Mode of Mechanical Ventilator

柳營奇美醫院呼吸治療科呼吸治療組長

龔淑貞

模式 (Mode)•模式的定義─

–病人與呼吸器交互作用，以完成一個呼吸器循環 (ventilator cycle) 的方法

–並沒有任何一種呼吸器模式是最好的–醫護人員的經驗與技巧才是決定一個呼吸器模式成功與否最重要的關鍵

Mode of MV

• Conventional methods of ventilator support

--CMV, A/C, PCV, VCV, IMV, SIMV, PSV

• Alternative methods of ventilator support

--IRV, MMV, APRV, Bi-phasic, Servo-controlled pressure(Paug, VAPS, PRVC, Auto-flow, APV) , PAV, ATC, ASV

• Control mechanical ventilation(CMV) -- time trigger, volume or pressure, no

effort at Pt.

• Assist-control Ventilation( A/C) -- Time or Pt trigger -- Set: f, Sensitivity., type of breath(V or P)

(1) flow controlled, volume cycled (VV): flow, volume preset, Vt reach →flow ends

(2) pressure controlled, time cycled (PV): pressure,Ti preset, Ti reach →cycle off

Assisted vs. ControlledAssisted vs. Controlled

Time (sec)

Assisted ControlledPressure (cmH20)

Volume Ventilation(VV)

• Set the volume delivered during the mandatory breath

• VV guarantees volume (C,R ↑↓→V 不變 ) • Lung worsens,↑peak and alveolar P. →overdiste

ntion →change flow pattern 改善• High volume give high peak and plateau P.• Set parameter(7200 ; 900)• Flow controlled, Time or Pt trigger, volume li

mit, Volume cycle

Controlled Mode (Volume-Targeted Ventilation)

Controlled Mode (Volume-Targeted Ventilation)

Preset VT

Volume Cycling

Dependent onCL & Raw

Time (sec)Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Preset Peak Flow

Time triggered, Flow limited, Volume cycled Ventilation

Pressure Ventilation (PV)

• Preset a pressure, P. limit ventilation(PCV, PSV)

• 影響 Vt : △P, Ti, TC (R, C), continuous flow rate (initial flow →P. waveform shape)

• 優點 : ↓A. overdistention, ↑distribution, constant P., ↑MAP.

• 缺點 :variability by volume

Controlled Mode (Pressure-Targeted Ventilation)

Controlled Mode (Pressure-Targeted Ventilation)

Pressure

Flow

Volume

(L/min)

(cm H2O)

(ml)

Time (sec)Time (sec)

Time-Time-Cycled

Set PC level

Time Triggered, Pressure Limited, Time Cycled Ventilation

比較 PCV vs VCV

• ↑ Oxygenation(↑ MAP) - PCV : PIP-PEEP*Ti / TCT+PEEP...…. 正方

形 - VC : ½(PIP-PEEP*Ti / TCT+PEEP)... 三角

形• ↑ gas exchange• ↓ PIP• 容易 lung healing

Assisted ventilation

-- Pt trigger ( PSV, VS, PAV)

-- Preset volume or pressure, no mandatory

breath -- time interval 不一定相等

Assisted Ventilation

• F5-20

Assisted Mode(Volume-Targeted Ventilation)

Assisted Mode(Volume-Targeted Ventilation)

Time (sec)Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Preset VT

Volume Cycling

Patient triggered, Flow limited, Volume cycled Ventilation

Assisted Mode (Pressure-Targeted Ventilation)

Assisted Mode (Pressure-Targeted Ventilation)

Pressure

Flow

Volume

(L/min)

(cm H2O)

(ml)

Set PC level

Time (sec)Time (sec)

Time-Cycled

Patient Triggered, Pressure Limited, Time Cycled Ventilation

Pressure Supported Ventilation(PSV)

• Pressure – targeted (or limit), Pt – trigger

• Patient-initiated, patient-terminated

• 自動調整 maintains flow to reach preset PSV level keep this pressure until expiration

The end of inspiration(PSV)

• Decrease of peak flow to specific threshold

• Above the fixed PSV level (1 to 3 cmH2O), sudden exp. effort from patient

• A time end of the insp.

