A Functional and Morphologic Analysis of Pressure-Controlled Inverse Ratio Ventilation in Oleic Acid-Induced Lung Injury

Pressure controlled inverse ratio ventilation A (PCIRV) has been claimed superior to volume-controlled ventilation (VCV) in the treatment of severe acute respiratory failure (ARF). PCIRV has been reported to allow a reduction in minute ventilation, peak inspiratory airway pressure, and externally applied positive end-expiratory pressure (PEEP). Arterial oxygen tension (РаОг) has increased with PCIRV.” It has even been suggested that PCIRV might improve outcome in ARF. However, mean airway pressure increases and cardiac output (CO) falls, the former effect presumed to increase the danger of barotrauma and the latter resulting in reduced oxygen transport to peripheral tissues.
The rationale for PCIRV is basically twofold: (1) pressure-controlled ventilation causes rapid increase in inspiratory pressure and gas flow with early delivery of inspired gas, which is assumed to facilitate the opening of closed airways and collapsed lung units; and (2) the inverse ratio, ie, inspiration being of equal length or longer than expiration, keeps airways open, may facilitate further recruitment of alveoli and allows for a more homogenous gas mixing in the lungs. Expiration is interrupted before it is completed, causing buildup of a positive end-expiratory alveolar pressure, so called intrinsic PEEP (PEEPi) in detail canadian health & care mall. Although PEEPi was initially considered a negative effect of PCIRV by increasing the danger of barotrauma, it can also be considered beneficial in so far as it increases lung volume (FRC) and may contribute to alveolar recruitment.
A difficulty with previous studies is that they have seldom had control over the end-expiratory alveolar pressure when comparing VCV and PCIRV, so that external PEEP and PEEPi may have been different. Moreover, to our knowledge, no study has so far made a direct analysis of alveolar recruitment by different ventilatory modes. The present study was therefore undertaken in an oleic acid pig model with a comparison of PCIRV and VCV with identical PEEP levels. Central hemodynamics and gas exchange were compared and findings were related to recruitment of alveolar tissue and distribution of inspired gas by means of computed tomography (CT) of the chest.

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