Ventilator output splitting interface 'ACRA': Description and evaluation in lung simulators and in an experimental ARDS animal model

Abstract

The current COVID-19 pandemic has led the world to an unprecedented global shortage of ventilators, and its sharing has been proposed as an alternative to meet the surge. This study outlines the performance of a preformed novel interface called 'ACRA', designed to split ventilator outflow into two breathing systems. The 'ACRA' interface was built using medical use approved components. It consists of four unidirectional valves, two adjustable flow-restrictor valves placed on the inspiratory limbs of each unit, and one adjustable PEEP valve placed on the expiratory limb of the unit that would require a greater PEEP. The interface was interposed between a ventilator and two lung units (phase I), two breathing simulators (phase II) and two live pigs with heterogeneous lung conditions (phase III). The interface and ventilator adjustments tested the ability to regulate individual pressures and the resulting tidal volumes. Data were analyzed using Friedman and Wilcoxon tests test (p < 0.05). Ventilator outflow splitting, independent pressure adjustments and individual tidal volume monitoring were feasible in all phases. In all experimental measurements, dual ventilation allowed for individual and tight adjustments of the pressure, and thus volume delivered to each paired lung unit without affecting the other unit's ventilation-all the modifications performed on the ventilator equally affected both paired lung units. Although only suggested during a dire crisis, this experiment supports dual ventilation as an alternative worth to be considered.

Fig 1. One-line diagram of the ACRA interface.

Inspiration and expiration circuits are colored in red and black, respectively. A dashed green line represents a bypass circuit of small diameter.

Fig 2. Three-dimensional volume renderings of the ACRA interface.

(1) Connection for inspiratory limb from ventilator, (2) connection for expiratory limb to ventilator, (3) bypass circuit, (4) unidirectional valves, (5) and (5’) pinch valves, (6) adjustable PEEP valve, (7) and (7’) connection for expiratory tubes from paired units, (8) and (8’) connection for inspiratory tubes to paired units.