Flow criterion: % of inspiratory Flow criterion: % of inspiratory peak flowpeak flow

Pressure

Pressure Support

Flow ETS

PEEP

Peak Flow

Wider ETS range

ETS can improve synchrony and change Ti of spontaneous breaths

P

F

Too late switchover Proper switchover Too early switchover

PSVPSV

Time (sec)

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Flow CyclingFlow Cycling

Set PS level

Set PS level

Patient Triggered, Flow Cycled, Pressure limited Mode

IMV / SIMV

• IMV -- Time trigger, continuous (neonatal)or demand flow -- open IMV( 通大氣 ), close IMV( 儲存袋 ) -- demand flow 外接 peep, 無法代償 ,trigger 困難→ WOB↑

• SIMV -- Pt or time trigger -- Wait for the next insp. Effort ( time window)

SIMV+PS(Volume-Targeted Ventilation)

SIMV+PS(Volume-Targeted Ventilation)

Flow

Pressure

Volume

(L/min)

(cm H2O)

(ml)

Set PS level

PS Breath

Flow-cycled

Pressure

Flow

Volume

(L/min)

(cm H2O)

(ml)

SIMV + PS (Pressure-Targeted

Ventilation)

SIMV + PS (Pressure-Targeted

Ventilation)

PS Breath

Set PS levelSet PC levelSet PC level

Time (sec)

Time-Cycled Flow-Cycled

CPAPCPAP

Time (sec)Time (sec)

CPAP level

Flow(L/m)

Pressure(cm H2O)

Volume(mL)

Inverse Ratio Ventilation (IRV)

• Techniques to increase I / E ratio

(1) VCIRV

-- slowing the flow rate → flow cycle 結束 -- use a inspiratory pause → time cycle 結束 (2) PCIRV -- increase Ti → time cycle 結束

Improving PaO2 with IRV

• Higher mean Paw• By the short Te →end exp. P.↑(intrinsic P.)• Improved distribution due to low mean insp.

flow• Physiologic effect

-- ↓intrapulmonary shunt, improved V/Q

matching, ↓dead space ventilation

PCIRV

• Selection I / E ratio in a PEEP- like effect• Trap gas and ↑FRC and MAP

• Monitor compliance, auto-PEEP, SvO2 and C.O.

• Will drop Vt as the auto-PEEP developed

( P = PIP – EEP)△

• Auto-PEEP : measurement by flow waveform

Mandatory Minute Ventilation(MMV)

• Allows spontaneously breath but ensure MV• Ventilator support automatically adjusts, can

be achieved by ↑PSV level or mandatory breaths ( veolar or CPUI )

• But Pt with low Vt and high RR will not initiate the ventilator support

• Disadvantages – Alveolar ventilation not monitor, ↓clinician evaluation, MMV level not well defined

MMV

• T10-1

Methods of delivery ( MMV )

• Change in mechanical breaths -- Bear 5, Erica, CPUI, Sechrist 2200B

• Change in tidal volume -- Veolar (change the PS level), Servo 300(VS)

• Target VE, maintain adequate ventilation • During weaning – 80% on A/C, 90% on

IMV• Set lower VE→ if Pt is alkalosis or hypocarbic

(PaCO2↓)

Servo–controlled Pressure Ventilation

A) Pressure augmentation → real breath by breath

*Paug – Bear 1000 *VAPS – Bird 8400sti

B) Closed-loop pressure ventilation →next breath

*PRVC and VS – Servo 300

*Auto - flow – Drager (Evita )

*APV – Galileo

C) PAV(proportional assisted ventilation), ASV(adaptic support v

entilation), ATC(automatic tube compensation)

