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Anesthesiology > 10: Ventilation > Flashcards

10: Ventilation Flashcards

1
Q

What are 4 ways by which we can measure ventilation?

A
  1. Observation of thorax or rebreathing bag
  2. Esophageal stethoscope
  3. Capnography
  4. Blood gas analysis
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2
Q

How can we evaluate if the patient is breathing?

A

Chest wall movements, excursion of reservoir bag, auscultation of lung sounds, fogging of ETT

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3
Q

How can we accurately measure adequacy of ventilation?

A

Need to measure RR and TV

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4
Q

What is the equation for minute ventilation?

A

V = Vt x f

(Vt = tidal vol, f = frequency)

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5
Q

CO2 is the end product of cellular _____.

A

metabolism

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6
Q

What are 3 ways by which CO2 is transported in the venous system?

A
  1. HCO3- (60-70%)
  2. Bound to protein/Hgb (20-30%)
  3. Dissolved in plasma (5-10%)
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7
Q

CO2 production and elimination is linked to patient’s _____, _____, and _____.

A

metabolism, perfusion, ventilation

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8
Q

What is capnography?

A

Nonivasive method to measure systemic metabolism, CO, pulm perfusion, and ventilation

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9
Q

What value does capnography give us?

A

EtCO2

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10
Q

If CO2 production, CO, and pulm perfusion are constant, then changes in EtCO2 reflect changes in ______.

A

ventilation

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11
Q

EtCO2 is an indirect measure of _____.

A

PaCO2 (3-5 mmHg < PaCO2)

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12
Q

What aspect of ventilation is EtCO2 most useful for detecting?

A

Apnea, hypoventilation

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13
Q

Capnography can be ____stream or ____stream.

A

main, side

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14
Q

Where is the sampling tube placed in sidestreat capnography?

A

Between ETT and breathing circuit

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15
Q

Where does the sampling tube transmit gases to in sidestream capnography?

A

To measurement devide located away from the breathing circuit

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16
Q

What is the optimal rate of sampling for a sidestream circuit?

A

50-200 ml/min

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17
Q

What are advantages of sidestream capnography?

A

Lightweight sampler, easy manipulation near patient, smaller sample chamber, ability to sample other gases

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18
Q

What are disadvantages to sidestream capnography?

A

Plugging of sample line by secretions/condensation, 2-3 second delay, dilution of sample from leaks in breathing circuit, need to scavenge aspirated gases

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19
Q

Where is the measurement device located in mainstream capnography?

A

Between ETT and breathing circuit

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20
Q

How does mainstream capnography work?

A

Infrared light within sensor traverses respiratory gases and detected by photodetector

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21
Q

Why are mainstream capnography sensors heated?

A

To prevent condensation of water vapor

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22
Q

What are advantages of mainstream capnography?

A

Real-time measurement, NO scavenging of aspirated gases needed

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23
Q

What are disadvantages of mainstream capnography?

A

Excessive dead space bc of sensing chamber can lead to false readings, weight can cause kinking of ETT, chamber may be contaminated by secretions/condensation, patients may be burned by heated cuvette

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24
Q

A

A

CO2 cleared from anatomic dead space

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25
Q

B

A

Dead space and alveolar CO2

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26
Q

C

A

alveolar plateau

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27
Q

D

A

EtCO2 tension = # displayed on monitor

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28
Q

What are 3 main reasons why there may be an increase in inspired CO2?

A
  1. Exhaustion of CO2 absorbent
  2. Incompetent one-way valve of circle system
  3. Inadequate O2 flow rate of NRB circuit
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29
Q

What are 4 causes of increased or decreased EtCO2 values?

A
  1. Metabolism
  2. Pulmonary perfusion
  3. Alveolar ventilation
  4. Technical errors
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30
Q

What aspects of metabolism may cause an increased EtCO2?

A

Fever, malignant hyperthermia, sodium bicarb treatment, tourniquet release

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31
Q

What aspect of pulm perfusion may cause an increased EtCO2?

A

Increased CO or BP

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32
Q

What aspects of alveolar ventilation may cause an increased EtCO2?

A

Hypoventilation, rebreathing

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33
Q

What technical errors may cause an increased EtCO2?

A

Exhausted soda lime, inadequate fresh gas flow (NRB), faulty one-way valves

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34
Q

What aspects of metabolism may cause a decreased EtCO2?

A

Hypothermia, hypothyroidism, muscle relaxants

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35
Q

What aspects of pulm perfusion may cause a decreased EtCO2?

A

Decreased CO, cardiac arrest

36
Q

What aspects of alveolar ventilation may cause a decreased EtCO2?

A

Hyperventilation, apnea

37
Q

What technical errors may cause a decreased EtCO2?

A

Patient disconnect, esophageal intubation, sampling line leak

38
Q

How does high fresh gas flow in NRB dilute sample?

A

Falsely decreases EtCO2 values, change waveform

(Sidestream > mainstream)

39
Q

How does a high RR underestimate EtCO2?

A

Due to inadequate emptying of alveoli

40
Q

What is the only thing that can determine PaCO2 – EtCO2 difference?

A

ABG

41
Q

What is a normal blood pH?

A

7.4

42
Q

What effect does resp acidosis have on PaCO2?

A

Increases it

43
Q

What effect does resp alkalosis have on PaCO2?

A

decreases it

44
Q

What effect does metabolic acidosis have on HCO3?

A

Decreases it

45
Q

What effect does metabolic alkalosis have on HCO3?

A

Increases it

46
Q

What does a decreased PaCO2 indicate the patient is doing?

A

Hyperventilation –> respiratory alkalosis

*rare under anesthesia*

47
Q

What does an increased PaCO2 indicate the patient is doing?

