MECHANICAL
VENTILATION
• Phunsup Wongsurakiat, MD, FCCP
• Division of Respiratory Disease and TB
• Department of Medicine, Siriraj Hospital
Mechanical VentilationMechanical Ventilation
• Invasive (intubation)• Non-invasive (other interface such as face mask):
- negative pressure
- positive pressure
Inspiratory Hold: PIP and Plateau pressures (VC)
Plateau
Peak Pressure
Inspiratory Hold
Proximal airway pressure
DISTENDING PRESSURESDISTENDING PRESSURESPlat P - Base P (PEEP) = pressure to distend resp systemPlat P - Base P (PEEP) = pressure to distend resp system
(lung + chest wall)(lung + chest wall)Plat P = peak alveolar pressure Plat P = peak alveolar pressure Transpulmonary pressure = Plat P – Pleural pressure Transpulmonary pressure = Plat P – Pleural pressure
35 cm H2O 35 cm H2O
5 cm H2O 10 cm H2O
30 cm H2O 25 cm H2O
Influence of chest wall Influence of chest wall stiffnessstiffness
FLOW Resistance (R)FLOW Resistance (R)Peak P - PlatP = pressure for flowPeak P - PlatP = pressure for flowR = Flow/(PeakP - Plat P)R = Flow/(PeakP - Plat P)
Physiology of RespirationPhysiology of Respiration
O2 consumption (VO2) ≈ 250 mL/ minO2 consumption (VO2) ≈ 250 mL/ min CO2 production (CO2 production (VCO2) ≈ 200 mL/ minVCO2) ≈ 200 mL/ min Cardiac output (CO) ≈ 5 L/minCardiac output (CO) ≈ 5 L/min Minute ventilation = RR X VT ≈ 5 - 8 L/min VT ≈ 5 - 8 mL / kg RR ≈ 12 - 20 bpm PaCO2 = 35-45 mmHg pH = 7.35-7.45
Physiology of RespirationPhysiology of Respiration
PAOPAO2 = 2 = PIOPIO22 – – PaCOPaCO22 / R / R
[PIO2 = FIO2 x (barometric pressure – 47)][PIO2 = FIO2 x (barometric pressure – 47)]
PaCO2 = k x VCO2 / VAPaCO2 = k x VCO2 / VA
Mechanical VentilationMechanical Ventilation
VariablesVariables
ModeMode
ObjectivesObjectives
Clinical settingsClinical settings
ComplicationsComplications
Mechanical VentilationMechanical VentilationVariablesVariables
Tidal volumeTidal volume
RateRate
Total time (inversely related to rate):Total time (inversely related to rate):
- inspiratory time (adjustable)- inspiratory time (adjustable)
- expiratory time (total time - inspiratory - expiratory time (total time - inspiratory time)time)
Flow (tidal volume / inspiratory time) Flow (tidal volume / inspiratory time)
Minute ventilationMinute ventilation
Minute ventilation
beginning of inspirationbeginning of inspiration
end of inspirationend of inspiration--beginning of expirationbeginning of expiration
total breath durationtotal breath duration
tidal volumetidal volumeVVTT tidal volumetidal volume
f breaths/ minute
VVEE = = VVTT * * ff
VVEE = = 500500 ml ml * * 1212
VVTT = = 500500 mlml
f f = = 1212 breathsbreaths//minuteminute
= = 66 LL
Mechanical VentilationMechanical VentilationVariablesVariables
Trigger sensitivityTrigger sensitivity
FiO2FiO2
Pressure: Pressure:
- peak pressure- peak pressure
- plateau pressure- plateau pressure
ComplianceCompliance
Monitoring Lung MechanicsMonitoring Lung Mechanics
Proximal Airway Pressures (end-inspiratory)
1. Peak Pressure Pk
Function of: Inflation volume, recoil force of
lungs and chest wall, airway resistance
2. Plateau Pressure Pl
Occlude expiratory tubing at end-inspiration
Function of elastance alone
LUNG COMPLIANCE CALCULATION
• Static & Dynamic Compliance Measurements:– STATIC COMPLIANCE:
• measured when there is no airflow (plateau pressure-PEEP), since airflow is absent, airway resistance is not a determining factor in the calculation.