Initial setting for Pressure Augmentation

• Paug only work with VV, target volume, an upper pressure limit (Bear 1000, 8400sti )

• Set P.= Pplateau – PEEP • Set appropriate flow rate:

-- >30% for peak flow for a PS breath

-- high enough Ti does not longer than Te

-- lower than the actual peak flow→ Paw↑ -- Select rectangular flow wave form ( )

• Weaning:

-- CL ↑ → Vt ↑ => reduce the P. and adjust flow rate

Peak flow100Lpmpressure 25cmH2Ovolume set 0.8 L

Peak flow100Lpmpressure 25cmH2Ovolume set 0.8 L

Dement peak flow 80Lpmset flow 40Lpm sustained until volume set 0.8 L

Dement peak flow 80Lpmset flow 40Lpm sustained until volume set 0.8 L

Insufficient pressure levelflow setting may too lowTI is increased acheved Vt

Insufficient pressure levelflow setting may too lowTI is increased acheved Vt

PS breath with high flow demand(strong active insp.)volume delivry before the flow decreases(flow drop 30% of peak flow into expiratory)

PS breath with high flow demand(strong active insp.)volume delivry before the flow decreases(flow drop 30% of peak flow into expiratory)

No p’t effort the breath is timeset flow 40Lpm(rectangular waveform) to deliverde Vt 0.8L

No p’t effort the breath is timeset flow 40Lpm(rectangular waveform) to deliverde Vt 0.8L

P’t triggerP’t trigger No P’t trigger

No P’t triggerP’t trigger

P’t triggerP’t trigger

P’t trigger

pressure spikepressure spike

Closed – loop Pressure Ventilation

• Insp. Pressure is regulated, calculation of previous breath, in next breath 校正

• Decelerating flow of PCV with volume guarantee ( )

• PRVC - VS (Servo 300 ), Auto flow (Drager ), APV(Galileo)

PRVC vs. VS

• Volume target ventilation, pressure regulator

• PRVC – Pt or time trigger, time cycle VS – Pt trigger, flow cycle (5% of peak flow in Servo

300)

• 4 test breath -- First one 5 (300c) or 10 (300a) cmH2O

-- The next 3 breaths will deliver 75% of the set Vt -- Calculates compliance for the previous breath and adjust

insp. P. level (<3 cmH2O) on the next breath

Auto - flow

• Volume ventilation 之下 , 使 MV 自動調節 Insp. flow( depended on lung C, R )to change pressure, flow wave form→

• 與 PRVC 不同點 : – allow Pt in any phases for spontaneous

breath– 包括 Bi-level V., IPPV, SIMV, MMV

AutoFlow - In Action

Set desired - Freq, Tinsp ,VT and PEEP

Set Upper Paw alarm(-5cmH2O)

Set Upper Insp. VT alarm

Insp. Pressure will automatically adjust (+3cmH2O)to equal set VT

Paw

Pinsp. = f (VT,C)

PEEPt

TI

1

Paw

TE

Flow

t

f

without spontaneous breathing with spontaneous breathing

VT

Adaptive Pressure Ventilation Adaptive Pressure Ventilation (APV) (APV)

1. The inspiratory pressure is adjusted within this range:(PEEP + 5cmH2O) to (high pressure alarm limit -10cmH2O)

2. If monitored TV is higher or lower than the TV(target).the insp pressure is gradually adjusted by up to 2cmH2O at per breath

Adaptive Pressure Ventilation Adaptive Pressure Ventilation (APV) (APV)

VT

Flow

PressureHigh Pressure limit -10cmHHigh Pressure limit -10cmH22OO

PEEP+5cmHPEEP+5cmH2OO

+2cmH+2cmH2O/breathO/breath

Proportional assisted ventilation( PAV )

• Pressure, flow and volume delivery are proportional to Pt spontaneous effort (Evita-PPS)

• Pressure produces by the ventilator depends on -- insp. flow and volume demanded by Pt effort ( 不需 setting)

-- only set amplification ( work load 的 ? % ) of ventilator response to Pt effort

• Disadvantages : – only provide for assisted ventilation– cannot compensate for system leaks– resistance and compliance measured aren’t real

time.

