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

The valves we used have a considerable resistance, 12 cmH20/(L/s), so contributing over half of the total flow path resistance (either inspiration or expiration) estimated to be 22 cmH20/(L/s). While this will mean the characteristics of the dual arrangement are markedly different from conventional single patient ventilation, the increased pressure loss within the flow path means that the airway flow and pressure will be less sensitive to changes in patient characteristics. 2) An unexpected result was that as the flow reduced to one test lung by the introduction of a flow restrictor, there was a small increase in flow to the other lung. For example, the most severe flow restrictor reduced tidal volume by 36% in the corresponding lung, but also caused the unaltered loop to provide 5% more volume to the other test lung. This is likely to be caused by the reduced pressure loss in the common part of the circuit at the ventilator, and effects within the ventilator itself. 3) Test lung 1 appears to have different time constants for inspiration and expiration, and the modelling approach would allow different inspiration and expiration airway resistances to be used to capture this and improve accuracy. As a general method however, minimising the number of parameters required is beneficial.