The Lancet has now published the multi-centre study (PROVHILO) which has looked at the role of positive end-expiratory pressure (PEEP) for mechanical ventilation during general anaesthesia. For that reason the PROVE network investigators have included almost 900 patients in a randomised controlled trial who were planned for open abdominal surgery. All patients were ventilated with a tidal volume (Vt) of 8ml/kg. One group received a PEEP of 12 cmH2O and recruitement maneuvres while the other group got alomst no PEEP (<2 cmH2O) and no recruitement maneuvres. Primary endpoint were pulmonary compications on day 5 postoperatively. They found no difference in pulmonary complications but significantly more introperative hypotension and use of vasoactive agents in the higher PEEP group.
So the investigators conclude that a higher level of PEEP and recruitment maneuvres do not protect against postoperative pulmonary complications. They actually advise to use low tidal volumes and very low PEEP for intraoperative ventilation.
The multicenter study is well designed and performed but some questions remain:
Why is PEEP never adjusted to weight?
One striking feature is that we all use tidal volumes according to the patients body weight, but interestingly nobody seems to use this adjustement for weight when it comes to PEEP. Using a PEEP of 12 in a small and slim 50kg patient has a different impact compared to a massively obese patient.
Is 12 cmH2O too high?
A PEEP of 12 can be considered generally high and is not used by most anaesthetists in their daily practice anyway. There was no third arm using intermediate levels of PEEP to answer the question on how these patient might have performed.
Why did other trial find differing conclusions?
The aspect of different levels of PEEP is interesting as previous studies actually were able to show improved outcome with 'protective' mechanical ventilation. The IMPROVE trial in the NEJM from Augut 2013 compared patients for abdominal surgery ventilated with Vt of 10-12ml/kg and 0 cmH2O of PEEP to patients ventilated with Vt of 6-8ml/kg and 6-10 cmH2O of PEEP. In this multicenter, double blind trial with 400 patients improved outcome and reduced health care utilazation were found in the group 'protectively' ventilated.
In june 2013 Anaesthesiology published a prospective randomized small trial with 56 patients undergoing open abdominal surgery for more than 2 hours. This time they compared Vt of 9ml/kg and O PEEP to Vt of 7ml/kg and 10 PEEP. This time 'protective' ventilation with PEEP improved respiratory function but did not affect length of hospital stay.
Taking these fact into account I think we remain with following conclusions:
- The PROVHILO trial is not reason enough to abandon PEEP for anaesthetic ventilation in theatre
- Instead we might have to consider adjusting PEEP to the patients clinical condition (e.g. weight)
- There is no evidence currently to recommend routine recruitment maneuvers in theatre
The Prove Network Investigators, The Lancet, Early Online Publication, 1 June 2014