College Answer

Basic Measures
°     Increase FiO2): Improve PAO2
°     Increase PEEP
°     surface area for gas exchange
°     Improvement of atelectasis
°     Redistribution of lung water

General Measures
°     Physio / suctioning
°     Sedation / Consider Paralysis: Decrease O2 requirements and CO2 production
°     Treat factors that increase metabolic demand, sepsis etc: Decrease O2 requirements and CO2 production
°     Optimise fluid balance: balance of interstitial overload and maximising cardiac output and DO2
°     Optimise Haemoglobin, optimal oxygen carriage / viscosity combination and minimise immune and volume effects of transfusion

Optimise Recruitment and FRC
°     Lung recruitment manoeuvre: Opening collapsed alveoli, increasing FRC and area available for gas exchange
°     Increase I:E Ratio towards 1:1: Increased FRC as above, recruitment, increase PAO2
°     Inverse ratio ventilation: Longer in inspiration with potential to gas trap and provide autoPEEP above set PEEP with subsequent increase FRC and area for gas exchange.
Positioning
°    Prone position: better VQ matching, improved mechanical advantage, less lung compression from abdominal and mediastinal contents

Optimise Flow to Ventilated  Alveoli
°    Inhaled Nitric oxide: inhaled dilator delivered only to ventilated alveoli
°    Prostacyclin: improved perfusion to ventilated alveoli

Last Resorts
°     Tracheal Gas insufflation and other measures to decrease circuit dead space: reduced dead space means lower CO2 with relative increase in partial pressure of O2
°     HFOV
°     ECMO, external membrane oxygenation and CO2 removal: lung rest and minimisation of VALI.

Discussion

This question is about the ventilation strategies in ARDS, which is a topic discussed elsewhere:

• Ventilation strategies for ARDS
• Supportive non-ventilation strategies for ARDS

In summary:

Initial ventilator strategy:

• Use a Pressure Control mode (it may be safer, though the evidence is not strong)
• Lung-protective ventilation: use low tidal volumes (6ml/kg)
• Open-lung ventilation: avoid derecruitment by using a high PEEP
  • The ideal PEEP can be found either by finding the lower inflection point or the pressure-volume curve or by observing a stepwise decrease in PEEP after a recruitment manoeuvre.
  • As the ARDS severity increases, consider using a higher PEEP. 
• Use a lower driving pressure (ΔP) -Amato et al, 2015. That means, using a higher PEEP and aiming for a lower plateau pressure
• Accept a level of "permissive hypercapnea"

Additional ventilator manoeuvres to improve oxygenation:

• Use an I:E ratio of 1:1, even though manipulating the I:E ratio does not seem to improve survival, even though it may improve oxygenation.
• One might attempt some recruitment manoeuvres if hemodynamics permit. Again, these offer a transient improvement in oxygenation, but do not influence survival.

Non-ventilator adjunctive therapies for ARDS:

Ventilator strategies to manage refractory hypoxia

• Prone ventilation, for at least 16 hours a day (PROSEVA, 2013)
• High frequency oscillatory ventilation may not improve mortality among all-comers (OSCAR, 2013) or it may actually increase mortality (OSCILLATE, 2013) but some authors feel that there were problems with methodology.

Non-ventilator adjuncts to manage refractory hypoxia

• Nitric oxide was a cause for some excitement, but is no longer recommended.
• Prostacyclin is still a cause for excitement, and is still vaguely recommended.
  • Neither agent improves mortality, but prostacyclin can improve oxygenation.
• ECMO may improve survival (CESAR, 2009) but again there were problems with methodology.