Newer modes of ventilation
Dr Babu K Abraham MD, MRCP(UK)
Senior Consultant
Department of Critical Care Medicine
Apollo Hospitals, Chennai
Newer Modes
Dual Mode –
PRVC
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
BiLEVEL/BIPAP
Allow spont breathing during both high & low
APRV
pressure setting
Closed Loop System
NAVA
Intelligent automated modes
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
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 ↓
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
?
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
Crit Care 1997;1(2):75-77*
J Crit Care1998;13(1):21-25**
Respir Care 2007;52:478-485***
Respir Care 2008;53:879-902****
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
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
This mode maintains a constant
pressure (set point) even in the
face of spontaneous breaths
There are two pressures to be set
Phigh
Plow
T high
T low
T high
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
CPAP
PCV
TIME
T high
T low
T high
BIPAP
Phigh
improves oxygenation
promotes alveolar recruitment
Plow
Allows exhalation
Maintains recruitment
Unrestricted spontaneous breathing
Allows reduced sedation and promote
weaning
P high & P low
The difference between the two
Two levels of functional FRC
Creates a driving pressure
Determines the VT
PCV
Permit gas to enter the lung units
Represents the difference between
airway pressure (Paw) and alveolar
pressure (Palv)
T high
T low
T high
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
APRV
Concept same as Bi LEVEL
There are some distinct differences
Plow level
In BIPAP – kept at PEEP
In APRV – kept at 0
APRV extended Thigh 4 to 6 seconds
Tlow 0.8 sec
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
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**
Closed Loop Systems
Advances in microcomputer technique
System that allow ventilators to manipulate
variables based on feed back
Commercially multiple modes available today
PAV
NAVA
Advanced version of PSV/PCV
Input from neural output of the respiratory
centers
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 spontaneous breath starts
with –
Impulse generated by the
respiratory center
Transmitted via the phrenic
nerves
Excitation of the diaphragm
In a healthy subject only 5%
of maximum capacity of
neuro ventilatory coupling is
used to generate an adequate
Vt
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
A specially designed (9 electrodes)
oesophageal catheter needs to be
inserted
Amplified on a real-time basis to
generate proportional Paw,insp
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
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.**
Conclusion
“A mode of ventilation is only as good
as the operator who applies it”