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Pulm > SM_160a-162a: Hypercapnia and Hypoxemia > Flashcards

SM_160a-162a: Hypercapnia and Hypoxemia Flashcards

1
Q

What is hypoxemia?

A

Decreased PO2 in blood

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2
Q

What is hypoxia?

A

Decreased PO2 in tissue

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3
Q

Most hypoxia is driven by ________

A

Most hypoxia is driven by hypoxemia

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4
Q

In clinical practice, problems with oxygenation are typically identified using ________

A

In clinical practice, problems with oxygenation are typically identified using pulse oximetry

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5
Q

What is SpO2?

A

Peripheral oxygen saturation

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6
Q

Standard ABG notation is ____ / ____ / ____

A

Standard ABG notation is pH / PaCO2 / PaO2

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7
Q

Normal ABG notation is ____ / ____ / ____

A

Normal ABG notation is pH 7.40 / PaCO2 40 mmHg / PaO2 95 mmHg

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8
Q

Point 1 on the oxygen-hemoglobin dissociation curve is _____ and corresponds to a PO2 of ____ mmHg and a Hgb sat of ____ %

A

Point 1 on the oxygen-hemoglobin dissociation curve is normal and corresponds to a PO2 of 95 mmHg and a Hgb sat of 97 %

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9
Q

Point 2 on the oxygen-hemoglobin dissociation curve is _____ and corresponds to a PO2 of ____ mmHg and a Hgb sat of ____ %

A

Point 2 on the oxygen-hemoglobin dissociation curve is the knee and corresponds to a PO2 of 60 mmHg and a Hgb sat of 90 %

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10
Q

Point 3 on the oxygen-hemoglobin dissociation curve is _____ and corresponds to a PO2 of ____ mmHg and a Hgb sat of ____ %

A

Point 3 on the oxygen-hemoglobin dissociation curve is mixed venous and corresponds to a PO2 of 40 mmHg and a Hgb sat of 75 %

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11
Q

Below point 1 on the oxygen-hemoglobin dissociation curve, _____ changes in Hgb sat are associated with _____ changes in PO2

A

Below point 1 on the oxygen-hemoglobin dissociation curve, small changes in Hgb sat are associated with large changes in PO2​

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12
Q

What is MvO2 or SVO2?

A

Mixed venous Hgb saturation

(mixed because blood contains venous drainage from SVC, IVC, and coronary sinus)

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13
Q

PA catheter measures _____, which is _____ venous Hgb saturation

Triple lumen catheter measures ______, which is _____ venous Hgb saturation

A

PA catheter measures MvO2 (SVO2), which is mixed venous Hgb saturation

Triple lumen catheter measures ScVO2, which is central venous Hgb saturation

(PA catheter goes farther in than triple lumen catheter)

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14
Q

A 65 year old patient is currently in the MICU with septic shock. He is febrile and has a worsening metabolic acidosis with an ABG of 7.15/30/60. His SpO2 is likely to be ____%

A

A 65 year old patient is currently in the MICU with septic shock. He is febrile and has a worsening metabolic acidosis with an ABG of 7.15/30/60. His SpO2 is likely to be 85%.

PO2 of 60 mmHg corresponds to Hgb sat of 90%, but this patient is acidemic and febrile -> shifts O2-Hgb dissociation curve to the right -> O2 offloaded to tissues -> Hgb less saturated for a given PaO2 (Bohr effect)

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15
Q

What shifts the oxygen-hemoglobin dissocation curve to the right?

A
  • Increased CO2
  • Decreased pH
  • Increased temperature
  • Increased 2,3-BPG
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16
Q

What are the normal values for the following?

PaO2: ___ mmHg

SpO2: ___ %

PvO2: ___ mmHg

SvO2: ___ %

A

Normal values

PaO2: 95 mmHg

SpO2: 97 %

PvO2: 40 mmHg

SvO2: 75 %

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17
Q

_____ is the driving force for oxygenating capillary blood coming through alveolar-capillary units

A

PAO2 is the driving force for oxygenating capillary blood coming through alveolar-capillary units

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18
Q

The more efficient gas exchange is at the alveolar-capillary interface, the ______ the A-a difference

A

The more efficient gas exchange is at the alveolar-capillary interface, the narrower the A-a difference

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19
Q

O2 taken in = ________ + ________

A

O2 taken in = O2 consimed (V·O2) + O2 delivered out of lung

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20
Q

What is the equation for PAO2?

