Optimization of MAP during HFOV Utilizing Visual analysis of Pressure/Time Waveform Tracings. Estetter B, Holland D, Hawkins K, et al. Parkland Hospital System, Dallas, TX.

Current strategies used to optimize mean airway pressure (MAP) during high frequency oscillatory ventilation (HFOV) may delay the response to dynamic changes in clinical condition and potentially result in deterioration of lung function. In order to identify changes in lung mechanics prior to overt clinical changes, the authors studied the use of pressure-time (PT) waveforms to optimize ventilator settings during HFOV. The study employed a balloon lung model attached to a 3100A HFOV. An analog pressure transducer placed in-line proximal to the lung model was used to isolate PT waveforms which were then digitized by an oscillascope (Tektronix TDS 3032). In the first phase of the study, clinicians were blinded to the lung model settings and asked to adjust the ventilator to maximize MAP without generating over-distension (as defined by upper P-flex). The adjustment was based solely upon visual interpretation of the PT waveform. In the second phase of the study, ventilator settings were held constant, and the mechanical forces acting on the lung were varied. Each clinician was asked to select the waveform which most closely corresponded to optimal ventilator settings. All of the clinicians had some experience in the reading and interpretation of the waveforms generated during HFOV, both in the test lung model and in a small number of patients. In the first part of the study, all clinicians optimized MAP to the shoulder of the P-flex curve +/- 2 cm H2O. In the second phase of the study, all clinicians picked the waveform which most closely identified optimal MAP in the model. These data suggest that MAP during HFOV can be optimized on a real-time basis by incorporating PT waveform analysis.