Objective: To determine the change of extravascular lung water (EVLW) and the effect of positive end-expiratory pressure (PEEP) and cardiac output (CO) on EVLW in the sheep with early acute respiratory distress syndrome (ARDS).
Methods: The sheep ARDS model was induced by infusion of endotoxin intravenously, and then divided into ARDS model group (n = 12), PEEP group (n = 21) and dobutamine group (n = 13). The PEEP group was further divided into three subgroups: PEEP 5 cm H(2)O (n = 7), 10 cm H(2)O (n = 8) and 15 cm H(2)O groups (n = 6). EVLW was measured by the single indicator thermodilution technique. The EVLW, hemodynamics and lung mechanics parameters were observed at 6 h after sheep ARDS model was induced, 2 h after mechanical ventilation with PEEP (5, 10, 15 cm H(2)O) respectively and 2 h after CO increase >/= 50% of the base value (induced by dobutamine infusion).
Results: (1) When ARDS was induced in sheep, EVLW increased from (12.8 +/- 4.7) ml/kg to (18.1 +/- 7.1) ml/kg (P < 0.01), and EVLW had no significant change (P > 0.05) during the early phase of ARDS (6 h). PaO(2)/FiO(2) was (136.8 +/- 34.9) mm Hg at ARDS 0 h, which was higher than that before infusion of endotoxin [(444.3 +/- 127.7) mm Hg, P < 0.01]. EVLW had no relationship with PaO(2)/FiO(2), but DeltaEVLW after ARDS model induced had good correlation with DeltaPaO(2)/FiO(2) (r = -0.501, P < 0.001). When ARDS was induced, static lung compliance decreased from 26.9 +/- 8.4 to 16.4 +/- 5.0 (P < 0.01). (2) After mechanical ventilation with PEEP 2 h, EVLW in PEEP 10 cm H(2)O group and 15 cm H(2)O group were (14.7 +/- 4.5) ml/kg and (15.3 +/- 3.7) ml/kg respectively, which was significantly less than that before PEEP [(16.5 +/- 4.7) ml/kg and (18.4 +/- 6.0) ml/kg respectively, all P < 0.05]. But EVLW in 5 cm H(2)O group showed no difference during 2 h PEEP application. (3) After CO increase >/= 50% of the base value 1 h and 2 h, EVLW was (16.3 +/- 4.9) ml/kg and (16.9 +/- 6.9) ml/kg respectively, which did not differ from that of the baseline value [(15.1 +/- 4.6) ml/kg, all P > 0.05].
Conclusions: EVLW in ARDS sheep increased significantly and remained at the same level during the early phase of ARDS. PEEP had a markedly effect in reducing EVLW, while the increase of CO induced by dobutamine did not significantly raise EVLW.