1. Mechanical Ventilation
The Basics
M.RADHA KRISHNAN BPT,PGDRT,PGDRCM
SENIOR RESPIRATORY THERAPIST(ICU)
KMCH
COIMBATORE.
Interesting to compare the viewpoints and biases of medicine/endocrinology articles, and the surgery articles

2. Mechanical Ventilation Basic concepts
Introduction
Indications
Modes
Initial Settings

3. Basic Physiology Transairway pressure Gradient
Gradient between mouth opening pressure (Pao)and Alveolar pressure (PA)
During inspiration the gradient becomes more negative as you approach the alveolus. This is an active process; part of the energy used for inspiration is stored in the tissues. This is used in exhalation, which is effectively a passive process.
Recall that work = volume x pressure. For infants with their more compliant chest wall, they will have a proportionally greater work of breathing which helps predispose them to respiratory distress.
The point at which the recoil between the alveolus and the chest wall is balanced is equivalent to functional residual capacity.
I wanted to try to give some background to this slide without getting too weighed down in the physiology of breathing and respiratory failure. Besides, it always confuses me.

5. Basic Physiology

6. Negative pressure ventilation
Pre = Pao (Zero) - Palv (Negative)

7. Positive pressure ventilation
Prs = Pao (+ve) Palv (0)

8. Basic Physiology +ve pressure ventiation PI CmH2o PA CmH20 ∆P FLOW
Inspiration 20
+20
In to lungs
End inspiration
No flow
Expiration
-20
Out of lungs
End exp

9. Delicate balance between Load and Capacity
Depressed Respiratory Drive
Drug brain Stem
Increased Minute Ventilation
Pain, Anxiety,
Excessive Feeding
Sepsis
Increased VD/VT
Muscular Disorders
Myasthenia
Gravis
Electrolyte
Disorders
Prolonged
Neuromuscular
blockade
Increased Elastic Loads
Low Lung
Compliance
Low Thoracic
Intrinsic PEEP
Loads
Capacity
Thoracic
Wall
abnormality
Increased Resistive Loads
Airway
Obstruction
Neuromuscular disorder

10. Type 2 Respiratory Failure
Def
PaO2 <60 mm Hg
PaCO2  45 mm Hg
Etiology
Gas Exchange failure
V/Q Mismatch
Shunts
Diseases
ARDS,Pulmonary
Edema, Pneumonia,
Pneumothorax, PE
PaCO2>45 mm Hg
Ventilatory failure
Min. Volume
COPD, Muscle
Weakness, Restrictive
Decreased MV is due to 1. Increased load – obstruction 2. Decreased central drive 3.muscle fatigue

11. WHAT IS A VENTILATOR?
Any machine used to PUSH Gas mixture (air & O2) in to the lungs. This can be done by applying positive pressure at the airway either
Invasively or Non invasively.

12. Note that the pressure is applied to the proximal end of the ETT and is not the pressure in the alveoli as some of the pressure will be dissipated across the ETT and the major airways.

13. Classification of mechanical ventilators
Negative pressure ventilators
Positive pressure ventilators
Tank ventilators
Cuirass ventilators

14. Origins of mechanical ventilation
The era of intensive care medicine began with positive-pressure ventilation
Negative-pressure ventilators (“iron lungs”)
Non-invasive ventilation first used in Boston Children’s Hospital in 1928
Used extensively during polio outbreaks in 1940s – 1950s
Positive-pressure ventilators
Invasive ventilation first used at Massachusetts General Hospital in 1955
Now the modern standard of mechanical ventilation
The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output.
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DNA methylation results in histone deacetylation, compacted chromatin, and repression of gene activity
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Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

15. Indications – simplified
Respiratory
Restrictive
ARDS
ILD
Obstructive
Bronchial asthma
COPD
Central airway obstruction
Non respiratory
Chest wall
Cardiac
Normal
Airway protection
Respiratory drive dysfunction

16. Mechanical Parameters Predicting Impending Failure
Criteria
Critical Values (Normal)
Muscle strength
Maximum Inspiratory Pressure
Peak Expiratory Pressure
Spiro metric data
Vital Capacity
Tidal Volume
Minute Volume
Bedside
PEFR
Respiratory Rate
<-20 cm H2O (-50 to –100)
<+40 cm H2O (+100 cm H2O)
<15mL/Kg (65-75mL/Kg)
<5mL/Kg (5-8mL/Kg)
>10L/min (5-6L/min)
<100L/min ( L/min)
>35/min
Akin to the definition of CCF
A MIP of 40 cm H20 is reqd for adeq cough
Show the instrument – Bourdon gauge meter
Other indications
Airway protection
Hyperventilation in c. edema

17. Modes CMV (Controlled Mandatory ventilation) ACMV IMV
Synchronized intermittent mandatory ventilation
CPAP
PS(Pressure support ventilation)

18. Mechanical Ventilation Basic Concepts
Introduction
Indications
Modes
Initial Settings

19. VOLUME CONTROL
Normal emphysema ARDS
alveoli

20. VOLUME CONTROL ADVANDAGE DISADVANTAGE
The patients is Guaranted to receive a preset tidal volume
High Plateau pressure leads to Baro trauma

21. Pressure Control ventilation
ADVANTAGE
DISADVANTAGE
Prevent Baro Trauma
Low lung compliance and high airway Resistances – Tidal volume drops & drop in minute ventilation & Paco2 Accumulation & respiratory acidosis

22. Common Modes CMV (Control Mode Ventilation)
ACMV (Assist Control Mandatory Ventilation)
IMV (Intermittent Mandatory Ventilation)
SIMV (Synchronized Intermittent Mandatory Ventilation)
PSV (Pressure Support Ventilation )
A/CMV Assist Control mode ventilation: Every breath is mandatory but can be patient triggered

23. CMV

24. Control Mode Ventilation
CMV
Control Mode Ventilation
Every breath is mandatory and ventilator triggered with no spontaneous breaths
Mandatory breaths at a set frequency and tidal volume delivered to the patient
The inspiratory valve is closed to the patient otherwise so that no additional breaths can be taken
In anesthesia practice constant flow, volume controlled, pressure limited, time controlled ventilation is administered that is usually limited to 35 cm H2O airway pressure.

