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JAMA Surg. 2016 Jan;151(1):64-72. doi: 10.1001/jamasurg.2015.2683.

Effect of Airway Pressure Release Ventilation on Dynamic Alveolar Heterogeneity.

Author information

1
Department of Surgery, State University of New York Upstate Medical University, Syracuse.
2
Department of Trauma Critical Care Medicine, R Adams Cowley Shock Trauma Center, University of Maryland School of Medicine, Baltimore.
3
Department of Medicine, University of Vermont, Burlington.
4
Department of Surgery, State University of New York Upstate Medical University, Syracuse4Syracuse Veterans Affairs Medical Center, Syracuse, New York.
5
Department of Surgery, State University of New York Upstate Medical University, Syracuse5Department of Biological Sciences, State University of New York at Cortland, Cortland.

Erratum in

Abstract

IMPORTANCE:

Ventilator-induced lung injury may arise from heterogeneous lung microanatomy, whereby some alveoli remain collapsed throughout the breath cycle while their more compliant or surfactant-replete neighbors become overdistended, and this is called dynamic alveolar heterogeneity.

OBJECTIVE:

To determine how dynamic alveolar heterogeneity is influenced by 2 modes of mechanical ventilation: low tidal-volume ventilation (LTVV) and airway pressure release ventilation (APRV), using in vivo microscopy to directly measure alveolar size distributions.

DESIGN, SETTING, AND PARTICIPANTS:

In a randomized, nonblinded laboratory animal study conducted between January 2013 and December 2014, 14 rats (450-500 g in size) were randomized to a control group with uninjured lungs (n = 4) and 2 experimental groups with surfactant deactivation induced by polysorbate lavage: the LTVV group (n = 5) and the APRV group (n = 5). For all groups, a thoracotomy and in vivo microscopy were performed. Following lung injury induced by polysorbate lavage, the LTVV group was ventilated with a tidal volume of 6 mL/kg and progressively higher positive end-expiratory pressure (PEEP) (5, 10, 16, 20, and 24 cm H2O). Following lung injury induced by polysorbate lavage, the APRV group was ventilated with a progressively shorter time at low pressure, which increased the ratio of the end-expiratory flow rate (EEFR) to the peak expiratory flow rate (PEFR; from 10% to 25% to 50% to 75%).

MAIN OUTCOMES AND MEASURES:

Alveolar areas were quantified (using PEEP and EEFR to PEFR ratio) to determine dynamic heterogeneity.

RESULTS:

Following lung injury induced by polysorbate lavage, a higher PEEP (20-24 cm H2O) with LTVV resulted in alveolar occupancy (reported as percentage of total frame area) at inspiration (39.9%-42.2%) and expiration (35.9%-38.7%) similar to that in the control group (inspiration 53.3%; expiration 50.3%; P > .01). Likewise, APRV with an increased EEFR to PEFR ratio (50%-75%) resulted in alveolar occupancy at inspiration (46.7%-47.9%) and expiration (40.2%-46.6%) similar to that in the control group (P > .01). At inspiration, the distribution of the alveolar area of the control group was similar to that of the APRV group (P > .01) (but not to that of the LTVV group [P < .01]). A lower PEEP (5-10 cm H2O) and a decreased EEFR to PEFR ratio (≤50%) demonstrated dynamic heterogeneity between inspiration and expiration (P < .01 for both) with a greater percentage of large alveoli at expiration. Dynamic alveolar homogeneity between inspiration and expiration occurred with higher PEEP (16-24 cm H2O) (P > .01) and an increased EEFR to PEFR ratio (75%) (P > .01).

CONCLUSIONS AND RELEVANCE:

Increasing PEEP during LTVV increased alveolar recruitment and dynamic homogeneity but had a significantly different alveolar size distribution compared with the control group. By comparison, reducing the time at low pressure (EEFR to PEFR ratio of 75%) in the APRV group provided dynamic homogeneity and a closer approximation of the dynamics observed in the control group.

Comment in

PMID:
26444302
DOI:
10.1001/jamasurg.2015.2683
[Indexed for MEDLINE]

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