

Why is it used?

A

40

used to detect ventilation problems

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5
Q

What is the normal PaO2?

Why is it used?

A

100

Used to detect oxygenation problems

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6
Q

Henderson Hassalbalch basic relationship

A

pH ~ HCO3- / PaCO2

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7
Q

Acidemia

A

blood pH < 7.35

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8
Q

Acidosisis

A

a primary physiologic process that, occurring alone, tends to cause academia

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9
Q

Alkalemia

A

blood pH > 7.45

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10
Q

Akalosis

A

a primary physiologic process that, occurring alone, tends to cause alkalemia

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11
Q

Primary acid-base disorder

A

Change that occurs first in the balance of HCO3- and PaCO2

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12
Q

Compensations

A

Change in HCO3- or PaCO2 that occurs as a result of the primary event

Never over compensate

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13
Q

Respiratory alkalosis

A

first change - lower PaCO2
causes elevated pH

then, kidney compensates - secondary lowering of HCO3-

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14
Q

Respiratory acidosis

A

first change - elevation of PaCO2
causes decreased pH

then, kidney compensates - retains HCO3-

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15
Q

Metabolic acidosis

A

first change - lowering of HCO3- b/c kidney is excreting it
causes decreased pH

then, lung compensate - hyperventilation - lowers PaCO2

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16
Q

Metabolic alkalosis

A

first change - elevation of HCO3-
causes increased pH

then, lungs compensation - hypoventilation - increases PaCO2

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17
Q

Anion Gap

A

Na+ - (Cl- + CO2)

Note: CO2 in this equation is the “total CO2” measured in the chemistry lab as part of a routine serum electrolytes

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18
Q

Metabolic acidosis and increased anion gap

A 
MUDPILES
Mehtanol
Uremia
Diabetic ketoacidosis
Propylene glycol
Isoniziad
Lactic acidosis
Ethylene glycol
Salicylates
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19
Q

Metabolic acidosis and normal anion gap

A 
HARDUPS
Hyperalimentation
Acetazolamide or carbonic anhydrase inhibitors
Renal tubular acidosis
Diarrhea
Ureteroenteric fistula
Pancreaticoduodenal fistual
Spironolactone
20
Q

Causes of metabolic alkalosis

–all of these are considered ..

A

Chloride responsive

  • Vomiting
  • Contraction alkalosis
  • Diuretics
  • Corticosteriods
  • Gastric suctioning

Chloride resistant
-hyperaldosterone state, e.g Cushings

21
Q

Respiratory acidosis causes

A 
CNS depression (e.g. drug overdose)
Chest bellows dysfunction (e.g. GBS, MG)
Disease of lungs and/or upper airway
22
Q

Respiratory alkalosis causes

A

Hypoxemia (includes altitude)
Anxiety
Sepsis
Acute pulmonary insult (e.g. pneumonia, etc.)

23
Q

Mixed acid-base disorders

A

more common than single disorders in those that are chronically ill

24
Q

A increase in PaCO2 by 10 will do what do the pH

–note, this is in an acute setting

A

decrease it by 0.08

25
Q

How does compensation change in chronic respiratory settings?

A

For every increase in PaCO2 by 10, the pH will decreased by 0.03

In chornic resp acidosis, the kidneys compensate by holding onto HCO3 to buffer the pH
These is a 5 pt bicarb rise for every 10 mm PaCO2 rise

26
Q

FiO2

A

fraction of inspired oxygen (O2 in air)

27
Q

SpO2

A

“pulse-ox” or bound oxygen % (finger probe)

28
Q

SaO2

A

Bound oxygen % (measured directly)

29
Q

PiO2

A

Pressure inspired oxygen in the trachea

30
Q

A-a gradient equation

A

Alveolar oxygen - arterial oxygen

PiO2 - (PaCO2 / R) - PaO2
R = 0.8 = respiratory quotient

Expected normal = Patient age/4 + 4

31
Q

What is a respiratory quotient?

A

Ratio of CO2 produced to O2 consumed

32
Q

What does a normal gradient mean?

A

A-a gradient will be normal if pure hypoventilation or altitude (not lung problem) is the cause of hypoxia

33
Q

What does an abnormally elevated gradient mean?

A

Abnormal (elevated) when gas diffusion is impaired (lung problem)

34
Q

What two additional relationships are important to know in order to quantify the degree of diffusion or hypoxemia (low O2 concentration)?

A
  1. the oxygen saturation to the dissolved oxygen concentration (SpO2 to PaO2)
  2. the dissolved oxygen concentration to the inspired oxygen concentration (PaO2 to FiO2)
35
Q

S curve

  • what is saturation like
  • what kind of curve
A

At 60 mmHg, you are saturating at 90%

Sigmoidal curve
–due to positive cooperatively of Hg

36
Q

What causes a right shift?

What does this mean?

A

O2 is released quicker from hemoglobin

High PCO2
Fever
Acidosis
High 2,3-DPG

37
Q

What causes a left shift?

What does this mean?

A

Hemoglobin holds more on to O2

Alkalosis
Hypothermia
Low PCO2
Lower 2-3, DPG

38
Q

Why is PaO2 to FiO2 useful?

What is a normal ratio?

A

It compares the concentration of dissolved oxygen (PaO2) to inspired or “inhaled” oxygen (FiO2)

As the severity of diffusion impairment increase this ratio decreases

Normal PaO2:FiO2 on room air = 100:21% = ~475
(short cut - normal is about 5x FiO2)

39
Q

Decreased V/Q

A

Areas in the lung that are better perfused than ventilation

aka SHUNT - blood is shunted from R to L w/o being oxygenation

40
Q

Increased V/Q

A

Areas that are better ventilated than perfused

aka DEAD SPACE

41
Q

Lung zones

-what does this lead to?

A

A normal expected V/Q mismatch

  • -at the lower part of the lungs V/Q = 0.6
  • -at the top part of the lung V/Q = 3
42
Q

Zone 1

A

PA > Pa > Pv

43
Q

Zone 2

A

Pa > PA > Pv

44
Q

Zone 3

A

Pa > Pv > PA

45
Q

What diseases cause increased V/Q

A

Pulmonary embolism

emphysema?

46
Q

What diseases cause decreased V/Q (shunt)

A

AV malformation
Pneumonia
Fibrosis
Secretions

47
Q

What are the two types of shunts?

A

Extra pulmonary

  • R to L cardiac shunts
  • e.g. tetralogy of fallot

Intra pulmonary

  • Blood is transported through the lungs without taking part in gas exchange
  • e.g. atelectasis, pneumonia, AVM

Clinical Medicine - Pulmonary (8 decks)

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