An automated method of separating patient from ventilator work on the lungs

This paper describes a method of determining the amount of work on the lungs done by the patient and the ventilator using various modes of ventilation. The method uses a pneumotachograph to measure air flow, and measures pressure from an esophageal balloon and at the airway. The patient's work is separated from the ventilator work by analysis of the esophageal pressure. When esophageal pressure is below end-expiratory esophageal pressure during inspiration, work is being done by the patient. When esophageal pressure is above end-expiratory level, the ventilator is doing the work. The calculations are done using an IBM PC computer. The studies of normal subjects show that in the assist mode with increased airway resistance, significant work by the subject is required to trigger the ventilator. Two patients are presented when the assist mode resulted in excessive amounts of work and fatal outcomes. Measurement of the mechanical work required of the patient can provide useful information for the control of ventilator therapy.