Proportional Pressure Support PPS

Airway pressureAirway pressure

Resistance

Compliance

Breathing musclesBreathing muscles

R

C

Pmus

Paw

Paw

Pmus P PC

V R Vaw mus 1 .

The Equation of Motion

Proportional Pressure Support PPS

• If R and C of the patient are known, deviations from normal values can be targeted and appropriately compensated

• During PPS, the patient should feel as if his lung mechanics are healthy

Automatic tube compensation ( ATC )

• The flow in a difference in pressure between the two ends of the tube(E-T)

• Compensates for the flow depend P. drop across the tracheal tube ( a function, not a mode )

• The narrower the tube’s diameter→ WOB ↑

• The length of the tube → no significant on Rtube

• Setting – the size of tube

– amount of compensation

( 100% or partially )

What is Tube Compensation?

• Not a mode, but a spontaneous breath type

• Accurately overcomes the imposed inspiratory WOB through an artificial airway

• Hybrid of PS (but more efficient at overcoming tube resistance)

• Controls the patients carinal pressure to a constant preset PEEP value during inspiration

• TC adds appropriate pressure to keep carina pressure at preset PEEP

Tube Compensation - What the Carina SeesHigher Circuit Pressure

No Decreased Carina Pressure

Paw

PS Limitations For ET-Tube Compensation• PS may under-support the WOB early in the inspirator

y phase when flows are high

• As patients wake, sleep, become agitated etc, PS is unable to compensate for variable demands

10PCIRC

cmH2O

INSP

Lmin

EXP

7.5

5

2.5

0

-5

-10

80604020

020

-80

40

60

V.

0 4 8 12s2 6 10

Higher Flow

Insufficient Support

On Evita, in Action

Green curve shows the calculated

tracheal pressure in combination

with increased airway pressure

Then What Is APRV?• APRV is similar but utilizes a very short expiratory time for

Pressure Release– this short time at low pressure allows for ventilation

• APRV always implies an inverse I:E ratio• All spontaneous breathing is done at upper pressure level

Spontaneous Breaths

P

T

“Release”

Airway pressure relieve ventilationAPRV

• Two level of CPAP, applied for set periods time, allows spontaneous breathing to occur at both level

• Set P high and P low and time spent at each level ( Th

igh, Tlow )

• If P’t isn’t spontaneous, PCIRV and APRV 是不能辨別

• Is a CPAP system, allow augmentation of alveolar ventilation 經由短暫 interrupting CPAP(relieve P. )

• Gas movement → by decreasing Paw below

APRV

• 傳統 pressure – limited IRV vs. APRV 之間關係 :

-- CPPV vs. IMV• Advantages : 1) Low peak Paw 2) Low intrathoracic P. 3)↑ V/Q matc

hing• Disadvantages : 1) ↓ transpulmonary P. ( 排除 CO2會有問題 ) 2) 沒有 spontaneous breath 時為 PCIRV 3) Effect of airway and circuit resistance on ventilation 4) Interference with spontaneous ventilation

Pressure Oriented Ventilation

• Spontaneous breathing on elevated pressure level with short pressure releases for improved CO2 eliminationsimple to adjust Thigh, Tlow, Phigh, Plow

• FiO2 and Ramp setting are still present

• Apnea ventilation with adjustable alarm time Tapnea

Paw

Flow

Phigh

PlowThigh

Tlow

t

t

14:39

add. settings

Other Modees

CPAPASB

MMV

ILV

0

20

40

60

80

Paw

-10

Other

Ventilation

---

---

IPPVAssist E ** ***

48

5

4.4

0.9

mbarPhoch

Ptief

Thoch

Ttiefmbar

s

sAPRV

Mode

APRV (optional)APRV (optional)

