Change of extravascular lung water in sheep with early acute respiratory distress syndrome

Abstract

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). 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). (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]. 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.