• Static compliance reflects the elastic properties of the lung & chest wall, and is also referred to as “elastic resistance”.
• Conditions such as ARDS, Atelectasis, Tension pneumothorax, and Obesity can all result in a decreased static compliance.
• Static Compliance =Corrected tidal volumeplateau pressure - peep
Mechanical VentilationMechanical VentilationModesModes
Limit Limit variables rise no higher than some preset variables rise no higher than some preset value and increase to preset value before value and increase to preset value before inspiration ends = limit variableinspiration ends = limit variable
CycleCycleVariable that terminate inspiration = cycle Variable that terminate inspiration = cycle variablevariable
Breath characteristicsBreath characteristicsGas DeliveryGas Delivery
Mechanical VentilationMechanical Ventilation
BirdBirdLimit: pressure, flowLimit: pressure, flowCycle: pressureCycle: pressure
Bennett 7200 (volume assist-control) Bennett 7200 (volume assist-control) Limit: volume, flowLimit: volume, flowCycle: volumeCycle: volume
Pressure supportPressure supportLimit: pressureLimit: pressureCycle: flowCycle: flow
Mechanical VentilationMechanical VentilationModesModes
Volume-targetedVolume-targeted: Pre-set tidal volume: Pre-set tidal volume
Pressure-targetedPressure-targeted: Pre-set inspiratory : Pre-set inspiratory pressurepressure
Mandatory breaths:Mandatory breaths: Breaths that the Breaths that the ventilator delivers to the patient at a set ventilator delivers to the patient at a set frequency, volume/pressure, flow/timefrequency, volume/pressure, flow/time
Spontaneous breathsSpontaneous breaths: Patient initiated : Patient initiated breathbreath
Mechanical VentilationMechanical VentilationModesModes
Volume-targetedVolume-targetedControlled mechanical ventilation (CMV)Controlled mechanical ventilation (CMV)
Assist/control (A/C) mechanical Assist/control (A/C) mechanical ventilation ventilation
Synchronized intermittent mandatory Synchronized intermittent mandatory ventilation (SIMV)ventilation (SIMV)
Background:
• Full preset tidal volume at a fixed preset rate
• Rate and minute ventilation cannot by patient effort
• Trigger sensitivity is locked out, need sedated or paralyzed
Modes of Ventilation
(CMV)
Modes of Ventilation Modes of Ventilation (CMV)(CMV)
Advantages: Advantages: Near complete resting of ventilatory musclesNear complete resting of ventilatory musclesRespiratory muscle rest, secured minute ventilation Respiratory muscle rest, secured minute ventilation
Disadvantages: Disadvantages:
““Stack" breaths (air trapping) and develop barotrauma Stack" breaths (air trapping) and develop barotrauma ““AutoPEEP" with barotrauma or hypotensionAutoPEEP" with barotrauma or hypotensionNeed sedated or paralyzedNeed sedated or paralyzedRespiratory muscle atrophy Respiratory muscle atrophy
Uses:Uses:
apnea, little breathing effort, unstableapnea, little breathing effort, unstable
Background:
• Full preset tidal volume at a minimum preset rate
• Additional full tidal volumes given if the patient initiates extra breaths
Modes of Ventilation (Assist/Control)
Modes of Ventilation (Assist/Control)
Advantages:
• Near complete resting of ventilatory muscles
• Comfortable, respiratory muscle rest, secured minute ventilation
• Effectively used in awake, sedated, or paralyzed patients Disadvantages:
• Hyperventilate and become alkalotic
• “Stack" breaths (air trapping) and develop barotrauma
• “AutoPEEP" with barotrauma or hypotension
Uses:
• apnea, little breathing effort, unstable
Background:
•Preset tidal volume at a fixed preset rate
•Ventilator waits a predetermined trigger period
•Patient can take additional breaths but tidal volume of these extra breaths is dependent on the patient's inspiratory effort
Modes of Ventilation
(SIMV + Pressure support)
Advantages: • Improved venous return: intermittent negative
pressure (spontaneous) breaths • More comfortable: more control over their ventilatory
pattern and minute ventilation Disadvantages: • Can result in chronic respiratory fatigue if set rate is too
low; Uses:• Weaning, bronchopleural fistula
Modes of Ventilation
(SIMV + Pressure support)
Mechanical Ventilation
Control, Assist Control and IMV/SIMV all deliver a guaranteed minute volume regardless of a patient’s ability to breath.
