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Mechanical Ventilation

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Alveolar Gas Equation: PO2(alv) = [(Patm PH2O) x FIO2] (pCO2/RQ) ... Alveolar hemorrhage. PTX/HTX/pleural effusion. Inadequate Ventilation. PaCO2 CO2 production ... – PowerPoint PPT presentation

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Title: 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
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