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Clinical Trial
. 2023 Dec 1;139(6):801-814.
doi: 10.1097/ALN.0000000000004716.

Recruitment-to-inflation Ratio Assessed through Sequential End-expiratory Lung Volume Measurement in Acute Respiratory Distress Syndrome

Domenico Luca Grieco  1 , Gabriele Pintaudi  1 , Filippo Bongiovanni  1 , Gian Marco Anzellotti  2 , Luca Salvatore Menga  1 , Melania Cesarano  1 , Antonio M Dell'Anna  1 , Tommaso Rosá  1 , Luca Delle Cese  1 , Giuseppe Bello  1 , Valentina Giammatteo  1 , Veronica Gennenzi  1 , Eloisa S Tanzarella  1 , Salvatore L Cutuli  1 , Gennaro De Pascale  1 , Andrea De Gaetano  3 , Salvatore M Maggiore  2 , Massimo Antonelli  1
Affiliations
Clinical Trial

Recruitment-to-inflation Ratio Assessed through Sequential End-expiratory Lung Volume Measurement in Acute Respiratory Distress Syndrome

Domenico Luca Grieco et al. Anesthesiology. .

Abstract

Background: Positive end-expiratory pressure (PEEP) benefits in acute respiratory distress syndrome are driven by lung dynamic strain reduction. This depends on the variable extent of alveolar recruitment. The recruitment-to-inflation ratio estimates recruitability across a 10-cm H2O PEEP range through a simplified maneuver. Whether recruitability is uniform or not across this range is unknown. The hypotheses of this study are that the recruitment-to-inflation ratio represents an accurate estimate of PEEP-induced changes in dynamic strain, but may show nonuniform behavior across the conventionally tested PEEP range (15 to 5 cm H2O).

Methods: Twenty patients with moderate-to-severe COVID-19 acute respiratory distress syndrome underwent a decremental PEEP trial (PEEP 15 to 13 to 10 to 8 to 5 cm H2O). Respiratory mechanics and end-expiratory lung volume by nitrogen dilution were measured the end of each step. Gas exchange, recruited volume, recruitment-to-inflation ratio, and changes in dynamic, static, and total strain were computed between 15 and 5 cm H2O (global recruitment-to-inflation ratio) and within narrower PEEP ranges (granular recruitment-to-inflation ratio).

Results: Between 15 and 5 cm H2O, median [interquartile range] global recruitment-to-inflation ratio was 1.27 [0.40 to 1.69] and displayed a linear correlation with PEEP-induced dynamic strain reduction (r = -0.94; P < 0.001). Intraindividual recruitment-to-inflation ratio variability within the narrower ranges was high (85% [70 to 109]). The relationship between granular recruitment-to-inflation ratio and PEEP was mathematically described by a nonlinear, quadratic equation (R2 = 0.96). Granular recruitment-to-inflation ratio across the narrower PEEP ranges itself had a linear correlation with PEEP-induced reduction in dynamic strain (r = -0.89; P < 0.001).

Conclusions: Both global and granular recruitment-to-inflation ratio accurately estimate PEEP-induced changes in lung dynamic strain. However, the effect of 10 cm H2O of PEEP on lung strain may be nonuniform. Granular recruitment-to-inflation ratio assessment within narrower PEEP ranges guided by end-expiratory lung volume measurement may aid more precise PEEP selection, especially when the recruitment-to-inflation ratio obtained with the simplified maneuver between PEEP 15 and 5 cm H2O yields intermediate values that are difficult to interpret for a proper choice between a high and low PEEP strategy.

