Development and assessment of the performance of a shared ventilatory system that uses clinically available components to individualize tidal volumes
Authors: Hannon David M. , Jones Tim , Conolly Jack , Judge Conor , Iqbal Talha , Shahzad Atif , Madden Michael , Kirrane Frank , Conneely Peter , Harte Brian H. , O’Halloran Martin , Laffey John G. 
Published: December 2020

Objectives

To develop and assess the performance of a system for shared ventilation that uses clinically available components to individualize tidal volumes under a variety of clinically relevant conditions.

Design

Evaluation and in vitro validation study.

Setting

Ventilator shortage during the SARS-CoV-2 global pandemic.

Participants

The design and validation team consisted of intensive care physicians, bioengineers, computer programmers, and representatives from the medtech sector.

Methods

Using standard clinical components, a system of shared ventilation consisting of two ventilatory limbs was assembled and connected to a single ventilator. Individual monitors for each circuit were developed using widely available equipment and open source software. System performance was determined under 2 sets of conditions. First, the effect of altering ventilator settings (Inspiratory Pressure, Respiratory rate, I:E ratio) on the tidal volumes delivered to each lung circuit was determined. Second, the impact of altering the compliance and resistance in one simulated lung circuit on the tidal volumes delivered to that lung and the second lung circuit was determined. All measurements at each setting were repeated three times to determine the variability in the system.

Results

The system permitted accurate and reproducible titration of tidal volumes to each ‘lung circuit’ over a wide range of ventilator settings and simulated lung conditions. Alteration of ventilator inspiratory pressures stepwise from 4-20cm H2O, of respiratory rates from 6-20 breaths/minute and I:E ratio from 1:1 to 1:4 resulted in near identical tidal volumes delivered under each set of conditions to each simulated ‘lung’. Stepwise alteration of compliance and resistance in one ‘test’ lung circuit resulted in reproducible alterations in tidal volume to the ‘test’ lung, with little change to tidal volumes in the ‘control’ lung (a change of only 6% is noted). All tidal volumes delivered were highly reproducible upon repetition.

Conclusions

We demonstrate the reliability of a simple shared ventilation system assembled using commonly available clinical components that allows individual titration of tidal volumes. This system may be useful as a temporary strategy of last resort where the numbers of patients requiring invasive mechanical ventilation exceeds supply of ventilators.

Article Summary

Strengths and limitations of this study

This solution provides the ability to safely and robustly ventilate two patients simultaneously while allowing differing tidal volumes in each limb.

The designed solution uses equipment readily available in most hospitals.

Accurate and reproducible titration of tidal volumes to each ‘lung’ was possible over a wide range of ventilator settings.

Alteration of one simulated ‘lung’ conditions had minimal impact on the tidal volumes delivered to the unaffected lung

The system relies on patients being sedated and paralysed.

We have not yet tested this solution in vivo, on COVID-19 patients.