In mid-March 2020, a group of engineers and scientists at Lawrence Livermore National Laboratory (LLNL) initiated a skunkworks effort to address the projected shortfall in mechanical ventilators. Their goal; to prototype a ventilator system using as few parts as possible and sourced from a supply chain completely separate from that of traditional ventilator manufacturers. The team gained insights from medical professionals, ventilator manufacturers, and published guidance on ventilator functional requirements, particularly for COVID-19 patients.
The team’s prototype is intended to be safe, simple and easy to build, while still achieving the minimally required functionality necessary to treat patients with COVID-19. The ventilator has two functional air flow circuits: an inhalation and an exhalation circuit (Figure 1). The pressure in each circuit—Peak Inspiratory Pressure (PIP) and Positive End-Expiratory Pressure (PEEP)—are controlled by two high-accuracy back pressure regulators. Thus, the device operates in pressure-controlled CMV (continuous mandatory ventilation) mode, which appears to be the most commonly used configuration for late-stage COVID-19 patients who require manual ventilation. The system is also designed to adapt to a patient in the case they spontaneously breathe on their own. Other critical patient parameters, such as inhalation-exhalation ratio (I-E), respiratory rate (RR), and tidal volume (VT), are managed by timing solenoid valves for each circuit.
User Interface and Safety Features
A user interface is intended to facilitate real-time adjustment of operational parameters and includes a simple display showing current and set-point parameter values after each breath cycle. The target user of the device is a trained member of a clinical care center, such as a doctor, nurse anesthetist, or respiratory therapist with an interface designed to be simple, robust and familiar to trained clinicians to minimize training time and facilitate the ventilator's safe use. As required by the FDA and standards for medical devices, there are a number of alarms included in the device that alert a user visually and audibly if critical parameter values such as PIP, PEEP, or VT fall out of range, or if a system failure occurs such as a power failure, high airway pressure, low supply gas pressure, disconnection or the obstruction of an air-handling line. In the case of power failure, a back-up battery provides temporary power. No provisions were made for visualization of data and closed-loop feedback. These features, typical of modern ventilators, were excluded for the sake of simplifying the manufacturing process and expediting FDA approval through Emergency Use Authorization.
To aid in rapid manufacturing of the device the assembly was kept simple and the components were selected based on availability. The approach allows for rapid prototyping, testing, production, and deployment into the clinical care system. The system makes use of standard ventilator accessories and controls typically available at a critical care center, including:
- House or bottle of Air/O2 mix supplied
- Measurement indicator of fraction of oxygen (FiO2) input into the device
- Thermal and humidity control of inhalation gas delivered to patient
- Endotracheal tubing (ET) tubing and associated fixtures, traps, viral filters
- CO2 or pulse oximeter (O2) measurement sensors
The ventilator is intended to be one that meets the minimal requirements necessary for Emergency Use Authorization by the FDA. Although it could be retrofitted later to include additional functionality, as it is currently planned, it will likely only be suitable for emergency use.
The prototype has been subjected to preliminary performance and verification testing measuring the necessary PIP, PEEP, and VT commonly necessary for ARDS patients. The testing evaluates the ventilator's ability to measure and control the necessary PIP, PEEP, VT, I:E and respiratory rate.