04 venugopal.

Advances in mechanical ventilation

Dr. Venugopal Reddy. MD, EDIC, FCARCSIAssociate Professor of Anesthesia & CCMDirector of Surgical Critical Care Medicine

Penn State College of Medicine Hershey Medical Center, Hershey

Pennsylvania, USA

Dual control modes2000: ARDS Network. Ventilation with low VTTraditional versus Dual control

Dual control Auto-regulated pressure controlled modes delivering desired tidal volume with-in-a-breath (PC to VC)breath-breathCombination of both

Advances in mechanical ventilation

Type Ventilator

Name

Dual Control breath to breath (Pressure limited time cycled)

ServoDrägerPuritan

PRVCAuto flowVolume Control+

Dual control breath to breath (pressure limited flow cycle)

ServoDräger

Volume supportProportional assist ventilation

Modes that allow spontaneous breathing

Dräger-Evita 4Servo Maquet

BiPAP and APRVBi Vent

Dual Control breath to breath

Hamilton Galileo

Adaptive Support ventilation

Pressure Regulated Volume Control Ventilation

Volume control ventilation

Volume Control vs PRVC

Pressure Regulated Volume Control ventilation

Volume Controlled

Airway Obstruction

Normal

Insp P Expiration

PRESSURE

cm H2O

Insp P Expiration

10

20

30

40

Tidal Volume

500 mL 350 mL

PAWP

Pause pressure

I:E Ratio = 1: 2

Control Trigger Limit

Volume Patient or time Pressure

TargetTarget Cycle

Lowest pressure for set volume

Time

(1)Test breath (5 cm H2O above PEEP) (2)Pressure increases to deliver set tidal volume (3)maximum available pressure (4)breath delivered at preset VE, f, and TI

(5)when VT corresponds to set value, pressure remains constant(6)if preset volume increases, pressure decreases

Pressure regulated volume control (PRVC)

Pressure Regulated Volume Control

Weaning is much easier Apnea: Pressure controlled time cycled breath Patient triggers 2 breaths switches to VSV Maximum pressure at any time is <5 cm H20

below the pressure alarm Activation of alarm: indicates change in

patient lung mechanics and requires evaluation

Pressur

eFlow

Volume Set tidal volume

PRVC: Advantages

Guaranteed VT and VE with minimum PIP Pressure automatically adjusted for changes in

compliance and resistance Decreases WOB Variable VE to meet patient demand Improved gas exchange with decelerating flow Breath by breath analysis Limits volutrauma and Prevents hypoventilation

Pres

sure

Flow

Volu

me

Set tidal volume

PRVC: Disadvantages Pressure delivery is based on previous VT and varies Intermittent patient effort variable VT

Varying mean airway pressure May cause or worsen auto-PEEP A sudden increase in respiratory rate and demand

may result in a decrease in ventilator support

PRVC: Indications

Patient who require the lowest possible pressure and a guaranteed consistent VT

When inspiratory pressure varies due to intra-abdominal pressure (laparoscopy, robotic)

ALI/ARDS Patients requiring high and/or variable MV Patient with changes in Compliance or

Resistance

Pressure Support

Volume Support

Volume support ventilation ServoControl Trigger Limit Target Cycle

Pressure Patient Pressure Volume Flow

5 cm H2O

Apnea

Constant exp. Flow

1 2 3 4 5

Upper Pressure limit 5 cm H2O

PRVC

Pressure support

0

5

10Pressure

Trigger Trigger Trigger

PEEP

Apnea

Volume Support

1. VS test breath (5 cm H2O)2. pressure is increased slowly until target volume is achieved3. maximum available pressure is 5 cm H2O below upper pressure4. VT higher than set VT delivered results in lower pressure5. patient can trigger breath6. if apnea alarm is detected, ventilator switches to PRVC

Volume Support: ServoStart Patient triggered (pressure or flow) Pressure targeted, flow cycled breath VT is used as feedback to adjust PS Automatic reduction in PS as and when needed PS Changes with each breath High pressure alarm prevents excessive PS Patient breaths deeper, Ventilator gives less

pressure Patients generates less pressure, ventilator gives

more support Back up (if rate is too low) is PRVC or VC

Volume support (VS)

Advantages Guaranteed VT and VE PS breaths using the lowest required pressure patient’s spontaneous respiratory rate patient WOB Allows patient control of I:E time Breath by breath analysis Variable inspiratory flow to meet the demand

