The document discusses the case of a 27-year-old postpartum woman presenting with worsening dyspnea and hypoxia. It then reviews the key considerations and management strategies for acute respiratory distress syndrome (ARDS), including low tidal volume ventilation, open lung strategies using recruitment maneuvers and high positive end-expiratory pressure, unconventional approaches like airway pressure release ventilation and high frequency oscillatory ventilation, and adjunctive therapies such as prone positioning. The optimal ventilator mode, settings, and adjunctive strategies depend on the individual patient's severity of lung injury and response to different interventions.

1. ARDS and Ventilator
Management
Amr Mohamed Elsharkawy
Critical care medicine department
Alexandria University

2. 27-year-old woman with dyspnea
• 4 days s/p C-section
• Gradual increase in dyspnea over 24
hours with fever of 101
• Evaluation
– Crackles R > L
– No peripheral edema
– Hypoxia (7.25/67/41 on 40% VM)
– Normal Echo

6. 27-year-old woman with dyspnea
• Clinical Course
– FiO2 100%; PEEP 20 cm H2O
– Peak and plateau airway pressures: 40s

7. 27-year-old woman with dyspnea
• Clinical Course
– FiO2 100%; PEEP 20 cm H2O
– Peak and plateau airway pressures: 40s
• Key questions
– What is the cause of acute respiratory
failure?
– How to oxygenate the patient?
– How to save her life?

8. Common Causes of Hypoxemic
Respiratory
Failure
Acute lung injury (ALI) / ARDS
Pulmonary Edema
Diffuse alveolar Hemorrhage
Pulmonary Embolism
Interstitial lung disease
Pneumonia
Neoplasm
Pulmonary contusion
Atelectasis
COPD
Asthma
Bronchiolitis

10. ARDS: Berlin Definition
JAMA 2012;307:2526-33
Category Criterion
Timing Within 1 week of clinical insult or
new/worsening respiratory sx
Chest Imaging Bilateral opacities – not fully explained
by effusions, lobar/lung collapse, or
nodules
Origin of edema Not fully explained by cardiac failure or
fluid overload. Objective measure to
rule out hydrostatic edema
Oxygenation: Mild 200 mm Hg < PaO2/FIO2 < 300 mm
Hg*
Oxygenation:
Moderate
100 mm Hg < PaO2/FIO2 < 200 mm
Hg**
Oxygenation:
Severe
PaO2/FIO2 < 100 mm Hg**
* PEEP or CPAP > 5 cm H2O; ** PEEP
> 5 cm H2O

11. • Di use bilateralff
infiltrates
– Patchy, confluent
– Alveolar, ground--‐
glass
• In contrast to CHF,
no prominence of..
– Cardiomegaly
– Pleural e usionff
– Widened vascular
pedicle

12. ARDS: Chest Radiograph Criteria
• Radiographic findings not attributable
to:
– Chronic changes
– Atelectasis
– Mass
– Pleural effusion

14. ARDS Management
Mechanical Ventilation :
• Low tidal volume
ventilation
• Open lung ventilation
• High peep –
recruitment
• Inverse ratio
ventilation
•Unconventional
approach:
• APRV
• HFV
General Measures:
•Prone positioning
•Nitric oxide
•NMBA
•Fluid Management
•ECMO

15. Strategies of mechanical ventilation of
adults in ARDS

16. LOW TIDAL VOLUME VENTILATION
- Low tidal volume ventilation (LTVV) is also referred to as lung
protective ventilation.
- For patients with acute respiratory distress syndrome (ARDS), low
tidal volume ventilation (4 to 8 mL/kg predicted body weight) is
recommended
- Adjust the tidal volume to achieve an inspiratory plateau airway
pressure =30 cm H O

17. Low tidal volume ventilation (LTVV)
Benefit
Evidence suggests that the early application of and
adherence to LTVV improves mortality, as well as
other clinically important outcomes in patients with
ARDS

18. Low tidal volume ventilation (LTVV)
Benefit
-The multicenter ARMA trial randomly assigned 861 mechanically
ventilated patients with ARDS to receive LTVV (initial tidal volume of 6
mL/kg predicted body weight [PBW]) or conventional mechanical
ventilation (initial tidal volume of 12 mL/kg PBW) .
The LTVV group had a lower mortality rate (31 versus 40 percent) and
more ventilator-free days (12 versus 10 days).

