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Critical Care Medicine:
doi: 10.1097/01.CCM.0000147832.13213.1E
Laboratory Investigations

Positive end-expiratory pressure above lower inflection point minimizes influx of activated neutrophils into lung*

Monkman, Shelley L. BSc, RRT; Andersen, Chad C. MBBS, FRACP; Nahmias, Claude PhD; Ghaffer, Hasan BSc; Bourgeois, Jacqueline M. MD, MSc, FRCP(C); Roberts, Robin S. MSc; Schmidt, Barbara MD, MSc, FRCP(C); Kirpalani, Haresh M. BM, FRCP(UK), MSc

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Objectives: To compare the effects of low vs. high tidal volume (Vt) with three positive end-expiratory pressure (PEEP) strategies on activated neutrophil influx into the lung.

Design: Prospective, randomized controlled animal study.

Setting: Animal laboratory in a university hospital.

Subjects: Newborn piglets.

Interventions: Surfactant-depleted piglets were randomized in littermate pairs; to PEEP of either 0 (zero end-expiratory pressure [ZEEP]; n = 6), 8 cm H2O (PEEP 8; n = 5), or 1 cm H2O above the lower inflection point (LIP) (PEEP>LIP; n = 6). Within each pair piglets were randomized to a low Vt (5–7 mL/kg) or high Vt strategy (17–19 mL/kg). After 4 hrs of mechanical ventilation, 18-fluorodeoxyglucose (18FDG) was injected and positron emission tomography scanning was performed.

Measurements and Main Results: Vt and PEEP changes on influx constants of 18FDG were assessed by analysis of variance. A within-litter comparison of Vt was nonsignificant (p = .50). A between-litter comparison, ordered in linear trend rank, from ZEEP, to PEEP 8, to PEEP>LIP, showed a strong effect of PEEP on influx constant (p = .019).

Conclusions: PEEP set above the LIP on the inspiratory limb of the pressure-volume curve affords a stronger lung protection than Vt strategy.

© 2004 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins

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