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Boards: Respiratory > AMP 32: Ventilator Waveform Analysis (old) > Flashcards

AMP 32: Ventilator Waveform Analysis (old) Flashcards

1
Q

Where are pressure, volume, and flow usually measured during ventilation and how does that potentially affect the accuracy of measurements?

A
  • sensors located inside the ventilator
  • the closer the sensors are to the patient the more accurate is the reading ⇒ compliance and resistance of the circuit and the compressibility of the gas affect readings
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2
Q

What are the 3 main scalars used?

A
  • flow versus time
  • volume versus time
  • pressure versus time
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3
Q

What are the 2 most common loops used?

A
  • pressure-volume loops
  • flow-volume loops
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4
Q

Name the type of waveforms (scalars)

A
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5
Q

What are the 6 stages of a mechanical breath?

A
  1. Beginning of inspiration
  2. Inspiration
  3. End of inspiration
  4. Beginning of expiration
  5. Expiration
  6. End of expiration
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6
Q

What is the cycling variable

A

The cycling variable determines how and when the ventilator changes from inspiration to expiration

i.e., ventilator ends the inspiration when cycling variable is reached

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7
Q

Explain “plateau pressure” and how it is achieved by the ventilator

A

At the end of inspiration the inspiratory gas flow stops but the expiratory valve does not open and retains the delivered volume in the lungs ⇒ will keep a static plateau pressure until expiratory valve is opened

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8
Q

What are the properties of expiration dependent on?

A
  • resistance of the animal’s airways
  • resistance of the artificial airways (i.e., tubing)
  • compliance of the lungs
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9
Q

Describe the differences of the Flow/Time scalar between volume-controlled and pressure-controlled ventilation

A
  • in volume controlled ventilation a set flow rate is administered and terminated at a set lung volume is reached, i.e., the flow stays at the same level throughout inspiration ⇒ square shape (right graph)
  • in pressure controlled ventilation a set pressure is achieved early during inspiration and kept constant, achieved by an initially high flow rate, which will gradually decrease (left graph)
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10
Q

What are risk factors for Auto-PEEP?

A
  • high ventilation rate
  • high tidal volume
  • PEEP set > 10 cm H2O
  • airway obstruction
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11
Q

What is auto-PEEP?

A

inspiration begins before complete expiration and air remains trapped within the small airways

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12
Q

What are strategies to reduce auto-PEEP?

A
  • administration of bronchodilator
  • change ET tube to larger size
  • increase the inspiratory flow rate (minimizes inspiration to expiration ratio)
  • decrease tidal volume
  • decrease RR but increase tidal volume
  • extrinsic PEEP
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13
Q

How does extrinsic PEEP reduce auto-PEEP

A

opens up small airways that are trapping air, especially applicable in chronic obstructive airway disease (pop the airways open/recruit more airways)

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14
Q

What are complications caused by auto-PEEP?

A
  • air remains in small airways ⇒ more patient effort required before patient-initiated breath
  • flattening of the diaphragm ⇒ decreases efficacy of diaphragmatic contraction during inspiration
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15
Q

What ventilator mode is this patient ventilated with?

Describe the difference between the first and third versus the second breath

How are these breaths initiated?

A

volume-controlled synchronized intermittend mandatory ventilation with pressure support

the first and third breath are mandatory ventilation

  • the flow rate is constant and the volume increases linearly
  • the flow stops when the desired volume is reached

the second breath is a patient triggered breath with pressure support

  • the flow starts at a certain levels and then decreases to a set termination value (flow-cycling)
  • a set pressure is maintained, achieved by the decreasing flow rate

All breaths are patient initiated, as seen from the negative deflection on the pressure-time scalar

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16
Q

Describe the differences of the Volume/Time scalar between volume-controlled and pressure-controlled ventilation

A
  • the flow rate in volume-controlled ventilation is constant and the volume therefore increases linearly
  • the flow rate in pressure-controlled ventilation the flow rate starts high and decreases to keep a steady pressure, the volume therefore increases more steeply initially and slows down when flow decreases
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17
Q

What ventilator mode is this patient ventilated with?

