Basics of mechanical ventilation

1. Dr. Sangeeta Dhanger
Assistant Professor
Department of Anaesthesiology
and Critical Care
IGMC & RI
Puducherry
BASIC MODES OF
MECHANICAL
VENTILATION

2. What should we know?
• Need for mechanical ventilation?
• Type of mechanical ventilation?
• Modes of mechanical ventilation?
• Initial setting of ventilator?
• Weaning from ventilator?

3. Need for mechanical ventilation?
•Assessment of patient for respiratory
distress:
•Patient’s level of consciousness.
•Appearance and texture of the patient’s skin?
•Nail beds or lips for evidence of cyanosis?
•Pale and diaphoretic (sweating)?
•Patient’s vital signs

4. Indications for ventilatory support

5. Bedside Measurements of Ventilatory
Mechanics

6. Need for mechanical ventilation?
Aim:
1. Adequacy of oxygenation and ventilation
2. Decrease WOB
3. Increase Patients comfort
4. Synchrony with the ventilator

7. Parts of Ventilator
1. Power source
2. Control system
3. Control panel
4. Patient’s circuit
5. Adjuncts to the patient’s circuit
6. Gas supply system

8. Basic concept of mechanical ventilation

11. •Resistance :
•The frictional forces that must be overcome during
breathing.
•Depends on the gas viscosity, gas density, the
length and diameter of the tube, and the flow rate
of the gas through the tube
Raw=(PIP−Pplateau)/ Flow
• High on intubated patients

12. Compliance
• Described as the relative ease with which the structure distends.
• Normal compliance
• Spontaneously breathing patients: 50 to 170 mL/cm H2O
• Intubated patients: 40 to 50 mL/cm H2O.
• Static Compliance:
• Reflects the elastic resistance of the lung and chest wall
• Dynamic Compliance:
• Reflects the condition of airway resistance (nonelastic resistance)

13. Pressures in spontaneous and controlled
ventilation

14. • Plateau pressure:
• The pressure needed to maintain lung inflation in the absence of
airflow.
• Measured by inspiratory hold.
• Peak inspiratory pressure:
• The pressure used to deliver the tidal volume by overcoming nonelastic
(airways) and elastic (lung parenchyma) resistance.
• Highest pressure during inspiration.

15. • Positive end-expiratory pressure(PEEP):
• Operator selects a higher pressure to be present at the end of
exhalation.
• Ventilator prevents the patient from exhaling to zero (atmospheric
pressure).
• PEEP therefore increases the volume of gas remaining in the lungs at
the end of a normal exhalation and

16. Types of mechanical ventilation

17. Non-InvasiveVentilation (NIV)
• Technique of providing ventilation without the use of an
artificial airway.

18. Non-InvasiveVentilation (NIV)
• Technique of providing ventilation without the use of an
artificial airway.

19. Indications :
• At least two of the following factors should be present:
• Respiratory rate >25 breaths/min
• Moderate to severe acidosis: pH, 7.25 to 7.30; PaCO2, 45 to 60 mm Hg
• Moderate to severe dyspnea with use of accessory muscles and
paradoxical breathing pattern
Contraindications:
• Upper airway obstruction
• Inability to protect the airway
• Inability to clear secretions
• Facial or head surgery or trauma
• Cardiovascular instability
• Uncooperative patient

20. Noninvasive Ventilation

21. Noninvasive Ventilation
There are two methods
• Continuous positive airway pressure (CPAP)
• Provides positive airway pressure during spontaneous
breaths and it does not include any mechanical breaths
• Bilevel positive airway pressure(BiPAP): Has two
pressure levels
• Inspiratory positive airway pressure (IPAP) setting that
provides mechanical breaths and
• Expiratory positive airway pressure (EPAP) level that
functions as positive end-expiratory pressure
(PEEP).