Purpose of APRV

• ALI : ↓ FRC→ elastic WOB↑→ arterial hypoxemia

not ventilatory failure

• Restoration of FRC to reverse hypoxemia before ventilatory failure occur

• Indication :

* ↓ Clung with oxygenation failure ex : ARDS

* Ventilation failure may be 不適用 ( auto-PEEP, PaCO2↑ )

Clinical use of APRV• Adjustment of CPAP (P high) result in pul. Gas

exchange and lung mechanics, by monitor of

-- PaO2, SpO2, PvO2, SvO2 or BP and HR• After P-high, relieve Paw to P-low (△P ), meas

ure Vt, 如必要↑ P-high level or ↓ P-low• If frequency release ↑, 則 release time (Tlow) 應逐漸↓ , 避免因 air trapping ↓→ Vt ↓

• Volume change depends on TC (C*R) -- C ↓ → release time ↓(<1.5sec) -- Airway obstruction → release time ↑

Guidelines for Adjusting APRV - Timing Variables

• Set frequency that results in acceptable alveolar ventilation– adjusted to maintain desired levels of PaCO2 / pH

– usual starting rate 6 - 10 b/min

• Release time 1- 2 seconds for adults (1 - 1.5 more common)– often set to achieve a slight amount of auto-PEEP

Guidelines for Adjusting APRV - Pressure Variables

• Upper PEEP level 10-30cmH2O determined by compliance, adjusted to achieve desired MAP and oxygenation

• Lower PEEP level 3-5 cmH2O adjusted to affect FRC, MAP, and thus oxygenation

• Oxygenation can be affected by increasing MAP through:– increasing PEEPL – increasing PEEPH if less than 30 - 35 cmH20– lengthening TH if changes to either set frequency or TL is

acceptable

Which patients may be poor candidates for APRV

• Patients with increased airway resistance

• Who are unable to empty their lungs in 2 seconds

• Asthma and COPD patients

• Examining expiratory flow pattern to determine increased resistance can be a reliable indicator

Bi–phasic Positive Airway Pressure

• Use the same principle as APRV• Pressure target with freedom of

spontaneous breath on two level • Synchronization of spontaneous and

mechanical ventilation (trigger window) with BiPAP

What is BiLevel Ventilation?• Cycling between the two pressure levels can be synch

ronized to patient breathing– BiLevel timing settings or triggered by patient eff

ort• The two pressure levels are called PEEPH and PEEPL

• The two timing levels are TH and TL

P

T

Synchronized Transitions

PEEPHIGH

PEEPLOW

TLOW

THIGH

Synchronized Transitions

What is BiLevel Ventilation?• At either pressure level the patient can breathe

spontaneously– spontaneous breaths may be supported by PS

– if PS is set higher than PEEPH, PS supports spontaneous breath at upper pressure

T

PEEPHigh + PS

P

PEEPL

PEEPH

Pressure Support

Depiction of DuoPAP Ventilation

Spontaneous Breaths

Synchronized Transitions

Clock Transition

PHIGH + PS

PLOW + Psupport

Spontaneous Breaths

P

T

PHIGH

PLOW/PEEP/CPAP

PLOW

PHIGH

P

T

BIPAP* allows Spontaneous Breathingduring the Mandatory Stroke

• Reduction of the invasivness of Ventilation

• Reduction of Sedation

• One Ventilation Mode from Intubation to Weaning

• More comfortable for the Patient

• Fewer Alarms (easier handling)

PCV

Spontaneous Breathing

BIPAP

BIPAP and the Synchronisation of Spontaneous Breathing

P

t

Exp. Trigger

Insp. Trigger

Trig. Window

Trig. Window

• The set BIPAP phase synchronises with Spontaneous Breath

• Smooth synchronisation of the mandatory strokes with appropriate time window

• Flow-trigger in Inspiration and Expiration

3 New BiLevel Settings• Timing button

• Upper pressure level button - PEEPH

• Lower pressure level button - PEEPL

f1

min16

0 5

V-TRIG.

