Airway Occlusion Pressure As an Estimate of Respiratory Drive and Inspiratory Effort during Assisted Ventilation

Rationale: Monitoring and controlling respiratory drive and effort may help to minimize lung and diaphragm injury. Airway occlusion pressure (P0.1) is a noninvasive measure of respiratory drive. Objectives: To determine 1) the validity of "ventilator" P0.1 (P0.1vent) displayed on the screen as a measure of drive, 2) the ability of P0.1 to detect potentially injurious levels of effort, and 3) how P0.1vent displayed by different ventilators compares to a "reference" P0.1 (P0.1ref) measured from airway pressure recording during an occlusion. Methods: Analysis of three studies in patients, one in healthy subjects, under assisted ventilation, and a bench study with six ventilators. P0.1 vent was validated against measures of drive (electrical activity of the diaphragm and muscular pressure over time) and P0.1ref Performance of P0.1ref and P0.1vent to detect predefined potentially injurious effort was tested using derivation and validation datasets using esophageal pressure-time product as the reference standard. Measurements and Main Results: P0.1vent correlated well with measures of drive and with the esophageal pressure-time product (within-subjects R-2 = 0.8). P0.1 ref >3.5 cm H2O was 80% sensitive and 77% specific for detecting high effort (>= 200 cm H2O center dot s.min(-1)); P0.1 ref <= 1.0 cm H2O was 100% sensitive and 92% specific for low effort (<= 50 cm H2O center dot s.min(-1)). The area under the receiver operating characteristics curve for P0.1 vent to detect potentially high and low effort were 0.81 and 0.92, respectively. Bench experiments showed a low mean bias for P0.1 vent compared with P0.1 ref for most ventilators but precision varied; in patients, precision was lower. Ventilators estimating P0.1 vent without occlusions could underestimate P0.1 ref. Conclusions: P0.1 is a reliable bedside tool to assess respiratory drive and detect potentially injurious inspiratory effort.