1. Ventilation Sam Petty Clinical Specialist Physiotherapist
John Farman ICU
Addenbrooke’s Hospital

2. Nomenclature Which ventilators ?
All modes called different things for the same basic principal e.g. PS/CPAP on Servo i and ASB on Draeger
All mean air in:air out

3. Why do we ventilate?

4. Why do we ventilate Airway protection Normalise CO2 Oxygenation
Lower consumption/unload respiratory muscles
Apnoea e.g. High SCI

5. Consider
Inspiration involves pumping high flow gas into a patient ventilation
Reliant on normal passive recoil
Bypasses usual URT therefore need to consider humidification
Requires an interface: NIV, ETT, tracheostomy
All contain built in software that recognises ‘normal’ flows in mammals therefore try to be as natural as possible
Dual limb in invasive ventilation which provides data (important if machine is capable of running NIV and interface choices)

6. How do we choose which mode?
Broadly speaking 3 choices
Full mandatory ventilation
Synchronised intermittent mandatory ventilation
Supported ventilation

7. Mandatory modes When you require full control
Patient will require sedation +/- muscle relaxant
Tolerance/synchronicity
Set volume or pressure
Set RR
PEEP
Triger
Rise time (rate of pressurisation)

8. Mandatory ventilation
How to calculate Vt

9. Mandatory ventilation
How to calculate Vt
Height of patient
6-8 mls/kg of ideal body weight
E.g. 170cm male
Ideal weight kg
360 mls is the lowest based on 6 mls/kg
576 mls is the highest based on 8 mls/kg
462 mls is the mid point based on mid range weight x 7 mls/kg

10. Mandatory ventilation
If using Volume pre-set mode set Vt at chosen level
If using Pressure pre-set mode set pressure that achieves approximately the chosen volume

11. So can a patient trigger a breath?

12. Volume Control
Machine driven

13. Volume Control

14. Benefits of VC Shorter inspiratory time Longer inspiratory time
Less risk of gas trapping
Less effect on CVS system
Longer inspiratory time
improve oxygenation
Higher mean airway pressure
Re-distribution of gas
Lower peak airway pressure
More time available to deliver set Vt

15. Disadvantages of VC Not synchronous
Inappropriate triggering will cause excessive minute ventilation
Decrease in compliance of lung tissue will increase the risk of barotrauma

16. Pressure control Set pressure dependent on Vt you wish to achieve
As with VC the patient can trigger the breath and will receive a mandatory breath
Pressure is not the same as the alveolar pressure as this is dissipated across the airways
Constant pressure applied. High initial flow as more alveoli to fill. Deceleration of flow falling to zero by end inspiration
Changes in resistance/compliance will cause a change in Vt

17. Advantages PC Avoids high inspiratory pressures
Rests muscles of respiration

18. Disadvantages PC Not synchronised
Inappropriate triggering results in excessive MV
Changes in lung compliance or resistance will result in a change in Vt

19. Pressure Support/ASB Patient ready to wean Set: FiO2 PEEP
Trigger type and sensitivity
Inspiratory rise time
Cycle off
Patient will determine RR and Vt

20. PS/ASB Trigger: flow v’s pressure
Risk of too difficult or too easy – autotriggering
Inspiratory flow – decelerating flow due to lung unit filling
End of inspiration – determined by fall in flow
End of expiration – when next breath is triggered

21. What to look for VT inspiration: VT expiration
They should remain similar (generally within mls variance and they will swap around)
Is the patient achieving Vt
RR limits
‘double triggering’
Apnoea
‘gas trapping’

22. Gas trapping

24. Gas trapping Likely in bronchospasm
Long inspiratory time (therefore short expiratory time)
High RR (ie. Absolute expiratory time is short)
Progressive increase in intra-thoracic pressure
Decreased venous return
Decreased cardiac output
May lead to PEA arrest

25. Synchronised modes Combination of mandatory mode + PS +PEEP
Minimum mandatory RR
Any additional breaths PS

26. Does asynchrony matter?
Poor sleep
Increased agitation
Increased use of sedatives/muscle relaxants
Prolonged ventilation
Respiratory muscle weakness
Increased LoS (both ICU and hospital)
Less likely to be mobile

27. Finally – where?

28. Any Questions?