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Anesthesiology 398 and 466 > Lecture 4 Monitoring the Anesthetized Patient 2 & Ventilators > Flashcards

Lecture 4 Monitoring the Anesthetized Patient 2 & Ventilators Flashcards

1
Q

What are different ways you can monitor ventilation

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

What are some ways you can check if your patient is breathing clinically

A
  1. Chest wall movements
  2. Excursion of reservoir bag
  3. Auscultation of lung sounds
    • Stethoscope, esophageal stethoscope
  4. Fogging of endotracheal tube
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3
Q

When you are looking at your patient breathing, what are different aspects of the breathing are you monitoring

A
  1. Presence/absence of breathing
  2. Respiratory rate, pattern, effort
  3. Subjective indication of Tital volume (TV)
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4
Q

How can you tell the adequacy of ventilation?

A
  • V = Vt x f
    • Minute Ventilation = tidal volume X frequency
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5
Q

How is CO2 exhaled

A
  1. Cells => venous system => transported as:
    • HCO3- 60 -70%
      • CO2 + H2O –> H2CO3 –> H+ + HCO3-
    • Bound to protein/hemoglobin 20 – 30%
    • Dissolved in plasma 5 – 10%
  2. CO2 transported to lungs => diffuses into alveoli => exhaled
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6
Q

Carbon dioxide (CO2) production & elimination linked to patient’s? (3 things)

A
  1. metabolism
  2. perfusion
  3. ventilation
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7
Q

End-tidal CO2 is a noninvasive method of measuring systemic what in a patient

A
  1. metabolism,
  2. cardiac output,
  3. pulmonary perfusion
  4. ventilation

Changes in any of these can change ETCO2

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8
Q

If there is a change in one of these systems (metabolism, cardiac output, pulmonary perfusion & ventilation), will ETCO2 reflect that change?

A
  • Yes
    • if all but one of these systems stay relatively constant, ETCO2 will reflect changes in system that has not been constant
    • So, if CO2 production (metabolism), CO & pulmonary perfusion are constant, then changes in ETCO2 reflect changes in ventilation
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9
Q

How does End tidal carbon dioxide (EtCO2) compare with PaCO2?

A

EtCO2 3-5mmHg < PaCO2

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10
Q

What is the most useful detection of apnea and hypoventilation?

A

End tidal carbon dioxide (EtCO2)

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11
Q

What are the 2 types of capnographs

A
  1. Mainstream
  2. Sidestream
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12
Q

How does sidestream Capnography work

A
  • Sampling tube placed between ET tube & breathing circuit
  • Sampling tube transmits gases to measurement device, located away from breathing circuit
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13
Q
  1. What is the Optimal rate of sampling for a sidestream capnograph?
  2. Why is this important to know?
A
  1. 50 - 200 ml/min
  2. If you have a low flow of oxygen (machine can go as low as 200ml/min) your patient can become hypoxemic since the capnograph is taking a lot of the oxygen
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14
Q

What are the advantages and disadvantages of a sidestream capnograph?

A
  1. Advantages
    • lightweight sampler
    • ease of manipulation near the patient
    • smaller sample chamber
    • ability to sample other gases (i.e. inhaled anesthetics)
  2. Disadvantages
    • plugging of sample line by secretions/condensation
    • 2- to 3-second delay
    • Need to scavenge aspirated gases***
    • dilution of sample from leaks in breathing circuit
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15
Q

How does Mainstream capnograph work?

A
  • Measurement device between ET tube & breathing circuit
  • Infrared light within sensor traverses respiratory gases & detected by photodetector
  • Sensors are heated to prevent condensation of water vapor
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16
Q

What are the Advantage/Disadvantages of a mainstream capnograph

A
  1. Advantages
    • Real-time measurement (response rate of <100 ms)
    • NO scavenging of aspirated gases needed
  2. Disadvantages
    • excessive dead space in patient breathing circuit produced by sensing chamber can lead to false readings
    • Weight can cause kinking of ET tube
    • Sensing chamber may be contaminated by secretions/condensation
    • patients may be burned by heated cuvette
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17
Q

What are the different parts of the capnograph

also include the downslope

A
  • (A), Carbon dioxide cleared from the anatomic dead space;
    • Phase I (expiratory baseline) is the beginning of exhalation and corresponds to exhalation of CO2-free dead space gas from the larger conducting airways. The CO2 value during this phase should be zero
  • (B), dead space and alveolar carbon dioxide
    • Phase II (expiratory upstroke) involves exhalation of mixed alveolar and
      decreasing dead space gas, which rapidly increases the CO2 concentration
  • (C), alveolar plateau
    • Phase III (expiratory plateau) occurs when all the dead space gas has
      been exhaled, resulting in exhalation of completely alveolar air. The highest point of phase III corresponds with the actual ETCO2 value. The
      plateau has a slight positive slope because of the continuous diffusion of
      CO
      2 from the capillaries into the alveolar space.
  • (D), end-tidal carbon dioxide tension (ETCO2)
  • Phase 0 (inspiratory downstroke)—
    • Because of inhalation of CO2-free
      gas, the CO2 concentration rapidly declines to zero.
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18
Q

What part of the graph is the end-tidal carbon dioxide number that the capnograph shows you?

