1. ARDS Ventilator Management
Nimesh Mehta, MD
Pulmonary and Critical Care
Salem Pulmonary Associates

2. AECC vs Berlin
AECC def 1994

3. ARDS Berlin Definition

4. Ventilator induced lung injury (VILI) in ARDS
The goal of ventilatory support in ARDS:
“Buy time and Protect lungs”
The injured lung is more susceptible to iatrogenic injury as a result of mechanical ventilation
Barotrauma - result of excess intrathoracic pressure (pneumothorax, subcut. emphysema, pneumomediastium)
Volutrauma - Over-inflation as a result of excess volume
Atelectotrauma – repetitive alveolar collapse and recruitment
Biotruama – stimulation of inflammatory response resulting from mechanic lung injury giving rise to further cytokine-mediated lung and other organ injury
Oxygen toxicity
* ATS International consensus conference in intensive care medicine: Ventilator associated lung injury in ARDS. Am J Respir Crit Care Med 1999; 160(18):

5. Slutsky AS, Lung injury caused by Mechanical Ventilaton
Slutsky AS, Lung injury caused by Mechanical Ventilaton. Chest 1999; 116 (Suppl_1):9S-15S.

6. ARDS
Areated
Recruitable
Non- recruitable

7. “Open Lung Ventilation” Strategy
First described by Amato*
Use of PEEP to over come lower inflation point and allowing ventilation at more favorable part of volume pressure relationship
Use of low tidal volumes to prevent over-distension of air-spaces and to avoid high-end inspiratory pressures or volumes
* Amato MBP, et al. Beneficial effects of the “open lung approach” in ARDS: a prospective randomized study. AJRCCM 1995; 152:1835.

8. ARMA Trial Low tidal Volume Strategy
861 patients randomized to
Vt mg/kg ideal body weight and plateau pressure ≤50cmH2O vs
Vt 6-8 mg/kg IBW and plateau pressure ≤30cm H2O

9. ARMA Trial Low tidal Volume Strategy
Decreased mortality by 22%
NEJM 2000;342:

10. LTVV – More evidence
Eisner MD, et al. AJRCCM 2001; 164:

11. LTVV – Adherence to protocol
Needham et al. BMJ 2012; 344:2124
 When adherence to LTVV fell from 100% to 50% or 0%; two year mortality increased by 4% and 8%; respectively
Needham et al. AJRCCM 2015; 191:177
Initial TV of 7 mL/kg PBW was associated with 23% increase in ICU mortality when compared to those receiving tidal volume of 6 mL/kg PBW.
Later increases in tidal volume by 1 mL/kg PBW also resulted in a 15% increase in mortality.

14. Optimal “PEEP”
Positive end-expiratory pressure should be high enough to shift the end-expiratory pressure above the lower inflection point by 2-3 cm H2O
Allows maximal alveolar recruitment
Decreases injury by repeated opening and closing of small airways

15. Low PEEP vs High PEEP ALVEOLI NEJM 2004 LOV JAMA 2008 EXPRESS
In hospital Mortality
27.5 vs 25.1
(p=0.47)
40.4 vs 36.4
(p=0.19)
35.4 vs 39.0
(p=0.30)
28 days Mortality
---
32.3 vs 28.4
(p=0.33)
35.4 vs 31.2
(p=0.31)
Ventilator free days
14.5 vs 13.8
(p=0.50)
7 vs 3
(p=0.04)
Barotrauma
10 vs 11
(p=0.51)
9.1 vs 11.2
6.8 vs 5.8
(p=0.57)
Rescue or adjuvant therapy
12 vs 7.8
(p=0.05)
18.7 vs 34.5
(p < 0.01)

16. PEEP Trials Incremental PEEP Strategy Vs Deremental PEEP Strategy
Combination of PEEP and FiO2 level in incremental or decremental fashion with close monitoring of
Mechanics: Compliance, Plateau pressure
Gas exchange: SpO2, PaO2, PaCo2, P/F ratio
Hemodynamics: HR, BP, CO
Optimal PEEP by Tidal Compliance
C = VT / (Pplat – PEEP)
If using fix VT, then titrate PEEP to lowest Pplat – PEEP

17. Stress Index A tool to monitor tidal recruitment and overdistension.
During inspiration with constant flow (with volume cycle mode)
Resistance is constent
All change in pressure-time curve depends on change in compliance during tidal breath.
Pre-requisite
Patient sedated and preferably paralysed
Constant flow condition
Low Vt – volume cycle mode

18. Stress Index Concave upward Overdistention Concave downward
(Decrease PEEP)
Concave downward
Potential for
recruitment
(Increase PEEP)

