Mechanical ventilation provides oxygen and removes carbon dioxide from the lungs using positive pressure when a patient's breathing is compromised. It is indicated to improve oxygenation, ventilation, or reduce work of breathing. Various ventilator modes exist depending on how breaths are triggered and cycled. The goal is to support the patient until their underlying condition improves enough for breathing without assistance. Adverse effects can impact the lungs, heart, gastrointestinal system, and brain, so strategies aim to prevent overdistention and repetitive opening/closing of alveoli. Weaning considers respiratory muscle strength and workload. Noninvasive ventilation can sometimes achieve the goals of mechanical ventilation without intubation.

1. Mechanical Ventilation
POS Seminar Series
December 2008
Dr. J. Wassermann
Anesthesia, Critical Care
St. Michael’s Hospital
University of Toronto

2. Outline
 Definition
– what is it
 Indications – when do you use it
 Ventilator Settings – how do you use it
 Modes of Ventilation
 Adverse Effects
 Weaning
 Specific Circumstances
 Summary

3. Mechanical Ventilation –
Definition
 Mechanical
Ventilation =
– Use of a mechanical apparatus to provide (or
augment) the requirements of a patient’s
breathing (i.e. get O2 into and CO2 out of
alveoli)

4. Mechanical Ventilation –
Definition
 Use
of positive pressure to physically
transport gases into and out of lungs
(earlier ventilators used negative pressure)
 Usually
performed via ETT but not always
(noninvasive ventilation)

5. Mechanical Ventilation
A
supportive measure – not a therapy
 Must
 Use
diagnose and treat underlying cause
ventilator to support &/or rest patient
until underlying disorder improved – and
hopefully, not cause harm in the process

6. Intubation - Indications
Airway patency (obstruction)
2. Airway protection (aspiration)
3. Oxygenation (pO2)*
1.
4.
Ventilation (pCO2)*
5.
Tracheal Toilet (secretions)
4 P’s: Patency, Protection, Positive Pressure,
Pulmonary toilet

7. Mechanical Ventilation –
Indications

Improve Oxygenation (↓pO2; ↓ SaO2)

Improve Ventilation (↑pCO2) or hyperventilation

Reduce work of breathing (WOB)
(i.e. asthma)
____________________________________________

CHF

+ Hemodynamic Instability

8. Inadequate Oxygenation
– Decreased FIO2/PIO2
– A/W obstruction
– Hypoventilation
– V/Q mismatch*
– Diffusion
– Decreased mixed venous O2 (↓DO2/↑VO2)
– RL shunt

9. Inadequate Oxygenation Decreased FIO2/PIO2
 Alveolar
Gas Equation:
PO2(alv) = [(Patm – PH2O) x FIO2] – (pCO2/RQ)
[(760 – 47) x 0.21] – (40/0.8) ~ 100 mm Hg
[(500 – 47) x 0.21] – (40/0.8) ~ 45 mm Hg

10. Inadequate Oxygenation
 V/Q
–
–
–
–
–
–
–
–
mismatch (low V/Q):
pneumonia
aspiration
pulmonary edema
atelectasis/collapse
ARDS
Pulmonary contusion
Alveolar hemorrhage
PTX/HTX/pleural effusion

11. Inadequate Ventilation
 PaCO2
∝ CO2 production
Minute Ventilation

(VE = RR x Vt)
Any condition  inadequate ventilation
 increased pCO2
Altered LOC
 NM disorders  weakness


12. Work of Breathing
 WOB
~ ventilatory demands (CO2 prod’n)
~ airway resistance (i.e. severe asthma)
~ compliance (lung, c/w, abdo)
 Increased
WOB usually  O2/CO2 problems
but:
 May need mech vent purely for WOB (i.e. asthma)

13. Summary thus far

Mechanical ventilation indicated in
situations with:
1. O2 problems (oxygenation)
2. CO2 problems (ventilation)
3. WOB (often assoc with 1 and/or 2)

Don’t always need an ETT

14. Mechanical Ventilators
 How
do you use them……

15. Ventilator Settings
 Mode
 Rate
 Volume
 Pressure
 FIO2
 PEEP
 I:E
(VT)

16. Ventilator Settings
 Flow
rate
 Flow pattern
 Alarms

17. Modes of Mechanical
Ventilation
 Spontaneous/Controlled/Dual
 Controlled
Mechanical Ventilation (CMV)
 Assist Control (AC)/Volume Control (VC)
 Intermittent Mandatory Ventilation (SIMV)
 Pressure Control (PCV)
 Pressure Support Ventilation (PSV)

18. Modes of Mechanical
Ventilation
 Trigger
 Target
 Cycle
– who/what starts a breath (pt/vent)
– what the vent is trying to achieve
– what causes the breath to end

