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Mechanical VentilationMechanical Ventilation POS Seminar Series
December 2008
Dr. J. Wassermann
Anesthesia, Critical Care
St. Michael’s Hospital
University of Toronto
OutlineOutlineDefinition – what is itIndications – when do you use itVentilator Settings – how do you use itModes of VentilationAdverse EffectsWeaningSpecific CircumstancesSummary
Mechanical Ventilation – Mechanical Ventilation – DefinitionDefinition
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)
Mechanical Ventilation – Mechanical Ventilation – DefinitionDefinition
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)
Mechanical VentilationMechanical 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
Intubation - IndicationsIntubation - Indications
1. Airway patency (obstruction)
2. Airway protection (aspiration)
3. Oxygenation (pO2)*
4. Ventilation (pCO2)*
5. Tracheal Toilet (secretions)
4 P’s: Patency, Protection, Positive Pressure, Pulmonary toilet
Mechanical Ventilation – Mechanical Ventilation – IndicationsIndications
Improve Oxygenation (pO2; SaO2)
Improve Ventilation (pCO2) or hyperventilation
Reduce work of breathing (WOB)(i.e. asthma)____________________________________________
CHF
+ Hemodynamic Instability
Inadequate OxygenationInadequate Oxygenation
– Decreased FIO2/PIO2
– A/W obstruction– Hypoventilation– V/Q mismatch*– Diffusion– Decreased mixed venous O2 (DO2/VO2)– RL shunt
Inadequate Oxygenation - Inadequate Oxygenation - Decreased FIODecreased FIO22/PIO/PIO22
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
Inadequate OxygenationInadequate OxygenationV/Q mismatch (low V/Q):
– pneumonia– aspiration– pulmonary edema– atelectasis/collapse– ARDS– Pulmonary contusion– Alveolar hemorrhage– PTX/HTX/pleural effusion
Inadequate VentilationInadequate Ventilation
PaCO2 CO2 production Minute Ventilation (VE = RR
x Vt)
Any condition inadequate ventilation
increased pCO2 Altered LOC NM disorders weakness
Work of BreathingWork 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)
Summary thus farSummary 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
Mechanical VentilatorsMechanical Ventilators
How do you use them……
Ventilator SettingsVentilator Settings
ModeRateVolume (VT)PressureFIO2
PEEPI:E
Ventilator SettingsVentilator Settings
Flow rateFlow patternAlarms
Modes of Mechanical Modes of Mechanical VentilationVentilation
Spontaneous/Controlled/DualControlled Mechanical Ventilation (CMV)Assist Control (AC)/Volume Control (VC)Intermittent Mandatory Ventilation (SIMV)Pressure Control (PCV)Pressure Support Ventilation (PSV)
Modes of Mechanical Modes of Mechanical VentilationVentilation
Trigger – who/what starts a breath (pt/vent)
Target – what the vent is trying to achieve
Cycle – what causes the breath to end
Continuous Mandatory Continuous Mandatory Ventilation (CMV)Ventilation (CMV)
Trigger –Machine initiates all breaths
Patient can not initiateTarget – Volumee.g.
vent gives 10 bpm @ 700cc each
pt gets zero extra breaths (even if tries)
Assist Control (Volume Assist Control (Volume Control)Control)
Trigger – machine and patientTarget – volume
e.g. vent gives 10 bpm @ 700cc each
pt initiates 6 bpm – vent provides 700cc
Synchronized Intermittent Synchronized Intermittent Mandatory Ventilation (SIMV)Mandatory Ventilation (SIMV)
Trigger – ventilator and patientTarget – ventilator breaths = volume
patient breaths = patient effortSettings-Mode: SIMV
Rate 10; Vt 700cc
FIO2 0.5; PEEP 5.0e.g. vent gives 10 bpm @ 700cc each
patient takes 6 bpm @ 150 cc each
Pressure Control (PC)Pressure Control (PC)
Trigger – ventilator and patientTarget – 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
Pressure Support Ventilation Pressure Support Ventilation (PSV)(PSV)
Trigger – patient onlyTarget - pressureCycle – patient flow decrease
Settings – Mode: PSV = 14 cm H2O FIO2 0.4; PEEP 5
e.g. pt takes 18 bpm @ Vt = 500ccmachine gives zero breaths
Completely Unassisted Completely Unassisted BreathsBreaths
Trigger – patientCycle – patient effort ceases
Settings: CPAP 5; FIO2 0.4
e.g. patient takes 24 bpm @ 250 cc each
Mechanical Ventilator SettingsMechanical Ventilator Settings
ModeRateTidal Volume (or Pressure)
• RR x VT = VE
FIO2
PEEP (or CPAP)I:E (time in inspiration vs. expiration)
Ventilator SettingsVentilator Settings
Flow rateFlow patternAlarms
Ventilator SettingsVentilator Settings
e.g.
Volume Control
Rate 12
VT 500 cc
FIO2 0.9
Peep 10
I:E = 1:2
Choosing a Ventilatory ModeChoosing 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
Noninvasive VentilationNoninvasive Ventilation
Indications for intubation:
1. Airway patency*
2. Airway protection (aspiration)*
3. Oxygenation
4. Ventilation
5. Tracheal suctioning (toilet)*
Noninvasive VentilationNoninvasive Ventilation
Avoids intubation and complicationsCan deliver various modes of ventilation
– CPAP/CPAP + PSV most common
Indications:– hypercapneic respiratory failure (COPD exac)– cardiogenic p. edema
Noninvasive VentilationNoninvasive Ventilation
Contraindications:– Inability to cooperate (i.e. confusion)
– Altered LOC (unless 2. pCO2 from COPD)– Inability to clear secretions– Hemodynamic instability
Adverse Effects of Mechanical Adverse Effects of Mechanical VentilationVentilation
Pulmonary:– Intubation effects– Air leaks – Ventilator-induced lung injury– Ventilator-associated pneumonia– Dynamic hyperinflation/Auto-PEEP
Adverse Effects of Mechanical Adverse Effects of Mechanical VentilationVentilation
Cardiovascular:– Hypotension– Increased CVP (↑intrathoracic pressure)– Decreased venous return– Increased RV afterload
GI:– Stress ulcers/GI bleeding
Adverse Effects of Mechanical Adverse Effects of Mechanical VentilationVentilation
CNS:– ↑ ICP– Prolonged sedation– NMB’s (myopathies/neuropathies)
Weaning from Mechanical Weaning from Mechanical VentilationVentilation
Once underlying pathology improves
Need to ensure:– Adequate respiratory muscle strength– WOB not excessive
Ventilatory demands Resistance Compliance
Weaning from Mechanical Weaning from Mechanical VentilationVentilation
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
Ventilation Strategies in Ventilation Strategies in Specific SituationsSpecific Situations
ARDSAsthmaIncreased intraabdominal pressure
SummarySummary
Mechanical ventilation used to:1. Improve oxygenation
2. Improve ventilation (CO2 removal)
3. Unload respiratory muscles
A support until patients condition improves
SummarySummary
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
Questions?Questions?
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