A
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21
Q

PO2 = _____ * _____

A

PO2​ = Patm * FIO2

(PO2 is set by barometric pressure and fractional concentration of oxygen)

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22
Q

Air is ______ and ______ in the upper airway, so PiO2 = _________

A

Air is warmed and humidified in the upper airway, so PiO2​ = (Patm - PH20) * 0.21

(warming and humidifying air in the upper airway adds water vapor)

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23
Q

Respiratory quotient is set by _____ and ______

In a typical American diet, R = ____

A

Respiratory quotient is set by diet and metabolism

In a typical American diet, R = 0.8

(V·CO2 = 200 mL/min and V·O2 = 250 mL/min)

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24
Q

What is the formula for respiratory quotient?

A

R = V·CO2 / V·O2

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25
Q

What is the alveolar gas equation?

A

PAO2 = (Patm - PH2O) * FiO2 - (PaCO2 / R)

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26
Q

What are the normal values for the pressures and saturations?

A
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27
Q

_____ sets the partial pressure gradient for oxygenating blood

A

PAO2 sets the partial pressure gradient for oxygenating blood

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28
Q

PiO2 ____ PAO2

A

PiO2 > PAO2​

(have to subtract water vapor pressure for inspired partial pressure of oxygen)

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29
Q

Decreasing PAO2 will _______ PaO2

A

Decreasing PAO2 will decrease PaO2​

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30
Q

What are the causes of hypoxemia?

A
  • Shunt (V·A/Q = 0)
  • Decreased V·A/Q (but not 0)
  • Diffusion limitation
  • Decreased MvO2 (SVO2)
  • Decreased Patm
  • Decreased FiO2
  • Increased PaCO2
  • Decreased R (respiratory coefficient)
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31
Q

______, ______, and ______ are causes of hypoxemia that are due to increased A-a difference

A

Shunt (V·A/Q = 0), decreased V·A/Q (but not 0), and diffusion limitation are causes of hypoxemia that are due to increased A-a difference

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32
Q

______, ______, ______, and ______ are causes of hypoxemia that are due to decreased PAO2 and have a small A-a difference

A

Decreased Patm, decreased FiO2, increased PaCO2, and decreased R are causes of hypoxemia that are due to decreased PAO2 and have a small A-a difference

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33
Q

Shunt (V·A/Q = 0), decreased V·A/Q (but not 0), and diffusion limitation are causes of hypoxemia resulting from _______

A

Shunt (V·A/Q = 0), decreased V·A/Q (but not 0), and diffusion limitation are causes of hypoxemia resulting from increased A-a difference

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34
Q

Decreased Patm, decreased FiO2, increased PaCO2, and decreased R are causes of hypoxemia resulting from ______ and that have a ______

A

Decreased Patm, decreased FiO2, increased PaCO2, and decreased R are causes of hypoxemia resulting from decreased PAO2 and have a small A-a difference

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35
Q

Altitude causes hypoxemia by _____

A

Altitude causes hypoxemia by decreasing Patm​

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36
Q

What is the immediate physiologic response to altitude?

A

Hyperventilating to drop PCO2 and raise PAO2

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37
Q

Fires and mining cause hypoxemia by ______

A

Fires and mining cause hypoxemia by decreasing FiO2

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38
Q

Increasing PaCO2 will ______ PAO2

A

Increasing PaCO2 will decrease PAO2​

39
Q

What caused this patient’s hypoxemia?

A

This patient is hypoxemic and hypercapnic and the A-a < 10 mmHg, so the patients hypoxemia is reasonably explained by hypercapnic respiratory failure driven by fentanyl overdose

40
Q

If A-a difference ≤ 10, hypoxemia _____ explained by hypercapnia

A

If A-a difference ≤ 10, hypoxemia is reasonably explained by hypercapnia

41
Q

If A-a difference > 10, hypoxemia ____ explained by hypercapnia

A

If A-a difference > 10, hypoxemia is NOT reasonably explained by hypercapnia
Something else must be causing the hypoxemia

42
Q

Q· represents perfusion and is analogous to ____ (5L/min)

A

Q· represents perfusion and is analogous to cardiac output (5L/min)

43
Q

What are the types of ventilation?

A
  • Minute ventilation (V·E)
  • Dead space ventilation (V·D)
  • Alveolar ventilation (V·A)
44
Q

What is the formula for minute ventilation?

A

V·E = RR * VT

(V·E = 14 breaths/min * 500 mL = 7L/min)

45
Q

______ is the fact that air stays in bronchi and trachea and does not contribute to ventilation

A

Anatomic dead space is the fact that air stays in bronchi and trachea and does not contribute to ventilation

46
Q

What is the formula for anatomic dead space?

A

V·D = RR * VD

(V·D = 14 breaths/min * 150 mL = 2.1 L/min)

47
Q

Alveolar dead space is when alveoli are ______ but not ______, so they _____ gas exchange

A

Alveolar dead space is when alveoli are ventilated but not perfused, so they do not contribute to gas exchange

(emphysema, pulmonary embolism)

48
Q

Physiologic dead space = ______ + ______

A

Physiologic dead space = anatomic dead space + alveolar dead space

49
Q

In health, anatomic dead space _____ physiologic dead space

A

In health, anatomic dead space = physiologic dead space

(should not have any alveolar dead space)

50
Q

What is the formula for alveolar ventilation?

