This document discusses various concepts related to mechanical ventilation including pressures, resistances, compliances, waveforms, and modes of ventilation. It defines key pressures like airway opening pressure, intrapulmonary pressure, and transpulmonary pressure. It also defines resistance and compliance. Graphics are presented to illustrate pressure-volume loops, flow-volume loops, and relationships between pressure, volume, and flow over time for different modes. Common modes discussed include pressure control, volume control, SIMV, and newer dual-control and proportional modes. Key concepts like triggers, targets, cycling, and breath types are also summarized.

1. Mechanical Ventilation
Mechanics, Graphics, Modes
Dr Mohit Roy

2. Few Basic concepts & a bit of Applied Respiratory Physiology
Graphics & Breath types
Modes

3. Definition of Pressures and Gradients in the
Lungs
Airway opening pressure (Pawo), is most often called mouth pressure (PM)
Intrapulmonary pressure = is alveolar pressure (PA or Palv)
Trans airway Pressure = difference between the airway opening and the alveolus
Pta = Paw − Palv
Transpulmonary Pressure or transalveolar pressure, is the pressure difference
between the alveolar space and the pleural space (Ppl) PL = Palv − Ppln ALSO known
as alveolar distending pressure

4. Two basic mechanical properties of interest..
Resistance
Elastance ..aka.. 1/compliance

5. Is defined as airflow obstruction in the airways
Primarily affected by the length, size, and
patency of the airway, endotracheal tube, and
ventilator circuit
Varies directly with the length and inversely with
the diameter of the airway or ET tube
R= Pressure / Flow
Resistance is for flow
If there is no flow there is no resistance

6. LUNG COMPLIANCE
Is volume change (lung expansion) per unit pressure change
C = V/ P
Low compliance makes lung expansion difficult lungs are stiff
High compliance induces incomplete exhalation, air trapping, and reduced CO2
elimination- exhalation is often incomplete due to reduced elastic recoil of the lungs
Static Compliance. Static compliance is calculated by dividing the volume by the
pressure measured when the flow is stopped, reflects the elastic resistance of the lung
and chest wall
Dynamic Compliance. Dynamic compliance is calculated by dividing the volume by the
pressure measured when airflow is present
Spontaneously breathing individual about 0.1 L/cm H2O (100 mL/cm H2O) For mechanically ventilated patients with normal lungs and a normal chest wall
about 40 to 50 mL/cm H2O

7. Equation of motion for the respiratory system
Pvent = (R X flow) + (E X Vol)
Pvent = (R X flow) + (Vol /C)
Relationship among the 3 most common ventilator parameters (ie, pressure, volume,
and flow as functions of time) and among the 2 respiratory mechanics factors (i.e,
elastance and airway resistance)
Pvent is the pressure generated by the ventilator
E is the respiratory system elastance
V is volume over time
R is airway resistance, V is flow over time
C is respiratory system compliance.

8. P V Asynchrony
Pressure Controlled
Volume Controlled
trigger
flow delivery
cycle-off criteria
RELATIONSHIP OF VOLUME, FLOW, PRESSURE, AND TIME

9. RELATIONSHIP OF VOLUME, FLOW,
PRESSURE, AND TIME
The volume (V) delivered depends on the amount of flow and the inspiratory time (TI)
(V = Flow × TI)
Volume flows due to the pressure gradient- difference between the pressure from the power
source (the ventilator) and the pressure inside the lungs
The pressure gradient depends upon C & R- The amount of pressure (ΔP) required to inflate the
lungs depends on the patient’s lung compliance and airway resistance.

10. Peak & Plateau Pressure

11. Waveforms for pressure, volume, and flow

12. Flow, pressure, and volume scalars during VC-CMV
with constant flow and an inspiratory pause
Flow and pressure scalars during PC-CMV

13. PRESSURE-VOLUME LOOPS
The loop represents the pressure and volume measured at the
upper airway
The highest point for tidal volume (VT [vertical axis]) and peak
inspiratory pressure (PIP[horizontal axis]) represents the
dynamic compliance for that pressure-volume relationship
static P-V line
Represents Palv

14. Variations in PV loop-flow, compliance
P-V loops with the flow set
at60,30, and15L/min.
P-V loops during pressure ventilation
P-V loop during volume-targeted
ventilation

15. As resistance increases, less volume is
delivered, and the loop shortens and widens
Variations in PV loop-Resistance

16. Flow-Volume Loops
Normal F-V loop during volume ventilation. F-V during PC-CMV

17. Increased airway resistance COPD Response to bronchodilator Air trapping

18. Ventilation- breaking it down
3 Ts – Trigger, Target, Termination (cycling)
Common breath types- Controlled, Assisted, Supported
Common modes

19. Signal to initiate breath (Trigger)
Timed (Controlled or Ventilator initiated)
Based upon set rate of ‘mandatory breaths’ –if rate =10/min then timed every 6 sec
Patient initiated
Decreased airway pressure or increased inspiratory flow- triggers the vent
Flow – has less WOB
‘Type of breath’ depends upon mode & timing
Mandatory – Assisted breath
Spontaneous- Supported breath

20. Breath Delivery Target
Volume
You set
TV
Peak Flow
Flow Pattern
Delivery of the breath
stops when set volume delivered
Airway pressure may vary
Pressure
You set
Inspiratory (or driving) pressure
(Plat- PEEP)
Insp time depends on breath type
(termination signal)
You set Insp time for ‘mandatory breaths’
Patient efforts determines insp. time in
‘spont breath’

