Pressure-Regulated Ventilator Splitting (PReVentS) – A COVID-19 Response Paradigm from Yale University

Abstract

In the current COVID-19 crisis, the US and many countries in the world are suffering acute shortages of modern ventilators to care for desperately ill patients. Since modern ICU ventilators are powerful devices that can deliver very high gas flow rates and pressures, multiple physicians have attempted to ventilate more than one patient on a single ventilatorso-called "vent splitting". Early applications of this approach have utilized simple concatenations of ventilator tubing and T-pieces, to provide flow to more than one patient. Additional approaches using custom flow splitters -sometimes made using 3D printing technologies -have also advanced into the clinic with FDA approval. However, heretofore there has been less progress made on controlling individual ventilatory pressures for patients with severe lung disease. Given the inherent variability and instability of lung compliance amongst patients with COVID-19, there remains an important need to provide a means of extending ventilator usefulness to more than one patient, but in a way that provides more tailored pressures that can be titrated over time. In this descriptive report, we provide the basis for a ventilator circuit that can support two patients with individualized peak inspiratory and end-expiratory pressures. The circuit is comprised of exclusively "off the shelf" materials and is inexpensive to produce. The circuit can be used with typical ICU ventilators, and with anesthesia ventilators used in operating rooms. Inspiratory and end-expiratory pressures for each patient can be titrated over time, without changes for one patient affecting the ventilation parameters of the other patient. Using in-line spirometry, individual tidal volumes can be measured for each patient. This Pressure-Regulated Ventilator Splitting (PReVentS) Yale University protocol operates under a pressure-control ventilatory mode, and may function optimally when patients are not triggering breaths from the ventilator. This method has been tested thus far only in the laboratory with mock lungs, and has not yet been deployed in animals or in patients. However, given the novelty and potential utility of this approach, we deemed it appropriate to provide this information to the broader critical care community at the present time. In coming days and weeks, we will continue to characterize and refine this approach, using large animal models and proof-of-principle human studies.

Inline Positive End-Expiratory Pressure Valves: The Essential Component of Individualized Split Ventilator Circuits

“…Although so-called “co-ventilation” strategies have been used in New York ( 1 ) and have received crisis approval by Health and Human Services and the Federal Drug Administration ( 2 , 3 ), there are major potential risks with such approaches, and major medical organizations have made statements against their use ( 4 ). To address these limitations, several international working groups have designed modified ventilator circuits which permit individualized settings for patients sharing a ventilator ( 5 – 7 ). These modified systems, also known as differential multiventilation (DMV), use flow restrictors and sensors to allow discrete adjustment and monitoring of inspiratory and expiratory variables (an example system is shown in Fig.…”

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

“…Implementation of split breathing circuits without compensating resistances was the model addressed in the joint statement by professional societies recommending against this practice [12]. Various means have been employed empirically to limit flow to the most compliant lungs [17][18][19][20]. Modeling flow restriction adds model parameters, greatly increasing the number of simulations needed.…”

“…Some of the assertions of the joint statement are addressed in an appendix [17]. Similar apparatus has been described by an on-line collaborative [18] and another prepublication document from Yale [19]. Clarke et al have reported using simple compression clamps on segments of tubing [20].…”

“…The Pulse ventilator model was first developed and tested with single-patient simulations and has been validated through pure simulation and integration with physical systems [30]. For this study, the Pulse ventilator model was executed in Pressure Control Continuous Mandatory Ventilation (PC-CMV) mode, following existing multi-patient ventilation guidelines [16,19]. A square driving pressure waveform was specified by user-defined Positive End Expiratory Pressure (PEEP), Peak Inspiratory Pressure (PIP), respiratory rate (RR), and Inspiratory: Expiratory (IE) ratio.…”

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

“…A recent non-peer-reviewed report using PCV with pressure-relief valves also implemented a bias flow with a one-way valve to prevent occlusion alarms on the ventilator. 21 Continuous monitoring of arterial oxygen saturation is also desirable in individual patients sharing a single ventilator, for appropriate titration of PEEP, F IO 2 , and detection of acute hypoxic events. Continuous flow monitoring in all connected patients is only necessary for individualization of delivered volume during shared VCV, during which the distribution of volume from the ventilator may suddenly change due to fluctuations in the mechanics of any single patient.…”