TH

S1.75

1.75

1:1.14

2.0

P

%50

O2

%50

_PCIRC

cmH2O25

PSPSUPP

H2O15

VSENSL

min5

BiLEVEL PC

10 %

PEEPH

20 cmH2O

PEEPL

5.0 H2Ocm

ESENS

3.75

cm

1.75

THIGH Setting

• TH can then be directly adjusted

• Range 0.2 to 30 seconds

f1

min16

0 5

V-TRIG.

3.75

TH

S1.75

1:1.14

2.0

P

%50

H2O

PEEPH

20 cmO2

%50

_PCIRC

cmH2O25

PSPSUPP

H2O15

VSENSL

min5

BiLEVEL PC

10 %

PEEPL5.0 cm

H2O

ESENS

1.75

cm

THIGH : TLOW Setting• When I:E ratio is locked, TH : TL is is the displayed button

and can be adjusted directly

• Range 1:299 to 149:1

f1

min16

0 5

V-TRIG.

3.75

1.75

1:1.14

2.0

P

%50

H2O

PEEPH

20 cmO2

%50

_PCIRC

cmH2O25

PSPSUPP

H2O15

VSENSL

min5

BiLEVEL PC

10 %

PEEPL5.0 cm

H2O

TH : TL 1: 1.14

ESENS

cm

TLow Setting• When TL is locked on the breath timing bar, TL is present

on the timing button and can be set directly

• Range .2 seconds or higher

f1

min16

0 5

V-TRIG.

3.75

1.75

1:1.14

P

%50

H2O

PEEPH

20 cmO2

%50

_PCIRC

cmH2O25

PSPSUPP

H2O15 cmVSENS

Lmin5

BiLEVEL PC

10 %

PEEPL5.0 cm

H2O

ESENS

TL

S2.0

2.0

APRV versus BIPAP different philosophies

BIPAP

Pinsp

CPAP

Ventilation

Phigh

Plow

APRV

Adaptic Support Ventilation (ASV )

Machine- and/or patient-triggered.Gas delivery is pressure-controlled for both

mandatory and spontaneous breaths. Pressure levels are identical.

Mandatory breaths are time-cycled if they were NOT triggered by the patient; spontaneous breaths are flow-cycled.

ASVASV

Pinsp

PEEP

No patient activity:

* Machine-triggered+ Time-cycled

Patient is active:

* Patient-triggered+ Flow-cycled

Flow I

Flow E * *

+ +

Optimal breath patternOptimal breath pattern

0

500

1000

1500

2000

0 20 40 60

f bpm

Vt m

l

1+2a*RCexp*(MV-V‘D)/VD -1f-target =

a*RCexp

Lung-protective rulesLung-protective rules (boundary conditions)(boundary conditions)

0

500

1000

1500

2000

0 20 40 60

f (b/min)

Vt (

ml)

DD

AA

CC

BB

5 test breaths

10*Vd10*Vd

5 b/min5 b/min 20/RCexp20/RCexp

2*Vd2*Vd

Optimal breath pattern: Lung Optimal breath pattern: Lung protective strategy protective strategy

Avoid:a:apneab:volume/barotraumac: AutoPEEPd: excessive VD ventilationon /tachypnea

0

500

1'000

1'500

2'000

0 10 20 30 40

Frequency in breaths per minute

Vt

in m

l

a

b

c

d

結語• 呼吸器是用來活命 (supportive) 而不是用來治病 (curative or therapeutic) 的─– 支持衰竭的呼吸系統 (failing respiratory system) ，直到病人的呼吸功能因治療或自然回復功能

– 避免呼吸器引起之「醫源性肺損傷」 (iatrogenic lung injury) 與其他併發症

• 不要用呼吸器來延長死亡過程─– 癌症末期病人– 末期之慢性呼吸衰竭– 無復原希望之疾病

Thanks for your attention