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VILI Pressure Resp Rate Volume Flow Lung Edema Edema Location... Pressure.[r]
(1)Driving Pressure
Definition, Physiology, Value and Limitations
JOSHUA SOLOMON, MD
ASSOCIATE PROFESSOR OF MEDICINE NATIONAL JEWISH HEALTH
(2)Outline
• Background
• What is Driving Pressure?
• Value of Driving Pressure
• How we use it in clinical practice
(3)Normal
(4)ARDS
“Functional Lung”
Lungs aren’t STIFF – they are SMALL!
Consolidation =
(5)(6)Tonetti et al Annals of Trans Med 2017; 5: 286
(7)(8)(9)Pressure
Resp Rate Volume
(10)POWER
(11)(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
(13)(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%
(15)(16)Where is the most benefit?
• Low VT
• Low plateau pressures
(17)Driving Pressure
• Driving pressure normalizes the tidal volume to the compliance of the respiratory system
△P = Vt / CRS
(18)Driving Pressure
• DP normalizes the tidal volume to the
compliance of the respiratory system
△P = Vt / CRS
(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
(20)How to determine Driving Pressure
(21)(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
(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 prior ARDS trials
(24)Amato et al NEJM 2016; 372: 747-755
VARIABLES IN MODEL
Treatment group (lung protective, control) Patient Characteristics
(25)(26)(27)Amato et al NEJM 2016; 372: 747-755
• One standard deviation increase in △P (7cm H2O) increases mortality by 40% (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
(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 CAN’T be breathing
◦ Can’t extrapolate to Pplat>40, PEEP <5, RR > 35
◦ Didn’t measure transpulmonary pressure
(29)Driving Pressure and
Transpulmonary Pressure
(30)• Looked at studies (5 secondary analyses and observational) with 6062 patients
• Association between higher △P and mortality
• Suggest a target pressure of 13 to 15 cmH2O
(31)How to use it today
• Not ready to start adjusting ventilators to a target △P
(32)What we need
• Prospective randomized trial looking at:
◦ Variables : △P, Pplat, Vt and transpulmonary pressure, PEEP
(33)Conclusion
• Driving pressure is an easily measured variable that corrects the VT for lung compliance
• Data SUGGEST that it may be a better predictor of outcome
• We should still use VT of 6cc/kg and Pplat as targets in ARDS ventilation