Title: Mechanical Ventilation
1Mechanical Ventilation
2Overview
- Intro
- NIV
- Basic Modes
- Settings
- Specific Conditions
- Ventilators
- Other modes
3Acute respiratory failure
- Hypoxia (PO2 lt 60mmHg)
- Low inspired O2
- Hypoventilation CNS, peripheral neuro, muscles,
chest wall - V/Q mismatch
- Shunt pneumonia, APO, collapse, contusions
- Alveoli perfused but not ventilated
- Venous admixture
- Anatomical shunt cardiac anomaly
- Increased dead space (hypercapnia)
hypovolaemia, PE, poor cardiac function - Diffusion abnormality severe destructive
disease of the lung fibrosis, severe APO, ARDS - Hypercapnia (PCO2 gt50mmHg)
- Hypoventilation
- Dead space ventilation
- Increased CO2 production
4Shunt
5Mechanical Ventilation
- Pump gas in and letting it flow out
- Function
- Gas exchange
- Manage work of breathing
- Avoid lung injury
- Physics
- Flow needs a pressure gradient
- Pressure to overcome airway resistance and
inflate lung - Pressure (to overcome resistance) Flow x
Resistance - Alveolar pressure (Volume/Compliance) PEEP
- Airway pressure (Flow x Resistance) (V/C)
PEEP
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9Gas Exchange
- Oxygenation get O2 in
- FiO2
- Ventilation (minor effect) alveolar gas
equation, CO2 effect - Mean alveolar pressure
- Mean airway pressure surrogate marker, affected
by airway resistance - Pressure over inspiration expiration
- Set Vt or inspiratory pressure
- Inspiratory time
- PEEP
- Reduce shunt
- Re-open alveoli PEEP
- Prolonging inspiration improve ventilation of
less compliant alveoli - Ventilation get CO2 out
- Alveolar ventilation RR x (Tidal volume Dead
space)
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11Adverse Effects
- Barotrauma
- High alveolar pressure
- High tidal volume
- Shear injury
- Repetitive collapse re-expansion of alveoli
- Tension at interface between open collapsed
alveoli - Pneumothorax, pneumomediastinum, surgical
emphysema, acute lung injury - Gas trapping
- Insufficient time for alveoli to empty
- Increase risk
- Airflow obstruction asthma, COPD
- Long inspiratory time
- High respiratory rate
- Progressive
- Hyperinflation
- Rise in end-expiratory pressure intrinsic-PEEP,
auto-PEEP - Result Barotrauma, Cardiovascular compromise
(high intrathoracic pressure) - Oxygen toxicity
- Acute lung injury due to high O2 concentrations
12Gas Trapping
13NIV
- CPAP
- Similar to PEEP
- Splint alveoli open reduce shunt
- Spontaneous breathing at elevated baseline
pressure - BiPAP
- Ventilatory assistance without invasive
artificial airway - Fitted face/nasal mask
- Initial settings 10/5
14NIV
15NIV
- Indicator of success
- Known benefits
- Younger age
- Lower APACHE score
- Cooperative
- Intact dentition
- Moderate hypercarbia (pHlt7.35, gt7.10)
- Improvement within first 2 hrs
- Contraindications
- Cardiac/Resp arrest
- Non-respiratory organ failure
- Encephalopathy GCS lt10
- GIH
- Haemodynamically unstable
- Facial or neurological surgery, trauma or
deformity - High aspiration risk
- Prolonged ventilation anticipated
- Recent oesophageal anastamosis
16NIV Benefits
- General
- COPD
- Cardiogenic pulmonary oedema
- Hypoxaemic respiratory failure
- Asthma
- Post-extubation
- Immunocompromised
- Other diseases
17What is a Mode?
