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Multi-Disciplinary Reviews > 2017 Hawaii > Flashcards

2017 Hawaii Flashcards

1
Q

What is the alveolar air equation

A

PAO2 = [FIO2 x (Barometric Pressure - Water vapor pressure)] - PaCO2/RQ

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2
Q

FIO2

A

Fraction of inspired oxygen

Can be measured as percentage or decimal
room air is considered 21% or 0.21

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3
Q

PAO2

A

partial pressure of oxygen in the alveolus

This is the quantity of oxygen in the alveolus

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4
Q

Barometric Pressure

A

760 mmHg at sea level

with increasing altitude the pressure falls and those at 600 mmHg barometric pressure will have a lower PAO2 than those at seal level. So normal blood oxygen level will change with altitude.

These people end up making more red blood cells.

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5
Q

water vapor pressure

A

50 mmHg

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6
Q

RQ

A

respiratory quotient = CO2Production/O2 Consumption

RQ ~ 0.9 (0.7/1.0)

A normal animal using an RQ of 0.9 at sea level will have a PAO2 of 105 mmHg

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7
Q

PaO2

A

amount of oxygen in arterial blood

<80 @ sea level is considered hypoxemia

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8
Q

A-a gradient

A

PAO2-PaO2

With normal lung function the partial pressure of oxygen in arterial blood (PaO2) will be slightly lower than PAO2

An A-a gradient of room air blood gases of < 15 mmHg is considered normal

The normal is due to small quantity of deoxygenated venous blood from the bronchial and coronary circulation draining into the left side of the heart.

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9
Q

Define Hypoxemia & give 2 main mechanisms

A

PaO2 < 80 mmHg

  1. Low Alveolar O2
  2. Abnormal transfer of O2 for alveoli to the arterial blood (increased A-a gradient)
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10
Q

Name the clinical causes of hypoxemia

A

Low PAO2 (normal A-a gradient)

  1. low inspired oxygen (could be due to low barometric pressure at high altitude or a breathing circuit without an adequate oxygen supply
  2. Hypoventilation (if breathing room air)

Increased A-a Gradient

  1. Venous admixture
    - Ventilation perfusion mismatch due to
    a. low venitlation/perfusion alveoli
    b. no ventilation/perfusion alveoli (intrapulmonary shunt)
    - Anatomical vascular right to left shunts
    - Diffusion defects
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11
Q

N2 = 565 mmHg
H20 = 50 mmHg
CO2 = 40 mmHg
O2 - 105 mmHg

A

Normal patient breathing room air

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12
Q 
N2 = 565
H20 = 50
CO2 = 80
O2 = 65
A

hypoventilation breathing room air: patient is hypoxemic

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13
Q 
N2 = 345
H20 = 50
CO2 = 80
O2 = 285
A

Hypoventilation Breathing 50% O2

Patinet would not be hypoxemic if normal lungs.

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14
Q

What is the difference between hypoxia and hypoxemia?

A

Hypoxemia: abnormally low arterial oxygen tension in the blood

Hypoxia: underoxygenation which is inadequate level of tissue oxygenation for cellular metabolism

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15
Q

What are the 4 types of hypoxia

A
  1. hypoxic hypoxia: inadequate oxygen at the tissue cells caused by low arterial oxygen tension (PaO2)
    - hypoventilation - increased CO2 in alveolus displaces oxygen
    - high altitude
    - diffusion defects
    - VQ mismatch
    - R to L shunt
2.  Hypoxemic Hypoxia: decreased O2 intent (CaO2)
anemic hypoxia PaO2 is normal but the oxygen carrying capacity of the Hb is inadequate
-decreased hemoglobin 
-anemia
-hemorrhage
-abnormal hemoglobin
-carboyxhyemoglobinemia
-Methemoglobinemia
  1. Circulatory hypoxia
    stagnant hypoxia or hypo perfusion where blood flow to the tissue cells is inadequate. Oxygen delivery is not adequate to meet tissue needs
    systemic= shock
    ischemia=local lack of perfusion
    -slow or stagnant (pooling) of peripheral blood flow
    -arterial-venous shunts
    -decreased cardiac output
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16
Q

Histotoxic hypoxia

A

impaired ability of the tissue cells to metabolize oxygen

  • cyanide poisioning
  • dysoxia: sepsis alters tissue ability to utilize oxygen
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17
Q

Causes of V/Q mismatch?

A

pulmonary disease

  • oedema
  • pneumonia
  • pulmonary hemorrhage

optimal V/Q matching would be an equal degree of ventilation as there is perfusion and = 1

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18
Q

What is the rule of 120?

A

Analyze: room air arterial blood gases at sea level and a quick easy A-a gradient is

IF PaO2 + PaCO2 > 120 mmHg it means normal A-a gradient

IF the value is lower then there is an increased or abnormal gradient

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19
Q

What is the 5x rule?

A

PaO2 you would expect with normal lungs at sea level on a given FIO2

does not take into account big changes in PCO2

so if FIO2 is 50% then PaO2 is 250 mmHg

20
Q

PaO2/FIO2 ratio?

A

can compare serial blood gases on differing FIO2
expressed as decimal in this ratio

FIO2 105 mmHg and room air 21%
so 105/0.21=500

~500 is consistent with normal function
200-300 is mild lung dysfn
100-200 is moderate a
<100 is severe

21
Q

What is ventilation?

