Measurement of Airway Occlusion Pressure (P0.1) by a Semi-Automated Bedside System

Recently, several studies have shown that airway occlusion pressure (P_0.1) generated in the first 100 milliseconds of inspiration is a useful noninvasive test to predict the outcome of patients weaning from mechanical ventilation. However, to perform the test a breathing circuit, transducers, and recording equipment must be assembled, and data to determine P_0.1 must be manually extracted. In this study, we compared P_0.1 measurements taken simultaneously by a computerized bedside respiratory cart and a transducer-oscillographic recording system. Studies were performed in 6 healthy subjects. Airway pressure was simultaneously measured by the semi-automated system and a differential pressure transducer, digitized to a computer-based data-acquisition system. Subjects were encouraged to vary breathing pattern to produce a wide range of P_0.1 values. The occlusion pressure waveforms collected were independently reviewed and P_0.1 visually determined. Seventy-four occlusions were conducted with P_0.1 values ranging from 0.3 to 26.2 cm H₂O. The semi-automated system rejected 21 occlusions (28%) as being unacceptable. However, the majority of these rejections were due to the operator's arming the occlusion device prematurely. High correlation (r = 0.999) was observed between the P_0.1 determined by the semi-automated system and the manual assessment (slope = 0.98, intercept = -0. 18), indicating that the semi-automated system that we studied made accurate determinations of P_0.1 over a wide range of breathing patterns. Studies are needed to determine their applicability in measuring P_0.1 in the ventilated ICU patient.