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Online ISSN 1827-1596
Schumann S.1, Goebel U. 1, Haberstroh J. 2, Vimlati L. 3, Schneider M. 1, Lichtwarck-Aschoff M. 3, Guttmann J. 1
1 Department of Anesthesiology and Critical Care Medicine, University Medical Centre Freiburg, Freiburg, Germany;
2 Experimental Surgery, CEMT, University Medical Centre Freiburg, Freiburg, Germany;
3 Department of Surgical Sciences/Section of Anaesthesiology and Critical Care Medicine, Uppsala University, Uppsala, Sweden
Background: Differences between inspiratory and expiratory lung mechanics result in the hysteresis of the pressure volume-loop. While hysteresis area is a global parameter describing the difference between inspiration and expiration in mechanics under quasi-static conditions, a detailed analysis of this difference under the dynamic conditions of mechanical ventilation is feasible once inspiratory and expiratory compliance (Cin/Cex) are determined separately. This requires uncoupling of expiratory flow rate and volume (V).
Methods: Five piglets were mechanically ventilated at positive end-expiratory pressure (PEEP) levels ranging from 0 to 15 cmH2O. Expiratory flow rate was linearized by a computer-controlled resistor (flow-controlled expiration). The volume-dependent Cin(V) and Cex(V) profiles were calculated from the tracheal pressure volume-loops.
Results: The intratidal curve-progression of Cex(V) was altogether higher with a steeper slope compared to Cin(V). With increasing positive end-expiratory pressure (PEEP) dynamic hysteresis area decreased and Cex(V) tended to run more parallel to Cin(V).
Conclusion: The relation between inspiratory and expiratory compliance profiles is associated with the hysteresis area and behaves PEEP dependent. Analysing the Cin-Cex-relation might therefore potentially offer a new approach to titrate PEEP and tidal volume.