Effects of early mechanical ventilation on oxygenation and hemodynamics in acute high altitude pulmonary edema patients complicated by acute respiratory distress syndrome

Abstract

To investigate the effect of early mechanical ventilation on oxygenation and hemodynamic of acute high altitude pulmonary edema (HAPE) patients complicated by acute respiratory distress syndrome (ARDS). From May 2001 to December 2006, 8 HAPE patients with secondary ARDS admitted to Germud City People's Hospital were enrolled in the study. All the patients received early invasive mechanical ventilation within 24 hours of HAPE. Hemodynamics, cardiac output, arterial and mixed venous blood gas and oxygen dynamics parameters were determined before and after 96 hours of mechanical ventilation. Before treatment the right atrial pressure (RAP), mean pulmonary artery pressure (mPAP), pulmonary vascular resistance index (PVRI) and shunt (Qs/Qt) were above normal values. Oxygen delivery (DO2), oxygen extraction rate (O2ER), and oxygenation index (PaO2/FiO2) were lower than normal values. After treatment with mechanical ventilation, arterial partial pressure of oxygen (PaO2), PaO2/FiO2, arterial oxygen saturation (SaO2), partial pressure of oxygen of mixed venous blood (PVO2) and mixed venous oxygen saturation (SVO2) were increased significantly compared with those before treatment [PaO2: 70.3±2.9 mm Hg (1 mm Hg=0.133 kPa) vs. 49.9±3.5 mm Hg, t=15.292, P=0.001; PaO2/FiO2: 201.6 ± 4.8 mm Hg vs. 134.5±5.2 mm Hg, t=19.618, P=0.004; SaO2: 0.929±0.021 vs. 0.780±0.073, t=6.226, P=0.002; PVO2: 54.8±2.9 mm Hg vs. 44.9±2.6 mm Hg, t=6.767, P=0.002; SVO2: 0.726±0.017 vs. 0.663±0.053, t=3.262, P=0.008]. Heart rate (HR), RAP, mPAP, pulmonary wedge pressure (PAWP), PVRI, right ventricular stroke work index (RVSWI) and Qs/Qt were decreased significantly compared with those before mechanical ventilation [HR: 73±2 bpm vs. 102±13 bpm, t=6.228, P=0.000; RAP: 6.9±1.0 mm Hg vs. 13.9±1.5 mm Hg, t=3.609, P=0.008; mPAP: 18.5±2.9 mm Hg vs. 41.6±3.0 mm Hg, t=4.773, P=0.000; PAWP: 6.9±2.2 mm Hg vs. 14.0±4.2 mm Hg, t=2.747, P=0.030; PVRI: 26.3±1.7 kPa×s×L(-1) vs. 49.6±10.0 kPa×s×L(-1), t=9.861, P=0.000; RVSWI: 11.0±1.9 g×cm(-1)×min×m(2) vs. 22.0±1.5 g×cm(-1)×min×m(2), t=12.704, P=0.000; Qs/Qt: (26±18)% vs. (35±15)%, t=7.603, P=0.000], and cardiac index (CI), DO2, oxygen consumption (VO2) and O2ER were also increased [CI: 71.68±6.67 mL×s(-1)×m(-2) vs. 70.01±6.67 mL×s(-1)×m(-2), t=2.832, P=0.036; DO2 (L×min(-1)×m(-2)): 460.9±14.0 vs. 410.0±3.1, t=9.268, P=0.000; VO2 (L×min(-1)×m(-2)): 158.5±9.2 vs. 129.9±5.3, t=2.818, P=0.004; O2ER: (20±1)% vs. (18±1)%, t=7.652, P=0.000]. All of the 8 patients survived. Pulmonary circulation hemodynamic and oxygen dynamic disorders were found in HAPE patients with secondary ARDS. Treatment with early mechanical ventilation not only improved oxygenation but also reduced pulmonary hypertension and increased cardiac output and DO2.