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Conflict of interest statement

Dr. Grieco has received payments for travel expenses from Getinge (Göteborg, Sweden), and personal fees from GE Healthcare (Chicago, Illinois), Intersurgical (Mirandola, Italy), Fisher & Paykel Healthcare (Auckland, New Zealand), and Merck Sharp & Dohme (Rahway, New Jersey). Dr. Maggiore is the principal investigator of the Re-intubation after nasal high-flow (RINO) trial (www.clinicaltrials.gov, NCT02107183), which was supported by Fisher & Paykel Healthcare, and declares receiving speaker’s fees from GE Healthcare, Masimo (Irvine, California), Aspen (Durban, South Africa), and Getinge and participating in an advisory board for Sanofi (Paris, France). Dr. Antonelli has received payments for board participation from Maquet (Rastatt, Germany), Air Liquide (Paris, France), and Chiesi (Parma, Italy). Drs. Grieco and Antonelli disclose a research grant from GE Healthcare. The other authors declare no competing interests.

Figures

Fig. 1.
Fig. 1.
Flow chart of the study protocol. After assessment of eligibility, a single-breath derecruitment maneuver, followed by slow inflation, was performed to assess the presence of airway closure. Patients presenting with airway closure were excluded. After enrollment, each patient was ventilated at positive end-expiratory pressure (PEEP) 15 cm H2O for 40 min to stabilize lung volumes. Before the start of the PEEP trial, an arterial blood gas sample was collected, and respiratory mechanics were assessed by the ventilator. Afterward, a five-step decremental PEEP trial (PEEP 15 to 13 to 10 to 8 to 5 cm H2O) was conducted with the dedicated software of the ventilator. Each PEEP step lasted 8 min. At each step, the ventilator automatically measured and collected respiratory mechanics (plateau pressure, total PEEP, driving pressure, respiratory system compliance, and end-expiratory lung volume). At the end of the PEEP trial, blood gases were analyzed, and a single-breath derecruitment maneuver was performed to assess functional residual capacity (FRC). After the end of the study, ventilation was resumed as clinically indicated by the attending physician.
Fig. 2.
Fig. 2.
(Top left) Heat map showing the recruitment-to-inflation ratio from 15 to 5 cm H2O (first column) and the recruitment-to-inflation ratio measured within the narrower positive end-expiratory pressure (PEEP) ranges of the trial. Each row represents an individual patient. (Top right) Heat map showing the compliance of the recruited volume (ml/cm H2O) from 15 to 5 cm H2O (first column) and the compliance of the recruited volume measured within the narrower PEEP ranges of the trial. Each row represents an individual patient. Darker colors indicate higher values of recruitment-to-inflation ratio and compliance of the recruited volume, respectively. Individual patients are ordered according to the 15– 5–cm H2O recruitment-to-inflation ratio values, from highest to lowest (and hence from the darkest to the lightest color in the first column). (Bottom) Intrapatient variability between the recruitment-to-inflation ratio (left) and compliance of the recruited volume (right) in narrow PEEP ranges. Each bar represents the value obtained across the 10–cm H2O range. Black dots represent the four values obtained in the PEEP steps. Each column represents an individual patient.
Fig. 3.
Fig. 3.
(Top) Nonlinear fit of the recruitment-to-inflation ratio versus positive end-expiratory pressure (PEEP) over the decremental steps yielded a quadratic (parabolic) curve for average values from all studied patients (mean and standard error displayed). (Bottom) Nonlinear fit of the recruitment-to-inflation ratio versus PEEP in two representative patients. This figure shows the behavior of two typical patients, No. 1 (left, with a saturating recruitment-to-inflation ratio response to increasing PEEP) and No. 16 (right, with an ever-increasing recruitment-to-inflation ratio response to increasing PEEP).
Fig. 4.
Fig. 4.
Relationship between the PEEP-induced percent change in dynamic strain, static strain, and total strain, and the corresponding recruitment-to-inflation ratio measured between 5 and 15 cm H2O of positive end-expiratory pressure (PEEP; upper row) and within narrower PEEP ranges (lower row). Recruitment-to-inflation ratio, both measured across a 10–cm H2O range and within narrower PEEP ranges, has a strong relationship with the reduction in lung strain induced by PEEP. Specifically, patients with higher recruitment-to-inflation ratio exhibit a greater reduction in dynamic strain and a lower increase in static strain due to PEEP.
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