1. Basic Concepts in Adult Mechanical VentilationPa

3. Points of Discussion Basic respiratory dynamics
Basic ventilator parameters
Control variables: pressure, volume
Phase variables: trigger, limit and cycle
Conditional variables
Breath types

4. Spontaneous Breathing
Exhalation
Inspiration

5. Precondition of Inspiration
Pa < Pb Pb
Pa < Pb
Spontaneous breath
Pb > Pa
Mechanical ventilation Pa
Gas Flow

6. Three - Dimensional Spring
Pleural
Pressure

7. Alveolar Pressure Changes
Mechanical Breath
Time
Spontaneous Breath
Inspiration

8. Spontaneous Inspiration
Volume Change
Pressure Difference
Gas Flow

9. Mechanical Ventilation
Pressure Difference
Gas Flow
Volume Change

10. Airway Resistance R = D P D F “The Feature of the Tube”
Pressure Difference = Flow Rate x Resistance of the Tube

11. Pressure Difference x Compliance of the Balloon
D V
Volume
Pressure
D V
D P
D P
Volume Change =
Pressure Difference x Compliance of the Balloon

12. Compliance Tidal volume / Plateau-PEEP Units = ml/cmH20
Measures compliance of the lung and thorax
Tidal volume / Plateau-PEEP
Units = ml/cmH20

13. Compliance and Resistance
D V
D P
R =
D P
D F
In the ventilator circuit, the peak inspiratory pressure is a combination of the resistance related pressure and the compliance related pressure. An end inspiratory pause eliminates the flow related pressure and thus reflects on the compliance related pressure.

14. Resistance Measures airway resistance Peak-plateau / Flowrate
Length
Viscosity
Flow
Radius4
Peak-plateau / Flowrate
Units = cmH20/Lps

15. Peak and Plateau Pressures
Peak airway pressure reflects
Baseline (PEEP)
Pressure due to compliance (L+T)
Pressure due to resistance
Plateau pressure (breath hold) reflects
(alveolar distending pressure)

16. Peak Alveolar and Transpulmonary Pressures
P(t) = VT/CR+ Flow x RR + PEEP tot + _
Peak Airway Pressure
Alveolar Pressure
Plateau pressure
meanPaw
Palveolar
Intrinsic PEEP
Ppleural
External PEEP
Ptranspulmonary = Palveolar - Ppleural
Pplat = Maximum Palveolar
Transpulmonary pressure is a key determinant of alveolar distension.

17. Basic Ventilator Parameters
FiO2
Fractional concentration of inspired oxygen delivered expressed as a % (21-100)
Breath Rate (f)
The number of times over a one minute period inspiration is initiated (bpm)
Tidal volume (VT)
The amount of gas that is delivered during inspiration expressed in mls or Liters. Inspired or exhaled.
Flow
The velocity of gas flow or volume of gas per minute
Some of these settings, such as FiO2, respiratory rate, tidal volume, inspiratory time or I:E ratio, and mode of ventilation, are specified primarily by the physician. Sensitivity, or how easily the patient can trigger the ventilator into the inspiratory phase, and peak flow are usually not physician ordered.
The goal with the FiO2 is to keep it below 50% if possible. Tidal volume is usually at 6-12 ml/kg, depending on the ventilation management strategy.
In volume-based ventilation, delivery of the set tidal volume is what terminates inspiration. Peak flow determines how fast the tidal volume is delivered. In pressure-based ventilation, reaching the set inspiratory pressure and inspiratory time is what normally terminates inspiration.
Let’s look more closely at the modes of ventilation. 16

18. Terminology

19. Peak Inspiratory Pressure
Terminology: PIP & MAP
 A=A1+A2+…+An
Pressure
Inspiration + Exhalation
 A
Mean Airway Pressure
Peak Inspiratory Pressure
Time

20. Terminology: PEEP, I:E Ratio
Pressure
Time
Positive End
Expiratory Pr.
T insp.
T exp.
I : E = 1 : 2
I : E = 4 : 1
PEEP
PIP

21. Terminology: Flow and Volume
Minute Ventilation = Tidal Volume x Breath Rate
Flow
Tidal Volume
Pressure
Time

22. Volume = Flow X Time
Volume
Flow Rate
Time

23. Expiratory - baseline Positive End Expiratory Pressure
Negative End Expiratory Pressure
Expiratory Hold
Time Limited Exhalation (APRV)

