Analysis of Patient Ventilator Asynchrony Using Electrical Impedance Tomography (EIT) in Patients With Acute Respiratory Failure

Patients and Methods:

Admitted ventilated patients who are greater than 18 years old and fulfilled the Berlin's diagnostic criteria of moderate to severe ARDS will be selected to enter our study. The exclusion criteria include (1) patients with metallic materials in the body (including wire, pin or implanted electrical devices etc.); (2) patients with cutaneous diseases which prohibited the application of electrode leads to attached the body; (3) severe chronic obstructive pulmonary diseases; (4) hemodynamically unstable; (5) proved barotrauma (including pneumothorax or pneumomediastinum etc.); (6) pregnancy; (7) diseases characterized with increased intracranial pressure; (8) patients or family who refused the informed consent. All patients who fulfilled the diagnosis of ARDS will receive standard care of low tidal volume ventilator therapy. The tidal volume 6 ml/Kg will be used. The investigators expect to enroll at least 20 analyzable cases. Sedation and paralysis are usually used in moderate to severe ARDS patients and daily interruption of sedation and paralysis is a standard practice. The investigators will perform recording during daily interruption of sedation and paralysis, up to 60 minutes period will be recorded during the interruption period. Recording will be done at least once for registered case and could be repeated in case of unsatisfactory signals.

Instrumentation In all patients, air flow will be measured using a pneumotachograph (Hamilton AG, or Hans Rudolf) connected to a differential pressure transducer (MP 45, Validyne Corp., Northridge, CA). The flow sensor will be placed between the endotracheal tube and the Y-piece of the ventilator. Tidal volume will be obtained by integrating the flow signal. Airway pressure and esophageal pressure will be measured using differential pressure transducers (P300D, Validyne Corp., Northridge, CA.). An appropriate esophageal pressure signal will be confirmed according to the standard guideline[27]. All signals are sampled and digitalized at 200 Hz and data are stored in a data acquisition system (MP150, Acqknowledgement, Biopac, Goleta, CA).

Measurements:

Electrical impedance tomography: