Lung-Protective Ventilation Settings

Once ARDS has been diagnosed, the patient should be placed on lung-protective ventilation settings according to the ARDSNet ventilator management card.23 The patient’s PBW is determined by measuring the patient’s height and then using the appropriate sex-based calculation. Note there are two different PEEP tables, one with a lower PEEP and higher FiO2 and the other with a higher PEEP and lower FiO2. Either is acceptable, but meta-analysis suggests a trend towards improved survival using the high PEEP table in patients with moderate to severe ARDS by modern criteria.24 In all cases, the “driving pressure” (PPLAT – PEEP) should be minimized to optimize the patient’s chances of survival.25 During the initial management, a VT of 8 mL/kg may be used, but this should be decreased to 6 mL/kg within 2-4 hours. If the PPLAT remains above 30 cm H2O, the tidal volume can be further reduced to 4 mL/kg so long as there is evidence of adequate oxygen delivery to peripheral tissues (normal lactate and base deficit).26 Other modes of ventilation besides volume-assist-control can be used, but this should be at the discretion of an intensivist experienced in the management of ARDS.

Rescue Oxygenation Therapies

Advanced therapies for ARDS patients are limited in an austere environment. Low-level recruitment maneuvers performed by holding 40 cm H2O pressure for 40 seconds can be performed by the patient’s provider, but the team should be prepared to manage unstable hemodynamics due to decreased venous return. Other measures such as inhaled Nitric Oxide (iNO) or inhaled prostacyclin (Flolan) are not typically available in Role 3 facilities. Advanced rescue ventilator modes such as inverse ratio ventilation or Airway Pressure Release Ventilation (APRV) should be utilized under the supervision of an experienced intensivist.

Extracorporeal Life Support

Early consideration for Veno-Venous Extracorporeal Life Support (vvECLS) is vital in patients who are failing attempts at lung-protective ventilation.27 If gas exchange and perfusion goals are not met after 12 hours of lung-protective ventilation and the patient has been paralyzed and proned, then extracorporeal support should be considered. Additionally, transport of patients who are supported with vvECLS may be safer and easier if an extracorporeal transport team is available. (See Transport of ARDS patients below).

Indications for initiating Extracorporeal Membrane Oxygenation (ECMO) for respiratory failure include:

1. P:F ration <100 or plateau pressures > 30cm H2O despite optimal ventilator management.
2. Respiratory acidosis with pCO2>70 and a pH <7.25 despite optimal ventilator management.
3. Initiation of ARDS rescue therapies (PEEP>15, prone positioning, High Frequency Oscillation (HFOC), iNO, prolonged paralysis).
4. Respiratory failure associated with significant barotrauma needed for ventilator support.

ECMO consultation is available 24 hours a day and can be coordinated through the Institute of Surgical Research (ISR) Burn Unit (210-222-BURN). Due to the dramatic sequelae of acute respiratory failure and the time required to generate a potential ECMO transport team, early notification is paramount. Early consultation with the ECMO team is essential, even if it is prior to 12 hours of respiratory failure.