The BathRC model: a method to estimate flow restrictor size for dual ventilation of dissimilar patients

Andrew R Plummer; Jonathan l du Bois; Siu Man Lee; Patrick Magee; Jens Roesner; Harinderjit S Gill

Modern ventilators often use a circle anaesthetic breathing system to supply oxygen-enriched air or anaesthetic gases to the patient via an inspiration tube, with expiratory gas returning via a separate expiration tube; exhaled carbon dioxide is either absorbed by an alkali or spilt out of an overflow valve. The splitting of both inspiratory and expiratory tubes, to allow two patients to be ventilated by the same ventilator, has been suggested a number of times, for example in Neyman & Irvin, 2006, and Paladino et al, 2008 . However, the potential for cross-flows between patients is a serious concern, and the ability to precisely control pressure and or/flow to each patient is lost. The former problem can be addressed by including additional non-return valves within each of the inspiration and expiration tubes. This has the effect of not only reducing gas contamination between patients, but also of reducing system dead-space for each half of the system, and the potential for CO2 rebreathing. A method of achieving individual control has not been demonstrated in practice, and COVID-19 patients require ventilation accurately tailored to their needs. In severe Acute Respiratory Distress Syndrome (ARDS), lung compliance can often reduce significantly, although evidence is emerging that COVID-19 is atypical in this regard (Gattinoni, 2020) .