19. Continuous Mandatory
Ventilation (CMV)
 Trigger
–Machine initiates all breaths
Patient can not initiate
 Target – Volume
 e.g.
vent gives 10 bpm @ 700cc each
pt gets zero extra breaths (even if tries)

20. Assist Control (Volume
Control)
 Trigger
– machine and patient
 Target – volume
e.g. vent gives 10 bpm @ 700cc each
pt initiates 6 bpm – vent provides 700cc

21. Synchronized Intermittent
Mandatory Ventilation (SIMV)
 Trigger
– ventilator and patient
 Target – ventilator breaths = volume
patient breaths = patient effort
 Settings-Mode: SIMV
Rate 10; Vt 700cc
FIO2 0.5; PEEP 5.0
e.g. vent gives 10 bpm @ 700cc each
patient takes 6 bpm @ 150 cc each

22. Pressure Control (PC)
 Trigger
– ventilator and patient
 Target – Pressure (above PEEP)
 Settings – Mode: PC
Rate 10; Pressure 24 cm H2O
FIO2 0.5; PEEP 5
e.g. vent gives 10 bpm to a peak Paw = 29
pt takes 6 bpm targeted to peak Paw =29

23. Pressure Support Ventilation
(PSV)
 Trigger
– patient only
 Target - pressure
 Cycle – patient flow decrease
 Settings
– Mode: PSV = 14 cm H2O
FIO2 0.4; PEEP 5
e.g. pt takes 18 bpm @ Vt = 500cc
machine gives zero breaths

24. Completely Unassisted
Breaths
 Trigger
– patient
 Cycle – patient effort ceases
 Settings:
 e.g.
CPAP 5; FIO2 0.4
patient takes 24 bpm @ 250 cc each

25. Mechanical Ventilator Settings
 Mode
 Rate
 Tidal
Volume (or Pressure)
• RR x VT = VE
 FIO2
 PEEP
(or CPAP)
 I:E (time in inspiration vs. expiration)

26. Ventilator Settings
 Flow
rate
 Flow pattern
 Alarms

27. Ventilator Settings
 e.g.
Volume Control
Rate 12
VT 500 cc
FIO2 0.9
Peep 10
I:E = 1:2

28. Choosing a Ventilatory Mode
 Initially,
 No
use mode to rest patient
benefit of any mode wrt better O2/CO2
 Use
strategy to prevent adverse effects
– Avoid overdistention
– Avoid repetitive opening and closing
– Small Vt
– High PEEP

29. Noninvasive Ventilation

1.
2.
3.
4.
5.
Indications for intubation:
Airway patency*
Airway protection (aspiration)*
Oxygenation
Ventilation
Tracheal suctioning (toilet)*

30. Noninvasive Ventilation
 Avoids
intubation and complications
 Can deliver various modes of ventilation
– CPAP/CPAP + PSV most common
 Indications:
– hypercapneic respiratory failure (COPD exac)
– cardiogenic p. edema

31. Noninvasive Ventilation
 Contraindications:
– Inability to cooperate (i.e. confusion)
– Altered LOC (unless 2. ↑pCO2 from COPD)
– Inability to clear secretions
– Hemodynamic instability

32. Adverse Effects of Mechanical
Ventilation
 Pulmonary:
– Intubation effects
– Air leaks
– Ventilator-induced lung injury
– Ventilator-associated pneumonia
– Dynamic hyperinflation/Auto-PEEP

33. Adverse Effects of Mechanical
Ventilation
 Cardiovascular:
–
–
–
–
Hypotension
Increased CVP (↑intrathoracic pressure)
Decreased venous return
Increased RV afterload
 GI:
– Stress ulcers/GI bleeding

34. Adverse Effects of Mechanical
Ventilation
 CNS:
– ↑ ICP
– Prolonged sedation
– NMB’s (myopathies/neuropathies)

35. Weaning from Mechanical
Ventilation
 Once
underlying pathology improves
 Need
to ensure:
– Adequate respiratory muscle strength
– WOB not excessive
Ventilatory demands
 Resistance
 Compliance


36. Weaning from Mechanical
Ventilation
 Volume
overload and myocardial ischemia
common causes of failure to wean
 RR/Vt
= good predictor if <80-100
 SIMV
inferior to SV trials or CPAP/PSV

37. Ventilation Strategies in
Specific Situations
 ARDS
 Asthma
 Increased
intraabdominal pressure

38. Summary

Mechanical ventilation used to:
1. Improve oxygenation
2. Improve ventilation (CO2 removal)
3. Unload respiratory muscles

A support until patients condition
improves

39. Summary
 Different
modes for ventilation
– differ in how breaths are initiated, ended and
assisted
– differ in independent and dependant variables
(i.e. what machine controls and what it doesn’t)
– no proven advantage of one mode
– use ventilator strategies to avoid volutrauma
and other adverse effects

40. Questions?