1. Newer modes of ventilation
Dr Babu K Abraham MD, MRCP(UK)
Senior Consultant
Department of Critical Care Medicine
Apollo Hospitals, Chennai

2. Newer Modes
Dual Mode –
Modes that try to deliver the benefit of both volume and pressure targeted breaths
Try to guarantee control of both pressure & volume settings
Partial Ventilatory Support –
Pressure targeted modes
Allow spont breathing during both high & low pressure setting
Closed Loop System
Intelligent automated modes
PRVC
BiLEVEL/BIPAP
APRV
NAVA

3. Pressure Regulated Volume Control (PRVC)
Maquet Servo-i
Also known by other names
Adaptive pressure control
AutoFlow - Dräger Medical AG
Adaptive Pressure Ventilation - Hamilton Galileo
Volume Control + - Puritan Bennett
Volume Targeted Pressure Control/ Pressure Controlled Volume Guaranteed - Engström, General Electric
Pressure targeted breaths (PCV)
Has a target VT
Time cycled

4. Machine adjusts the inspiratory pressure to deliver the set minimal VT
If the VT is ↑ above the set target the machine ↓ the inspiratory pressure & vice versa
Problems –
The inspiratoy pressure is set based on the preceding VT
If pt’s effort is large the VT will ↑ despite the inspiratory pressure ↓

5. Settings for PRVC VT – minimal desired RR – minimal desired
Ti or I:E ratio
Upper pressure limit -
Machine will deliver a maximum pressure < 5 cm set
Inspiratory rise time
FiO2
PEEP

6. ? Benefits of using PRVC Guarantees a minimum average VT
Flow benefits of PCV retained – so better flow synchrony
Less ventilatory manipulation required
Near automatic weaning
Evidence
Compared to VCV – lower Ppeak*
Compared to PCV – no difference even in Ppeak**
No study on outcome***
May be less comfortable than PSV****
Relatively easy to use and set
Can increase WOB in pts with increased resp drive – Eg Metabolic Acidosis. This is because these pts take large Vt due to their increased resp drive. The machine decrease the inspiratory pressure to maintain the target Vt. This then leads to inapp shifting of WOB onto the pt.
Crit Care 1997;1(2):75-77*
J Crit Care1998;13(1):21-25**
Respir Care 2007;52: ***
Respir Care 2008;53: ****

7. Biphasic Intermittent Positive Airway Pressure
(BIPAP)
Also called
Bilevel
Bivent
DuoPAP
These modes deliver
pressure-controlled breaths
time-triggered
time-cycled breaths
using a set-point targeting scheme

8. There are two pressures to be set Phigh Plow
This mode maintains a constant pressure (set point) even in the face of spontaneous breaths
There are two pressures to be set
Phigh
Plow
There are two time intervals to be set
Time spent on Phigh – Thigh
Time spent on P low - T low
Pt can breath spontaneously at both these pressures
T high
T low

9. CPAP PCV BIPAP Phigh Unrestricted spontaneous breathing
TIME
T high
T low
PCV
BIPAP
Phigh
improves oxygenation
promotes alveolar recruitment
Unrestricted spontaneous breathing
Allows reduced sedation and promote weaning
Plow
Allows exhalation
Maintains recruitment

10. The difference between the two
P high & P low
The difference between the two
Two levels of functional FRC
Creates a driving pressure
Determines the VT
Permit gas to enter the lung units
Represents the difference between airway pressure (Paw) and alveolar pressure (Palv)
T high
T low
PCV

11. Settings for BiLEVEL Clinician needs to set Phigh and Plow
Thigh and Tlow
Thigh and Tlow can be adjusted independently of the 2 pressure levels
Recommendation for changing over
Plow equivalent to PEEP
Phigh equivalent to the Pplat
or 12 to 16 cm H2O above the Plow
Cycling –
time cycling that approximately maintain a 1:1- I:E ratio
Careful consideration of the patient’s underlying pathophysiology is required when adjusting these settings – ARDS vs COPD

12. APRV Concept same as Bi LEVEL There are some distinct differences
Plow level
In BIPAP – kept at PEEP
In APRV – kept at 0
Relation between Thigh and Tlow
In BIPAP – traditional to 1:1
In APRV - inverse ratio
Original description
Thigh 1.8 sec
Tlow 1.3 sec
APRV extended -
Thigh 4 to 6 seconds
Tlow 0.8 sec