What distinguishes the 3 modes is how the ventilator responds to a patients spontaneous breathing effort.
Each mode responds differently, but still delivers a baseline minute volume.
Mechanical Ventilation
Control 800 10 8 L 0 8 LAssist Control 800 10 8 L 4.8L 12.8LIMV/SIMV 800 10 8L 5.5L 13.5L
MODE VT R MV MV MVMANDATORY SPONTAN TOTAL
6 spont triggeredmachine deliveredbreaths
Varying spont tidalvolumes, 300 cc, 500 cc275cc etc, at a variablespont rate.
volume mode chart
Mechanical VentilationMechanical VentilationModesModes
Pressure-targetedPressure-targetedPressure support ventilation (PSV)Pressure support ventilation (PSV)
Pressure-control ventilation (PCV)Pressure-control ventilation (PCV)
Pressure-targeted assist-control (A/C-PC)Pressure-targeted assist-control (A/C-PC)
Pressure-targeted SIMV (SIMV-PC)Pressure-targeted SIMV (SIMV-PC)
Background:
• Patient triggers, a preset pressure support is delivered
• Terminate inspiration by flow rate
• Tidal volume and minute ventilation are dependent on the preset pressure
and patient’s lung-thorax compliance
Pressure support Ventilation
Pressure support Ventilation
Advantages:
• Avoids patient-ventilator asynchrony
• More comfortable: full control over ventilatory pattern and minute ventilation
• Avoids breath stacking and autoPEEP (especially in patients with COPD)
Disadvantages:
• Required patient’s triggering, cannot be used in heavily sedated, paralyzed, or comatose patients
• Respiratory muscle fatigue if pressure support is set too low
Background:
• Ventilator control predetermined pressure in a
fixed predetermined time and rate
Pressure Control Ventilation
Pressure Control Ventilation
Advantages:
• Pressure and time are controlled
• High flow rateDisadvantages:
• Tidal volume variable
• Produced autoPEEP if inspiratory time too long
• Uncomfortable mode for most patients
Pressure-targeted assist-control Pressure-targeted assist-control (A/C-PC)(A/C-PC)
All breaths machine-delivered at a preset All breaths machine-delivered at a preset inflation pressureinflation pressure
Patients can Patients can rate by triggering additional rate by triggering additional machine breaths if desiredmachine breaths if desired
Same as assist/control volume targeted mode Same as assist/control volume targeted mode
Pressure-targeted SIMVPressure-targeted SIMV(SIMV-PC)(SIMV-PC)
Fixed rate of machine-delivered breaths at a Fixed rate of machine-delivered breaths at a preset inflation pressurepreset inflation pressure
Patients can breathe spontaneously between Patients can breathe spontaneously between machine-delivered breaths if desiredmachine-delivered breaths if desired
Same as SIMV volume targeted mode Same as SIMV volume targeted mode
Mechanical Ventilation
Objectives:• Physiology
• Comfortable
• Least complications
Usual settings• Minute Ventilation = RR X VT ( 5 - 8 L/min)
• VT = 5 - 8 mL / kg
• RR = 12 - 20 bpm
• PaCO2 = 35-45 mmHg
• pH = 7.35-7.45
Mechanical Ventilation
Mechanical Ventilation
Triggering: sensitivity of ventilator to patient’s respiratory effort.