19. Low tidal volume ventilation (LTVV)
Harm
- LTVV is generally well tolerated.
- It was not associated with any clinically important adverse
outcomes in the ARMA trial.
-With respect to physiologic adverse outcomes, LTVV
caused hypercapnic respiratory acidosis in some patients.
- Hypercapnic respiratory acidosis was an expected and
generally well tolerated consequence of LTVV.

20. Low tidal volume ventilation (LTVV)
Harm
- Two major concerns were expressed after publication of the ARMA
trial.
(1) Auto-PEEP:
The higher respiratory rater in LTVV may create auto-PEEP by
decreasing the time available for complete expiration
(2) sedation:
- Work of breathing and patient-ventilator asynchrony may increase
when tidal volumes are <7 mL/kg of predicted body weight.
- While asynchrony may require increased sedation soon after the
initiation of LTVV, the need for increased sedation does not appear
to persist

21. Low tidal volume ventilation (LTVV)
Application

22. Copyrights apply

23. Permissive Hypercapnia
- LTVV frequently requires permissive hypercapnic
ventilation (PHV), a ventilatory strategy that accepts
alveolar hypoventilation in order to maintain a low alveolar
pressure and minimize the complications of alveolar
overdistension (eg, ventilator-associated lung injury).
- Hypercapnia and respiratory acidosis are a consequence of
this strategy.
- Minimum accepted PH = 7.25
- The degree of hypercapnia can be minimized by using the
highest respiratory rate that does not induce auto-PEEP
and shortening the ventilator tubing to decrease dead space

24. Open Lung ventilation (OLV)
- a strategy that combines low tidal volume ventilation
(LTVV) with a recruitment maneuver and subsequent
titration of applied PEEP to maximize alveolar
recruitment.
- The LTVV and set limits on plateau pressure aim to
mitigate alveolar overdistension, while the applied
PEEP seeks to minimize cyclic atelectasis.
- Together, these effects are expected to
decrease the risk of ventilator-associated lung injury.

25. Open Lung ventilation (OLV)
- On balance, most trials do not show convincing
benefit and some show possible harm such that it is
better to avoid the routine application of open lung
strategies as an initial strategy in patients with
ARDS.
- Any use of OLV strategies should be limited to
those with severe ARDS refractory to standard
LTVV strategies; in addition, when employed,
patients should be closely observed for an
oxygenation response, so that the clinician can
decide whether it is appropriate to continue or
abandon the OLV trial.

26. High PEEP
- The routine use of a high PEEP strategy in ARDS
patients as an initial strategy is not recommended.
- However, in patients refractory to standard
methods of mechanical ventilation, some experts use a
high PEEP strategy such as that employed in the
ALVEOLI or LOVS trials

27. Recruitment maneuvers Approaches
Four different approaches•
• Single breath 1.5 – 2 times the set VT is applied every one
or two minutes
•PEEP is temporarily ++,subsequent end inspiratory
volume is ↑
•VT can be raised temporarily
•High levels of CPAP applied for set point of time
•RM can be applied with PCV 20cmH2O and PEEP 30-
40cmH20 for 1-2min
Karmarek RM strategies to optimize alveolar recruitment. Curr.

28. Aggressive
RMS
• CT images showed improvement in
•
collapse lung
Better oxygenation ↓
mortality
Amato MB et al : N Engl J Med 1998:338;
345-54

29. Copyrights apply

30. High PEEP
- It is thought that use of higher levels of PEEP benefit
patients by opening collapsed alveoli, which in turn
serves to decrease alveolar overdistension because the
volume of each subsequent tidal breath is shared
by more open alveoli.
- If the alveoli remain open throughout the respiratory
cycle, cyclic atelectasis is also reduced. Alveolar
overdistension and cyclic atelectasis are the principal
causes of ventilator-associated lung injury.

