The struggle to make a dent in the mortality of acute respiratory distress syndrome (ARDS) has frustrated clinicians and researchers for decades. It is perhaps for this reason that there has been much tinkering with a vast array of technological advances and novel modalities, most of which have not been supported by high level clinical studies. Among the latest approaches to fail the rigorous test of evidence based medicine was the use of high “recruitment” levels of positive end expiratory pressure (PEEP). This was discussed in my recent post about ARDS.
As a follow up I should mention the paper by Gattonini and colleagues in the April 27 issue of NEJM (also recently cited by Pulmonary Roundtable). Gattonini has done pioneering work to help advance understanding of the pathophysiology of ARDS. The investigators demonstrated a method of CT imaging to determine the amount of recruitable lung in patients with ARDS. Not surprisingly patients were heterogeneous in the amount of recruitable lung present. A significant number of patients had little recruitable lung. Such patients might be harmed by high levels of PEEP. For those patients with larger degrees of recruitable lung, this study does not tell us how much PEEP is optimal.
An accompanying editorial discusses physiologic rationale and contains illustrations (with a video clip in the on line version) of ex vivo rat lung ventilation with and without PEEP, demonstrating dramatically how PEEP restores homogeneity of aeration by recruiting atelectatic areas. Striking as this illustration is the editorial writer reminds us that the ARDSnet study found no benefit of high level PEEP compared with conventional PEEP.
So what approach should we use? The best guide is still the ARDSnet PEEP scale.