TRACING BEST PEEP BY APPLYING PEEP AS A RAMP

Objective: The aim of this study was to show the feasibility of a slow , continuously increasing level of positive end-expiratory pressure (P EEP) (ramp manoeuvre) in selecting best PEEP and to evaluate whether b est PEEP, as definded by maximal oxygen transport, coincides with best systemic arterial oxygenation or best compliance. Design: In 11 anaes thetized piglets, PEEP was increased between 0 cmH(2)O (zero end-expir atory pressure; ZEEP) and 15 cmH(2)O (PEEP15) with a constant rate of 0.67 cmH(2)O.min(-1). This ramp manoeuvre was performed both under nor mal conditions and after induction of an experimental lung oedema. Dur ing the ramp manoeuvre, haemodynamic and pulmonary variables were moni tored almost continuously. Results: During the rise in PEEP cardiac ou tput declined in a non-linear way. In the series with normal condition s, best PEEP was always found at ZEEP In the series with experimental lung oedema, best PEEP, as defined by maximum oxygen transport, was fo und at PEEP1-6, as defined by maximal compliance, at PEEP7.5 and by ma ximal arterial oxygen tension (PaO2) at PEEP10-14. Conclusions: Best P EEP according to oxygen transport is lower than best PEEP according to compliance and PaO2; the use of PEEP as a ramp might prevent unnecess arily high levels of PEEP.