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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
B
Dead space and alveolar CO2
26
C
alveolar plateau
27
D
EtCO2 tension = # displayed on monitor
28
What are 3 main reasons why there may be an increase in **inspired** CO2?
1. Exhaustion of CO2 absorbent 2. Incompetent one-way valve of circle system 3. Inadequate O2 flow rate of NRB circuit
29
What are 4 causes of increased or decreased EtCO2 values?
1. Metabolism 2. Pulmonary perfusion 3. Alveolar ventilation 4. Technical errors
30
What aspects of metabolism may cause an increased EtCO2?
Fever, malignant hyperthermia, sodium bicarb treatment, tourniquet release
31
What aspect of pulm perfusion may cause an increased EtCO2?
Increased CO or BP
32
What aspects of alveolar ventilation may cause an increased EtCO2?
Hypoventilation, rebreathing
33
What technical errors may cause an increased EtCO2?
Exhausted soda lime, inadequate fresh gas flow (NRB), faulty one-way valves
34
What aspects of metabolism may cause a decreased EtCO2?
Hypothermia, hypothyroidism, muscle relaxants
35
What aspects of pulm perfusion may cause a decreased EtCO2?
Decreased CO, cardiac arrest
36
What aspects of alveolar ventilation may cause a decreased EtCO2?
Hyperventilation, apnea
37
What technical errors may cause a decreased EtCO2?
Patient disconnect, esophageal intubation, sampling line leak
38
How does high fresh gas flow in NRB dilute sample?
Falsely decreases EtCO2 values, change waveform (Sidestream \> mainstream)
39
How does a high RR underestimate EtCO2?
Due to inadequate emptying of alveoli
40
What is the only thing that can determine PaCO2 -- EtCO2 difference?
ABG
41
What is a normal blood pH?
7.4
42
What effect does resp acidosis have on PaCO2?
Increases it
43
What effect does resp alkalosis have on PaCO2?
decreases it
44
What effect does metabolic acidosis have on HCO3?
Decreases it
45
What effect does metabolic alkalosis have on HCO3?
Increases it
46
What does a decreased PaCO2 indicate the patient is doing?
Hyperventilation --\> respiratory alkalosis ## Footnote **\*rare under anesthesia\***
47
What does an increased PaCO2 indicate the patient is doing?
Hypoventilation --\> respiratory acidosis
48
What is a normal PaCO2 in an awake patient?
35-45 mmHg
49
PaCO2 should be kept \< _____ and EtCO2 \< \_\_\_\_\_
60 mmHg, 55-57 mmHg
50
Cellular enzymes malfunction outside pH range of \_\_\_\_\_.
7.2 - 7.5
51
How much does pH change for every 10 mmHg increase in PaCO2?
0.08
52
What is the difference in EtCO2 from PaCO2 in horses?
EtCO2 10-15 mmHg \< PaCO2
53
What 3 things can pale MM be indicative of?
1. Vasoconstriction (pain, drugs, blood loss) 2. Decreased CO, anemia 3. Hypoxia (cyanosis \>5 g/100ml reduced Hgb)
54
What 3 things can dark pink MM be indicative of?
1. Vasodilation 2. Increased CO2 3. Endotoxemia
55
What does pulse oximetry provide?
Pulse rate and noninvasive, continuous detection of pulsatile arterial blood in tissue bed
56
What does pulse ox calculate?
% of oxyhgb and reduced hgb in arterial blood
57
What are sites used to measure pulse ox?
Tongue, lip, ear, interdigital space, prepuce
58
What 5 things can affect function/accuracy of pulse ox?
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
What should PaO2 in patients on 100% oxygen be?
\>250-650 mmHg
60
SpO2 in patients breathing 100% oxygen should be \_\_\_\_?
98-100%
61
T/F: A patient with a PaO2 of 500 mmHg will have a higher SpO2 than a patient with a PaO2 of 100 mmHg.
False; they will both be 98-100%
62
How can PaO2 be used to estimate pulse ox?
PaO2 = SpO2 - 30 ## Footnote **\*Only for pulse ox readings between 75-90%\***
63
When can PaO2 not be estimated?
When SpO2 is outside of the mid-portion values of the hgb dissociation curve and also **not during GA with 100% O2**
64
When is pulse ox most helpful?
When patients are breathing room air or transitioning (induction, recovery)
65
What does an SpO2 of 90% indicate?
PaO2 is ~60 mmHg --\> hypoxemia
66
What is the ideal SpO2?
\>93-95%
67
What is the equation used in blood gas analysis to measure PAO2?
PAO2 = FIO2 (PA-47) - PaCO2/R
68
What are 4 causes of hypothermia?
1. Decreased heat production (muscle relaxation) 2. Re-distribution of peripheral blood 3. Open body cavity 4. Cold inspired gas, IVF/environment
69
What are 5 consequences of hypothermia in patients?
1. Decreased MAC 2. Increased risk for surgical infection 3. Impaired wound healing 4. Impaired platelet function 5. Decreased coagulation
70
What disadvantage does shivering have during recovery?
Increases oxygen consumption \>200%; supplement O2 @ recovery
71
What are some ways that we can prevent/treat hypothermia?
Warm water blanket, "hot dog", bair hugger, fluid warmers, others
72
What are 3 causes of hyperthermia?
1. Excessive patient warming\*\* 2. Opioids in cats (hydromorphone\*\*) 3. Malignant hyperthermia (humans, swine, syndrome in dogs)
73
What are 3 consequences of hyperthermia?
1. Increased metabolic rate/O2 consumption 2. Increased circulatory work 3. Cellular hypoxia --\> organ failure
74
What are 2 treatments for hyperthermia?
Active cooling, supplemental O2
75
What is a demand valve?
Used in LA to deliver intermittent positive pressure ventilation (IPPV) by pressing activation button; Supplements O2 after induction and at recovery
76
How much O2 does a demand valve deliver?
~200 L/min of O2
77
What are 6 indications for use of IPPV?
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
What is the tidal volume delivered by IPPV?
10-20 mls/kg
79
What is the peak inspiratory pressure (PIP) of IPPV in SA?
15-20 cmH2O
80
What is the peak inspiratory pressure (PIP) of IPPV in LA?
20-30 cmH2O
81
What is the ideal inspiratory:expiratory ratio in IPPV?
1:2 - 1:3
82
What do bellows of IPPV replace?
Reservoir bag
83
What does the arrow on the left represent on this image of IPPV?
Driving gas (oxygen only)
84
What does the arrow on the right represent on this image of IPPV?
Breathing circuit (oxygen + inhalant)
85
What 2 things should be done when weaning a patient from IPPV?
1. Lower respiratory rate to increase PaCO2 2. Discontinue inhalant to decrease CO2 set point in brain Or a combo of both
86
What animals should not be weaned off of IPPV?
horses
87
What medical conditions should not be weaned off of IPPV?
Head trauma, tumor (only d/c inhalant in these cases)

Anesthesiology (12 decks)

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