A

the tidal movement of air in and out of lungs

quantified as minute ventilation

22
Q

What is minute ventilation

A

total amount of gas inhaled in one minute and equals RR x TV of each breath

23
Q

How is PCO2 determined primarily?

A

arterial CO2 levels are directly proportional to the rate of CO2 production by the tissues and inversely proportional to effective alveolar minute ventilation. PCO2 doesn’t really change substantially in clinical setting so it is primarily determined by alveolar minute ventilation.

24
Q

What is alveolar minute ventilation?

A

the portion of TV that ventilates functional alveoli.

25
Q

What is Alveolar TV?

A

the alveolar TV = TV minus volume of dead space (part not participating in gas exchange)

26
Q

What is normal arterial PCO2 in cat and dog?

A

cat: 32mmHG

dog 37 mmHg

27
Q

What are normal venous CO2 levels?

A

~ 5 mmHg higher than arterial

28
Q

What can you deduce from PaCO2 levels higher than 60?

A

severe hypercapnia

in away patients rule out brain dz/central res depression
cervical spine disease
peripheral neuropathy
neuromuscular jxn disorders
myopathies of respiratory muscles

in anesthetized:
soda lime reproaching
excess circuit dead space
valve malfunction

29
Q

What do you need for patients to maintain normal PCO2 levels?

A

patent airway
normal brain function
intact neuro pathways from brain to high cervical s/c to diaphragm and intercostal muscles
normal resp. m. fxn

30
Q

Does pulmonary parenchymal disease lead to hypercapnia?

A

Not commonly

31
Q

What is ETCO2? how is it measured

A

ETCO2 is usually 2-6 mmHg less than arterial PCO2 and is considered an accurate representation of arterial PCO2 in most things.

This can be measured from nasal cannula in the awake patient using a side stream ETCO2 monitor.

Not useful with severe cardiovascular compromise or cardiac arrest

Pulmonary thromboembolism will cause a significant disparity between arterial PCO2 and ETCO2 a finding that you can use to support PTE

32
Q

What is pH? What can changes do?

A

measure of the hydrogen ion concentration

changes will alter protein structure, enzymatic activity and metabolic fxn.

33
Q

What is the Henderson-Hasselbalch equation?

A

pH = 6.1 + log [HCO3-]/0.03PCO2

pH is dependent on the ratio of bicarbonate concentration to PCO2

34
Q

What is the carbonic acid equilibration system?

A

CO2 + H2O H2CO3 H+ + HCO3-

35
Q

Normal pH in the face of abnormal PCO2 and HCO3-

A

mixed disorder

36
Q

pH

A

low acidic

high alkalemia

37
Q

PCO2

A

normal
low = respiratory alkalosis
high = respiratory acidosis

38
Q

HCO3-

A

normal
low (metabolic acidosis)
high (metabolic alkalosis)

39
Q

What is anion gap?

A

the difference between the measured plasma concentrations of major cations and major anions

dog normal 18 +/- 6 cat is 20 +/-7

40
Q

What is anion gap equation?

A

Na + K = CL + HCO3 + AG or

AG = (Na + K) - (CL +HCO3)

41
Q

Name two types of metabolic acidosis

A

High anion gap (normochloremic) metabolic acidosis

Hyperchloremic (Non-AG) metabolic acidosis

42
Q

What is High anion gap metabolic acidosis?

A

Due to a gain of acid in the body

D. DKA
U. Uremic acids
E. Ethylene glycol toxiciy
L. Lactic acidosis

43
Q

What is hyperchloremic metabolic acidosis and name examplesq

A

Normal AG due to diseases associated with bicarbonate loss

Gastrointestinal loss:

  • diarrhea
  • vomiting with reflux from duodenum

renal loss

  • renal tubular acidosis
  • hypomineralocorticism i.e. Addison’s dz

Dilutional Acidosis - large volume saline admin

44
Q

What is metabolic alkalosis and name causes

A

due to acid loss or bicarb gain
patients are most often hypochloremic usually because of concurrent CL- loss with H + loss

Gastric loss of volume:

  • vomiting due to pyloric obstruction
  • gastric suctioning

Renal acid excretion
-furosemide therapy

Contraction alkalosis
Excessive alkalization therapy (iatrogenic)

45
Q

What is respiratory acidosis and name causes

A

due to increased inspired CO2 or decreased RR and or effort.
High venous PCO2 due to poor perfusion

Rebreathing (circuit problem)
Hypoventilation: 
-neuromuscular dz
-airway obstruciton
-open pneumothorax or flail chest
-anterior displacement of the diaphragm by abdominal space filling disorders
-pleural space filling disorders severe
late pulmonary parenchymal disease

Elevated venous PCO2 due to poor tissue perfusion

46
Q

What is respiratory alkalosis and name causes

A

increased respiratory rate and or effort causing alkalosis

hypotension
fever
SIRS/Sepsis
Excitement
Excercise/Pain
Pulmonary thromboembolism
Early pulmonary parenchymal disease
Inappropriate ventilator settings
47
Q

What is the bicarb equiation

A

Bicarbonate (mEq) = 0.3 x body weight (kg x Base Deficit mEq/L)

you can estimate base deficit based on bicarb of blood work.

give 1/2 to 1/3 IV

can have side effects of hypervolema/hypernatremia/hypokalemia/hypocalcemia

Multi-Disciplinary Reviews (2 decks)

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