Longitudinal PEEP Responses Differ Between Children With ARDS and at Risk for ARDS

Abstract

BACKGROUND: It is unknown whether lung mechanics differ between patients with pediatric ARDS and at risk for ARDS. We aimed to examine the hypothesis that, compared to ARDS, subjects at risk of ARDS are characterized by higher end-expiratory lung volume (EELV) or respiratory system compliance (C RS) and lower distending pressure (stress) applied on the lung or parenchymal deformation (strain) during mechanical ventilation. METHODS: Consecutively admitted subjects fulfilling the PALICC ARDS criteria were considered eligible for inclusion in this study. A ventilator with an integrated gas exchange module was used to calculate EELV, C RS , strain, and stress after a steady state had been achieved based on nitrogen washout/washin technique. All subjects were subjected to incremental PEEP trials at 0, 6, 12, 24, 48, and 72 h. RESULTS: A total of 896 measurements were longitudinally calculated in 32 mechanically ventilated subjects (n 5 15 subjects with ARDS; n 5 17 subjects at risk for ARDS). EELV correlated positively with strain or stress in the ARDS group (r 5 0.30, P < .001) and the at risk group (r 5 0.60, P < .001). C RS correlated with strain (r 5 0.40, P < .001) only in subjects at risk for ARDS. EELV increased over time as PEEP rose from 4 to 10 cm H 2 O in subjects with ARDS (P 5 .001). In the at risk group, EELV only increased at 48 h (P 5 .001). Longitudinally, C RS (P 5 .001) and EELV (P 5 .002) were lower and strain and stress were higher in subjects with ARDS compared to those at risk for ARDS (P 5 .002), remaining within safe limits. Strain and stress increased by 24 h but declined by 72 h in subjects with ARDS at a PEEP of 4 cm H 2 O (P 5 .02). In the at risk group, strain and stress declined from 6 h to 72 h at a PEEP of 10 cm H 2 O (P 5 .001). CONCLUSIONS: Longitudinally, C RS and EELV were lower and strain and stress were higher in subjects with ARDS compared to subjects at risk for ARDS. These parameters behaved differently over time at PEEP values of 4 or 10 cm H 2 O. At these PEEP levels, strain and stress remained within safe limits in both groups.

Pathobiology, Severity, and Risk Stratification of Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference

“…Explicit protocols, definitions, and reporting of variables will allow us to combine data to detect differences in patient-centered outcomes in both observational studies and treatment trials (160). Our literature review confirmed that currently investigators use different strategies for assessing and reporting of oxygenation indices (Pao 2 /Fio 2 , OI, OSI, and/or Spo 2 / Fio 2 ), static and/or dynamic compliance, peak inspiratory pressure (PIP), positive end-expiratory pressure (PEEP), PIP minus PEEP, changes in these variables, driving pressure, mechanical power, stepwise recruitment maneuvers, and other mechanical ventilator parameters at onset of PARDS and at various timepoints within the first 24, and occasionally 48 to 72 hours, after PARDS onset (4,12,20,137,(163)(164)(165)(166)(167)(168)(169)(170)(171)(172)(173)(174). Methodology of measurements has been explicitly reported by some investigators (but not all) who each describe use of ideal body weight measurement in determining Vt (166,168).…”

The impact of PEEP on hemodynamics, respiratory mechanics, and oxygenation of children with PARDS

“…Virk et al observed a statistically significant decrease in dynamic compliance from 0.38 ml.cmH 2 O -1 .kg -1 (IQR 0.27 – 0.50) at a median PEEP of 8 cmH 2 O to 0.31 ml.cmH 2 O -1 .kg -1 (IQR 0.22 – 0.42) when PEEP was increased by 4 cmH 2 O (22). In another study, respiratory system compliance of 15 children with PARDS remained unchanged between PEEP levels of 4 and 10 cmH 2 O (30). As in the present study, these authors evaluated respiratory mechanics after a few minutes of increasing PEEP, which may not have been enough time to significantly open the collapsed lung regions.…”

“…However, other pediatric studies evaluating children with PARDS also did not observe improvement in respiratory system compliance when increasing PEEP (22,30). Virk et al observed a statistically significant decrease in dynamic compliance from 0.38 ml.cmH 2 O -1 .kg -1 (IQR 0.27 -0.50) at a median PEEP of 8 cmH 2 O to 0.31 ml.cmH 2 O -1 .kg -1 (IQR 0.22 -0.42) when PEEP was increased by 4 cmH 2 O (22).…”

The best PEEP or the optimal PEEP or the piece PEEP of the mechanical power puzzle?

“…In ARDS, strain and stress increased by 24 h, remaining within safe limits, and declined by 72 h at PEEP 10 (p = 0.02). In the at-risk group, strain and stress declined steadily from 6 to 72 h at PEEP 10 (p = 0.001) [4].…”

“…In a total of 896 measurements calculated in 32 mechanically ventilated subjects, we showed that time interacted differently with the two pediatric ARDS phenotypes at PEEP 4 and 10 cmH 2 O. In ARDS, strain and stress increased by 24 h, remaining within safe limits, and declined by 72 h at PEEP 10 ( p = 0.02).In the at-risk group, strain and stress declined steadily from 6 to 72 h at PEEP 10 ( p = 0.001) [ 4 ].…”