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J Appl Physiol 102: 331-339, 2007. First published September 7, 2006; doi:10.1152/japplphysiol.00002.2006
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Maintenance of end-expiratory recruitment with increased respiratory rate after saline-lavage lung injury

¹Department of Clinical Studies, Section of Critical Care, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; ²Department of Anesthesiology, Johannes Gutenberg University, Mainz, Germany; ³Department of Anesthesiology and Critical Care, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; and ⁴Oscillogy, Folsom, Pennsylvania

Submitted 3 January 2006 ; accepted in final form 19 August 2006

Cyclical recruitment of atelectasis with each breath is thought to contribute to ventilator-associated lung injury. Extrinsic positive end-expiratory pressure (PEEPe) can maintain alveolar recruitment at end exhalation, but PEEPe depresses cardiac output and increases overdistension. Short exhalation times can also maintain end-expiratory recruitment, but if the mechanism of this recruitment is generation of intrinsic PEEP (PEEPi), there would be little advantage compared with PEEPe. In seven New Zealand White rabbits, we compared recruitment from increased respiratory rate (RR) to recruitment from increased PEEPe after saline lavage. Rabbits were ventilated in pressure control mode with a fraction of inspired O₂ (FI_O2) of 1.0, inspiratory-to-expiratory ratio of 2:1, and plateau pressure of 28 cmH₂O, and either 1) high RR (24) and low PEEPe (3.5) or 2) low RR (7) and high PEEPe (14). We assessed cyclical lung recruitment with a fast arterial PO₂ probe, and we assessed average recruitment with blood gas data. We measured PEEPi, cardiac output, and mixed venous saturation at each ventilator setting. Recruitment achieved by increased RR and short exhalation time was nearly equivalent to recruitment achieved by increased PEEPe. The short exhalation time at increased RR, however, did not generate PEEPi. Cardiac output was increased on average 13% in the high RR group compared with the high PEEPe group (P < 0.001), and mixed venous saturation was consistently greater in the high RR group (P < 0.001). Prevention of end-expiratory derecruitment without increased end-expiratory pressure suggests that another mechanism, distinct from intrinsic PEEP, plays a role in the dynamic behavior of atelectasis.

acute lung injury; atelectasis; cyclical recruitment; intrinsic positive end-expiratory pressure; viscoelasticity; arterial oxygen oscillations

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				C. M. Otto, K. Markstaller, O. Kajikawa, J. Karmrodt, R. S. Syring, B. Pfeiffer, V. P. Good, C. W. Frevert, and J. E. Baumgardner Spatial and temporal heterogeneity of ventilator-associated lung injury after surfactant depletion J Appl Physiol, May 1, 2008; 104(5): 1485 - 1494. [Abstract] [Full Text] [PDF]

				E. Costa and M. Amato Maintenance of end-expiratory recruitment with increased respiratory rate after saline-lavage lung injury J Appl Physiol, June 1, 2007; 102(6): 2414 - 2414. [Full Text] [PDF]

				J. E. Baumgardner and R. S. Syring Reply to Costa and Amato J Appl Physiol, June 1, 2007; 102(6): 2415 - 2415. [Full Text] [PDF]