A

(D), end-tidal carbon dioxide tension (ETCO2)

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19
Q

Other than EtCO2, what can a capnograph show you

A
  1. esophageal intubation,
  2. airway disconnection,
  3. airway obstruction,
  4. leak in endotracheal tube cuff,
  5. exhaustion of CO2 absorbent**,
  6. incompetent one-way valve of anesthetic circle system**,
  7. inadequate O2 flow rate for non-rebreathing (NRB) circuit ** =>∗∗ ↑Inspired CO2
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20
Q

What are Causes of ↑EtCO2 Values

A
  1. Metabolism: Fever, Malignant Hyperthermia, sodium bicarbonate treatment, tourniquet release
  2. Pulmonary Perfusion: ↑cardiac output or BP
  3. Alveolar Ventilation: **hypoventilation, rebreathing
  4. Technical Errors*: Exhausted soda lime, inadequate fresh gas flow (NRB), faulty one way valves
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21
Q

What are Causes of ↓ EtCO2 Values

A
  1. Metabolism: Hypothermia, hypothyroidism, muscle relaxants
  2. Pulmonary Perfusion: *↓ CO, BP, hypovolemia, pulmonary embolism, *cardiac arrest
  3. Alveolar Ventilation: *hyperventilation, *apnea, partial airway obstruction
  4. Technical Errors: patient disconnect, esophageal intubation, sampling line leak
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22
Q

What are Sources of Error or limitations of a capnograph (6)

A
  1. High FGF in NRB dilute sample
    • falsely ↓ EtCO2 values, change waveform
      • sidestream > mainstream
  2. High RR underestimates EtCO2
    • due to inadequate emptying of alveoli
  3. EtCO2 ~ 3 – 5mmHg < PaCO2, if ventilation/perfusion well matched
  4. Gradient is PaCO2 – EtCO2 difference
  5. ↑ VA/Q mismatch, EtCO2 underestimates PaCO2, ↑ PaCO2 – EtCO2 difference
  6. Only arterial blood gas (ABG) can determine PaCO2 – EtCO2 difference
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23
Q

What is the normal difference of EtCO2 and PaCO2 in horses?

A

can be 10-15 mmHg difference!

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24
Q
  1. What is the normal pH of blood
  2. What is it called if pH is lower than normal
  3. Higher than normal?
A
  1. Normal blood pH: 7.4
  2. < 7.4 = acidosis
  3. >7.4 = alkalosis
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25
Q
  1. What is Respiratory acidosis
  2. Respiratory alkalosis
  3. Metabolic acidosis
  4. Metabolic alkalosis
A
  1. Respiratory alkalosis (↓PaCO2)
  2. Metabolic acidosis (↓HCO3)
  3. Metabolic alkalosis (↑HCO3)
  4. Respiratory acidosis (↑PaCO2)
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26
Q

Explain the correlation between the PCO2 value and the HCO3 value

A

arterial CO2=pCO2

  • the bicarbonate is going to be higher to try and buffer the high arterial CO2 to keep the pH at a normal level
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27
Q
  1. What does PaCO2 mean?
  2. What is it a measure of?
A
  1. PaCO2 – partial pressure of CO2 in arterial blood
  2. measure of ventilation status
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28
Q

What is the normal Blood Gas (PaCO2) of an awake patient

A

35-45mmHg

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29
Q
  1. When PaCO2 is low what will happen to:
    • Ventilation?
    • What type of alkalosis or acidosis will happen?
  2. When PaCO2 is high what will happen to:
    • Ventilation?
    • What type of alkalosis or acidosis will happen?
A
  1. ↓ PaCO2 –
    • hyperventilation =>
    • respiratory alkalosis
  2. ↑ PaCO2** –
    • hypoventilation =>
    • respiratory acidosis
30
Q
  1. What should PaCO2 be kept at during anesthesia?
  2. EtCO2?
A
  1. PaCO2 should be kept < 60mmHg
  2. EtCO2 < 55-57mmHg
31
Q

Because anesthetic drugs cause dose dependent respiratory depression, what should the following values be under anesthesia?