22. Circumstances in Which Noninvasive Positive
Pressure Ventilation Should Be Changed to Invasive
Ventilation
• Respiratory arrest
• Respiratory rate >35 breaths/min
• Severe dyspnea with use of accessory muscles and paradoxical breathing
• Life-threatening hypoxemia: PaO2 < 40 mm Hg or PaO2/FIO2 < 200
• Severe acidosis (pH <7.25) and hypercapnia (PaCO2 >60 mm Hg)
• Cardiovascular complications (hypotension, shock, heart failure)
• Failure of noninvasive positive pressure ventilation

23. Invasive Positive-Pressure Ventilation

24. Mechanical Breath Terminology

25. Volume Control:
• It guarantees a specific volume delivery, regardless of
changes in lung compliance and resistance or patient effort.
• The goal of volume-targeted ventilation is to maintain a
certain level of PaCO2.
• Factors That affect Pressures During Volume-Controlled
Ventilation :
• Patient Lung Characteristics
• Inspiratory Flow Pattern
• Volume Setting
• Positive End-Expiratory Pressure (PEEP)
• Auto-PEEP

26. Pressure control:
• Allows to set a maximum pressure, which reduces the risk of
over distention of the lungs by limiting the amount of
positive pressure applied to the lung.
• The ventilator delivers a decelerating flow pattern during
pressure control ventilation
• It is considered a component of lung protective strategies.
• It also may be more comfortable for patients who can
breathe spontaneously and reduce WOB
• Disadvantages
1. Volume delivery varies.
2. Less familiar with pressure-control ventilation
3. VT and VE decrease when lung characteristics deteriorate

27. Factors that affect volume delivery during
pressure-controlled ventilation:
•Pressure Setting
•Pressure Gradient
•Patient Lung Characteristics
•Inspiratory Time
•Patient Effort

28. Trigger Variable
Time-triggered :Initiation of a mechanical breath based on
the set time interval for one complete respiratory cycle
(inspiratory time and expiratory time).
• Pressure-triggered: Initiation of
a mechanical breath based on the
drop in airway pressure that occurs
at the beginning of a spontaneous
inspiratory effort.
• Flow-triggered: Flow-triggering
strategy uses a combination of
continuous flow and demand flow.

29. Cycle Variable :
•A measurement that causes the breath to end.
• Pressure-cycled,
• Volume-cycled,
• Flow-cycled,
• Time-cycle.
• Must be measured by the ventilator and used as a feedback
signal to end inspiratory flow delivery, which then allows
exhalation to begin.

30. Basic modes of ventilation
• Controlled Mandatory Ventilation ( CMV)
• Volume controlled ventilation
• Pressure controlled ventilation
• Synchronized intermittent mandatory ventilation (SIMV)
• Spontaneous ventilation / Pressure support ventilation (
PSV)

31. Volume controlled ventilation

32. Pressure controlled ventilation

33. SIMV

34. PSV

35. Initial setting of ventilator

36. SN Setting
1 MV ( VE) Male = 4x BSA, Female 3.5 x BSA
2 TV ( V T) 4-8 ml/kg bw
3 RR VE / V T
4 FIO2 SPO2= 90-94%, PaO2=60-90mmHg
5 Flow
6 TI (Insp Time ) V T/Flow
7 T CT 60/ RR
8 Inspiratory pause
9 Peep
10 Trigger P or Flow
11 Pressure Support PIP-Pplatau /Flow

37. Volume
control
Pressure
control
Pressure
support
SIMV & PS
FIO2 + + + +
RR + +
TV + +
Insp. Pressure + +
Insp. flow + +
I:E ratio + + +
Insp. Pause + +
PEEP + + + +
Trigger + + + +
Alarms + + + +

38. Weaning from ventilator

39. Common Weaning Criteria:-

40. Weaning procedure
1.Spontaneous breathing trial (SBT):
• Use T-tube, CPAP
• Let patient breathe spontaneously for up to 30 min
• May use low level pressure support (up to 8 cm H2O) to augment
spontaneous breathing
2.SIMV :
• Reduce SIMV frequency by 1 to 3 breaths per min
• Monitor SpO2, obtain ABG as needed
3.PSV:
• In conjunction with spontaneous breathing or SIMV mode
• Start at a level of 5 to 15 cm H2O to augment spontaneous VT until a
desired VT (10 to 15 mL/kg) or spontaneous frequency (#25/min) is
reached
• Decrease pressure support level by 3 to 6 cm H2O intervals until a
level of close to 5 cm H2O is reached

