Áp lực đẩy: Khái niệm, Sinh lý học, Giá trị và giới hạn, Điều chỉnh trong bệnh nhân ARDS

<span class='text_page_counter'>(1)</span><div class='page_container' data-page=1>

Driving Pressure

Definition, Physiology, Value and Limitations

JOSHUA SOLOMON, MD

ASSOCIATE PROFESSOR OF MEDICINE
NATIONAL JEWISH HEALTH

</div>
<span class='text_page_counter'>(2)</span><div class='page_container' data-page=2>

Outline

• Background

• What is Driving Pressure?

• Value of Driving Pressure

• How do we use it in clinical practice

</div>
<span class='text_page_counter'>(3)</span><div class='page_container' data-page=3>

Normal

</div>
<span class='text_page_counter'>(4)</span><div class='page_container' data-page=4>

ARDS

“Functional
Lung”

Lungs aren’t STIFF – they are SMALL!

Consolidation
=

</div>
<span class='text_page_counter'>(5)</span><div class='page_container' data-page=5></div>
<span class='text_page_counter'>(6)</span><div class='page_container' data-page=6>

Tonetti et al. Annals of Trans Med 2017; 5: 286

</div>
<span class='text_page_counter'>(7)</span><div class='page_container' data-page=7></div>
<span class='text_page_counter'>(8)</span><div class='page_container' data-page=8></div>
<span class='text_page_counter'>(9)</span><div class='page_container' data-page=9>

Pressure

Resp
Rate
Volume

</div>
<span class='text_page_counter'>(10)</span><div class='page_container' data-page=10>

POWER

</div>
<span class='text_page_counter'>(11)</span><div class='page_container' data-page=11></div>
<span class='text_page_counter'>(12)</span><div class='page_container' data-page=12>

Lung Compliance

• Is change in volume for
any given change in

pressure

• Formula - △V/△P

• Hysteresis – inspiration
and exhalation are

different due to the extra
work to recruit and

</div>
<span class='text_page_counter'>(13)</span><div class='page_container' data-page=13></div>
<span class='text_page_counter'>(14)</span><div class='page_container' data-page=14>

ARDS Net Trial

◦ Low tidal volume

◦ <6 ml/kg vs. 12ml/kg

◦ Low plateau pressure

◦ <30 cm H₂0

◦ Reduced mortality by 9% (39%
to 31%)

◦ Survival with ARDS 69%

</div>
<span class='text_page_counter'>(15)</span><div class='page_container' data-page=15></div>
<span class='text_page_counter'>(16)</span><div class='page_container' data-page=16>

Where is the most benefit?

• Low VT

• Low plateau pressures

</div>
<span class='text_page_counter'>(17)</span><div class='page_container' data-page=17>

Driving Pressure

• Driving pressure normalizes the tidal volume to
the compliance of the respiratory system

△

P = V

_t

/ C

_RS

</div>
<span class='text_page_counter'>(18)</span><div class='page_container' data-page=18>

Driving Pressure

•

DP normalizes the tidal volume to the

compliance of the respiratory system

△

P = V

_t

/ C

_RS

</div>
<span class='text_page_counter'>(19)</span><div class='page_container' data-page=19>

www.pulmccm.org

• PEEP and VT set by
clinician

• Plateau are dependent on
settings

• Crs is derived and forms
slope of △V/△P

• The Crs changes

• Curve A – over distention

• Curve B – recruitment
maneuver

</div>
<span class='text_page_counter'>(20)</span><div class='page_container' data-page=20>

How to determine Driving Pressure

</div>
<span class='text_page_counter'>(21)</span><div class='page_container' data-page=21></div>
<span class='text_page_counter'>(22)</span><div class='page_container' data-page=22>

Limitations to Driving Pressure

• Its value is dependent on compliance

◦ Low compliance will result in low VT
◦ Hard to develop a universal DP

• Doesn’t accurately reflect transpulmonary
pressure

</div>
<span class='text_page_counter'>(23)</span><div class='page_container' data-page=23>

Amato et al. NEJM 2016; 372: 747-755x

• Hypothesis that △P would be more predictive of
survival than PEEP and tidal volume

• Looked at data on 3562 patients in 9 prior ARDS
trials

</div>
<span class='text_page_counter'>(24)</span><div class='page_container' data-page=24>

Amato et al. NEJM 2016; 372: 747-755

VARIABLES IN MODEL

Treatment group (lung protective, control)
Patient Characteristics

</div>
<span class='text_page_counter'>(25)</span><div class='page_container' data-page=25></div>
<span class='text_page_counter'>(26)</span><div class='page_container' data-page=26></div>
<span class='text_page_counter'>(27)</span><div class='page_container' data-page=27>

Amato et al. NEJM 2016; 372: 747-755

• One standard deviation increase in △P (7cm
H2O) <i>increases mortality by 40% </i>(p < 0.001)

◦ This holds true for patients on “protective” plateau and
VT (mortality increase 36%, p < 0.001)

• Changes in VT or PEEP didn’t improve mortality

</div>
<span class='text_page_counter'>(28)</span><div class='page_container' data-page=28>

Amato et al. NEJM 2016; 372: 747-755

• CONCLUSION

◦ △P is a better measure of the functional lung size (better

than predicted weight) and correlated with cyclic strain

◦ Vt should be adjusted to Crs

• LIMITATIONS

◦ Patients <i>CAN’T </i>be breathing

◦ Can’t extrapolate to Pplat>40, PEEP <5, RR > 35

◦ Didn’t measure transpulmonary pressure

</div>
<span class='text_page_counter'>(29)</span><div class='page_container' data-page=29>

Driving Pressure and

Transpulmonary Pressure

</div>
<span class='text_page_counter'>(30)</span><div class='page_container' data-page=30>

• Looked at 7 studies (5 secondary analyses and 2
observational) with 6062 patients

• Association between higher △P and mortality

• Suggest a target pressure of 13 to 15 cmH2O

</div>
<span class='text_page_counter'>(31)</span><div class='page_container' data-page=31>

How to use it today

• Not ready to start adjusting ventilators to a
target △P

</div>
<span class='text_page_counter'>(32)</span><div class='page_container' data-page=32>

What we need

• Prospective randomized trial looking at:

◦ Variables : △P, Pplat, Vt and transpulmonary pressure,
PEEP

</div>
<span class='text_page_counter'>(33)</span><div class='page_container' data-page=33>

Conclusion

• Driving pressure is an easily measured variable
that corrects the VT for lung compliance

• Data <i><b>SUGGEST</b></i> that it may be a better predictor
of outcome

• We should still use VT of 6cc/kg and Pplat as
targets in ARDS ventilation

</div>

<!--links-->