The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

HIGH FREQUENCY AND CONVENTIONAL VENTILATION: IMPACT OF LUNG VOLUME RECRUITMENT STRATEGIES ON PATHOPHYSIOLOGIC OUTCOMES AND INFLAMMATORY RESPONSES IN AN ANIMAL MODEL OF RESPIRATORY DISTRESS SYNDROME.

Patricia Meyers RRT, Ramesh Krishnan MD, Catherine Worwa RRT, Ron Goertz BS, Galen Schauer MD, Mark Mammel MD. Infant Pulmonary Research Center, Children's Hospitals and Clinics, St. Paul, MN

Introduction:
The impact of lung volume recruitment (LVR) strategies during high frequency oscillation (HFO, SensorMedics 3100) and conventional ventilation (CV, Dräger Babylog) on inflammation has not been studied. We hypothesized that in an animal model of saline lavage induced lung injury with artificial surfactant (Survanta ®) replacement,

the use of sustained inflation techniques (SI) during HFO would improve pathophysiologic outcomes and decrease inflammation compared to conventional inflation techniques during HFO and CV.

Methods: We compared synchronized intermittent mandatory ventilation with volume targeting (SIMV+V) to HFO in spontaneously breathing newborn piglets. Lung injury, defined as PaO2<60 torr at FiO2 of 1.0, was induced via saline lavage, surfactant was replaced and animal were randomized into 3 groups (n=8): SIMV+V with LVR achieved by stepwise 2 cm H2O increases in mean airway pressure (Paw), high frequency oscillation with conventional inflation (HFOCI) with LVR achieved by stepwise 2 cm H2O increases in Paw, or high frequency sustained inflation (HFOSI) Paw to 25 cm H2O for 30 seconds, then Paw was returned to 5 cm H2O above baseline. All groups were treated for 6 hours. Functional residual capacity (FRC) was estimated by chest impedance. Static pressure volume curves (P/V) were obtained at baseline, after lung injury and at 6 hours. Serum and bronchoalveolar lavage samples were collected for cytokines IL6, IL8 and TNF-α at baseline, after lung injury and at 6 hrs. Animals were euthanized and lungs were fixed for histopathology and morphometrics. Tissue samples for cytokine mRNA analysis were collected at the end of the study, and from an untreated control group of animals (n=8) prior to and after lung injury.

RESULTS:
FRC change during LVR was greatest using SIMV+V and HFOCI vs HFOSI (p<0.05); HFOSI required higher Paw for LVR compared to SIMV+V (p,0.005). P/V curves showed higher lung compliance with SIMV+V vs HFOCI (p<0.05). The mRNA expression, lavage & serum cytokine responses, histopathology and morphometrics were similar in all 3 groups.
Conclusions: SIMV+V and HFOCI adequately recruited lung volumes without creating more lung injury. A single SI during HFO may not be adequate for LVR.

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