Spatial distribution of sequential ventilation during mechanical ventilation of the uninjured lung: an argument for cyclical airway collapse and expansion

Scott E Sinclair,Nayak L Polissar,William A Altemeier

doi:10.1186/1471-2466-10-25

Abstract

BackgroundVentilator-induced lung injury (VILI) is a recognized complication of mechanical ventilation. Although the specific mechanism by which mechanical ventilation causes lung injury remains an active area of study, the application of positive end expiratory pressure (PEEP) reduces its severity. We have previously reported that VILI is spatially heterogeneous with the most severe injury in the dorsal-caudal lung. This regional injury heterogeneity was abolished by the application of PEEP = 8 cm H2O. We hypothesized that the spatial distribution of lung injury correlates with areas in which cyclical airway collapse and recruitment occurs.MethodsTo test this hypothesis, rabbits were mechanically ventilated in the supine posture, and regional ventilation distribution was measured under four conditions: tidal volumes (VT) of 6 and 12 ml/kg with PEEP levels of 0 and 8 cm H2O.ResultsWe found that relative ventilation was sequentially redistributed towards dorsal-caudal lung with increasing tidal volume. This sequential ventilation redistribution was abolished with the addition of PEEP.ConclusionsThese results suggest that cyclical airway collapse and recruitment is regionally heterogeneous and spatially correlated with areas most susceptible to VILI.

Highlights

Ventilator-induced lung injury (VILI) is a recognized complication of mechanical ventilation
Several of the hemodynamic parameters were similar among the four ventilation conditions, both mean arterial pressure (MAP) and cardiac output were lower during ventilation with positive end expiratory pressure (PEEP) for both tidal volumes (p = 0.08 and 0.01 for PEEP effect on MAP and cardiac output, respectively, at 6 ml/kg)
In the absence of PEEP, four out of five animals demonstrated a pattern in which relative ventilation increased to dorsal-caudal lung regions and decreased to ventral-rostral regions when tidal volumes were increased from 6 ml/kg to 12 ml/kg (Figure 1A)

Summary

Introduction

Ventilator-induced lung injury (VILI) is a recognized complication of mechanical ventilation. Lung injury and edema are well-documented consequences of mechanical ventilation with high distending pressures in multiple experimental models [1,2,3]. Similar outcomes have been observed in two subsequent trials employing either oxygenation-based [12] or plateau pressure-based [13] PEEP protocols Another recent study documented significant heterogeneity in how patients with ALI/ARDS respond to higher PEEP levels [14]. They identified two populations of patients: those with a significant recruitable lung volume, and those with negligible recruitable volume. A recent study by Talmor and colleagues [15] examined the effect of higher PEEP based on a trans-pulmonary pressure-based protocol and found a strong trend toward improved survival in the higher PEEP group

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Results

Discussion

Conclusion