Differential Ventilation Using Flow Control Valves as a Potential Bridge to Full Ventilatory Support During the COVID-19 Crisis

From Bench to Bedside

Matthew A. Levin, M.D.; Anjan Shah, M.D.; Ronak Shah, M.D.; Erica Kane, M.D., M.P.H.; George Zhou, M.D.; James B. Eisenkraft, M.D.; Martin D. Chen, M.D.

Disclosures

Anesthesiology. 2020;133(4):892-904. 

In This Article

Abstract and Introduction

Abstract

Background: During the COVID-19 pandemic, ventilator sharing was suggested to increase availability of mechanical ventilation. The safety and feasibility of ventilator sharing is unknown.

Methods: A single ventilator in pressure control mode was used with flow control valves to simultaneously ventilate two patients with different lung compliances. The system was first evaluated using high-fidelity human patient simulator mannequins and then tested for 1 h in two pairs of COVID-19 patients with acute respiratory failure. Patients were matched on positive end-expiratory pressure, fractional inspired oxygen tension, and respiratory rate. Tidal volume and peak airway pressure (PMAX) were recorded from each patient using separate independent spirometers and arterial blood gas samples drawn at 0, 30, and 60 min. The authors assessed acid-base status, oxygenation, tidal volume, and PMAX for each patient. Stability was assessed by calculating the coefficient of variation.

Results: The valves performed as expected in simulation, providing a stable tidal volume of 400 ml each to two mannequins with compliance ratios varying from 20:20 to 20:90 ml/cm H2O. The system was then tested in two pairs of patients. Pair 1 was a 49-yr-old woman, ideal body weight 46 kg, and a 55-yr-old man, ideal body weight 64 kg, with lung compliance 27 ml/cm H2O versus 35 ml/cm H2O. The coefficient of variation for tidal volume was 0.2 to 1.7%, and for PMAX 0 to 1.1%. Pair 2 was a 32-yr-old man, ideal body weight 62 kg, and a 56-yr-old woman, ideal body weight 46 kg, with lung compliance 12 ml/cm H2O versus 21 ml/cm H2O. The coefficient of variation for tidal volume was 0.4 to 5.6%, and for PMAX 0 to 2.1%.

Conclusions: Differential ventilation using a single ventilator is feasible. Flow control valves enable delivery of stable tidal volume and PMAX similar to those provided by individual ventilators.

Introduction

THE COVID-19 (SARS CoV-2) pandemic during early 2020 resulted in an unprecedented number of hospital and intensive care unit admissions, with patients requiring mechanical ventilation for prolonged periods of time.[1,2] Our experience in the Mount Sinai Health System in New York City was similarly overwhelming. Between February 27 and April 9, 2020, hospitals in the Mount Sinai Health System admitted 4,241 COVID-19–positive patients, of whom ~10% required ventilation. The median duration of ongoing ventilation was 9.3 days. Of those ventilated, 26% died and only 25% had been successfully extubated, leaving nearly 50% in need of continuing ventilation. Although the Mount Sinai Health System had enough ventilators to meet demand at that time, the steady increase in the number of patients needing prolonged ventilation led to concern that there would be too few ventilators to meet the growing demand, and that potentially salvageable patients could be lost because ventilation would be unavailable for them.[3]

The United States Public Health Service Commissioned Corps' statement on Optimizing Ventilator Use during the COVID-19 Pandemic asserted that a possible "crisis standard of care" strategy was the ventilation of two patients with a single mechanical ventilator, although such a strategy should only be considered as an absolute last resort.[4] The Institute of Medicine defines crisis standards of care as "a substantial change in the usual health care operations and the level of care it is possible to deliver…justified by specific circumstances and…formally declared by a state government in recognition that crisis operations will be in effect for a sustained period."[5] The Institute of Medicine further stated that "CSC [crisis standards of care], planned and implemented in accordance with ethical values, are necessary for the allocation of scarce resources."[6]

In light of the extraordinary circumstances and in accordance with the Institute of Medicine's crisis standards of care guidelines, the Governor of New York, Andrew M. Cuomo, issued a statement at the end of March 2020 approving the use of ventilator sharing as a last resort.[7] We therefore proceeded to design a novel system and method of differential ventilation that uses a custom-manufactured flow control valve to overcome the important challenges of safely ventilating two patients with one ventilator. This work is similar to that done by several other groups during the COVID-19 crisis, both domestically and internationally, and was inspired by earlier work done in the mid-2000s.[8–12]

The purpose of this study was to (1) test the feasibility, in a simulation laboratory, of ventilating two patients simultaneously using a single standard mechanical ventilator and a system that allows individualized setting of tidal volumes and airway pressures, and (2) test the system in consented COVID-19 patients as a proof of concept.

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