Evaluation of a Modified Circuit for Multiplex Ventilation: A Simulation Study

Abstract

Background: Ventilation of two patients with one machine during a ventilator shortage became a popular topic during the COVID-19 pandemic. Our previous study indicated failure of a multiplex circuit to ventilate patients with different lung mechanics in 67% of simulations (PMID: 32345741). Four safety problems must be solved to provide practical multiplex ventilation: 1) individual adjustment of tidal volume (V_T), 2) individual measurement of V_T, 3) individual adjustment of PEEP, 4) individual PEEP measurement. The purpose of this study was to evaluate potential solutions developed at our institution.

Methods: Two separate IngMar ASL 5000 breathing simulators were ventilated with a modified multiplex circuit using pressure control continuous mandatory ventilation set-point targeting (PC-CMVs). Parameters of the lung models used for simulations (resistance and compliance) were evidence-based from published studies. Individual circuit modification devices were first evaluated for accuracy. The modified circuit was designed to solve the four safety problems above by implementing an adjustable flow diverter valve (AFDV), prototype dual volume display, PEEP valve, and disposable PEEP display. The modified multiplex circuit was assessed by ventilating six pairs of simulated patients with different lung models. The AFDV and PEEP valves were adjusted until both lung simulators received equal ventilation. Ventilation was considered equalized when V_T and EELV were within 10% for each simulation.

Results: The multiplex circuit allowed for adjustments that equalized ventilation to both simulators regardless of differences in resistance and/or compliance, reversing the failure modes of our previous study.

Conclusions: This study shows that our multiplex circuit modifications allow for individualization and monitoring of volume and PEEP to each patient. These modifications allow for safer ventilation of two patients with different lung mechanics in the event of a ventilator shortage.