Angiotensin II formation and endothelin clearance in ARDS patients in supine and prone positions

Objective: Inpatients with acute respiratory distress syndrome (ARDS), the prone position may enhance oxygenation by changing ventilation/perfusion ratio. In this study, we investigated whether the prone position affects the net balance: between pulmonary endothelin (ET-1) and angiotensin II (Ang II:) production and clearance, two metabolic functions of lung endothelial cells. Setting: Anaesthesiological intensive care unit of a university hospital. Patients: Ten ARDS patients (Murray score > 2.5) were studied in both the supine position (SP) and the prone position (PP). Measurements and design: Blood samples were taken simultaneously from the patient in SP for assessment of mixed venous and arterial ET-1 and Ang II concentrations, and plasma renin concentration (PRC). This was repeated after 60 min in SP, immediately after turning the patient into PP, and 60 min thereafter. Net arterial/mixed venous ET-1 clearances and net Ang II formations were calculated. Results: arterial oxygen tension increased from SP to PP by an average of 60 mmHg, about 20 %. Arterial ET-1 concentrations of ARDS patients were 1.57 +/- 1.1 pg/ml (mean +/- SD) and within the range of healthy persons. Net ET-1 clearances were negative in SP, indicating pulmonary release of ET-1, and did not change in PP. Arterial Ang II concentrations (73 +/- 56 pg/ml) as well as PRC (126 +/- 85 pg/ml) were markedly elevated. Net transpulmonary Ang II formation did not change. Conclusion: Acute changes of oxygenation in ARDS patients by positioning do not induce any short-term effects on pulmonary ET-1 net clearance or Ang II net formation.