- 3 components
- Control variable
- Pressure or volume
- Breath sequence
- Continuous mandatory
- Intermittent mandatory
- Continuous spontaneous
- Targeting scheme (settings)
- Vt, inspiratory time, frequency, FiO2, PEEP, flow
trigger
18Volume Control Ventilation
- Set tidal volume
- Minimum respiratory rate
- Assist mode both ventilator and patient can
initiate breaths - Advantage
- Simple, guaranteed ventilation, rests respiratory
muscle - Disadvantages
- Not synchronised ventilator breath on top of
patient breath - Inadequate flow patient sucks gas out of
ventilator - Inappropriate triggering
- Decreased compliance high airway pressure
- Requires sedation for synchrony
19VCV
20Pressure Control Ventilation
- Set inspiratory pressure
- Constant pressure during inspiration
- High initial flow
- Inspiratory pause built in
- Advantages
- Simple, avoids high inspiratory pressures,
improved oxygenation - Disadvantages
- Not synchronised
- Inappropriate triggers
- Decreased compliance reduced tidal volume
21PCV
22Pressure Support
- Set inspiratory pressure
- Patient initiates breath
- Back-up mode apnoea
- Cycle from inspiration to expiration
- Inspiratory flow falls below set proportion of
peak inspiratory flow - Advantages
- Simple, avoids high inspiratory pressure,
synchrony, less sedation, better haemodynamics - Disadvantages
- Dependent on patient breaths
- Affected by changes in lung compliance
23PS
24Synchronised Intermittent Mandatory Ventilation
- Mandatory breaths VCV, PCV
- Patient breaths depends on SIMV cycle
- Synchronised mandatory breath
- Pressure support breath
- Advantages
- Synchrony, guaranteed minute ventilation
- Disadvantages
- Sometimes complicated to set
25SIMV
26VCV vs PCV
27VCV vs PCV
28VCV vs PCV - Advantages
- PCV PS
- Variable flow
- Reduced WOB
- Max Palveolar Max Pairway (or less)
- Palveolar controlled
- Variable I-time pattern (PS)
- Better with leaks
- VCV
- Consistent TV
- changing impedance
- Auto-PEEP
- Minimum min. vent. (f x TV) set
- Variety of flow waves
29VCV vs PCV - Disadvantages
- PCV PS
- Variable tidal volume
- Too large or too small
- No alarm/limit for excessive TV (except some new
gen. vents) - Some variablity in max pressures (PC, expir.
effort)
- VCV
- Variable pressures
- airway
- alveolar
- Fixed flow pattern
- Variable effort variable work/breath
- Compressible vol.
- Leaks vol. loss
30Settings
- FiO2 start at 1.0
- RR average 12, higher for those with
sepsis/acidosis - Tidal volume 500ml, 8ml/kg, smaller volumes in
ARDS - Inspiratory pressure - lt30cmH2O, sum of PEEP
Pinsp - Inspiratory time
- IE normally 12, simulates normal breathing
synchrony - PCV easy to set
- VCV complicated, Time Volume/Flow
- PEEP
- Start at 5cmH2O
- Higher APO, ARDS
- Lower asthma, COPD
- Triggering
- Flow triggering more sensitive, synchrony,
-2cmH2O - Pressure triggering
- Inappropriate triggering triggering when no
patient effort - Oxygenation
- ?FiO2, ?PEEP?, ?Insp Time, ?InspP, ?Insp pause
- Problems CVS effects, gas trapping, barotrauma
31Troubleshooting
- Airway pressure
- Ventilator settings, malfunction
- Circuit kinking, water pooling, wet filter
- ETT kinked, obstructed, endobronchial
intubation - Patient bronchospasm, ?compliance (lungm,
pleura, chest wall), dysynchrony, coughing - Inspiratory pause pressure - Estimate of alveolar
pressure - Tidal volume
- Reduced respiratory acidosis
- Monitor in PCV/PS
- Changes in compliance anywhere in system
- Expired Vt more accurate
- Minute ventilation determined by RR Vt
- Apnoea important in PS
- Intrinsic PEEP (gas trapping)
- Expiratory pause hold
- Hypotension after initiating IPPV
- Hypovolaemia/Reduced VR
- Drugs
- Gas trapping disconnect
32Troubleshooting
- Desaturation
- Patient causes
- All causes of hypoxic respiratory failure
- Endobronchial intubation, PTx, collapse, APO,
bronchospasm, PE - Equipment causes
- FIO2 1.0
- Sat O2 waveform
- Chest moving?
