1. Mechanical Ventilation
POS Seminar Series December 2010
Dr. J. Wassermann
Department of Anesthesia
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
Summary

3. Mechanical Ventilation – Definition
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 diagnose and treat underlying cause
Use ventilator to support patient until underlying disorder improved – and try not to cause harm in the process

6. Intubation - Indications
Airway patency (obstruction)
Airway protection (aspiration)
Oxygenation (pO2)*
Ventilation (pCO2)*
Tracheal Toilet (secretions)
* don’t necessarily need intubation for these

7. Mechanical Ventilation – Indications
Improve Oxygenation (pO2;  SaO2)
Improve Ventilation (pCO2) - or hyperventilate pt
Reduce work of breathing (WOB)
(i.e. asthma; COPD)
____________________________________________
CHF
Hemodynamic Instability

8. Inadequate Oxygenation
Decreased FIO2/PIO2
A/W obstruction
Hypoventilation
V/Q mismatch*
Diffusion
Decreased mixed venous O2
RL shunt (i.e. intra-cardiac shunt)

9. Alveolar Gas Equation PALVO2 = [(PATM – PH2O) × FIO2] – (PCO2 ) RQ
NOTE: On 100% O2 , PALVO2 should be ~ 650

10. Inadequate Oxygenation
V/Q mismatch (low V/Q):
Pneumonia
Aspiration
Pulmonary edema
Atelectasis/collapse (plug/PTX/HTX/effusions)
ARDS
Pulmonary contusion
Alveolar hemorrhage

11. Inadequate Ventilation
PaCO2  CO2 production
Minute Ventilation (VE )
VE = RR x Vt
Any condition  inadequate ventilation
 increased pCO2
Altered LOC
S. cord injuries/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;
May need mech vent purely for WOB (i.e. asthma)
c/w = chest wall

13. Summary thus far Mechanical ventilation indicated in situations with:
O2 problems (oxygenation)
CO2 problems (ventilation)
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 (VT) Pressure FIO2 PEEP
I:E (ratio of insp vs exp time)
Insp Flow rate
Flow pattern
Alarms

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

17. Modes of Mechanical Ventilation
Trigger – what initiates a breath
Target – what the vent is trying to achieve
Cycle – what causes the breath to end

18. Continuous Mandatory Ventilation (CMV)
Trigger –Ventilator initiates all breaths
Patient can not initiate
Target – Volume
Cycle - Time

19. Continuous Mandatory Ventilation (CMV)
e.g. Settings - Mode: CMV
Rate 10; Vt 700cc
FIO2 0.5; PEEP 5.0
vent gives cc each
pt gets zero extra breaths (even if tries)
very uncomfortable for pt
only used if pt paralyzed (i.e. in O.R.)

20. Assist Control (Volume Control)
Trigger – machine and patient
Target – volume
Settings-Mode: VC
Rate 10; Vt 700cc
FIO2 0.5; PEEP 5.0
e.g. vent gives cc each
pt initiates 6 bpm – vent provides 700cc

21. Synchronized Intermittent Mandatory Ventilation (SIMV)
Trigger – ventilator and patient
Target – ventilator breaths = set volume
patient breaths = patient effort
Settings-Mode: SIMV
Rate 10; Vt 700cc
FIO2 0.5; PEEP 5.0
e.g. vent gives cc each
patient takes 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 Vt = 500cc
machine gives zero breaths

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

25. Mechanical Ventilator Settings
Mode (usually VC or PC to start)
Rate
Tidal Volume (VC) [or Pressure (PC)]
FIO2
PEEP
I:E

26. Choosing a Ventilatory Mode
No proven benefit of any mode of another
Keys are to:
Support pt to allow time for underlying process to improve
Avoid/minimize adverse effects of mech ventilation

27. Adverse Effects of Mechanical Ventilation
Pulmonary:
Intubation effects
Air leaks (pneumothorax/BPF)
Ventilator-associated lung injury
Ventilator-associated pneumonia
Dynamic hyperinflation/Auto-PEEP

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

29. Adverse Effects of Mechanical Ventilation
Neuro/muscular:
↑ ICP
Prolonged sedation
Myopathies/Neuropathies

30. Ventilator-Associated Lung Injury (VALI)
Volutrauma
Barotrauma
Atelectotrauma
Biotrauma

31. Ventilator-Associated Lung Injury (VALI)
Volutrauma – overdistension of alveoli
Barotrauma – high alveolar pressures
Atelectotrauma – repetitive opening and closing of alveoli
Biotrauma – release of infl mediators into systemic circulation  organ dysfunction

33. Ventilation of ARDS (baby lung)
Moderate PEEP (to keep alveoli open)
10 – 15 cm H20
Small Vt’s (to avoid overdistension)
< 6 cc/kg
Plateau pressure < 30 cm H2O
Permissive hypercapnia & hypoxemia

34. Summary Mechanical ventilation used to:
Improve oxygenation
Improve ventilation (CO2 removal)
Unload respiratory muscles
A support until patients condition improves

35. 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 lung injury
and other adverse effects

36. Questions?

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

38. 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

39. Noninvasive Ventilation
Indications for intubation:
Airway patency*
Airway protection (aspiration)*
Oxygenation
Ventilation
Tracheal suctioning (toilet)*

40. 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

41. Noninvasive Ventilation
Contraindications:
Inability to cooperate (i.e. confusion)
Altered LOC
Inability to clear secretions
Hemodynamic instability

42. Ventilation Strategies in Specific Situations
ARDS
Asthma
Increased intraabdominal pressure