Volume support (VS)

Disadvantages Spontaneous ventilation required VT selected may be too large or small for patient Varying mean airway pressure Auto-PEEP may affect proper functioning A sudden increase in respiratory rate and demand

may result in a decrease in ventilator support

Volume Support (VS)

Indications• Spontaneous breathing patient who require

minimum VE

• Patients who have inspiratory effort who need adaptive support

• Patients who are asynchronous with the ventilator• Used for patient who are ready to wean

Pressure Controlled Inverse Ratio ventilation (PC-IRV)

Airway Pressure Release Ventilation (APRV)

Pressure Controlled ventilationWith Normal I:E Ratio

Airway Pressure release ventilation (APRV)

Synchronized TransitionsSpontaneous Breaths

Spontaneous BreathsPP awawcmH2200

6060

-20-20 1 2 3 4 5 6 7

PPawccmH2200

6060

-20-20 1 3 6 1 3 6 1 3 6

Spontaneous Breaths

Releases

PP awawcmH2200

6060

-20-20 1 2 3 4 1 2 3 4

PC-IRV

BIPAP

APRV

Airway Pressure Release ventilation (APRV) Dräger

An extended version of BIPAP Ventilation between two pressures PC-IRV with preserved spontaneous breaths Apnea: PC-IRV ventilation

How does APRV differ from conventional ventilation?

Conventional: Elevate airway pressure from baseline

APRV: deflates from high pressure to low pressure for a very brief period

Spontaneous Breaths

Patient Trigger(On P High)

(On P High)

APRV: Terminology

IRV with spontaneous breathingPhigh: Insp pressure + Plow pressure (peak pressure)Plow: Expiratory pressure (PEEP)Thigh: Time spent during inspiration (Insp time)Tlow: Time during deflation (Exp time)

Airway Pressure Release Ventilation (APRV)

Advantages Higher pressure: Alveolar recruitment, better

oxygenation, maintenance of mean alveolar pressure

Lower pressure: alveolar ventilation and CO2 removal

Allows spontaneous breathing in IRV mode better gas distribution to the dependent lung regions Recruits slow open alveoli venous return and CO work of breathing

Airway Pressure Release Ventilation (APRV)

Indication ARDS Hypoxemia Atelectasis high PEEP

Settings P high plateau pressure of conventional

ventilation T high Inspiratory time (5.5-6.5 sec) P low 0 cm H20(PEEP) (intentional auto-PEEP) T Low 0.4-0.8 sec

T Low should be equal to 40%-50% of peak expiratory flowdo not let expiratory flow returning to zero

Airway Pressure Release Ventilation (APRV)

Disadvantages and Risks Variable VT with change in lung compliance and

resistance Could be harmful to patients with high expiratory

resistance (i.e., COPD or asthma) Caution: hemodynamically unstable patients Increase RV after load, and PHT Spontaneous breath during T low: Increase WOB Worsening of air-leak (BPF) Auto-PEEP is usually present

PC ventilationPS ventilation

SIMV

Adaptive support ventilation

Adaptive support ventilation (ASV)

Closed loop control systemOnly available in Hamilton Galileo ventilators

Adaptive support ventilation (ASV)Behaves asP.S.V: if patient respiratory rate is higher than

target ratePCV: ApneaSIMV when the patient respiratory rate is

lower than target rate

InitiationConcept Maintenance

Weaning

Adaptive support ventilation

Clinician enters patient’s IBW Desired Ve of 100% means 100ml/min/kg Target % of minute volume Maximum plateau pressure, PEEP, FIO2, Weaning: reduce the % setting of the VE

Ventilator Ventilator chooses an algorithm.

Delivers 100 mL/kg/min Test breaths measures compliance, resistance

and auto-PEEP

Adaptive Support ventilation: Advantages

Guaranteed VT and VE Minimal patient WOB Ventilator adapts to the patient Prevents tachypnea, auto-PEEP, and

dyspnea Weaning is done automatically Variable flow to meet patient demand Decelerating flow waveform Breath by breath analysis

Adaptive support ventilation: Disadvantages

Does not allow direct programing of VT, RR, I:E ratio Inability to recognize and adjust to changes in

alveolar VD Possible respiratory muscle atrophy Varying mean airway pressure Patients with COPD, a longer TE may be required Sudden increase in respiratory rate and demand

may result in a decrease in ventilator support Algorithm tends to ventilate with low VT & high RR