25. ACMV

26. ACMV ADVANTAGE DISADVANTAGE WOB is very small
Pt maintain their Own Pco2 or minute Volume
Alvoelar hyperventilation

27. IMV, volume-limited
Ref: Ingento EP and Drazen J: Mechanical ventilators, in Hall JB, Scmidt GA, and Wood LDH(eds.): Principles of Critical Care. New York, McGraw-Hill, Inc., 1992, p.145.
“Positive pressure, volume-cycled breaths are delivered at a preset rate similar to control mode ventilation, except that between breaths, the inspiratory valve to the patient is open, allowing for spontaneous breathing.”
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt GA, & Wood LDH(eds.): Principles of Critical Care

28. IMV TYPE OF BREATH : ASSIST & CONTROL TRIGGERING : ASSIST & CONTROL
CYCLING : VOLUME CYCLED
COMPLCATION: BREATH STACKING

29. SIMV, volume-limited
Ref: Ingento EP and Drazen J: Mechanical ventilators, in Hall JB, Scmidt GA, and Wood LDH(eds.): Principles of Critical Care. New York, McGraw-Hill, Inc., 1992, p.146.
(Would we also want to put slides with pressure mode graphs as well to show the different flow characteristics ??)
During SIMV, the ventilator divides time by the set rate to determine cycle-length. During the early part of this cycle, the patient may breath spontaneously without support. During the terminal phase of this cycle (% varies by manufacturer) the ventilator will synchronize a full breath with detected effort by the patient.
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt GA, & Wood LDH(eds.): Principles of Critical Care

30. CPAP
Flow
(L/m)
Pressure
(cm H2O)
CPAP level
Volume
(mL)
Time (sec)

31. CPAP
CPAP is PEEP is applied to the airway of a patient who is breathing spontaneously

32. PSV Patient Triggered, Flow Cycled, Pressure limited Mode Time (sec)
(L/m)
Flow Cycling
Set PS level
Pressure
(cm H2O)
Volume
(mL)
Time (sec)

33. PRESSURE SUPPORT VENTILATION
Î Spontaneous Tidal Volume
Reduces RR
Reduces WOB

34. Initial Settings Mode- ACMV Tidal volume : 7 to 8 ml/kg
COPD 6ml/kg & ARDS 5 to 6 ml/kg
Fio2 100% or 60%
RR NORMAL 16 to 18 b/m
PEEP 5 CMH2O
I:E RATIO 1:2 , COPD 1:4
PIF 60L/MIN
VC Monitor PIP & plateau , PC Monitor Tidal volume & Minute ventilation

35. Recapitulation Spont. Breath Mandatory Breath Mode Trigger Limit Cycle
CMV
Time
Pres.,Flow
Volume/time No
A/CMV
Pressure or Flow, Time
yes
PSV
Pressure or Flow
Flow
Only
SIMV
Pressure or Flow/ Time
Yes
PCV(PC-CMV)
Pressure or flow, Time
Pressure/ time
Control
Volume
Pressure

36. SCALARS
Flow/Time
Pressure/Time
Volume/Time

37. LOOPS
Pressure-Volume
Flow-Volume

38. Spontaneous Breath
Inspiration
Time (sec)
Flow (L/min)
Expiration

39. Mechanical Breath
Inspiration
Time (sec)
Flow (L/min)
Expiration

40. Inspiratory Tidal Volume
Volume vs Time
Inspiratory Tidal Volume
Volume (ml)
Inspiration
Expiration TI
Time (sec)

41. Transairway Pressure (PTA) Exhalation Valve Opens
Begin Expiration
Paw (cm H2O)
Time (sec)
Begin Inspiration
PIP
Pplateau
(Palveolar
Transairway Pressure (PTA) }
Exhalation Valve Opens
Expiration
Paw (cm H2O)
Time (sec)
PIP
Inflation Hold
(seconds)
Airway Resistance
Distending
(Alveolar)
Pressure
Expiration
Begin Inspiration
Begin Expiration

42. Inspiratory Flow Pattern
Beginning of expiration
exhalation valve opens
Peak inspiratory flow rate
PIFR
Inspiration
Insp. time TI
Expiratory Time TE
Flow (L/min)
Total cycle time
TCT
Time (sec)
Beginning of inspiration
exhalation valve closes
Expiration

43. Expiratory Flow Pattern
Beginning of expiration
exhalation valve opens
Inspiration
Expiratory time TE
Time (sec)
Flow (L/min)
Duration of
expiratory flow
Expiration
Peak Expiratory Flow Rate
PEFR

44. Components of Pressure-Volume LoopVT
Expiration
Volume (mL)
Inspiration
PIP
Paw (cm H2O)

45. Flow-Volume Loop Inspiration PIFR FRC VT PEFR Expiration Flow (L/min)
Volume (ml)
FRC VT
Flow (L/min)
PEFR
Expiration

46. Thank you
Questions ?