Utilization of the Lower Inflection Point of the Pressure-Volume Curve Results In Protective Conventional Ventilation Comparable to High Frequency Oscillatory Ventilation in an Animal Model of Acute Respiratory Distress Syndrome

Abstract

aRossi FS, Mascaretti RS, Haddad LB, Freddi NA, Mauad T, Rebello CM. Utilization of the lower inflection point of the pressure-volume curve results in protective conventional ventilation comparable to high frequency oscillatory ventilation in an animal model of acute respiratory distress syndrome. Clinics. 2008;63:237-44. INTRODUCTION:Studies comparing high frequency oscillatory and conventional ventilation in acute respiratory distress syndrome have used low values of positive end-expiratory pressure and identified a need for better recruitment and pulmonary stability with high frequency. OBJECTIVE: To compare conventional and high frequency ventilation using the lower inflection point of the pressure-volume curve as the determinant of positive end-expiratory pressure to obtain similar levels of recruitment and alveolar stability. METHODS: After lung lavage of adult rabbits and lower inflection point determination, two groups were randomized: conventional (positive end-expiratory pressure = lower inflection point; tidal volume=6 ml/kg) and high frequency ventilation (mean airway pressures= lower inflection point +4 cmH 2 O). Blood gas and hemodynamic data were recorded over 4 h. After sacrifice, protein analysis from lung lavage and histologic evaluation were performed. RESULTS: The oxygenation parameters, protein and histological data were similar, except for the fact that significantly more normal alveoli were observed upon protective ventilation. High frequency ventilation led to lower PaCO 2 levels. DISCUSSION: Determination of the lower inflection point of the pressure-volume curve is important for setting the minimum end expiratory pressure needed to keep the airways opened. This is useful when comparing different strategies to treat severe respiratory insufficiency, optimizing conventional ventilation, improving oxygenation and reducing lung injury. CONCLUSIONS: Utilization of the lower inflection point of the pressure-volume curve in the ventilation strategies considered in this study resulted in comparable efficacy with regards to oxygenation and hemodynamics, a high PaCO 2 level and a lower pH. In addition, a greater number of normal alveoli were found after protective conventional ventilation in an animal model of acute respiratory distress syndrome.

Lung Morphometry, Collagen and Elastin Content: Changes after Hyperoxic Exposure in Preterm Rabbits

“…This study investigated, for the first time, the effects of hyperoxia on lung morphometry and the collagen and elastin content in the preterm rabbit model. In rabbits, the gestational period is 31 days, with 28 days of gestation representing the limit of viability, 22 , 23 which corresponds to 87% of the gestation term, and to the saccular phase of lung development. When the alveolarization process starts it would correspond with a premature newborn in the saccular phase of normal lung development.…”

Optimal PEEP settings in mechanical ventilation using EIT

“…In this study the lower inflection point were reported to be similar to other papers using the same animal model and showed that setting PEEP to the lower inflection point achieves more normal states compared to High Frequency Oscillatory Venti lation (HFOV) when the possible states were collapsed, normal and overdistended [Rossi et al, 2008] [Venegas et al, 1998] introduced the use of the sigmoid model as an automated method to find inflection points and has been used by many other researches since [Hinz et al, 2006, Albaiceta et al, 2004, Harris et al, 2000.…”

“…[ Martin-Lefevre et al, 2001] also compared the visually inspected inflection points to a linear segmental regression method and found a correlation of 0.54 and 0.84 for the lower and upper inflection points respectively. [Rossi et al, 2008] conducted a study in which the LIP were found by multiple people and averaged together with a repeat of the experiment if the two inflection points differed by more then 2 mbar.…”