24. PEEP
Definition
Positive end expiratory pressure
Application of a constant, positive pressure such that at end exhalation, airway pressure does not return to a 0 baseline
Used with other mechanical ventilation modes such as A/C, SIMV, or PCV
Referred to as CPAP when applied to spontaneous breaths
Let’s begin with a definition of PEEP or positive end expiratory pressure. PEEP is the application of a clinician-set, positive pressure applied at end exhalation. This prevents pressure from returning to zero, or atmospheric, at the end of the breath. When positive pressure is applied at the end of a mechanical breath, it is referred to as PEEP. When positive pressure is applied throughout the spontaneous breathing cycle, it is referred to as CPAP, or continuous positive airway pressure. Let’s look at a graphic representation of PEEP. 35

25. PEEP
Increases functional residual capacity (FRC) and improves oxygenation
Recruits collapsed alveoli
Splints and distends patent alveoli
Redistributes lung fluid from alveoli to perivascular space
On this pressure-time graph, we know that the first breath is mechanically initiated since there is no negative deflection preceding that breath. Note the breath does not begin at the zero base line, but instead begins at 5 cm H2O pressure. The mechanical breath is delivered, but at end exhalation, pressure remains at 5 cm H2O. The next breath is spontaneous (note the inspiratory deflection). Here again, pressure throughout the breath cycle is elevated by 5 cm H2O. The final breath is a patient-initiated, mechanical breath, again showing that at end exhalation, pressure is maintained at 5 cm H2O.
Why do we add PEEP? Once again, we’ll try to mimic this effect. Take a normal breath in, but do not exhale all the way, thus maintaining some positive pressure in your lungs. What could be the benefit of positive pressure at the end of exhalation? PEEP causes an increase in functional residual capacity or FRC. The FRC is the amount of air left in your lungs at the end of a normal exhalation. This increased volume can improve oxygenation; more air remains available to participate in gas exchange.
In sick lungs, PEEP can also help recruit or open collapsed alveoli. Keep in mind that with many lung pathologies, alveoli have the tendency to collapse. PEEP can be applied at pressures sufficient to overcome this tendency to collapse, keeping the alveoli patent and functional. Finally, in cases of excess pulmonary fluid, PEEP can cause this unwanted lung fluid to move from the alveoli into the perivascular space.
5 cm H2O PEEP 36

26. Classification Control variable Phase variable Conditional variable
Flow (volume)
Pressure
Phase variable
Trigger, limit, cycle, baseline
Conditional variable
Patient effort and time

27. Pressure Generated Breath
“Control Variable”
Which parameter remains constant despite changes in pulmonary mechanics?
Pressure Generated Breath
Pressure
Flow
Time

28. Control variables Volume Ventilation Pressure Ventilation Pressure
time
time
Flow
Flow

29. Volume Control Breath Types60 P aw
cmH 2
SEC 1 2 3 4 5 6
-20
120
INSP
Flow
SEC
How do you know the problem is with the patient? Look at your flow curve. 1 2 3
L/min 4 5 6
120
EXH
If compliance decreases the pressure increases to maintain the same Vt 45

30. Volume Targeted (Pressure Controlled)
As compliance changes - flow and volumes change 28 28

31. New Volume Targeted Breath Pressure Variability is Controlled
Pressure then raises to assure that the set tidal volume is delivered 30 30

32. Phase Variables A B C A. Trigger mechanism B. Limit variable
What causes the breath to begin? Patient (assisted)
Machine (controlled)
B. Limit variable
Which parameter is sustained at a preset level during the breath?
Flow
Pressure
C. Cycle mechanism
What causes the breath to end?
Volume
Time A B C

33. Trigger Variable- Start of a Breath
Time - control ventilation
Pressure - patient assisted
Flow - patient assisted
Volume - patient assisted
Manual - operator control

34. Inspiratory Trigger Mechanism
Time
Controlled Mechanical Ventilation
Pressure
Flow
Chest impedance
Abdominal movement

35. Inspiratory - delivery limits
Maximum value that can be reached but will not end the breath-
Volume
Flow
Pressure

36. Cycle Mechanism: Termination of Inspiration
Time
Conventional Neonatal ventilators
Volume
Adult / Pediatric ventilators
Pressure
Bird Mark® series
Flow
Pressure Support
Advanced neonatal modalities (FSV)

37. Cycling vs. Limiting
Cycled
Pressure
Time
Limited

38. Breath Types Mandatory Spontaneous Assisted Supported
Ventilator does the work
Ventilator controls start and stop
Spontaneous
Patient takes on work
Patient controls start and stop
Assisted
Patients triggers the breath
The ventilator delivers the breath as per control variable
Supported
Ventilator delivers pressure support
Breath cycles at set flow

39. Thank You