AMP 28: Ventilator Waveform Analysis Flashcards
Where are pressure, volume, and flow usually measured during ventilation and how does that potentially affect the accuracy of measurements?
- 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
What are the 3 main scalars used?
- flow versus time
- volume versus time
- pressure versus time
What are the 2 most common loops used?
- pressure-volume loops
- flow-volume loops
Name the type of waveforms (scalars)
What are the 6 stages of a mechanical breath?
- Beginning of inspiration
- Inspiration
- End of inspiration
- Beginning of expiration
- Expiration
- End of expiration
What is the cycling variable
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
Explain “plateau pressure” and how it is achieved by the ventilator
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
What are the properties of expiration dependent on?
- resistance of the animal’s airways
- resistance of the artificial airways (i.e., tubing)
- compliance of the lungs
Describe the differences of the Flow/Time scalar between volume-controlled and pressure-controlled ventilation
- 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)
What are risk factors for Auto-PEEP?
- high ventilation rate
- high tidal volume
- PEEP set > 10 cm H2O
- airway obstruction
What is auto-PEEP?
inspiration begins before complete expiration and air remains trapped within the small airways
What are strategies to reduce auto-PEEP?
- 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
How does extrinsic PEEP reduce auto-PEEP
opens up small airways that are trapping air, especially applicable in chronic obstructive airway disease (pop the airways open/recruit more airways)
What are complications caused by auto-PEEP?
- air remains in small airways ⇒ more patient effort required before patient-initiated breath
- flattening of the diaphragm ⇒ decreases efficacy of diaphragmatic contraction during inspiration
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?
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
Describe the differences of the Volume/Time scalar between volume-controlled and pressure-controlled ventilation
- 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
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?
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
What ventilator mode is this patient ventilated with?
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
What ventilator mode is this patient ventilated with?
Assist-control pressure-controlled
What ventilator mode is this patient ventilated with?
Assist-control volume controlled
What complication is occuring in this ventilated patient?
Explain how you identify it.
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
What complication is occuring in this ventilated patient?
Explain how you identify it.
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
Explain “compliance”
indicates how the lungs will expend with a certain pressure
a change in volume in relation to a change in pressure
how with the pressure-volume loop move when the compliance decreases or increases
decreased compliance –> to the right
increased compliance –> to the left
Which graph shows the most compliance?
the steepest one
List 5 common causes for decreased compliance
- pleural space disease
- pulmonary parenchymal disease
- single-lung intubation
- abdominal distention
- chest-wall disease or deformity
When examining a pressure-volume loop, what are the inflection points believed to represent?
- increased alveolar recruitement during inspiration (at certain point of inspiration, less pressure needed to increase volume)
- increased alveolar decruitment during expiration
What do A and B represent and who is initiating this breath?
A: lower inflection point, inspiration
B: upper inflection point, expiration
the machine is initiating this breath
Who is initiating this breath?
patient triggered breath
pressure is negative at beginning of inspiration
What does this movement of the pressure-volume loop indicate?
increased compliance
What does this shift of the pressure-volume loop indicate?
decreased compliance
What does this change in the pressure-volume loop indicate?
increased resistance
What is hysteresis
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.
Is the pressure-volume or the flow-volume loop better to assess for changes in airway resistance?
The F-V loop is better to assess for increases resistance because the changes on the P-V loop are very subtle
Name 4 common causes for increased airway resistance during ventilation
- bronchospasm
- mucosal edema of airways
- small endotracheal tube
- airway secretions
What is the definition of “work of breathing”
= the pressure required to move a specific volume of gas
What increases the work of breathing?
- decreased compliance
- decreased functional residual capacity
What is A and B?
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
What are A, B, and C?
A = beginning of inspiration
B = beginning of expiration
C = peak expiratory flow during passive expiration
What type of breath is this?
spontaneous breath
explain this loop
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”
How does the flow-volume loop change when there is a air leak during inspiration?
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
What is happening?
there is an air leak downstream (on the patient side)
- the volume is not completely returned (i.e., does not go back to zero)
what does an air leak between the flow transducer and the ventilator look like?
the set volume is not being delivered, but all the delivered volume returns to the ventilator.
What does air trapping look like on ventilator loops
Flow-volume loop: the flow never reaches zero/baseline before new inspiration takes place
What ventilation mode is this?
spontaneous breath with pressure support
inspirtory and expiratory line cross each other at about 2 cm H2O, when the patient attempts to inspire
Describe the scalar
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)
what does the difference between PIP and Palv/plateau pressure show?
resistive properties of the system (i.e., either artificial or patient airways)
What does the difference between PIP and EEP/PEEP show?
the dynamic compliance = measure of impedance (resistance and compliance components)
What does the difference between Palv and PEEP indicate?
the elastic properties of the system (i.e., lung and chest wall compliance)
How do you determine effective respiratory system compliance?
= tidal volume / (PIP - EEP)
How do you determine dynamic compliance?
= PIP - EEP
Explain what these 2 graphs demonstrate
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)
Explain what these 2 graphs demonstrate
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
list potential causes for increased inspiratory airway resistance
- patient-ventilator dyssynchrony
- secretions or exudate in the endotracheal tube or large airways
- collapse or mass on trachea
Explain whatthese 2 graphs demonstrate
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
