MECHANICAL VENTILATION

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


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


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


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


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


(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


(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.


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


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


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



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


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

MECHANICAL VENTILATION

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