Mechanical Ventilation“ Rise Time, E sens, Triggering”

A - work to trigger

B - rate of rise to pressure adjustment C - preventing pressure overshoot and sustaining the breath

D - transition into expiration

Smarter Breath Delivery

Pressur

e

A

C (PCV Only)

D (PS Only)B

Improving Patient-Ventilator Synchrony

“Smart” Rise Time

1. WOB, specifically insp. muscle effort , associated with inappropriate flow rateduring PSV or PCV.

2. less problems associated with flow and achievement of set pressure in response to changes in lung condition as SRT is self-adjusting due to a Pressure Memory

Algorithm

• Usually applicable in all pressure breaths if available

• Tailors inspiratory rise in pressure ventilation to match patient demand or reach MAP goals

• Should allow rise to be tailored from slow to fast

1. Rise to Pressure Adjustment

40PCIRC

cmH2O

INSP

Lmin

EXP

PLOT SETUP

30

20

10

0

10

-20

80604020

020

-80

40

60

V.

0 4 8 12s2 6 10

UNFREEZE

Slow rise Moderate rise Fast rise

A - work to triggerB - rate of rise to pressure adjustment

C - preventing pressure overshoot and sustaining the breath

D - transition into expiration

Smarter Breath Delivery

Pressur

e

A

C (PCV Only) D (PS Only)B

Patient with Airway Resistance

Gas flow is greatest where resistance is low, hence overinflation of normal lung units.

V/Q

PvCO2 = 46 mmHg

PvO2 = 40 mmHg

PaO2 = 70 mmHg

PaCO2 = 45 mmHg

PaCO2 = 43 mmHg

PaO2 = 60 mmHg

40PCIRC

cmH2O

INSP

Lmin

EXP

PLOT SETUP

30

20

10

0

10

-20

80604020

020

-80

40

60

V.

0 4 8 12s2 6 10

UNFREEZE

RES = 5 RES = 20 RES = 50 cmH20/L/SEC cmH20/L/SEC cmH20/L/SEC

Without Adjustment of Pressure Rise• Most ventilators are sensitive to changes in impedance

– increasing resistance causes pressure to rise more quickly

• Not all clinicians want to adjust rate of rise (time, interest)

• Smarter rise settings should automatically adjusts flow output as resistance or compliance varies

– maintains similar shape of curve through any patient size or impedance change which reduces the need for intervention

40PCIRC

cmH2O

INSP

Lmin

EXP

PLOT SETUP

30

20

10

0

10

-20

80604020

020

-80

40

60

V.

0 4 8 12s2 6 10

UNFREEZE

RES = 5 RES = 20 RES = 50 cmH20/L/SEC cmH20/L/SEC cmH20/L/SEC

A - work to trigger

B - rate of rise to pressure adjustment

C - preventing pressure overshoot and sustaining the breath

D - transition into exhalation

Smarter Breath Delivery

Pressur

e

A

C (PCV Only)

D (PS Only)B

Expiratory W.O.B. and auto-PEEP in the COPD Patient

MJ Tobin. NEJM 2001; 344: 1986-96.

PS and WOB during Expiration

PRESSURE

Esens allows the clinician to adjust the ventilator’s onset of expiration to match the patient’s breathing pattern.

FLOW

PS overshoots target

Esens fixed 25%

Esens adjusted to 50%

NormalProblem resolved

0

100

0

15

Expiratory Sensitivity

PS Termination Criteria

Pressure support breaths terminate when patient flow decelerates to a percentage of peak flow

Flow

Expiratory Sensitivity

20% (Set)35% (Leak Rate)

• Leaks can cause inability to terminate pressure supports breaths causing profound asynchrony

Flow

Expiratory Sensitivity

20% (Set)40% (Set)

35% (Leak Rate)

• ESENS allows adjustment of the termination criteria for pressure supported breaths– sets the percent of peak flow that cycles the pressure

support breath into exhalation– helpful in compensating for prolonged inspiratory times

when leaks are present or titrating insp times in PS– can improve synchrony between patient and ventilator

Flow

How FlowHow Flow--Triggering Works!Triggering Works!

Base Flow 5Sens 1 lpm

5 lpm

1 lpm

4 lpm

Patientremoves

Base Flow 14Sens 7 lpm

14 lpm

Chest tube leakremoves 6 lpm

Patient mustremove only1 lpm

7 lpm

Without a Leak With a Leak

How Much Does It Take To Trigger A Breath?

Imagine setting the Flow Sensitivity at 1 LPM:

1 LPM = 16.6ml/100msecor

.83 ml/5msecs

Pressure vs Flow Triggering

• Pressure Triggering– No gas flow

– Longer delay time

– Poor approach with leaks

– Higher WOB

– Not a mode of ventilation

• Flow Triggering– Flow at the wye

– Decreased delay

– Electronic signal

– Less WOB

– Not a mode of Ventilation

Flow Triggering Articles

• Sassoon - flow-by causes lower WOB at 10 cm H2O during CPAP breathing than pressureCrit care med 1989

• Saito - Inspiratory WOB is lower with flow-by and similar to PS of 5 cm H2OCrit care med 1990