A

V·A = V·E - V·D

(V·A = 7 L/min - 2 L/min = 5 L/min -> because Q· = 5 L/min, V·A/Q· = 1)

51
Q

Shunts can be ______ or ______

A

Shunts can be intracardiac (PDA, ASD, AVM) or intrapulmonary (blood, pus, water, atelectasis)

52
Q

What is the differential for an intrapulmonary shunt?

A

Blood, pus, water, atelectasis

53
Q

When circulations are mixed, _____ and _____ are averaged, but _____ is not averaged

A

When circulations are mixed, Hgb sat and O2 content are averaged, but PO2 is not averaged

54
Q

In a large shunt, the patient may be ______ to supplemental oxygen and still ______ as a result

A

In a large shunt, the patient may be unresponsive to supplemental oxygen and still hypoxemic as a result

55
Q

Shunts are difficult to deal with because the oxygen-hemoglobin dissociation curve is _____ under normal physiologic circumstances

A

Shunts are difficult to deal with because the oxygen-hemoglobin dissociation curve is flat under normal physiologic circumstances

(oxygen content of Hgb is maximum at maximum Hgb sat)

56
Q

________ is an example of a “blood” cause of intrapulmonary shunt

A

Diffuse alveolar hemorrhage is an example of a “blood” cause of intrapulmonary shunt

57
Q

________ is an example of a “pus” cause of intrapulmonary shunt

A

Pneumonia is an example of a “pus” cause of intrapulmonary shunt

58
Q

________ is an example of a “water” cause of intrapulmonary shunt

A

Pulmonary edema is an example of a “water” cause of intrapulmonary shunt

59
Q

Contrast high pressure/cardiogenic and low pressure/non-cardiogenic pulmonary edema

A
  • High pressure/cardiogenic: increased microvascular hydrostatic pressure, vascular endothelium intact, low protein
  • Low pressure/non-cardiogenic: vascular endothelium damaged, high protein
60
Q

Reflection coefficient in the Starling equation represents _______

A

Reflection coefficient in the Starling equation represents how effective the microvascular endothelium is at holding fluid in capillary vessels

61
Q

ARDS is a type of ______ pulmonary edema

A

ARDS is a type of low pressure/non-cardiogenic pulmonary edema

62
Q

What are the diagnostic criteria for ARDS?

A
63
Q

On room air, use _____ to look for a primary lung problem

A

On room air, use A-a difference to look for a primary lung problem

(higher is worse)

64
Q

On supplemental oxygen, use ______ to look for a primary lung problem

A

On supplemental oxygen, use PaO2/FiO2 ratio to look for a primary lung problem

(also called P-F ratio, <400 is abnormal)

(lower is worse)

65
Q

What would you expect to see on an X-ray of a patient with ARDS?

A

Diffuse white matter

66
Q

What is the pathobiology of ARDS?

A
  • Injury to alveolar-capillary barrier
  • Influx of protein-rich edema fluid into alveolar space

(reflection coefficient drops to nearly zero -> high-protein pulmonary edema)

67
Q

________ is the pathologic hallmark of ARDS

A

Diffuse alveolar damage (DAD) is the pathologic hallmark of ARDS

68
Q

Atelectasis means ______

A

Atelectasis means collapse of the alveolar unit

(occurs w/ endobronchial cancer or in supine ventilated patients, alveoli vasoconstrict in response to hypoxia)

69
Q

A cause of hypoxemia, decreased V·A/Q· occurs when V·A ______ or Q· ______

A

A cause of hypoxemia, decreased V·A/Q· occurs when V·A decreases (chronic bronchitis, asthma) or Q· increases (pulmonary embolism)

70
Q

A cause of hypoxemia, diffusion impairment occurs when t _____ or A ______

A

A cause of hypoxemia, diffusion impairment occurs when t increases (interstitial lung disease) or A decreases (emphysema)

V·gas = (A/t) * D * ∆P

71
Q

Decreased MvO2 (SvO2) is only relevant in modulated the causes of hypoxemia that ______ because healthy alveoli maintain normal PAO2

A

Decreased MvO2 (SvO2) is only relevant in modulated the causes of hypoxemia that increase A-a difference because healthy alveoli maintain normal PAO2​

(shunt, decreased but not zero V·A/Q, and diffusion limitation increase A-a difference)

72
Q

What is the Fick equation?

A

CO = V·O2 / (CaO2 - CvO2)

73
Q

What is the formula for CaO2 or CvO2?