- Yes Examine patient, treat cause
- No Manually ventilate
- No ETT/Patient problem
- Yes Ventilator problem setting, failure, O2
failure
33Ventilators
- Maquet
- VCV
- PCV
- PRVC
- PS/CPAP
- SIMV (VC) PS
- SIMV (PC) PS
- SIMV (PRVC) PS
- MMV
- NAVA
- Evita
- PS
- PCV
- SIMV
- PCVA
- Autoflow
34Adaptive Modes - PRVC
- PCV unable to deliver guaranteed minimum minute
ventilation - Changing lung mechanics patient effort
- Pressure controlled breaths with target tidal
volume - Inspiratory pressure adjusted to deliver minimum
target volume - Not VCV - average minimum tidal volume guaranteed
- Like PCV constant airway pressure, variable
flow (flow as demanded by patient)
35Adaptive Modes - PRVC
- Consistent tidal volumes
- Promotes inspiratory flow synchrony
- Automatic weaning
- Inappropriate increased respiratory drive, eg
severe metabolic acidosis - Evidence lower peak inspiratory pressures
36VCV vs PRVC
37Adaptive Modes - Autoflow
- First breath uses set TV I-time
- Pplateau measured
- Pplateau then used
- V/P measured each breath
- Press. changed if needed (/- 3)
- Dual mode similar to PRVC
- Targets vol., applies variable press. based on
mechanics measurements - Allows highly variable inspiratory flows
- Time ends mandatory breaths
- Adds ability to freely exhale during mandatory
inspiration (maintains pressure)
38PCV Assist
- Like PCV, flow varies automatically to varying
patient demands - Constant press. during each breath - variable
press. from breath to breath - Mandatory patient breaths the same
39Inverse Ratio Ventilation
- Increased mean airway pressure
- Prolonged IE ratio
- Improved oxygenation
- Reduced shunting
- Improved V/Q matching
- Decreased dead space
- Heavy sedation, paralysis
- Preferred PCV
- Benefit no effect in mortality in ARDS
40Other Modes
- Adaptive support ventilation
- Mandatory minute ventilation
- Adaptive pressure control
- Proportional assist ventilation
- Pressure support (spontaneous breaths)
- Pressure applied function of patient effort
- Automatic tube compensation
- adjusts its pressure output in accordance with
flow, theoretically giving an appropriate amount
of pressure support
41Airway Pressure-Release Ventilation
- High constant PEEP intermittent releases
- Unrestricted spontaneous breaths reduced
sedation - Extreme form of inverse ratio ventilation
- EI 14
- Spontaneous breaths 10-40 total minute
ventilation
42APRV
- Settings 2 pressure levels, 2 time durations
- Uses ALI, ARDS
- Caution COPD, increased respiratory drive
43APRV
- Increase mean airway pressure
- Alveolar recruitment, improve oxygenation
- Promote spontaneous breathing
- Improved V/Q match, haemodynamics
- Improved synchrony
- Evidence no difference in mortality, decreased
duration of ventilation
44High-Frequency Ventilation
- 4 types
- High frequency jet ventilation
- Ventilation by jet of gas
- 14-16G cannula, specialised ventilator
- 35 psi, RR100-150, Insp 40
- High frequency oscillatory ventilation
- High frequency percussive ventilation
- HFV PCV
- HFOV oscillating around 2 pressure levels
- Less sedation, better clearance of secretions
- High frequency positive pressure ventilation
- Conventional ventilation at setting limits
45High Frequency Oscillatory Ventilation
- Ventilator delivers a constant flow (bias flow)
- Valve creates resistance maintain airway
pressure - Piston pump oscillates 3-15Hz (RR160-900)
- Chest wiggle assess amplitude
- Tidal volumes less than dead space
- Ventilation achieved by laminar flow
- Deep sedation, paralysis
46HFOV
- CO2 clearance
- Decrease oscillation frequency, increase
amplitude, increase inspiratory time, increase
bias flow (with ETT cuff leak) - Oxygenation
- Mean airway pressure, FiO2
- Settings
- Airway pressure amplitude
- Mean airway pressure
- inspiration
- Inspiratory bias flow
- FiO2
47HFOV
- Applications
- ARDS
- Lung protection highest mean airway pressure
lowest tidal volumes - Ventilatory failure FiO2gt0.7, PEEPgt14, pH
lt7.25, Vt gt6ml/kg, plateau pressure gt30) - Contraindicated
- Severe airflow obstruction
- Intracranial hypertension
- Evidence
- Animal models less histologic damage lung
inflammation - Better oxygenation as rescure therapy in ARDS
- No difference in mortality
48Mean Airway Pressure
- Main factor in recruitment and oxygenation
- Increased surface area for O2 diffusion
- Problems
- Barotrauma
- Haemodynamic instability
- Contraindicated patients
- Deep sedation, paralysis
49Specific Conditions
