Original Publication Date: 2001-Apr-01
Included in the Prior Art Database: 2003-Jul-23
When a spontaneously breathing patient is ventilated using a conventional mechanical ventilator and a tracheal-tube then the breathing effort required of the patient is increased because of the tube's resistance. By wholly or partially compensating for the pressure drop across the tracheal- tube the increased breathing effort may be respectively removed or reduced. Pressure Support (PS) and Proportional Assist Ventilation (PAV) ventilator modes provide this compensation by adding a drive pressure from the ventilator up to a value equivalent to (flow x resistance). However the resistance is not linearly dependent on the flow, being rather quadratically dependent, and therefore one must directly measure a value indicative of the resistance of the tracheal-tube. This is difficult to achieve, primarily because of the location of the tube, and so one rarely attempts to fully compensate for this during PS or PAV ventilation. By providing at an accessible location a tube, 2, such as a second tracheal-tube, having substantially identical flow properties to the tracheal tube used to ventilate the patient (not shown) and by measuring a pressure drop, ?P T , across the tube, 2, caused by gas flowing at the same flow rate, FI, as through the inspiration line, 4, then the resistance of the tracheal-tube used to ventilate the patient may be accurately measured and compensated for at any inspiration gas flow, F I. Conveniently the second tracheal-tube, 2, may be located within the actual inspiration gas flow path, 6, such as within the ventilator, 8, itself.