• Flow or pressure setting that allows ventilator to detect patient’s inspiratory effort
• Allows ventilator synchronize with patient’s spontaneous respiratory efforts
• Improving patient’s comfort during mechanical ventilation.
Setting: lowest but not self cycling Less work in flow triggering
Mechanical Ventilation
Flow rate: • adjust to patient’s comfort• Usually > 60 L/min
Pressure:• Plateau pressure < 30 cmH2O
Positive End Expiratory Pressure(PEEP)
Functional residual capacity• Move fluid from alveoli into interstitial space• Improve oxygenation
PEEPPEEP
In COPD : To offset auto-PEEPIn COPD : To offset auto-PEEP
To improve oxygenation in acute lung injuryTo improve oxygenation in acute lung injury
To improve oxygenation, To improve oxygenation, preload, preload, afterload afterload in cardiogenic pulmonary edemain cardiogenic pulmonary edema
PEEP TitrationPEEP Titration
GoalGoal :: - - PaO PaO22
- - FiO FiO22 ( (<< 0.5) 0.5) - No adverse effect:- No adverse effect: cardiac outputcardiac output lung compliance from overdistension lung compliance from overdistension
(( plateau pressure) plateau pressure)
• Obtained baseline respiratory & hemodynamic Obtained baseline respiratory & hemodynamic • Change (PEEP) only , keep other parameter constant Change (PEEP) only , keep other parameter constant PEEP 5 cmH2O q 15 – 20 minPEEP 5 cmH2O q 15 – 20 min• Repeat respiratory and hemodynamic data at each new Repeat respiratory and hemodynamic data at each new
PEEP level PEEP level
O2 delivery
Indequate
PEEP more
SaO2
No adverse effect
Adequate
SaO2
Compliance
Tidal volume
Use current PEEP
FiO2
O2 delivery
SaO2
SaO2 BP or co
PEEP to previous level
Volume + vasopressor
ContraindicationContraindication
Absolute: noneAbsolute: none
Relative: unilateral lung disease, Relative: unilateral lung disease, bronchopleural fistulae, bronchopleural fistulae, intracranial intracranial pressure, high plateau pressure, pulmonary pressure, high plateau pressure, pulmonary embolismembolism
Ventilator Alarms Setting
AlarmAlarm SettingSettingHigh minute ventilationHigh minute ventilation 10-15% > set or target minute volume10-15% > set or target minute volume
Low minute ventilationLow minute ventilation 10-15% < set or target minute volume10-15% < set or target minute volume
High VtHigh Vt 10-15% > set or target Vt10-15% > set or target Vt
Low VtLow Vt 10-15% < set or target Vt10-15% < set or target Vt
High-system pressureHigh-system pressure 10 cmH20 > average peak airway 10 cmH20 > average peak airway pressurepressure
Low-system pressureLow-system pressure 5-10 cmH20 < average peak airway 5-10 cmH20 < average peak airway pressurepressure
Loss of PEEPLoss of PEEP 3-5 cmH2O < PEEP3-5 cmH2O < PEEP
O2 analyzerO2 analyzer 0.05 </> Fio20.05 </> Fio2
Alarms & Troubleshooting
High Peak Inspiratory Pressure:
• Secretions
• Patient biting ETT
• Patient coughing
• Changing patient’s clinical statusLow Pressure Alarm or low PEEP alarm:
• Disconnect (check all connections)
• Apnea
• Disconnection
• Malfunction
• Patient-ventilator asynchrony
• hemodynamic effects:
• Barotrauma
• Ventilator-induced lung injury • Oxygen toxicity
• Infection
- ventilator-associated pneumonia
- sinusitis
Mechanical Ventilation Complications
Mechanical Ventilation Mechanical Ventilation ComplicationsComplications
