How to personalize PEEP and tidal volume in ARDS?

By Dr Tomasso Mauri, University of Milan

  • ARDS is a heterogenous disease with several sub-phenotypes. Therefore, it makes sense to personalize ventilatory management.
  • To personalize the management, we need individualized bedside monitoring –
    • Respiratory mechanics, Esophageal pressure, Electrical impedance tomography are some of the bedside tools available for monitoring

Personalizing PEEP in patients with potential lung recruitability:

  • Goals of PEEP – Stabilize recruitment and avoiding VILI
  • PEEP when set between closing and opening pressure provides stable recruitment
  • Stable recruitment –> decreases inflammation
  • PEEP personalized using one of P/F ratio, Esophageal Pressure (EP), Electrical Impedance tomography (EIT) or Recruitment/Inflation index (R/I)
  • Recruitment correlated with P/F at PEEP 5 (low P/F – higher potential for recruitment)
  • Heavy lung (more oedema) -> higher EP -> higher potential for recruitment; choose the PEEP associated with zero transpulmonary pressure at end expiration
  • Assessment of volume of recruitment between lower and higher PEEP (5-15 cmH2O) levels used to calculate R/I index (>0.5 indicates higher potential for recruitment); use the double PV loop method
  • EIT aids in dynamic assessment of tidal volume in the dependent lung (EIT ventilation/EIT perfusion) – personalizing PEEP based on this leads to homogenous V/Q -> evolving technology.

Personalizing tidal volume in ARDS:

  • Height can help calculate PBW to get 6ml/kg tidal volume, but not the size of the baby lung
  • Better estimate the size of the baby lung is the compliance (=tidal volume/driving pressure)
  • Driving pressure = Tidal volume/Compliance (baby lung)
  • Driving pressure <14 cmH2O is associated with reduced mortality
  • Start at 6ml/kg tidal volume, personalize the PEEP and measure driving pressure -> aim is to keep driving pressure under 15 cmH2O and Plateau under 30 cmH2O
  • With very low tidal volumes, CO2 can accumulate causing respiratory acidosis – consider ECCO2-R in such a situation
  • Tidal volume, once selected after personalizing the PEEP, must be maintained for 48 hours or until spontaneous breathing established