  1. PaCO2
  2. EtCO2
  3. pH
A
  1. PaCO2 should be kept < 60mmHg
  2. EtCO2 < 55-57mmHg
  3. ~ 7.2pH
    • (pH ∆ .08/ every 10mmHg ↑ PaCO2)
    • Cellular enzymes malfunction outside pH range 7.2-7.5
32
Q
  1. For dogs and cats with a good V/Q matching, how should EtCO2 relate to PaCO2 values
  2. Horses?
A
  1. EtCO2 to be 3 - 5 mmHg < PaCO2
  2. Horses PaCO2 - EtCO2 > 10-15mmHg
33
Q

Becauses horses may have a PaCO2 - EtCO2 difference of 10-15mmHg normally, what can you do to make sure the PaCO2 is normal?

A

Arterial blood gas analysis will tell true PaCO2 – EtCO2 difference

34
Q
  1. What do pale Mucous Membrane (MM) Color tell you under anesthesia?
  2. Dark pink MM?
A
  1. Pale MM =>
    • Vasoconstriction (Pain, drugs, blood loss)
    • ↓ cardiac output, anemia
    • Hypoxia: Cyanosis > 5g/100ml reduced Hb
  2. Dark pink MM may indicate:
    • Vasodilation
    • ↑ CO2
    • Endotoxemia

Affected by drugs

35
Q

How does Pulse Oximetry work?

A
  • Provides pulse rate & noninvasive, continuous detection of pulsatile arterial blood in tissue bed
  • Calculates the percentage of oxyhemoglobin and reduced hemoglobin in arterial blood - R/iR ratio calculated & converted to % SpO2
36
Q

What are different probe sites for Pulse Oximetry

A
  1. tongue
  2. lip
  3. ear
  4. interdigital space
  5. prepuce
37
Q

Pulse Oximetry’s funciton/accuracy is affected by? (5)

A
  1. motion artifact (eg, shivering or body movement)
  2. dark pigment of skin or MM
  3. poor peripheral blood flow (hypotension, vasoconstriction)
  4. fluorescent light
  5. ↑ blood carboxyhemoglobin and methemoglobin levels
38
Q
  1. What should the PaO2 be in patients on 100% O2?
  2. What should the SpO2 be in patients on 100% O2?
A
  1. PaO2 in patients on 100% O2 should be
    • > 250 – 650 mmHg
  2. SpO2 in patients breathing 100% O2 =
    • 98% to 100%
39
Q

What are the pulse oximetry limitations?

A
  • Pulse Oximetry has limitations in patients breathing 100% O2
    • PaO2 = 100 mmHg => SpO2 = 98 – 100%
    • PaO2 = 500 mmHg => SpO2 = 98 – 100%

So if a patient has less than normal PaO2, you will not know!

40
Q
  1. PaO2 can be estimated using pulse oximetry when?
  2. How do you estimate it?
A
  1. Only for pulse oximeter readings between 75% and 90%
    • Due to linear relationship between PaO2 & SpO2 values on mid portion of hemoglobin disassociation curve. Outside of these values, this rule cannot be applied ie. Not during GA with 100% O2
  2. PaO2 = SpO2 – 30
41
Q

Pulse Oximetry is MOST helpful when patients are:

  1. breathing room air
  2. transitioning (induction, recovery)
  3. under anesthesia
A

Both:

  1. breathing room air
  2. transitioning (induction, recovery)
42
Q
  1. When SpO2 = 90%, what will PaO2 be?
  2. Will the patient have normal O2 levels or be hypoxemic?
  3. What should SpO2 be?
A
  1. PaO2 = 60 mmHg =>
  2. hypoxemia
  3. Ideally, SpO2 > 93-95%
43
Q
  1. What is the normal PaO2 on room air?
  2. On 100% O2?
  3. PaO2/FiO2 ration?
A
  1. Room air-
    • 95-100 mmHg
  2. 100% O2-
    • 250-650 mmHg
  3. PaO2/FiO2 ration
    • > 250
44
Q

How do you calculate PaO2?

A

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

  • PAO2 - alveolar partial pressure of O2 (in mmHg)
  • FIO2 - fraction of inspired oxygen
  • PA - ambient pressure in mmHg
  • 47 - saturated vapor pressure of water at 37 degrees celcius
  • PaCO2 - arterial partial pressure of CO2 (in mmHg)
  • R - respiratory quotient (assumed to be 0.8)
45
Q

What are 2 ways to monitor body temperature

A
  1. Thermister probe in esophagus/rectum
  2. Digital Thermometer
46
Q

What are causes of hypothermia?

A
  1. ↓ heat production
    • Muscle relaxation
  2. Re-distribution of peripheral blood
  3. Open body cavity
  4. Cold IV fluids/environment
47
Q

What are Consequences of hypothermia in patients:

A
  1. ↓ MAC
  2. ↑ risk surgical infection
  3. Impaired wound healing
  4. Impaired platelet function
  5. ↓ coagulation
48
Q
  1. Why is shivering bad at recovery?
  2. What can you do to help patient (other than warm patient up)?
A
  1. ↑ oxygen consumption >200%
  2. Supplement O2 @ recovery
49
Q

What are different ways a patient can be heated?

