Closed-loop control of airway occlusion pressure at 0.1 second (P0.1) applied to pressure-support ventilation: algorithm and application in intubated patients

Crit Care Med. 1996 May;24(5):771-9. doi: 10.1097/00003246-199605000-00008.


Objective: Airway occlusion pressure at 0.1 sec (P0.1) is an index of respiratory center output. During pressure-support ventilation, P0.1 correlates with the mechanical output of the inspiratory muscles and has an inverse relationship with the amount of pressure-support ventilation. Based on these observations, we designed a closed-loop control which, by automatically adjusting pressure-support ventilation, stabilizes P0.1, and hence patient inspiratory activity, at a desired target. The purpose of the study was to demonstrate the feasibility of the method, rather than its efficacy or even its influence on patient outcome.

Design: Prospective, randomized trial.

Setting: A general intensive care unit of a university hospital in Italy.

Patients: Eight stable patients intubated and ventilated with pressure-support ventilation for acute respiratory failure.

Interventions: Patients were transiently connected to a computer-controlled ventilator on which the algorithm for closed-loop control was implemented. The closed-loop control was based on breath by breath measurement of P0.1, and on comparison with a target set by the user. When actual P0.1 proved to be higher than the target value, the P0.1 controller automatically increased pressure-support ventilation, and decreased it when P0.1 proved to be lower than the target value. For safety, a volume controller was also implemented. Four P0.1 targets (1.5, 2.5, 3.5, and 4.5 cm H2O) were applied at random for 15 mins each.

Measurements and main results: The closed-loop algorithm was able to control P0.1, with a difference from the set targets of 0.59 +/- 0.27 (SD) cm H2O.

Conclusions: The study shows that P0.1 can be automatically controlled by pressure-support ventilation adjustments with a computer. Inspiratory activity can thus be stabilized at a level prescribed by the physician.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute Disease
  • Adult
  • Aged
  • Aged, 80 and over
  • Airway Resistance* / physiology
  • Algorithms
  • Feasibility Studies
  • Feedback*
  • Female
  • Humans
  • Intubation, Intratracheal
  • Male
  • Middle Aged
  • Positive-Pressure Respiration / methods*
  • Pressure
  • Prospective Studies
  • Respiratory Insufficiency / physiopathology
  • Respiratory Insufficiency / therapy*
  • Therapy, Computer-Assisted / methods*
  • Treatment Outcome
  • Work of Breathing