Model and clinical studies of a novel differential lung ventilation system for adults

Introduction

In clinical conditions when the mechanical properties of each lung of a patient differ very much, it is necessary to ventilate them separately. The connection of each lung with one respirator, by means of a double-lumen endotracheal tube, enables its physical separation and control of its ventilation. Generally, therefore, two synchronized respirators are required to perform differential ventilation of lungs. It is also possible to use one respirator with a feedback-controlled variable pneumatic valve to divide the total ventilation volume from a respirator between two lungs.

Materials and methods

A prototype of a flow divider based on stabilization of tidal volume measurement, according to adjustments made by an anesthesiologist, was designed. This feedback-controlled circuit can precisely keep the tidal volume division on a constant value, irrespective of lung mechanics (alveolar/chest compliance, airway resistance) and ventilatory parameter (frequency, total tidal volume and selective PEEP) changes. In order to assess the solution that was realized, one respirator with a feedback control of tidal volume division was tested using a physical model of the adult respiratory system and in clinical conditions, during thoracic surgery.

Results

The physical model of respiratory system consisted of two parallel circuits of artificial lung. The model study has proved that maximal errors of tidal volume division are less than 10% in a wide range of division ratio and PEEP value, which is acceptable in clinical practice. Differential ventilation was applied to 10 patients undergoing thoracic surgery. Measurement of each lung parameter showed the stable tidal volume division (error < 10%) in all patients.

Conclusion

Clinical data show that the proposed system fulfils the same function as two synchronized ventilators, with independent adjustment of volume and PEEP to each lung.