- ARDS
- Definition
- Diffuse bilateral pulmonary infiltrates
- No clinical evidence of Left Atrial Hypertension
(CWPlt18mmHg) - PaO2/FiO2 of 300 or less
- Exclusions
- Unilateral lung disease
- Children (wt less than 25kg)
- Severe obstructive lung disease (asthma, COPD)
- Raised intracranial pressure
- High PEEP, low volumes pressure
- SIMV(PRVC) PS
- Vt 6ml/gk check plateau pressure
- Pins gt30cmH2O reduce Vt
- Lowest plateau pressure possible
- RR 6-35, aim pH 7.3-7.45
- Evidence improved mortality
FiO2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
PEEP 5 5-8 8-10 10 10-14 14 14-18 18-22
50Ventilator Induced Lung Injury
- Excessive inflation pressure
- Mechanical tissue damage
- Inflammation mechano-signaling due to tensile
forces - Overstretching of lung units
- Shear force at junction of open and collapsed
tissue - Repeated opening and closing of small airways
under high pressure
51Pathways to VILI
End-Expiration
Moderate Stress/Strain
Tidal Forces (Transpulmonary and Microvascular
Pressures)
Extreme Stress/Strain
Rupture
Signaling
Mechano signaling via integrins, cytoskeleton,
ion channels
inflammatory cascade
Cellular Infiltration and Inflammation
Marini / Gattinoni CCM 2004
52Spectrum of Regional Opening Pressures (Supine
Position)
Superimposed Pressure
Lung Units at Risk for Tidal Opening Closure
53Lung Protection Strategies
- Heterogenous lung units
- PEEP
- Tidal volume
- Keep the lung as open as possible without
generating excessive regional tissue stresses is
a major goal of modern practice
54Prone Ventilation
- Homogenise transpleural pressure
- Compression reduced compression from heart
abdomen - Improved recruitment
- Increase in FRC
- Decreased shunt
- Benefit
- Improved oxygenation in 60-80 patient, even on
return to supine position - No change mortality
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56Recruitment Manoeuvres
- Open collapsed lung tissue so it can remain open
during tidal ventilation with lower pressures and
PEEP, thereby improving gas exchange and helping
to eliminate high stress interfaces - Although applying high pressure is fundamental to
recruitment, sustaining high pressure is also
important - Methods of performing a recruiting maneuver
include single sustained inflations and
ventilation with high PEEP
57Three Types of Recruitment Maneuvers
58Specific Conditions
- Unilateral lung disease
- Similar approach to ARDS
- Increase Insp time improve gas distribution
- Lateral position normal lung down
- Reduce shunt
- Reduce normal lung compliance
- Risk of contamination
- Independent lung ventilator
- Asthma
- Maximise expiratory time, low RR permissive
hypercarbia - Short inspiratory time
- High airway pressure - ?significance
- Expiratory hold
- Aim PEEPi lt 10cmH20, Pplat lt20cmH2O
- COPD
- Similar to asthma
- Bronchospasm not as great, reduced lung compliance
59Airway Obstruction
- Aim relieve work of breathing, minimise
auto-PEEP - Gas trapping
- Increases work of breathing
- Haemodynamic compromise
- Predisposes to barotrauma
- Decreases ventilation
- PEEP
- Effects Depend on Type and Severity of Airflow
Obstruction - Generally Helpful if PEEP ? Original Auto-PEEP
- Potential Benefits
- Decreased Work of Breathing
- Increased VT
- Improved Distribution of Ventilation
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62NAVA
- Neurally adjusted ventilatory assist
- Controls ventilator output by measuring the
neural traffic to the diaphragm - NAVA senses the desired assist using an array of
esophageal EMG electrodes positioned to detect
the diaphragms contraction signal - Flexible response to effort
- Improves synchrony and weaning
63Neural Control of Ventilatory Assist (NAVA)
Ideal Technology
Central Nervous System ? Phrenic
Nerve ? Diaphragm Excitation ? Diaphragm
Contraction ? Chest Wall and Lung
Expansion ? Airway Pressure, Flow and Volume
New Technology
Ventilator Unit
Neuro-Ventilatory Coupling
Current Technology
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65- References
- Cleveland clinic journal of medicine 2009 76(7)
417-430 - UpToDate
- BASIC course notes
- Wests Respiratory Essentials
- Links
- http//emedicine.medscape.com/
- http//www.anaesthetist.com/anaes/vent/Findex.htm
index.htm - http//en.wikipedia.org/wiki/Mechanical_ventilatio
n - http//www.merck.com/mmpe/sec06/ch065/ch065b.html
- http//www.ccmtutorials.com/rs/index.htm
- http//www.aic.cuhk.edu.hk/web8/mechanical_ventila
tion.htm