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 ra tio. 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 ce lls. Setting: Anaesthesiological intensive care unit of a university hospital. Patients: Ten ARDS patients (Murray score > 2.5) were studied in both the s upine position (SP) and the prone position (PP). Measurements and design: Blood samples were taken simultaneously from the p atient in SP for assessment of mixed venous and arterial ET-1 and Ang II co ncentrations, and plasma renin concentration (PRC). This was repeated after 60 min in SP, immediately after turning the patient into PP, and 60 min th ereafter. Net arterial/mixed venous ET-1 clearances and net Ang II formatio ns were calculated. Results: arterial oxygen tension increased from SP to PP by an average of 6 0 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 E T-1 clearances were negative in SP, indicating pulmonary release of ET-1, a nd did not change in PP. Arterial Ang II concentrations (73 +/- 56 pg/ml) a s 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 I I net formation.