21. Signal to Terminate Breath
Volume cycled – Inspiration terminated after pre-set tidal volume delivered (i.e. volume
targeted AC or SIMV)
Flow Cycled- Inspiration terminated when flow rate reached, such as flow decreased to 25%
of peak flow (i.e. PSV)- effort dependent
Time Cycled- Inspiration terminated after pre-set insp. time (i.e. Pressure targeted AC or
SIMV)
Pressure cycled- Inspiration terminated when pre-set maximum pressure reached

22. Breath types based on Initiation (trigger)
& Termination
Controlled (Mandatory)
•Pressure or Volume
targeted
•Time triggered
•Time or Volume
terminated
Assisted (Mandatory)
•Pressure or Volume
targeted
•(Flow or Pressure)
triggered
•Time or Volume
terminated
Supported (Spontaneous)
•Pressure
•Patient (Flow or Pressure)
triggered
•Flow terminated

23. MODES

24. Basically there are three breath delivery
techniques, or modes..
o Spontaneous modes
o Continuous mandatory ventilation (CMV) / assist/control ventilation
o Synchronized intermittent mechanical ventilation (SIMV)
OTHERS..
o Bilevel positive airway pressure (PAP), dual control modes, and other closed-loop
modes of ventilation (e.g., mandatory minute ventilation [MMV], airway pressure-
release ventilation [APRV], and proportional assist ventilation [PAV])

25. Positive End-Expiratory Pressure (PEEP)
o end-expiratory or baseline airway pressure
o Normally, the alveolar end-expiratory pressure equilibrates with atmospheric
pressure (i.e., zero pressure) and the average pleural pressure is approximately –5
cm H2O. Under these conditions, the alveolar distending pressure is 5 cm H2O
o Intrapulmonary Shunt and Refractory Hypoxemia
o Auto-PEEP- Air trapping may be caused by severe airflow obstruction or
insufficient expiratory time
o Decreased Venous Return, Barotrauma, increased Intracranial Pressure etc.

26. CPAP, BiPAP

27. Volume targeted Pressure Targeted
Peak pressure is higher with a constant flow and lower with a decelerating flow pattern. Decelerating flow pattern
has a higher mean airway pressure; constant flow generates the lowest mean airway pressure
Deaccellerating flow

28. PC-CMV
(PC-SIMV) mode with spontaneous ventilation at zero baseline
PC-SIMV mode in which pressure support (PS) has been added
Peak flow and pressure are higher for mandatory pressure-
control breaths and that flow returns to zero before end-
inspiration. In PS breaths, inspiration is flow cycled at 25% of
peak flow

29. (A) spontaneous ventilation,
(B) intermittent mandatory ventilation,
(C) synchronized intermittent mandatory ventilation
(SIMV), and
(D) SIMV with positive end-expiratory pressure
(PEEP).
Note that during intermittent mandatory ventilation,
mandatory breaths (vertical arrows) and
spontaneous breaths are not synchronized

30. Newer Modes
Dual control
Combining the advantages of volume-control ventilation (constant MV) and Pressure control
ventilation (rapid, variable flow)
From a classification standpoint, all of the dual-control modes are pressure-control breaths.. i.e
(Volume is variable with changing patient effort and pulmonary impedance)
Compared to traditional pressure control.. Ability to change the output (pressure) based on a measured
input (volume)..
The one exception is Adaptive support ventilation (Also alter the respiratory frequency and the
inspiratory-expiratory ratio)

31. Types of Dual Control Modes
Within-a-breath (intra-breath)-ventilator switches from pressure control to volume
control during a single breath
volume-assured pressure support or pressure augmentation
Breath-to breath (inter-breath)
Volume Support Ventilation
Pressure regulated Volume Control
Airway Pressure release ventilation
Proportional assist Ventilation

32. Volume Assured
Pressure Support
Pressure
Augmentation
High pressure alarm is important…

33. Volume Support Vent
.
Desired VT * respiratory
frequency= V˙ E
If the patient’s respiratory
frequency decreases below 15
breaths/min, the VT target will
be automatically increased
by the ventilator, up to 150% of
the initial value, to maintain
a constant minimum V˙ E

34. Pressure-Regulated Volume Control
Adaptive Pressure Ventilation -Hamilton Galileo
Autoflow -Dra¨ger Evita 4
Proposed advantages of this approach
Positive attributes of pressure-control ventilation with
constant V˙ E and VT at lowest possible peak pressure,
FAR FROM TRUE!

35. Automode

36. Proportional Assist Ventilation
Increase or decrease airway pressure in proportion to patient effort
The amount of pressure the ventilator produces depends on two factors: (1) the amount of inspiratory flow and volume
demanded by the patient’s effort, and (2) the degree of amplification selected by the clinician

37. Provides two levels of CPAP
Airway Pressure-Release Ventilation
(APRV)

38. Adaptive Support Ventilation (ASV)
Based on ‘minimal work of breathing’
concept

39. Neurally adjusted ventilatory assist
(NAVA)
Assisted ventilation mode synchronized and
proportional to the effort of the patient
(EAdi) - Electrical activity of the diaphragm
Trans-esophageal electromyography
EAdi catheter
NAVA level - The inspiratory assist
Inspiratory cycling is determined by the detection
of the elevation of EAdi over the expiratory level
Allows us to evaluate the response to changes in
assist level, detect apneas, evaluate sedation
effects, and also assess the neural respiratory
stimulus

40. Questions?
Thoughts?