Shared Ventilation in the Era of COVID-19: A Theoretical Consideration of the Dangers and Potential Solutions

Abstract

BACKGROUND: The use of shared ventilation, or the simultaneous support of multiple patients connected in parallel to a single mechanical ventilator, is receiving considerable interest for addressing the severe shortage of mechanical ventilators available during the novel coronavirus pandemic (COVID-19). In this paper we highlight the potentially disastrous consequences of naïve shared ventilation, in which patients are simply connected in parallel to a ventilator without any regard to their individual ventilatory requirements. We then examine possible approaches for individualization of mechanical ventilation, using modifications to the breathing circuit that may enable tuning of individual tidal volumes and driving pressures during either volume-controlled ventilation (VCV) or pressure-controlled ventilation (PCV). METHODS: Breathing circuit modifications included a PEEP valve on each expiratory limb for both VCV and PCV, an adjustable constriction and one-way valve on the inspiratory limb for VCV, and a pressure-relief valve for peak inspiratory pressure reduction on the inspiratory limb for PCV. The ability to regulate individual tidal volumes using these breathing circuit modifications was tested both theoretically in computer simulations as well as experimentally in mechanical test lungs. RESULTS: In both the simulations and experimental measurements, naïve shared ventilation resulted in large imbalances across individual tidal volume delivery, dependent on imbalances across patient mechanical properties. The proposed breathing circuit modifications for shared VCV and shared PCV enabled optimization of tidal volume distributions. Individual tidal volume for one patient during shared VCV was sensitive to changes in the mechanical properties of other patients. By contrast, shared PCV enabled independent control of individual patient-received ventilation. CONCLUSIONS: Of the shared ventilation strategies considered, shared PCV, with the inclusion of in-line pressure-relief valves in the individual inspiratory and expiratory limbs, offers the greatest degree of safety and lowest risk of catastrophic mechanical interactions between multiple patients connected to a single ventilator.

PEEP/FIO2 ARDSNet Scale Grouping of a Single Ventilator for Two Patients: Modeling Tidal Volume Response

“…The dependence of V T on resistance presents a pathway to patientspecific V T adjustments through the use of a variable flow resistor on the inspiratory circuit. 8 In addition, ventilator groups 2 and 4, which both had the same pressure control setting but different PEEP, revealed almost identical V T values, but ventilator 4 had significantly increased endinspiratory volume, which is almost entirely dependent on compliance.…”

“…Simply placing multiple patients on a single machine could lead to large imbalances across individual V T delivery and disastrous consequences. 8 Ventilation of any patient must be done with great care to avoid ventilator-induced lung injury 9 that damages the lung through the combined effects of tissue overdistention (volutrauma), 10-14 cyclic de-recruitment and recruitment of small airways and alveoli (atelectrauma), [15][16][17][18][19] inflammatory effects (biotrauma), [20][21][22][23] and energy dissipation across parenchymal tissue (ergotrauma). 24 This is of particular concern when attempting to ventilate multiple patients on a single machine because ventilator adjustments are applied to both patients, making titration to avoid ventilatorinduced lung injury challenging.…”

A novel inline PEEP valve design for differential multi-ventilation

“…A key component of these systems is an inline Positive End Expiratory Pressure (PEEP) valve. With the ventilator in a pressure control mode, which is recommended for DVM setups [ [1] , [2] , [3] , [4] , 6 ], a pressure relief type valve like an inline PEEP valve allows for adjustment of individual inspiratory and expiratory pressures. When placed on the expiratory limb, they allow for increased PEEP above the ventilator.…”

Computational simulation to assess patient safety of uncompensated COVID-19 two-patient ventilator sharing using the Pulse Physiology Engine

“…Simulated carbon dioxide tensions were estimated and used to estimate pH for each modeled patient [9]. Hermann et al have studied pressure and volume ventilation modes using a computational model of lung ventilation and by test lung experimental simulation [10].…”