DOI: 10.1097/pcc.0000000000004074 ISSN: 1529-7535

Flow-to-Compliance Ratio as a Bedside Marker of Strain Rate in Pediatric Acute Respiratory Distress Syndrome: Analysis of Observational Cohort Data From 2022

Pablo Cruces, Marjorie Améstica, Juan P. Cruces, Franco Díaz
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Objectives:

To determine the relationship between the ratio of peak inspiratory flow and respiratory system compliance (Flow/C RS ) and strain rate in cases of pediatric acute respiratory distress syndrome (PARDS).

Design:

Secondary analysis of observational cohort data collected in 2022.

Setting:

Single-center tertiary PICU in Chile.

Patients:

Thirty-one mechanically ventilated patients with early PARDS, 15 years or younger.

Interventions:

None.

Measurements and Main Results:

All patients were supported with volume-controlled ventilation during measurement of pulmonary mechanics, including tidal volume (V

t
), inspiratory time (Ti), inspiratory flow, and respiratory system compliance (C RS ). End-expiratory lung volume (EELV) was assessed using the nitrogen multiple-breath wash-in/washout method. Lung strain (V
t
/EELV), strain rate (lung strain/Ti, s –1 ), and the Flow/C RS ratio ([L·min –1 ]/[mL·cm H 2 O –1 ]) were calculated. The median (interquartile range [IQR]) strain rate was 0.56 s –1 (IQR, 0.40–0.73 s –1 ) and the median Flow/C RS ratio was 0.94 (IQR, 0.77–1.20). In the complete dataset, Flow/C RS ratio demonstrated a moderate positive correlation with measured strain rate (Spearman, ρ = 0.42; 95% CI, 0.08–0.67; p = 0.009). Linear regression confirmed a proportional relationship ( R 2 = 0.17; p = 0.022), but the Bland-Altman analysis showed systematic bias (mean difference, −0.43 ± 0.29 s −1 ) with 95% limits of agreement from −0.99 to 0.14 s −1 . Sensitivity analysis excluding three outliers (leaving data from 28 patients) demonstrated a stronger association (ρ = 0.63; p = 0.0018) and improved model fit ( R 2 = 0.41; p < 0.001), with the following equation: strain rate = 0.61·(Flow/C RS ) + 0.01.

Conclusions:

In PARDS, the Flow/C RS ratio is associated with measured strain rate but exhibits systematic bias, precluding direct interchangeability. Flow/C RS may serve as a pragmatic bedside marker reflecting deformation-velocity behavior. Prospective validation in larger and more heterogeneous cohorts is required.

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