Individualized mechanical ventilation in a shared ventilator setting: limits, safety and technical details

Abstract

The COVID-19 pandemic has resulted in an increased need for ventilators. The potential to ventilate more than one patient with a single ventilator, a so-called split ventilator setup, provides an emergency solution. Our hypothesis is that ventilation can be individualized by adding a flow restrictor to limit tidal volumes, add PEEP, titrate FiO₂ and monitor ventilation. This way we could enhance optimization of patient safety and clinical applicability. We performed bench testing to test our hypothesis and identify limitations. We performed a bench testing in two test lungs: (1) determine lung compliance (2) determine volume, plateau pressure and PEEP, (3) illustrate individualization of airway pressures and tidal volume with a flow restrictor, (4a) illustrate that PEEP can be applied and individualized (4b) create and measure intrinsic PEEP (4c and d) determine PEEP as a function of flow restriction, (5) individualization of FiO₂. The lung compliance varied between 13 and 27 mL/cmH₂O. Set ventilator settings could be applied and measured. Extrinsic PEEP can be applied except for settings with a large expiratory time. Volume and pressure regulation is possible between 70 and 39% flow restrictor valve closure. Flow restriction in the tested circuit had no effect on the other circuit or on intrinsic PEEP. FiO₂ could be modulated individually between 0.21 and 0.8 by gradually adjusting the additional flow, and minimal affecting FiO₂ in the other circuit. Tidal volumes, PEEP and FiO₂ can be individualized and monitored in a bench testing of a split ventilator. In vivo research is needed to further explore the clinical limitations and outcomes, making implementation possible as a last resort ventilation strategy.

Keywords: ARDS; Bench testing; COVID-19; Individualized split ventilation.

Fig. 1

Determining volume, plateau pressure and PEEP in two test lungs without in-line PEEP or flow restriction. The Heat and Moisture Exchanger Filter (HMEF) is indicated and the pressure and spirometry module is colored yellow

Fig. 2

Measurement of the Volumes and Plateau Pressures as a function of the flow restrictor. a Set-up used for this experiment with the flow restrictor on the inspiratory limb of circuit A. b Tidal Volume in red and Plateau Pressure in blue as function of the valve closure for setting 1 (circles) and setting 5 (triangles)

Fig. 3

Illustration that PEEP can be applied and individualized. The in-line PEEP in the expiratory tract of circuit A was the variable in this experiment. The Heat and Moisture Exchanger Filter (HMEF) is indicated and the pressure and spirometry module is colored yellow

Fig. 4

Applying intrinsic PEEP and measurement of the total PEEP to determine intrinsic PEEP. a Set-up used for this experiment with the flow restrictor and in-line PEEP on the expiratory limb of traject A to induce intrinsic PEEP. b Intrinsic PEEP as function of the applied flow restriction in the expiratory limb for the different ventilator settings, displayed with their expiratory time. The vertical bars represent an uncertainty resulting from the difference between the units of the pressure transducer (mmHg) and of the ventilator (cmH₂O)

Fig. 5

Measurement of the total PEEP on the ventilator, in circuit A and B and as function of the flow restriction to determine intrinsic PEEP in both circuits. a Set-up used for this experiment with the flow restrictor on the inspiratory limb of circuit A. b Total PEEP as function of valve closure for ventilator settings 1 and 5 displayed with their inspiratory times

Fig. 6

Measurement of the total PEEP on the ventilator, in circuit A and B and as function of the flow restriction with an additional in-line PEEP to determine intrinsic PEEP in both circuits. a Set-up used for this experiment with the flow restrictor on the inspiratory limb and the in-line PEEP on the expiratory limb of circuit A. b Total PEEP as function of valve closure for ventilator settings 2 and 5 displayed with their inspiratory times.

Fig. 7

Measurement of the effective FiO2 % in lung A and B as a function of added oxygen flow in circuit A. a Set-up used for this experiment with the laterally inserted varying oxygen flow in two different positions 1 and 2. b FiO2% as function of the inserted flow on position 1 (blue) and 2 (red).