[Therapy of ARDS. 2. New management methods--first clinical experiences]

Abstract

Conventional treatment of the adult respiratory distress syndrome (ARDS) includes pressure-limited ventilation, permissive hypercapnia, posture changes, aggressive dehydration, selective lung ventilation, and extracorporeal gas exchange. New strategies such as nitric oxide inhalation, the implantation of an intravenous membrane oxygenator (IVOX), and surfactant replacement are currently under evaluation. Nitric oxide (NO) is an important endothelium-derived relaxing factor that is rapidly inactivated by binding to haemoglobin. Inhaling this substance has been shown to induce selective vasodilatation of ventilated lung regions. Thus, inhaled NO reduces pulmonary hypertension, increases right heart ejection fraction, and improves arterial oxygenation by redistributing blood flow away from areas with intrapulmonary shunts to areas with a normal ventilation/perfusion ratio. Dose-response analysis has revealed that effective doses for improvement of oxygenation are lower than for reduction of mean pulmonary artery pressure. The use of a miniaturised membrane lung, IVOX, for intracaval oxygen and carbon dioxide exchange is a new approach to augment gas exchange. The IVOX is inserted via an introducer into the femoral vein and is designed for placement in the full length of the vena cava. Initial experiences with this device show that the currently used prototype provides a maximum of one-third of basal gas exchange. Therefore, a more efficient device will be needed to significantly reduce high inspired oxygen concentrations and airway pressures. Moreover, there exists evidence that IVOX causes caval obstruction. Lung surfactant recovered in BAL from patients with ARDS demonstrates that fractional contents of phosphatidylcholine and phosphatidylglycerol are reduced, and that the total concentration of apoproteins is decreased. Furthermore, the surfactant surface tension-lowering activity is abnormal. Thus, administration of exogenous surfactant may have therapeutic benefits. However, the optimal surfactant preparation, the optimal amount required to restore lung surfactant activity, and the optimal method to deliver it to patients with ARDS are unknown and currently under evaluation.