A

CaO2 or CvO2​ = (1.34 mL O2/g * Hgb * % sat) + (0.003 * PaO2)

74
Q

What is the formula for SvO2?

A

SvO2 = CO * [(1.34 mL O2/g * Hgb * % sat) + (0.003 * PaO2)] - V·O2

75
Q

_______, _______, _______, and _______ are causes of low SvO2

A

Low cardiac output, anemia, hypoxemia, and increased oxygen consumption are causes of low SvO2

(less O2 sent out, so less comes back)

76
Q

What are the causes of low SvO2?

A
  • Low cardiac output
  • Anemia
  • Hypoxemia
  • Increased oxygen consumption
77
Q

Low SvO2 is important for the following causes of hypoxia: ______, _______, and _______

A

Low SvO2 is important for the following causes of hypoxia: shunt (V·A/Q· = 0), decreased V·A/Q· (but not zero), and diffusion impairment

78
Q

What is the formula for PaCO2?

A

PaCO2 = (V·CO2 * 863 mmHg) / V·A

79
Q

PACO2 and PaCO2 are ______, while PAO2 and PaO2 are ______

A

PACO2 and PaCO2 are interchangeable, while PAO2 and PaO2​ are not interchangeable

80
Q

PaCO2 and V·A are _____ related

A

PaCO2 and V·A​ are inversely related

81
Q

What is the alveolar ventilation equation for CO2?

A

PaCO2 = (V·CO2 * 863 mmHg) / [RR * VT (1 - VD/VT)

82
Q

Problems with ______, ______, and ______ can cause abnormal PaCO2

A

Problems with CO2 production (V·CO2), minute ventilation (RR * VT), and ratio of dead space to tidal volume (VD/VT) can cause abnormal PaCO2​

83
Q

A 75 year old patient with severe emphysema presents to the ED with 3 days of fever and cough. He is visibly tachypneic with a RR of 30 breaths/min. Temperature is 102.5 F. What is true regarding PaCO2?

A

Despite the high RR, PaCO2 is likely high

(cannot assume tachypneic patient is hypocapnic)

84
Q

RR ___ PaCO2

A

RR ≠ PaCO2​

85
Q

You are caring for a mechanically ventilated and deeply sedated patient with ARDS in the MICU. The set RR and VT on the ventilator are 28 breaths/minute and 350 mL respectively, On the morning rounds, you note the PaCO2 has risen from 50 to 65 mmHg since yesterday evening. The ventilator settings and vital settings are unchanged. What do you do?

A

Evaluate for pulmonary edema

Dead space to tidal volume ratio has changed acutely resulting from a pulmonary embolism, which corresponds to ventilated but not perfused (V/Q = infinity)

86
Q

_____, _____, and _____ cause increased PaCO2

A

Increased V·CO2, decreased V·E, and increased VD/VT cause increased PaCO2

87
Q

What raises V·CO2 and subsequently increases PaCO2?

A
  • Fever
  • Seizures
  • Over-feeding
  • Hypermetabolic states such as hyperthyroidism
88
Q

What decreases V·E and subsequently increases PaCO2?

A
  • Will not breathe: head injuries, stroke/ICH, CNS infections, CNS depressant drugs (opioids, benzodiazepines, barbiturates), obesity leading to hypoventilation, hypothyroidism
  • Cannot breathe: neuromuscular disease (ALS, myasthenia gravis, Guillan-Barre, polio, muscular dystrophy), chest wall deformities, obstructive and restrictive lung disease (severe) + respiratory muscle fatigue
89
Q

What increases VD/VT and subsequently increases PaCO2?

A
  • Pulmonary embolism
  • Emphysema
  • Pulmonary hyperinflation
90
Q

Hypercapnia is often caused by ______ coupled with _______

A

Hypercapnia is often caused by impaired strength coupled with increased elastic or resistive load on respiratory system

91
Q

For every ___ mmHg change in PaCO2, pH changes by ___ in the _____ direction

A

For every 10 mmHg change in PaCO2, pH changes by 0.08 in the opposite direction

92
Q

Respiratory alkalosis can be caused by ____ V·E

A

Respiratory alkalosis can be caused by increased V·E​

  • Drugs (cocaine, meth)
  • Fever
  • Sepsis
  • Pain/anxiety
  • Thyrotoxicosis
  • Mild respiratory disease: mild asthma, pneumonia, PE, pulmonary edema
  • Pregnancy
  • Cirrhosis/liver disease
  • Salicylate toxicity
93
Q

A 21 year-old medical student presents to the ED with acute anxiety and tingling in her hands. Her exam and CXR are unrevealing. SpO2 on room air is 97%. Room air ABG is 7.56/20/95. She has ______ and [further / no further] evaluation is needed.

A

She has acute respiratory alkalosis and no further evaluation is needed

Low PaCO2, high pH so respiratory alkalosis

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