14. APRV in ARDS pts shown to **
What is the evidence?
BiLEVEL -Shown to be beneficial in patients during the acute phase of ALI and ARDS – improves dependent gas distribution*
APRV in ARDS pts shown to **
- Improve oxygenation & hemodynamic parameters
- ↓ in sedation and inotrope use
- ↓ the durations of ventilation and ICU stay
AJRCCM1999;159:1241–1248*
AJRCCM 2001;164:43–49**

15. Closed Loop Systems Advances in microcomputer technique
System that allow ventilators to manipulate variables based on feed back
Commercially multiple modes available today
Advanced version of PSV/PCV
Input from neural output of the respiratory centers
PAV
NAVA

16. Neurally adjusted ventilatory assistance (NAVA)
Advanced version of PSV
Pt’s own spontaneous breathing is required
Neural output - Electromyographic activity of the diaphragm (Edi) is captured
Delivers assist in proportion to and in synchrony with the patient’s Edi signal
A specially designed (9 electrodes) esophageal
catheter needs to be inserted
Amplified on a real-time basis to generate proportional Paw,insp

17. A spontaneous breath starts with –
Impulse generated by the respiratory center
Transmitted via the phrenic nerves
Excitation of the diaphragm

18. In a healthy subject only 5% of maximum capacity of neuro ventilatory coupling is used to generate an adequate Vt
In a healthy subject, the low amplitude of diaphragm excitation reflects the fact that neuroventilatory coupling is highly efficient and that only about 5% of m In disease, muscle performance may not be up to expectation, leading to an increased output from the respiratory center with the aim of recruiting additional motor units in the diaphrag maximum capacity is used.
In this example, the increased signal seen in
COPD and post-polio patients thus reflects
the fact that a larger part of the muscular
reserve is used. Only 5-8% of maximum
capacity is used in healthy subjects, while up
to 40% is used in COPD patients.
If the diaphragm becomes weaker and/or the inspiratory load increases, the diaphragm´s electrical activation must increase to maintain a given volume. (Adapted from Sinderby et al JAP 1998)
The electrical activity of the diaphragm (Edi) is measured in μV (micro volt). 1 μV = 10-6V, thus 1,000,000 μV = 1V.

19. Conventionally a pressure drop or flow reversal is used to initiate the ventilatory support
The earliest signal that can be registered is the excitation of the diaphragm
Adjusting the support level in synchrony with the rise and fall of the electrical discharge - the ventilator and the diaphragm works with the same signal input
Conventional ventilator technology uses a pressure drop or flow reversal to initiate the assist delivered to the patient. This is the last step of the signal chain leading to inhalation and is subject to disturbances such as intrinsic PEEP, hyperinflation and leakage.
The earliest signal that can be registered with a low degree of invasivity is the excitation of the diaphragm (as shown on the left-hand side
of the picture). The excitation of the diaphragm is independent of pneumatic influence and insensitive to the above problems associated with pneumatic triggering technologies.
By following diaphragm excitation and adjusting the support level in synchrony with the rise and fall of the electrical discharge, the ventilator and the diaphragm will work with the same signal input. In effect, this allows the ventilator to function as an extra muscle, unloading extra respiratory work induced by the disease process

20. A specially designed (9 electrodes) oesophageal catheter needs to be inserted
Amplified on a real-time basis to generate proportional Paw,insp

21. What does the clinician set?
Insert Edi Catheter
Confirm the position of the catheter
Adjust the NAVA Level - gain factor between the Edi and Paw,insp generated
Set PEEP
Set FiO2
Set Back up ventilation

22. Few clinical data are available so far with NAVA
(especially in patients who have weak EMGdia signal)
Studies in healthy subjects found the system able to match perfectly the patient’s timing and generate Paw,insp in proportion to the patient’s Edi*
Beneficial effects
Better patient–ventilator synchrony
Facilitate physiological weaning**
Concern - esophageal catheter placement may limit its clinical application
Nat Med 1999;5(12):1433–6*
Intensive Care Med.2008.**

23. Conclusion
“A mode of ventilation is only as good as the operator who applies it”

24. Thank you