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

Abstract

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