Volume Targeted Ventilation Flashcards
While ventilating patient on volume control, what needs to be measured and evaluated?
Monitoring a ventilated patient includes monitoring and evaluation of:
- Measurement of set parameters Eg. Vt
- Measurement of results of ventilation. Eg Ppeak
- Calculation of values such as compliance and resistance
- Patients overall condition: BP, ABG’s, ECG’s
Why do we monitoring set values
To ensure patient is receiving set parameters
- Vt: If it is lower than set you may have a circuit leak. If it is higher, patient may be breathing in more than is set
- FiO2: Use oxygen anaylyzer
- PEEP - to ensure there is no air-trapping
What will cause these pressure’s to increase:
- Ppeak
- Pplateau
- Pmean
- Expiratory pause pressure
- Ppeak will change due to compliance, resistance, volume or flow
- Pplateau will change due to compliance or volume
- Pmean is affected by Ti, PEEP and to a lesser degree is affected by Ppeak
- Expiratory pause pressure - If patient doesn’t have enough time to exhale you can measure to see if PEEP has increased. Causes air-trapping. Called auto-peep
What is Pplateau and how is it measured
Measured by doing an inspiratory pause. There is no flow so there is no pressure due to resistance. Pplateau equals pressure in alveoli after inspiration. It is affected by compliance and volume changes.
What is Ppeak and what affects it?
Highest pressure reached during inspiration. Pressure is a result of compliance, volume, flow, and resistance changes.
Mean airway pressure
Average pressure over entire respiratory cycle.
Significant affect on PaO2
Most effective way to increase Pmean is to increase PEEP or to increase I:E ratio. Ppeak effects Pmean as well but much less
What happens to Pmean if you increase flow
Results in a lower Pmean. Increasing flow rate decreasing Ti. Pmean will always follow I:E ratio
How does Ppeak effect Pmean
Ppeak will only effect Pmean if Ppeak increases and Ti stays the same. In this case Pmean will increase
Tidal volume displayed
The tidal volume displayed is the expiatory tidal volume. Vt displayed during inspiration is the previous tidal volume. If patient is on compensated ventilator the tidal volume displayed should be the tidal volume set.
How can you increase the I:E ratio
Can be increased by Increasing Ti or decreasing Te
- Decrease flow
- Increase Vt
- Increase RR
To determine if it is increased or decreased think of 1:2 if greater than 1:3
Higher I:E = higher Pmean
When would you want a low I:E ratio and when would you want a high I:E ratio
Low I:E ratio for asthmatic and COPD patients that need a longer time to exhale. This will help avoid auto-PEEP
High I:E ratio for patients with stiff lungs (low compliance) They are able to exhale easier so they don’t need as much time and need more time to push air into lungs
What will an decrease compliance affect when using volume control
Decrease compliance will increase Plateau directly and Ppeak indirectly. The Tidal volume will not change
What will an increase in resistance affect while using volume control?
Will increase Ppeak but will not increase Pplateau. Why? Because Pplateau is measured when there is no flow so there will be no pressure due to resistance.
What are volume alarms used for
May be tidal volume, minute volume, or both
Low VT or Ve indicate underventilation (could be a circuit leak)
Higher VE alarm could indicate overventilation due to auto triggering or patient over triggering due to pain
What are rate alarms used for
Low rate (won’t go off because ventilator will trigger a breath)
- Not necessary while on AC mode
- Useful on other modes
Higher rate: May indicate over ventilating due to:
- Patient triggering (hyperventilating)
- Auto-triggering
