Project Tetra Overview

Current medical standard operating procedure requires that patients who become severely ill with COVID-19 be treated using external ventilation. As the virus spreads, projections suggest that there are not enough ventilators to meet the expected numbers of patients throughout the world. Project Tetra seeks to create a ventilator splitter so that hospitals inundated with covid-19 patients can effectively increase the number of already available ventilators by up to a factor of 4. The project aims to produce two versions of the device: one that has been approved by the FDA under the Emergency Use Authorization guidance, and an open source model intended to be made with locally sourced materials.

As of May 19, 2020, 5 million cases of coronavirus have been reported worldwide, with over 320,000 deaths attributed to the virus [1]. Initial clinical reports of those infected with the virus indicated that the fatality rate nears 2-3%, but closer inspection of the number of cases shows that up to 5% of patients require ventilation (see Figure 1, the bottom bar):

Figure 1: A breakdown of how individuals react to a COVID-19 infection sourced from March, 2020. At that point in time, 85% of the infected population appeared to recover without medical intervention, while 5% of the infected population would require invasive ventilation to recover, and up to half of those patients were not surviving. If that 5% of infected individuals do not receive ventilation, then the entire group is at serious risk of death.[2]

Patients who require ventilation will die without it. If the hospital cannot provide ventilation due to a lack of ventilators, then health care providers will be required to make “god decisions” about which patients live and which patients die [3, 4]. The added stress of these decisions negatively impacts mental health of clinicians treating patients, weakening the support these patients can receive[5].

Several projects already exist that aim to increase the supply of ventilators [6, 7, 8]. Ventilators are complicated devices, however, that require four touchpoints of control for a respiratory therapist or clinician:

FDA EUA approved ventilator splitters are far less complicated than a full ventilator. The simplest FDA approved ventilator splitters provide none of these control points [12, 13]. Because these devices provide no control points, severe complications can arise during the course of their use, as enumerated by the American Society of Anesthesiologists [14]. Since none of these control points are available to the clinician or respiratory therapist, patient lung compliance becomes a serious concern, as does cross-contamination between patients.

The most serious concern is the death of both patients. Two patients on the same ventilator may begin recovering at different rates. As a patient recovers, that patient’s lungs become more compliant, meaning that more air can go into those lungs. The other patient, who is less healthy, remains with compromised lungs. With no valves or other flow control mechanisms, pressure in the system will naturally increase in the more compliant lungs, causing that healthier patient’s lungs to become damaged through an increase in PIP. The less healthy patient, on the other hand, receives less air, and slowly drowns. Project Tetra aims to address this scenario by providing flow control mechanisms and flow monitoring on the splitter. In this example, if one patient recovers faster than another, the clinician can adjust flow using a Tetra valve for each patient, decreasing PIP for the healthier lungs, and increasing PIP for the less healthy patient. In effect, the Tetra decouples the mechanics of ventilation from the control of ventilation, allowing for the ventilator to control breath frequency, PEEP, and FiO2, while tetra provides control points for individual patient tidal volume.