VOLUME RECRUITMENT AND OXYGENATION IN PULMONARY-EDEMA - A COMPARISON BETWEEN HFOV AND CMV

Purpose: In acute lung injury, edema floods alveoli decreasing mean lu ng volume (MLV) and increasing pulmonary venous admixture (Qva/Qt). We reasoned that a ventilatory strategy that uses large tidal volumes (V T) might recruit volume differently than a strategy that uses very sma ll VT (high-frequency oscillatory ventilation, HFOV) which may require an inflation maneuver to total lung capacity (TLC) for full recruitme nt. Materials and Methods: We studied six dogs with pulmonary edema in duced by oleic acid injury and compared HFOV with conventional mechani cal ventilation (CMV). Increasing mean airway opening pressure (Pao) f rom 6 to 14 cm H2O raised MLV from 932 +/- 162 to 1,550 +/- 210 mL and from 872 +/- 145 to 1,242 +/- 192 mL during CMV and HFOV, respectivel y, whereas Ova/Qt decreased from 24.1 +/- 8.5 to 9.3 +/- 4.3% and from 42.2 +/- 6.8 to 30.4 +/- 9.3%. We repeated our measurements at a Pao of 14 cm H2O after an inflation maneuver to TLC. Results: Intlation to TLC recruited additional lung volume and decreased Qva/Qt further onl y during HFOV. After an inflation to TLC, we observed a rapid isobaric volume loss from the deflation limb of the pressure-volume curve duri ng both CMV and HFOV. Conclusions: We conclude that after oleic acid i njury in dogs pressure-volume hysteresis has two components: a recruit able portion associated with gas exchange improvement and a nonrecruit able portion. At the level of PEEP used in this study (8.5 cm H2O), fu ll lung recruitment during HFOV required inflation to TLC, whereas dur ing CMV it was accomplished by the relatively large VT. Copyright (C) 1998 by W.B. Saunders Company.