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Delayed derecruitment after removal of PEEP in patients with acute lung injury
M Lichtwarck-Aschoff1, J Guttmann, L Eberhard
1Department of Anesthesiology and Surgical Intensive Care, Central Hospital Augsburg, Federal Republic of Germany.
Background:
A step decrease in positive end-expiratory airway pressure (PEEP) is not followed by an instantaneous loss of the PEEP-induced increase in end-expiratory lung volume (EELV). Rather, the reduction of EELV is delayed, while adverse PEEP effects on hemodynamics are immediately attenuated upon the drop in airway pressure. Step PEEP increments were applied to the lungs of patients with acute lung injury. It was investigated retrospectively whether enlargement of end-expiratory lung volume and changes in lung mechanics persist 45 min after removal of the PEEP increment.
Methods:
In 14 patients with acute lung injury (LIS score 2.7) EELV and volume-dependent dynamic compliance of the respiratory system (Cdyn,rs) were determined 45 min after removal of an additional PEEP increment (0.64 kPa added to baseline PEEP of 1.0 kPa).
Results:
Nine patients kept an EELV gain of 13% (SD 7) and showed improved Cdyn,rs. In 5 patients, EELV was reduced (by 9% (SD 6)) and Cdyn,rs unchanged after removal of the PEEP increment compared to baseline.
Conclusion:
A subgroup of patients with acute lung injury, the characteristics of which remain to be defined, benefit from prolonged recruitment effects up to 45 min after removal of a PEEP increment, while sequelae of continuously increased airway pressures are minimised.