31. High PEEP
- The application of high PEEP does not appear to be
associated with improved mortality except perhaps
in those with severe gas exchange abnormalities.
- Further study is needed to determine the optimal
level of PEEP and the ARDS population in whom a
clear mortality benefit might be expected

32. Mode of ventilation
- Patients with ARDS can be supported using either a volume
limited or a pressure limited mode of Ventilation
-In most patients with ARDS, a volume limited mode will
produce a stable airway pressure and a pressure limited mode
will deliver stable tidal volumes, assuming that breath to
breath lung mechanics and patient effort are stable.
- Abrupt changes in the airway pressure in a patient receiving
volume limited ventilation, or in tidal volumes in a patient
receiving pressure limited ventilation, should prompt an
immediate search for a cause of an acute change in compliance
(eg, pneumothorax or an obstructed endotracheal tube).

33. Mode of ventilation
- In order to adhere to a strategy of LTVV, it is probably
easier to use a volume limited approach. However, a pressure
limited mode is an acceptable alternative, as long as the
resulting tidal volumes are stable and consistent with the
strategy of LTVV.
-Regardless of whether volume limited or pressure limited
ventilation is chosen, fully supported modes of mechanical
ventilation (eg, assist control) are generally favored over
partially supported modes (eg, [SIMV]). This is particularly
true early in the course of disease.
-Ultimately, the choice of mode depends primarily on clinician
comfort and familiarity.

34. Copyrights apply

35. Inspiratory time adjustment
(Inverse ratio ventilation)
- Refractory hypoxemia can occur even if the applied
PEEP and FiO2 are optimized. In this situation,
increasing the I:E ratio by prolonging inspiratory time
may improve oxygenation.
-Increasing the I:E ratio will increase the mean airway
pressure and may improve oxygenation in some
patients.

36. Inspiratory time adjustment
(Inverse ratio ventilation)
- There are potential costs associated with prolonging the
inspiratory time that should be considered. When the
inspiratory time is increased, there is an obligatory
decrease in the expiratory time. This can lead to air
trapping, auto-PEEP, barotrauma, hemodynamic
instability, and decreased oxygen delivery.
- In addition, a prolonged inspiratory time may require
significant sedation or neuromuscular blockade,
particularly if the inspiratory time surpasses the expiratory
time (inverse ratio ventilation).

37. Unconventional vent. approach

38. ARDS
–Unconventional approaches:
• Airway Pressure Release Ventilation (APRV)
• High frequency oscillatory ventilation (HFOV)

39. APRV

40. Airway Pressure Release Ventilation
• Can minimize lung volume
•
•
expansion
Inflation pressure is CPAP
level – Best compliance ,
oxygenation
APRV supports ventilation at
optimal resting volumes
• Pulmonary volume is
maximized at FRC

41. Airway Pressure Release Ventilation
• APRV used in patients with lung injury
•
•
•
•
•
•
Improved haemodynamics
Reduced peak and mean airway pressures
Decreased use of sedatives and relaxants
Improved cardiac index
Pressor agents usage is reduced
Shortened the length of mech ventilation
Kaplan et al , Crit Care 2001,5(4) ;221-226

42. Prone position in ARDS
Proposed Explanations
•
•
•
•
Increased FRC
Blood Flow Redistribution
Changes in Diaphragmatic
Motion
Improved Secretion Removal

43. Ventral
Dorsal
Dorsal
Ventral
Mechanism of Prone Positioning

44. Prone Positioning:
Procedure
• Appropriate staff to manage patient and
“tubes”.
•
•
•
Minimize abdominal pressure.
Maintain pt in Swimming position (one
arm extended over head, head turned
to that side)
Sedation generally required.

45. Prone Positioning: How
Long?
Fridrich et al, Anesth Analg 1996;83:1206-1211

46. Prone Position
• Prone-Supine Study Group
•
•
•
•
Multicenter randomized clinical trial 304
adult patients prospectively
randomized to 10 days of supine vs. prone
ventilation 6 hours/day
Improved oxygenation in prone position
No improvement in survival
NEJM 2001;345:568-73