Describe the difference between the first and fourth versus the second and third breath

How are these breaths initiated?

A

volume-controlled SIMV (synchronized intermittend mandatory ventilation) (no pressure support for spontaneously triggered breaths)

Breath 1 and 4 are mandatory and controlled breaths

  • same flow throughout ventilation creates a linear increase in volume
  • the flow stops when a set volume is reached

Breath 2 and 3 are spontaneous unsupported breaths

  • inspiration is negative on the pressure scalar and positive on the flow and volume scalar
  • expiration is positive on the pressure scalar

All breaths here are patient triggered

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18
Q

What ventilator mode is this patient ventilated with?

A

volume-controlled SIMV with PEEP and pressure support

first and third breath are mandatory and machine-controlled breaths, second breath is pressure supported but spontaneous

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19
Q

What ventilator mode is this patient ventilated with?

A

Assist-control pressure-controlled

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20
Q

What ventilator mode is this patient ventilated with?

A

Assist-control volume controlled

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21
Q

What complication is occuring in this ventilated patient?

Explain how you identify it.

A

Auto-PEEP

syn. intrinsic PEEP, air-stacking, air-trapping

the volume curve does not reach zero/baseline by the end of the expiration, indicating that not all volume/air has been exhaled before the next inspiratory cycle restarts

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22
Q

What complication is occuring in this ventilated patient?

Explain how you identify it.

A

Auto-PEEP

syn. intrinsic PEEP, air-stacking, air-trapping

Note how the flow abruptly increases before it can gradually go back to zero at the end of the expiration

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23
Q

Explain “compliance”

A

indicates how the lungs will expend with a certain pressure

a change in volume in relation to a change in pressure

24
Q

how will the pressure-volume loop move when the compliance decreases or increases

A

decreased compliance –> to the right

increased compliance –> to the left

25
Q

Which graph shows the most compliance?

A

the steepest one

26
Q

List 5 common causes for decreased compliance

A
  • pleural space disease
  • pulmonary parenchymal disease
  • single-lung intubation
  • abdominal distention
  • chest-wall disease or deformity
27
Q

When examining a pressure-volume loop, what are the inflection points believed to represent?

A
  • increased alveolar recruitement during inspiration (at certain point of inspiration, less pressure needed to increase volume)
  • increased alveolar decruitment during expiration
28
Q

What do A and B represent and who is initiating this breath?

A

A: lower inflection point, inspiration

B: upper inflection point, expiration

the machine is initiating this breath

29
Q

Who is initiating this breath?

A

patient triggered breath

pressure is negative at beginning of inspiration

30
Q

What does this movement of the pressure-volume loop indicate?

A

increased compliance

31
Q

What does this shift of the pressure-volume loop indicate?

A

decreased compliance

32
Q

What does this change in the pressure-volume loop indicate?

A

increased resistance

33
Q

What is hysteresis

A

hysteresis, a lag in the change in volume compared with the rate of change in pressure that results from resistance to deformation (elasticity) and resistance of the airways.

34
Q

Is the pressure-volume or the flow-volume loop better to assess for changes in airway resistance?

A

The F-V loop is better to assess for increases resistance because the changes on the P-V loop are very subtle

35
Q

Name 4 common causes for increased airway resistance during ventilation

A
  • bronchospasm
  • mucosal edema of airways
  • small endotracheal tube
  • airway secretions
36
Q

What is the definition of “work of breathing”

A

= the pressure required to move a specific volume of gas

37
Q

What increases the work of breathing?

A
  • decreased compliance
  • decreased functional residual capacity
38
Q

What is A and B?