19. PV curve

21. PV curve - Limitations Requires sedation/paralysis No easily available
No good correlation between different methods
Difficult to identify “inflection points”
Harris et al, AJRCCM 2000; 161:432
Unable to differentiate chest wall and lung compliance
Mergoni et al, AJRCCM 1997; 156:846
Ranieri et al, AJRCCM 1997; 156:1082
Deflation limb may be more useful than inflation limb
Holzapfel et al, Crit Care Med 1983;11:561
Hickling, AJRCCM 2001;163:69
Pressure-volume curves of individual lung units not known
Hickling, AJRCCM 1998;158:194
No evidence, other than retrospective case reports

22. Esophageal balloon pressure monitoring Surrogate for pleural pressure

23.  Titrating applied PEEP to an end­-expiratory transpulmonary pressure (Tp-PEEP) between 0 and 10 cm H2O
To reduce cyclic alveolar collapse
Maintaining an end­-inspiratory transpulmonary pressure (Tp Plateau) ≤25 cm H2O
To reduce alveolar overdistension
61 patients assigned to
Adjustment of the FiO2 and applied PEEP to achieve specific end-expiratory transpulmonary pressures
Adjustment of the FiO2 and applied PEEP according to a table similar to used in ARMA trial
NEJM 2008; 359: 20

25. Esophageal balloon pressure monitoring Limitations
Is it true representation of pleural pressure
Supine position
Weight of mediastinum
Heterogeneity of lung pathology
Focal rather than global pleural pressure
Malpositioning and changing positions.
Single trial to aim to look at only oxygenation
Using merely high PEEP has already shown similar results
Approximately trans-pulmonary end-inspiratory pressure to 25 cm H2O
No evidence base.

26. Recruitment Maneuvers
Hodgson C, et al. Recruitment manoeuvers in ALI. Cochrane Database Sys Rev 2009
7 trials reviewed, total patients = 1170
Fan E, et al. Recruitment maneuvers for ALI: a systematic review. AJRCCM. 2008:178;1156
40 studies, total patients 1185

27. Recruitment Maneuvers ~ Evidence based ~
Did not differentiate between different RM strategies
Improved oxygenation (did not persist)
No change in ventilator parameter, except higher PEEP after RM
No significant difference on 28th day mortality
No statistical difference in risk of barotrauma
No significant changes in hemodynamic parameters after an RM.
Hypotension (12%) and desaturation (9%) were the most common adverse events
Only 1% patients had their RMs terminated prematurely due to adverse events.
Current recommendation: to use after brief disconnection of patient from ventilator.

28. APRV Application of CPAP a relatively high level (Phigh)
Time-cycled release phase to lower level of CPAP (Plow)
Unrestricted spontaneous breathing is permitted in any phase of respiratory cycle.

29. APRV- Evidence Based Study Study design Groups Results
Rasanen et al. 1991
Prospective Crossover trial
50 pts with ALI/ARDS
APRV Vs CMV
Lower peak airway pressure
Similar oxygenation and hemodynamics
Sydow et al. 1994
Randomized controlled trial
18 pts with ALI
APRV Vs VC-IRV
Better oxygenation
Similar hemodynamics
Kaplan LF, et al. 2001
12 pts with ALI
APRV Vs PC-IRV
Lower peak and mean airway pressure
Better CO, CVP, Oxygen delivery
Lower sedative and NMB
Putensen et al. 2001
30 trauma pts with ALI/ARDS
APRV Vs PCV
High CO
Less sedative and NMB
Less MV and ICU days
Required paralysis in control group for first 3 days
Varpula et al. 2004
58 pts with ALI/ARDS
APRV Vs SIMV-PS
No diff. in term of gas exchange, sedation needs, ventilator free days and mortality
Only study after ARDSNet low tidal volume study

30. Prone Ventilation

31. Prone Ventilation PROSEVA trial - NEJM 2014
466 patients with severe ARDS
undergo prone-positioning sessions of at least 16 hours or to be left in the supine position.
Severe ARDS was defined as PF ratio < 150 with FiO2 > 0.6 with PEEP > 5.
Supine Group
(n = 229)
Prone Group
(n = 237)
Mortality at 28 days 75 38
< 0.001
Mortality at 90 days 94 56
Vent free days at 28 days 10 14
Vent free days at 90 days 43 57

32. Summary Identify ARDS early
Low tidal volume – aim is 6 mL/kg (not 8 mL/kg)
Aim to have plateau pressure minimum (not just < 30 cm H2O) with some degree of permissive hypercapnia
PEEP titration based on FiO2
Recruitable ARDS vs non
Decremental PEEP titration
PV curve
Recruitment Maneuvers – good only after any circuit disconnection
Esophageal balloon – know limitation
Rescue therapies: APRV; Prone Ventilation  ECMO

33. Questions