Diagnosis of ARDS:

  1. non-cardiogenic pulmonary edema
  2. acute onset
  3. bilateral opacities on imaging
  4. PaO2/FiO2 < 300

In treating ARDS, we want to prevent:

  1. barotrauma
  2. atelectatrauma
  3. volutrauma
  4. biotrauma
  5. O2 toxicity

To increase oxygenation, the parameters to adjust are FiO2 and PEEP.

To decrease hypercarbia, the parameters to adjust are respiratory rate and tidal volume.

Set tidal volume low (6cc/kg) to prevent volutrauma. Compensate for this with higher respiratory rate (20, for instance).

Recall that compliance is tidal volume over (plateau - PEEP). The denominator here is also known as driving pressure.

In ARDS, the goal is to maintain pH > 7.2, PaO2 > 55, O2 sat > 88%, and plateau pressure <30. We allow for some “permissive hypercarbia” to achieve these other parameters.

The best PEEP can be determined with:

  1. esophageal balloon, which measures pleural pressure. Set a PEEP such that PEEP - pleural pressure = transpulmonary pressure > 0.
  2. PEEP table (ARDSnet)
  3. P/V tracing (choose a PEEP where volume is responsive)
  4. Calculate driving pressure to achieve good compliance.

In refractory hypoxemia, you can try the following (but it probably won’t help too much):

  1. Diuresis
  2. Recruitment (high PEEP for short time intervals)
  3. Proning (the earlier the better, do for severely low P/F)
  4. Paralysis/sedation to decrease metabolic demands
  5. Pulmonary vasodilators (preferentially delivered to healthy alveoli)
  6. ECMO
  7. APRV
  8. Surfactant