41. Weaning Protocol for Mechanical Ventilation
Step 1
Does the patient show:
1. Evidence of some reversal of underlying cause?
2. Presence of inspiratory effort?
3. Hemodynamic stability?
4. Adequate oxygenation and acid-base status? (PaO2/F1O2 .150
mm Hg, PEEP <8 cm H2O and pH 7.25)
5. Light sedation or better? (brief eye contact to voice command)
If YES to all five questions, proceed to STEP 2. If NO to any one
question, postpone weaning until next day.

42. Step 2
• Is RSBI (f/VT), 100 breaths/min/L?
If YES, proceed to STEP 3. If NO, postpone weaning until next
day.
Step 3
• Can patient tolerate: Spontaneous breathing trial for up to 30
minutes without termination?
• If YES, proceed to ventilator discontinuance or evaluate for
extubation. If NO, repeat weaning until next day.

45. Q 1. Following admission to a hospital for
myocardial infarction, a 55-year-old man is
intubated and placed on ventilatory support. e
patient’s IBW is 70 kg and BSA is 1.5 m2. The
physician requests the VC-CMV mode. How
will you set the ventilator?

46. Q 2.A 65-year-old man with a history of
COPD is brought to the emergency
department complaining of severe shortness
of breath. SpO2 of 75% obtained while he was
breathing room air is very low. What will be
your next step?

47. Q 3 A 13-year-old girl with a history of severe
persistent asthma is brought to the emergency room
at 2:30 AM. Wheezing is audible without the use of a
stethoscope. A chest radiograph shows increased
radiolucency and depressed hemidiaphragms. ABGs
on a 2 L/min nasal cannula are: pH = 7.43; PaCO2 =
25 mm Hg; PaO2 = 43 mm Hg; HCO3− = 17 mEq/L.
Her SpO2 is 73%. She is started on bronchodilators
(albuterol and Atrovent) by continuous aerosol and
intravenous corticosteroids but the patient’s
condition does not improved over the next 5 hours,
in spite of therapy.

48. Q4. A 72-year-old woman with a history of COPD is
receiving NIV for ventilatory failure secondary to
postoperative pneumonia. The patient is wearing a
full facemask but is having difficulty swallowing and
coughing. She appears very weak and has become
more agitated and confused in the past hour. The
respiratory rate is 24 breaths/min, and the SpO2 is
92%. Oxygen is being bled into the patient’s mask at
the rate of 5 L/min. What action should be taken at
this time?

49. Q 5. A patient who appears to be ready for discontinuation of
ventilatory support is being weaned with SIMV. The data below
indicate the patient’s progress. No pressure-support ventilation or
continuous positive airway pressure is used to support
spontaneous breaths.
• Do you think the patient is being managed correctly during the
weaning process? If not, what would you recommend?

50. Q 6 A 76-year-old man with a history of chronic
obstructive pulmo- nary disease has been on ventilatory
support for 4 days, since he had an acute myocardial
infarction. The ventilator settings are VT = 700 mL;
SIMV rate = 8 breaths/min; FIO2 = 0.5; PEEP/ CPAP =
5 cm H2O. ABG results on these settings are: pH = 7.37;
PaCO2 =36mmHg;PaO2 =78mmHg;SpO2 =93%.
• The patient currently meets all criteria for weaning and
is placed on a T-piece. Within 10 minutes he develops
restless- ness, tachycardia, rapid, shallow breathing,
and diaphoresis. The SpO2 drops from 93% to 90%.The
patient does not complain of chest pain and has no
dysrhythmias.
• What do you think is responsible for the failed weaning
attempt?