A
  1. Circulating warm water blanket
  2. ‘Hot Dog’
  3. Bair Hugger
  4. Fluid Warmers
  5. Other: warm saline rinse/flush, lower O2 flow, pre-warming of patient
50
Q

Hyperthermia causes?

A
  1. Excessive patient warming**
  2. Opioids in cats
    • Hydromorphone**
    • Can occur up to 5hrs PO
  3. Malignant hyperthermia
    • Humans, swine, syndrome in dogs
51
Q
  1. What are 3 consequences of Hyperthermia
  2. How can you treat?
A
  1. Consequences:
    • ↑ metabolic rate/O2 consumption
    • ↑ circulatory work
    • Cellular hypoxia
  2. Treatment:
    • Active cooling
    • Supplemental O2
52
Q

What is a Demand Valve?

A
  • Delivers Intermittent Positive Pressure Ventilation (IPPV) by pressing activation button
  • supplements O2 after induction & @ recovery
  • Delivers ~ 200 L/min of O2
53
Q

Intermittent Positive Pressure Ventilation (IPPV) indications?

A
  1. Significant hypoventilation => PaCO2 > 60mmHg
  2. Apnea
  3. Use of Neuromuscular Blocking agents
  4. Intra-thoracic surgery
  5. Head trauma/brain tumor
  6. Horses – inhalant anesthesia
    • All horses maintained on IPPV
54
Q

What should the normal values be for Intermittent Positive Pressure Ventilation (IPPV):

  1. Tidal volume (TV)
  2. Peek Inspiratory Pressure (PIP)
  3. Inspiratory:Expiratory (I:E) ratio
A
  1. Tidal volume (TV)
    • 10-20mls/kg
  2. Peek Inspiratory Pressure (PIP)
    • 15-20 cmH2O – SA
    • 20-30 cmH2O – LA
  3. Inspiratory:Expiratory (I:E) ratio
    • 1:2 – 1:3

Use EtCO2/PaCO2 as guideline

55
Q

What animal would you use each ventilator on?

A
  1. large animal
  2. adult small animal
  3. pediatric small animal
56
Q

Bellows in a ventilator takes the place of the?

A

reservoir bag

57
Q
  1. What gas is in this compartment?
  2. This one?
A
  1. Driving Gas (Oxygen only)
  2. Breathing Circuit (Oxygen + Inhalant)
58
Q

What gas comes out of here?

A

Breathing Circuit Exhaust (Oxygen + Inhalant)

59
Q

What gas comes out of here?

A

Driving Gas Exhaust (Oxygen only)

60
Q

How do you wean from IPPV?

A
  1. Lower Respiratory rate to ↑ PaCO2
  2. Discontinue inhalant to ↓ CO2 set point in brain

Or Combination of both

61
Q

When will you not wean from IPPV?

A
  1. Do Not wean horses
    • they wake up more quickly and prone to injury
  2. **brain cases** (Head trauma, tumor)
    • Don’t want to increase CO2
    • ONLY D/C inhalant
62
Q
A
  • Capnogram demonstrating a gradual increase in baseline and ETCO2.
  • Rebreathing of exhaled gases is the primary reason that the inspiratory phase does not return to the zero baseline
63
Q
A
  • Capnogram of a nonrebreathing anesthetic system.
  • During inspiration, a small rebreathing wave can result from inhalation of CO2.
  • The extent of rebreathing depends on fresh gas flow, the tidal volume, and the respiratory rate
64
Q
A

Upward sloping plateau representing a bronchospasm or another expiratory obstructive process that prevents complete alveolar emptying.

65
Q
A

Capnogram of a patient emerging from neuromuscular blockade
and demonstrating a curare cleft

66
Q
A
  • Capnogram demonstrating a normal shape but decreased plateau height.
  • This can be the result of hypovolemia, hyperventilation, hypothermia, and increased dead space ventilation.
67
Q
A

Capnogram demonstrating dilution of ETCO2 by fresh gas flow,
which produces a terminal dip in the plateau.

68
Q
A
  • Capnogram displaying oscillations during the inspiratory phase.
  • They result from cardiac pulsations or fluttering of the inspiratory valve in a rebreathing circuit.
69
Q
A

Capnogram with an abnormal plateau and inspiratory downstroke, representing endotracheal tube cuff leakage

70
Q
A

Normal time base capnogram demonstrating the waveform after a patient has been mask ventilated with esophageal intubation.

71
Q
A

Trend capnogram showing a progressive decrease in ETCO2 associated with onset of cardiopulmonary arrest followed by a progressive increase in ETCO2 with successful CPCR and ROSC

Anesthesiology 398 and 466 (22 decks)

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