PEEP – a “cheap” and effective lung protection

Idealised pressure–volume curve of a single breath to demonstrate the principles underlying the location of the points referred to in the text. The up-going arrow represents the inflationary limb and the down-going arrow the deflationary limb. A, the lower inflection point or appropriate positive end-expiratory pressure, as described by Mathe et al.³⁶ or the P flex mentioned by Gattinoni et al.⁴⁵ B, the end of the linear portion of the curve that represents the most desirable portion of the curve avoiding underdistension and collapse and overdistension and the potential for barovolutrauma. This corresponds to the so-called upper inflection point, described by Mergoni et al.⁴⁶ and used by Rimensberger et al.³⁸ C, the point of ‘maximum’ inflation, at which inflation ends and deflation begins. D, the so-called closing pressure, as used by Rimensberger et al.³⁸ Rimensberger et al. found that the pressure at point D was less than that at B.