Mechanical Ventilation

1
Mechanical Ventilation

• POS Seminar SeriesDecember 2008
• Dr. J. Wassermann
• Anesthesia, Critical Care
• St. Michaels 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 patients
  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 /or rest patient until
  underlying disorder improved and hopefully, not
  cause harm in the process

6
Intubation - Indications

• Airway patency (obstruction)
• Airway protection (aspiration)
• Oxygenation (pO2)
• Ventilation (pCO2)
• Tracheal Toilet (secretions)
• 4 Ps 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 prodn)
• 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
• O2 problems (oxygenation)
• CO2 problems (ventilation)
• WOB (often assoc with 1 and/or 2)
• Dont always need an ETT

14
Mechanical Ventilators

• How do you use them

15
Ventilator Settings

• Mode
• Rate
• Volume (VT)
• Pressure
• FIO2
• PEEP
• IE

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 who/what starts a breath (pt/vent)
• Target what the vent is trying to achieve
• Cycle 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 _at_ 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 _at_ 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 _at_ 700cc each
• patient takes 6 bpm _at_ 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 _at_ 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 24 bpm _at_ 250 cc each

25
Mechanical Ventilator Settings

• Mode
• Rate
• Tidal Volume (or Pressure)
• RR x VT VE
• FIO2
• PEEP (or CPAP)
• IE (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
• IE 12

28
Choosing a Ventilatory Mode

• Initially, use mode to rest patient
• No 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

• 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
• NMBs (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 lt80-100
• 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
• Improve oxygenation
• Improve ventilation (CO2 removal)
• 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 doesnt)
• no proven advantage of one mode
• use ventilator strategies to avoid volutrauma
• and other adverse effects

40
Questions?