triggering rise time e sens
TRANSCRIPT
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Mechanical Ventilation“ Rise Time, E sens, Triggering”
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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
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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
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• 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
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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
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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
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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
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• 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
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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
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Expiratory W.O.B. and auto-PEEP in the COPD Patient
MJ Tobin. NEJM 2001; 344: 1986-96.
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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
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Expiratory Sensitivity
PS Termination Criteria
Pressure support breaths terminate when patient flow decelerates to a percentage of peak flow
Flow
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Expiratory Sensitivity
20% (Set)35% (Leak Rate)
• Leaks can cause inability to terminate pressure supports breaths causing profound asynchrony
Flow
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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
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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
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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
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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
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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
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