SHOULD MECHANICAL VENTILATION BE OPTIMIZED TO BLOOD CASES, LUNG-MECHANICS, OR THORACIC CT SCAN

This study was aimed at providing data for optimization of mechanical ventilation in patients with acute respiratory distress syndrome (ARDS ). The effects of ventilation with positive end-expiratory pressure (P EEP) titrated to blood gases were studied by thoracic computed tomogra phic (CT) scans and lung mechanics measurements in eight patients. CT density histograms at end-expiration were used to investigate the effe cts of PEEP on three differently aerated zones. Static pressure-volume (P-V) curves were used to determine the deflection point above which baro-volotrauma (a combination of barotrauma and volotrauma) may occur . Peak pressures, plateau pressures, and lung volumes measured by Resp itrace(R) were compared with the deflection point. CT scan showed that PEEP increased ''normally aerated'' areas, decreased ''nonaerated'' a reas, and did not change ''poorly aerated'' zones. No correlations wer e found between CT scan and either Pa-O2 or mechanical data. Pressure at the deflection point was lower than the usually recommended 35 to 4 0 cm H2O for peak pressure in four patients (range, 28 to 32 cm H2O). With regard to plateau pressures, only one patient was ventilated abov e the deflection point. However, monitoring of volumes showed that the se four patients had an end-inspiratory volume above this point. We co nclude that mechanical ventilation may be initially adjusted on the ba sis of blood gas values and then optimized on the basis of lung mechan ics to limit the risk of barovolotrauma.