4 Inch Ventilator Adapter for Adding Resistance to Ventilator Circuit
Sharing one ventilator between 2 to 4 patients is hypothetically feasible but certainly not tested in humans and not within the scope of the ventilator manufacturers' intended design use. The possibility of sharing ventilators between two severely affected patients in the event of an extreme ventilator shortage has come up as a theoretical consideration during the COVID-19 pandemic as an alternative to rationing (https://emcrit.org/pulmcrit/split-ven.... This following description and this video shows a theoretical "variable resistor" connector part intended to be added to the terminal inspiratory limb of a shared ventilator setup that may help minimize some of the issues of inter-patient dependency (related to variable of lung mechanics over time of one patient) and differences at a given point in time between patients in lung mechanical properties. To be clear, in no way am I endorsing the use of sharing ventilators with my description of this part.
Tidal volume ventilation's main drawback is the interdependency of the patients with respect to relative lung mechanics (for example, the less affected lung would receive over 50% of the total delivered tidal volume in a two patient setup). On the other hand, in a pressure controlled strategy, there is no patient interpendency (that is changing lung mechanics in one patient will affect that patient's delivered volume but as the pressure is maintained in the system, the other patients are not affected). Nonetheless, there will still be imbalance in returned tidal volumes with a common pressure settings if the lung mechanics vary. For example, a patient with extremely low lung compliance may require an inspiratory driving pressure of 28 to achieve a target tidal volume of ~6 cc kg PBW - that pressure my lead to over-inflation of a less affected lung of a shared patient to over 8 cc/kg PBW and promote ventilator induced lung injury via volutrauma.
A strategy to mitigate these factors would be to utilize a pressure control mode, set the pressure to optimize volume to the "sickest lung" and then add a "variable" resistor to the terminal end of the inspiratory circuit of the less affected patient(s). This would predictable cause a pressure drop off that is directly proportionate to the length and inversely proportionate to the fourth power to the radius of the resistance tubing (assuming laminar flow).
This connector part is designed to fit into a standard ET tube connection between the male ET tube hub and female circuit connector.
Although the video shows variable radii of the opening (from 2 mm to 22 mm), in reality, I envision a set of fixed size tubes (perhaps radii of 6, 10, 14, 18 and 22 mm), which could be color coded and labeled with the size.