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. 2024 Jul 4;14(1):106.
doi: 10.1186/s13613-024-01343-w.

Recruitment-to-inflation ratio reflects the impact of peep on dynamic lung strain in a highly recruitable model of ARDS

Francesco Murgolo #  1   2 , Domenico L Grieco #  3   4 , Savino Spadaro  5 , Nicola Bartolomeo  6 , Rossella di Mussi  7 , Luigi Pisani  7 , Marco Fiorentino  8 , Alberto Maria Crovace  9 , Luca Lacitignola  10 , Francesco Staffieri  10 , Salvatore Grasso  7
Affiliations

Recruitment-to-inflation ratio reflects the impact of peep on dynamic lung strain in a highly recruitable model of ARDS

Francesco Murgolo et al. Ann Intensive Care. .

Abstract

Background: The recruitment-to-inflation ratio (R/I) has been recently proposed to bedside assess response to PEEP. The impact of PEEP on ventilator-induced lung injury depends on the extent of dynamic strain reduction. We hypothesized that R/I may reflect the potential for lung recruitment (i.e. recruitability) and, consequently, estimate the impact of PEEP on dynamic lung strain, both assessed through computed tomography scan.

Methods: Fourteen lung-damaged pigs (lipopolysaccharide infusion) underwent ventilation at low (5 cmH2O) and high PEEP (i.e., PEEP generating a plateau pressure of 28-30 cmH2O). R/I was measured through a one-breath derecruitment maneuver from high to low PEEP. PEEP-induced changes in dynamic lung strain, difference in nonaerated lung tissue weight (tissue recruitment) and amount of gas entering previously nonaerated lung units (gas recruitment) were assessed through computed tomography scan. Tissue and gas recruitment were normalized to the weight and gas volume of previously ventilated lung areas at low PEEP (normalized-tissue recruitment and normalized-gas recruitment, respectively).

Results: Between high (median [interquartile range] 20 cmH2O [18-21]) and low PEEP, median R/I was 1.08 [0.88-1.82], indicating high lung recruitability. Compared to low PEEP, tissue and gas recruitment at high PEEP were 246 g [182-288] and 385 ml [318-668], respectively. R/I was linearly related to normalized-gas recruitment (r = 0.90; [95% CI 0.71 to 0.97) and normalized-tissue recruitment (r = 0.69; [95% CI 0.25 to 0.89]). Dynamic lung strain was 0.37 [0.29-0.44] at high PEEP and 0.59 [0.46-0.80] at low PEEP (p < 0.001). R/I was significantly related to PEEP-induced reduction in dynamic (r = - 0.93; [95% CI - 0.78 to - 0.98]) and global lung strain (r = - 0.57; [95% CI - 0.05 to - 0.84]). No correlation was found between R/I and and PEEP-induced changes in static lung strain (r = 0.34; [95% CI - 0.23 to 0.74]).

Conclusions: In a highly recruitable ARDS model, R/I reflects the potential for lung recruitment and well estimates the extent of PEEP-induced reduction in dynamic lung strain.

Keywords: Acute respiratory distress syndrome; Dynamic lung strain; Lung recruitment; Mechanical ventilation; Recruitment-to-inflation ratio.

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Conflict of interest statement

Salvatore Grasso in the past 2 years received fees for lectures and board membership from: Getinge Critical Care (Solna SW), Estor Critical Care (Pero, Milan Italy). Domenico Luca Grieco has received speaking fees by Gilead, Intersurgical, MSD and GE, reports having received travel accommodation by Fisher and Paykel, and discloses a research grant by GE. The other authors declare that they have no competing interest.

Figures

Fig. 1
Fig. 1
In the upper panel, box-violin graphs represent variation in global, dynamic and static lung strain going from PEEPLOW (light gray) to PEEPHIGH (dark gray). The lower panel depicts the correlations between recruitment-to-inflation (R/I) ratio and the changes in in global, dynamic and static lung strain going from PEEPLOW to PEEPHIGH. The dotted line represents linear regressions, and each dot represents one pig
Fig. 2
Fig. 2
Individual values of hyperinflated, normally aerated, poorly aerated, and non-aerated lung tissue, going from PEEPLOW to PEEPHIGH at end-expiratory and end-inspiratory time
Fig. 3
Fig. 3
Left and middle panels: Representative computed tomography (CT) images and corresponding voxel density histograms of a large transverse lung section acquired under two different experimental ventilation conditions at end-expiration. Each image was interpreted using the UCLA color coding table (OsiriX image processing software, http://www.osirixfoundation.com, Geneva, Switzerland). Non-aerated lung tissue, ranging from − 100 to + 100 Hounsfield Units (HU), was depicted in shades of red (from dark red to orange), poorly aerated lung tissue (between − 500 to − 100 HU) was represented in shades of green, and normally aerated lung tissue (between − 900 to − 500 HU) was coded in dark and light blue. However, hyperinflated lung tissue (ranging from − 1000 to − 900 HU), which would have been represented in purple, was not observed upon raising PEEP from PEEPLOW to PEEPHIGH. Right panel: experimental records in a representative animal showing the air flow and the opening airway pressure (Pao) traces during both experimental ventilation conditions. Dashed lines indicate the constant flow period
Fig. 4
Fig. 4
Left panels: Correlations between the absolute extent of PEEP-induced recruited volume (VREC) and tissue recruitment (TREC, upper panel) and gas recruitment (GASREC, lower panel). Middle and right panels: Correlations between the recruitment-to-inflation ratio (R/I) and absolute and normalized values of TREC (upper panel) and GASREC (lower panel). The dotted line represents linear regression, and each dot represents one pig
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