2001 OPEN FORUM Abstracts
OPTIMIZINGMAP SETTINGS DURING HFOV BY ANALYZING WAVEFORM DIFFERENCES PRE & POST THEETT
Jennifer De La Garza RRT,Robert Estetter RRT, Dean Holland RRT, Ken Hawkins RRT, Grant O?Keefe MD MPH.Departments of Respiratory Care and Surgery, Parkland Health & HospitalSystem, Dallas, Texas
Introduction:Timely adjustments of MAP during HFOV are necessary to limit ventilator inducedlung injury (VILI). Current literature and clinical management practice supportsthe adjustment of MAP to deliver sub-tidal volumes at or just below the upperinflection point of the static pressure/volume curve (P/Vstatic). Current monitoringtools (radiological, pulse-ox and ABG?s) provide supportive evidence. We hypothesizethat optimal MAP can be set and maintained by interpretation of real-time pressure-timetracings (P/T) captured pre and post ETT.
Methods: P/Vstaticcurves were generated in a multiple balloon lung model submerged in a fifty-gallontank at three different depths. A HFOV was then attached to the lung model viaa #9 ETT. Analog P/T waveform tracings were collected pre- & post- the patientwye utilizing four study conditions as follows: HFOV circuit capped, MAP seton the linear portion of the P/Vstatic curve, MAP set on the shoulder of theP/Vstatic curve and MAP set at over-distension. The MAP, bias flow, inspiratorytime percent (IT%) and frequency were kept constant (MAP=20, bias flow=30, IT%=.50, freq= 5 Hz). Power setting was adjusted to maintain the same amplitude ateach compliance and data recorded. The signals were then converted to digitalat 50,000 data points per second (using a Tektronix TDS 3020). Data was collectedand differences graphed and overlaid for each study condition. Our analysisfocused on the portion of P/T waveform at actuation of the expiratory hold.
Results:Qualitative differences between pre and post ETT tracings in the model increasedwith decreasing compliance. Negligible variation was observed with the circuitcapped.
Discussion: Wehave identified a method for real-time identification of over-distention inHFOV. Our findings represent an improvement over currently recognized monitoringtechniques that are limited by sensitivity or specificity issues. We believethat further investigation is necessary and suggest that it be directed to developmentof this method and other real-time monitoring options adaptable to the clinical environment.