Ventilator Basics Flashcards
This information was covered in ICP, from lecture titled Mechanical Ventilation.
What is the purpose of the ventilator?
- ventilate patient 2. oxygenate patient
what are the 4 main modes of ventilation?
- Volume Control Ventilation (VCV) 2. Pressure Control Ventilation (PCV) 3. Pressure Support Ventilation (PSV) 4. Synchronized Intermittent Mandatory Ventilation (SIMV)
What exactly is minute ventilation?
the amount of air a person breaths in 1 minute
What is the formula for minute ventilation?
RR x TV
What is the normal range for minute ventilation?
5-6 L/min
What is the difference between Peak Airway Pressure(PAP) and Peak Inspiratory Pressure (PIP)?
PIP is the setting on the ventilator. PAP is the actual measure of pressure in the major airway.
Where is PAP measured?
major airways (bronchi)
What is plateau pressure?
positive pressure appleid to small airways and alveoli
What is the goal for plateau pressure? Why?
a. under 30 cmH2O b. decrease risk of alveoli stretch (ventilator induced lung injury)
What is Peak Flow?
determines the rate of tidal volume delivery to patient during mandatory volume control breaths
What does peak flow affect in the breathing cycle?
I:E ratio
What is VCV
Volume control ventilation. Tidal volume is preset & the resultant airway pressure is a function of lung compliance & other factors
What are the independent variables of VCV?
- tidal volume 2. RR 3. I:E ratio 4. FiO2 5. PEEP (opt)
What are the dependent variables of VCV?
- PIP/PAP 2. Plateau pressure
What are advantages of VCV?
- guaranteed minute ventilation 2. improve lung compliance in certain surgeries
What are disadvantages of VCV?
- patient does NOT trigger breath 2. may need to reduce TV if you get high PIP/PAP
How would you know the patient is trying to take a breath in VCV?
distorted CO2 waveform
What is PCV?
Pressure Control Ventilation. Peak airway pressure is preset & the delivered tidal volume is a product of lung compliance & other factors
What is the result of VCV on peak pressures?
Since the volume delivered is constant, applied airway pressures vary with changing pulmonary compliance (plateau pressure) & airway resistance (peak pressure).
What ventilation mode produces this wave form?
VCV
What are the independet variables (settings) of PCV?
- PIP
- RR
- I:E ratio
- FiO2
- PEEP
What are the depedent variable of PCV?
- Tidal Volume
What are the advantages of PCV
- reduced barotrama
- improved gas distribution d/t decelerating flow
- more rapid improvement in lung compliance and 02 compared to VCV
what is disadvantage of PCV?
does not guarantee minute ventilation
What does decelerating flow mean?
decelerating inspiratory flow pattern, in which inspiratory flow tapers off as the lung inflates. This usually results in a more homogeneous gas distribution throughout the lungs.
If minute ventilation isn’t guaranteed, what may occur?
The minute ventilation is a complex mix of the peak pressure, the inspiratory time, the lung and chest wall compliance, resistance in the airway and from other thoracic structures. If there is a rapid change in the compliance, then the patient may hypoventilate and become hypoxic.
What is the difference btw PIP and Plateau pressure in VCV?
PIP is determine by the set tidal volume
Plateau is determined by applying an inspiratory hold (.5 -1 s) (no flow)
What is the difference btw PIP and Plateau pressure in PCV?
PIP is usually the same as Plateau b/c of dispersion of gas in inspiration.
What is PSV?
Spontaneous ventilation mode that provides constant pressure once patient inspiratory effort is sensed
What parts of the breath does the patient control when on PSV?
all parts of the breath EXCEPT the pressure limit
How does PSV work?
For spontaneously breathing patients, PSV provides a constant pressure once the ventilator senses that the patient has made an inspiratory effort. Pressure support sets a level of support pressure (not TV) to assist every spontaneous effort. Airway pressure support is maintained until the patient’s inspiratory flow falls below a certain cutoff (eg, 25% of peak flow).
What indicates that the patient is taking a breath in a PSV waveform?
downward diflection
What are the indepedent variables (settings) for PSV?
- support pressure
- inspiratory time
- flow trigger
- FiO2
- PEEP
What are the dependent variables of PSV?
- Tidal volume
- Respiratory Rate
What are the advantages of PSV?
- Able to have patient breath spontaneously & not “fight” the ventilator
- Able to augment tidal volume
- Able to adjust ETCO2 with support pressure
What are the disadvantages of PSV?
Requires the patient to be breathing spontaneously
What can PSV be used for?
- build up CO2 to get patient back to breathing
- when your patient is apnic with an LMA in place since you can set a backup rate with the PSVPro
What is SIMV?
method of partial ventilatory support to facilitate liberation from mechanical ventilation
Patient can breathe spontanously between the ventilator breaths
Ventilator will not give a breath if the patient inspires at that same instant
What are the independent variables of SIMV?
- Tidal Volume
- Respiratory Rate
- I:E Ratio
- FIO2
- Pressure Support Level
- PEEP (Optional)
What are the dependent variables of SIMV?
PIP/PAP
Plateau pressure
What is SIMV used for ?
- Can be used to build up CO2
- Back up mode for PSV
What is the disadvantage of SIMV
Can be confusing to the patient’s brain center. The brain is used to breathing being rhythmic in nature, the difference in the mechanical breath versus the pressure supported breath can be confusing to the brain
How is tidal volume calculated?
5 - 10 mL/kg
What pressure should we keep PIP under?
40 cmH2O
What pressure should we keep plateau pressure under?
30 cmH2O
How do you calculate inspiratory time?
I time = I / (I+E)
What drives the bellows?
Bellows falling— drive gas from the control module (inhaling for patient)
Bellows rising— passive exhalation from patient
what is fresh gas flow coupling? formula?
fresh gas flows add to Tidal volume delivered
FGF = (Flow x I time)/ RR
then add this to setting on machine (newer machines compensate for this)
What is the purpose of an inspiratory pause? What mode can it be used in?
a. allow breath to diffuse into lungs beter (holds breath at end of inspiration) (25% of I time)
does not effect E time
b. only in VCV
What is auto-peep? what indicators are there?
- a. Air trapping in the lungs because of insufficient exhalation time
b. Non-zero end expiratory pressure and Increasing PIP/PAP