A

A and B constitute the “work of breathing” (WOB)

A = WOB to overcome airway resistance

B = WOB to overcome the elastic nature of the lungs

A + B = total mechanical work done during breath

39
Q

What are A, B, and C?

A

A = beginning of inspiration

B = beginning of expiration

C = peak expiratory flow during passive expiration

40
Q

What type of breath is this?

A

spontaneous breath

41
Q

explain this loop

A

different orientation

volume increases to the left, pressure is positive on the bottom ⇒ inspiratory loop on the bottom, expiratory on the top

peak expiratory flow rate is reduced due to small or medium airway obstruction, more curvilinear ⇒ “scooping”

42
Q

How does the flow-volume loop change when there is a air leak during inspiration?

A

the expiratory volume will be smaller than the inspiratory volum

explanation: the full volume is administered, but leaks at some point during inspiration, so when the animal is breathing out, not all of the administered volume comes back

43
Q

What is happening?

A

there is an air leak downstream (on the patient side)

  • the volume is not completely returned (i.e., does not go back to zero)
44
Q

what does an air leak between the flow transducer and the ventilator look like?

A

the set volume is not being delivered, but all the delivered volume returns to the ventilator.

45
Q

What does air trapping look like on ventilator loops

A

Flow-volume loop: the flow never reaches zero/baseline before new inspiration takes place

46
Q

What ventilation mode is this?

A

spontaneous breath with pressure support

inspirtory and expiratory line cross each other at about 2 cm H2O, when the patient attempts to inspire

47
Q

Describe the scalar

A

pressure-time scalar from volume controlled ventilation

  • 1 is the peak inspiratory pressure (PIP)
  • the inspiratory flow is then stopped but the expiratory valves stay closed = inspiratory pause, i.e. no flow between the patient and ventilator
  • quilibration between proximal airway pressure and alveolar airway pressure (Palv)
  • peak alveolar pressure/ plateau pressure = at the end of inspiratory hold ( = static compliance)
48
Q

what does the difference between PIP and Palv/plateau pressure show?

A

resistive properties of the system (i.e., either artificial or patient airways)

49
Q

What does the difference between PIP and EEP/PEEP show?

A

the dynamic compliance = measure of impedance (resistance and compliance components)

50
Q

What does the difference between Palv and PEEP indicate?

A

the elastic properties of the system (i.e., lung and chest wall compliance)

51
Q

How do you determine effective respiratory system compliance?

A

= tidal volume / (PIP - EEP)

52
Q

How do you determine dynamic compliance?

A

= PIP - EEP

53
Q

Explain what these 2 graphs demonstrate

A

increased or decreased compliance

flow-volume loop:

  • inspiratory flow stays similar, tidal volume increases with increased compliance
  • the expiratory peak flow rate (EPFR) decreases with increased compliance (“less push for air to flow out fast)

pressure-volume loop:

  • increased compliance –> loop moves to left and up (less pressure needed for more volume
  • decreased compliance –> loop moves to right and down (more pressure needed for less volume)
54
Q

Explain what these 2 graphs demonstrate

A

increased inspiratory airway resistance

flow-volume loop:

  • only subtle changes
  • very mild decrease in PEFR and tidal volume

pressure-volume loop:

  • expiratory loop is very similar to normal
  • inspiratory loop requires more pressure to achieve less volume
55
Q

list potential causes for increased inspiratory airway resistance

A
  • patient-ventilator dyssynchrony
  • secretions or exudate in the endotracheal tube or large airways
  • collapse or mass on trachea
56
Q

Explain whatthese 2 graphs demonstrate

A

increased expiratory resistance

flow-volume loop:

  • PEFR is significantly decreased (i.e., air can’t flow out as fast)
  • some air leakage is notable too (volume doesn’t go back to baseline)
  • no scooping –> usually indicates a large airway obstuction

pressure-volume loop

  • markedly affected: increased histeresis –> usually indicative of small airway obstruction

Boards: Respiratory (27 decks)

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