What has been learnt fromP/Vcurves in patients with acute lung injury/acute respiratory distress syndrome

Abstract

What has been learnt from P/V curves in patients with acute lung injury/acute respiratory distress syndrome. S.M. Maggiore, J-C. Richard, L. Brochard. #ERS Journals Ltd 2003. ABSTRACT: Mechanical impairment of the respiratory system was recognised soon after the description of acute respiratory distress syndrome. The analysis of the pressure/volume (P/V) curve of the respiratory system contributed a lot to the understanding of the pathophysiology of acute lung injury and formed the basis for lung protection. The lower and upper inflection points were regarded as points of interest to avoid cyclic derecruitment and overdistension and to optimise ventilatory settings. However, because of the heterogeneity of lung injury, reducing the mechanical properties of the whole respiratory system to a single curve is a schematic approach, which makes interpretation difficult.New data suggest that alveolar re-inflation occurs along the whole P/V curve that can, therefore, be considered as a recruitment curve. The lower inflection point has no relationship with alveolar opening and closure and does not indicate the positive endexpiratory pressure needed to prevent alveolar collapse. The shape of the P/V curve gives information about the extension and the homogeneity of lung injury, indicating the possibility of lung recruitment. The upper inflection point, classically seen as the beginning of overdistension, may also indicate the end of recruitment.The pressure/volume curve offers the unique opportunity of evaluating alveolar recruitment/derecruitment at the bedside that can be helpful for the identification of optimal ventilatory settings and makes the curve a valuable tool for the ventilatory management of acute lung injury. Eur Respir J 2003; 22: Suppl. 42, 22s-26s. Since its first description, acute respiratory distress syndrome (ARDS) was recognised as a condition characterised by the decrease of lung volume and mechanical abnormalities of the respiratory system [1]. It was therefore tempting to correlate the mechanical impairment of the respiratory system with the severity of the disease and to set the ventilatory parameters accordingly. In 1972, FALKE et al.[2] described the changes in dynamic compliance and tidal pressure/volume (P/V) loops with the application of positive end-expiratory pressure (PEEP) in patients with acute respiratory failure (currently classified as acute lung injury (ALI) or ARDS) [2]. A few years later, SUTER et al. [3] showed in a classical paper that the measurement of static or effective compliance (calculated by dividing the tidal volume (VT) by the difference between end-inspiratory plateau pressure and end-expiratory pressure) could be helpful in determining the PEEP level resulting in optimum cardiopulmonary function. The PEEP level corresponding to the highest static compliance resulted in the best oxygen transport and the lowest deadspace fraction, suggesting optimal alveolar recruitment without overdistension. However, the interaction between ventilatory settings and respiratory mechan...

Ventilating the Lungs Safely: What’s New for Infants and Children?

“…A superior correlation was found between alveolar de-recruitment and the deflation limb of the P-V curve [5,6]. This finding may be explained by ventilation heterogeneity that has been observed in both healthy and injured lungs [7,8].…”

Paediatric lung recruitment: a review of the clinical evidence

“…43 Two studies caution clinicians against using inbuilt ventilator P-V software as they had significant deleterious results in their research. [44][45][46][47] P-V loops may provide clinicians with data regarding lung aeration yet do not distinguish between hyperinflation and recruitment and provide no information in regard to distribution of ventilation. 46 Due to the heterogeneity of the techniques used to conduct lung recruitment it is not possible to pool the data for further analysis.…”

Crackle-sound recording to monitor airway closure and recruitment in ventilated pigs

“…The patency of the peripheral airways can be assessed qualitatively by analysing the lower inflection point of the static pressure-volume (P-V) curve [1, 5, 11, 15-18, 20, 21]. Although the shape of the P-V curve around the lower inflection point depends on many factors, such as chest wall tissue nonlinearities [16], surfactant redistribution [17,22], collapse and reopening of the alveoli and bronchi [15,21], and dynamic hyperinflation [18], it is the analysis of the P-V relationships of the respiratory system that has afforded the most comprehensive data on pulmonary recruitment [1,15,17,20,21]. Quantitative analysis of the small airway function can also be accomplished by using lungimaging techniques, such as thoracic computed tomography or magnetic resonance imaging [23], although performance of these investigations in a continuous bedside setting is not yet feasible.…”