A

Hypoventilation –> respiratory acidosis

48
Q

What is a normal PaCO2 in an awake patient?

A

35-45 mmHg

49
Q

PaCO2 should be kept < _____ and EtCO2 < _____

A

60 mmHg, 55-57 mmHg

50
Q

Cellular enzymes malfunction outside pH range of _____.

A

7.2 - 7.5

51
Q

How much does pH change for every 10 mmHg increase in PaCO2?

A

0.08

52
Q

What is the difference in EtCO2 from PaCO2 in horses?

A

EtCO2 10-15 mmHg < PaCO2

53
Q

What 3 things can pale MM be indicative of?

A
  1. Vasoconstriction (pain, drugs, blood loss)
  2. Decreased CO, anemia
  3. Hypoxia (cyanosis >5 g/100ml reduced Hgb)
54
Q

What 3 things can dark pink MM be indicative of?

A
  1. Vasodilation
  2. Increased CO2
  3. Endotoxemia
55
Q

What does pulse oximetry provide?

A

Pulse rate and noninvasive, continuous detection of pulsatile arterial blood in tissue bed

56
Q

What does pulse ox calculate?

A

% of oxyhgb and reduced hgb in arterial blood

57
Q

What are sites used to measure pulse ox?

A

Tongue, lip, ear, interdigital space, prepuce

58
Q

What 5 things can affect function/accuracy of pulse ox?

A
  1. Motion artifact
  2. Dark pigment of skin or MM
  3. Poor peripheral blood flow
  4. Fluorescent light
  5. Increased blood carboxyhgb and methgb levels
59
Q

What should PaO2 in patients on 100% oxygen be?

A

>250-650 mmHg

60
Q

SpO2 in patients breathing 100% oxygen should be ____?

A

98-100%

61
Q

T/F: A patient with a PaO2 of 500 mmHg will have a higher SpO2 than a patient with a PaO2 of 100 mmHg.

A

False; they will both be 98-100%

62
Q

How can PaO2 be used to estimate pulse ox?

A

PaO2 = SpO2 - 30

*Only for pulse ox readings between 75-90%*

63
Q

When can PaO2 not be estimated?

A

When SpO2 is outside of the mid-portion values of the hgb dissociation curve and also not during GA with 100% O2

64
Q

When is pulse ox most helpful?

A

When patients are breathing room air or transitioning (induction, recovery)

65
Q

What does an SpO2 of 90% indicate?

A

PaO2 is ~60 mmHg –> hypoxemia

66
Q

What is the ideal SpO2?

A

>93-95%

67
Q

What is the equation used in blood gas analysis to measure PAO2?

A

PAO2 = FIO2 (PA-47) - PaCO2/R

68
Q

What are 4 causes of hypothermia?

A
  1. Decreased heat production (muscle relaxation)
  2. Re-distribution of peripheral blood
  3. Open body cavity
  4. Cold inspired gas, IVF/environment
69
Q

What are 5 consequences of hypothermia in patients?

A
  1. Decreased MAC
  2. Increased risk for surgical infection
  3. Impaired wound healing
  4. Impaired platelet function
  5. Decreased coagulation
70
Q

What disadvantage does shivering have during recovery?

A

Increases oxygen consumption >200%; supplement O2 @ recovery

71
Q

What are some ways that we can prevent/treat hypothermia?

A

Warm water blanket, “hot dog”, bair hugger, fluid warmers, others

72
Q

What are 3 causes of hyperthermia?

A
  1. Excessive patient warming**
  2. Opioids in cats (hydromorphone**)
  3. Malignant hyperthermia (humans, swine, syndrome in dogs)
73
Q

What are 3 consequences of hyperthermia?

A
  1. Increased metabolic rate/O2 consumption
  2. Increased circulatory work
  3. Cellular hypoxia –> organ failure
74
Q

What are 2 treatments for hyperthermia?

A

Active cooling, supplemental O2

75
Q

What is a demand valve?

A

Used in LA to deliver intermittent positive pressure ventilation (IPPV) by pressing activation button;

Supplements O2 after induction and at recovery

76
Q

How much O2 does a demand valve deliver?

A

~200 L/min of O2

77
Q

What are 6 indications for use of IPPV?

A
  1. Significant hypoventilation –> PaCO2 > 60 mmHg
  2. Apnea
  3. Use of neuromuscular blocking agents
  4. Intra-thoracic surgery
  5. Head trauma/brain tumor
  6. Horses (all are maintained on IPPV)
78
Q

What is the tidal volume delivered by IPPV?

A

10-20 mls/kg

79
Q

What is the peak inspiratory pressure (PIP) of IPPV in SA?

A

15-20 cmH2O

80
Q

What is the peak inspiratory pressure (PIP) of IPPV in LA?

A

20-30 cmH2O

81
Q

What is the ideal inspiratory:expiratory ratio in IPPV?

A

1:2 - 1:3

82
Q

What do bellows of IPPV replace?

A

Reservoir bag

83
Q

What does the arrow on the left represent on this image of IPPV?

A

Driving gas (oxygen only)

84
Q

What does the arrow on the right represent on this image of IPPV?

A

Breathing circuit (oxygen + inhalant)

85
Q

What 2 things should be done when weaning a patient from IPPV?

A
  1. Lower respiratory rate to increase PaCO2
  2. Discontinue inhalant to decrease CO2 set point in brain

Or a combo of both

86
Q

What animals should not be weaned off of IPPV?

A

horses

87
Q

What medical conditions should not be weaned off of IPPV?

A

Head trauma, tumor (only d/c inhalant in these cases)

Anesthesiology (12 decks)

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