The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

INSPIRATORY PRESSURE-TIME CURVE DURING CONSTANT FLOW INFLATION PREDICTS VENTILATOR INDUCED LUNG INJURY (VILI).

M. Aubin RRT, H. Zhang MD, S. Mehta MD, A.S. Slutsky MD, V.M. Ranieri MD, University of Toronto, ON. Canada, and University of Bari, Italy

The static volume-pressure curve may be a valuable tool to minimize VILI in ARDS patients, however some limitations have been identified. As an alternative, the dynamic pressure-time curve found on most modern ventilators may overcome these limitations. The pressure profile at the airway opening (Pao) during constant flow inflation reflects changes in the elastic properties of the respiratory system. During tidal inflation, a straight Pao curve indicates that compliance (C) is constant (no stress), an upward concavity indicates progressive reduction of C (overdistension), and a downward concavity indicates progressive increase of C (recruitment-derecruitment). We hypothesized that continuous measurement of such profiles can be used to predict the development of VILI. Lung injury (PaO2/FiO2<100) was induced by saline lavage in 30 rats. The lungs were excised and ventilated with a constant inspiratory flow. Inspiratory Pao was continuously fitted to a power equation (Pao=a×tb+c) where ?b? represents the shape of the curve. Peep(cmH20) and Vt (ml/kg) were set to obtain a ?b? of 1 (straight line) and a lung recruitment maneuver was performed. The lungs were then randomized to 3 groups: recruitment/derecruitment (R/D)(b=0.1-0.3), no stress (b=0.9-1.2), and overdistension(OD) (b>1.5). The lungs were ventilated for 3 hours, then 1 lung was fixed with buffered formalin for morphologic examination and the other lung was lavaged for cytokine measurements (IL-6 and MIP-2)

Vt PEEP Pplat b IL-6 MIP-2 Airway injury score
R/D 7±2 0±0* 25±2 0.3±0.03 3750±370* 1252±146* 36.7±9.3*
No stress 5±2 15±1 31±7 1.1±0.0 1632±245 511±71 5.7±2.0
OD 11±3* 13±2 65±11* 1.7±0.09 2758±379* 1016±181* 33.3±11.4*
*p<0.05 vs. no stress Values are means ±SE

Continuous monitoring and adjustment of the inspiratory portion of the dynamic pressure-time curve can be used to set ventilatory settings which minimize VILI.. MRC Canada and CNR Italy

OF-99-156

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