Prone who, when and for how long? Are we clear now?

prone sud forrestProning in ICU is 40 years old now. Meta-analyse 11 high-quality studies in a thorough manner (including blinding to authors!) and it appears strikingly good, with an NNT of 11 – definitely better than protective ventilation alone.  Do it in the severely hypoxic (P/F <100 mmHg), do it early (within 72 hours), do it for more than 16 hours and expect some excess skin pressure damage and the odd airway panic. Is it safe and ‘externally valid’ to apply this in units that prone only occasionally? How about practice sessions to keep up team proning skills?