Hemodynamic effects:Hemodynamic effects: Impaired venous return, increased Impaired venous return, increased pulmonary vascular resistance pulmonary vascular resistance cardiac outputcardiac outputAutoPEEP AutoPEEP Mean lung volume or mean Mean lung volume or mean alveolar pressure correlate best alveolar pressure correlate best with hemodynamic effectswith hemodynamic effects
AutoPEEPAutoPEEP
Exhalation is not complete by the time the next Exhalation is not complete by the time the next breath is given:breath is given:
- expiratory airflow obstruction- expiratory airflow obstruction
- high minute ventilation (> 15-20 l/min)- high minute ventilation (> 15-20 l/min)
Alveolar pressure & volume remain increased Alveolar pressure & volume remain increased at end-expirationat end-expiration
AutoPEEPAutoPEEP
Adverse EffectAdverse EffectSame effect as externally applied PEEP:Same effect as externally applied PEEP:
- Hyperinflation- Hyperinflation - - cardiac output cardiac output
Difficult to trigger ventilator → ↑ work of Difficult to trigger ventilator → ↑ work of breathingbreathing
AUTOPEEPAUTOPEEP
Auscultation: persistent exhalation (specific Auscultation: persistent exhalation (specific but not sensitive)but not sensitive)
UntriggeringUntriggering
Flow-time graphsFlow-time graphs
End-expiratory holdEnd-expiratory hold
Steps for Reducing Steps for Reducing Dynamic Hyperinflation & AutoPEEPDynamic Hyperinflation & AutoPEEP
Eliminate unnecessary ventilation:Eliminate unnecessary ventilation:WeaningWeaningMinute ventilationMinute ventilationPermissive hypercapniaPermissive hypercapnia
Expiratory airflow obstruction:Expiratory airflow obstruction:Rx bronchospasmRx bronchospasmKeep airways free of secretionsKeep airways free of secretions
Maximize expiratory time:Maximize expiratory time:peak inspiratory flow rate to 70 – 100 l/minpeak inspiratory flow rate to 70 – 100 l/min
Mechanical Ventilation Complications
Oxygen toxicity• High FiO2 is potentially injurious• Tissue injury depends on FiO2 and duration of
exposure and some diseases/conditions• No evidence that sustained exposure to FiO2 < 0.5
causes tissue injury• Lowest FiO2 with adequate tissue oxygenation• Measurements to keep FiO2 < 0.5
Hemoglobin and 0Hemoglobin and 022 Transport Transport
280 million 280 million hemoglobin/RBC.hemoglobin/RBC.Each hemoglobin Each hemoglobin has 4 polypeptide has 4 polypeptide chains and 4 chains and 4 hemes.hemes.In the center of In the center of each heme group each heme group is 1 atom of iron is 1 atom of iron that can combine that can combine with 1 molecule 0with 1 molecule 022..
Insert fig. 16.32
Oxyhemoglobin Dissociation CurveOxyhemoglobin Dissociation Curve
Insert fig.16.34
Mechanical Ventilation Respiratory Distress
• Patient
• Ventilator (malfunction)
• Patient-ventilator asynchrony
- flow rate
- trigger
- autoPEEP
Ventilator-Induced Lung Injury (VILI)
• Barotrauma : extraalveolar air, pneumothorax
• Diffuse alveolar damage, pulmonary edema
OverdistentionOverdistention
Overdistention may be regionalOverdistention may be regional Even a “normal” VT can create regional Even a “normal” VT can create regional
overdistentionoverdistention
Ventilator Management of ARDS
INITIAL VENTILATOR TIDAL VOLUME AND RATE ADJUSTMENTS
Calculate predicted body weight (PBW) • Male= 50 + 2.3 [height (inches) - 60] • Female= 45.5 + 2.3 [height (inches) - 60]
Mode: Volume Assist-Control
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