Effect of indomethacin on arterial oxygenation in critically ill patients with severe bacterial pneumonia.

The effect of indomethacin (1 mg/kg) on gas exchange was studied in ten patients with hypoxaemic respiratory failure precipitated by bacterial pneumonia. Mean arterial oxygen tension (PaO2) improved significantly (79 +/- 16 mm Hg to 98 +/- 20 mm Hg) but the response varied between patients: five showed substantial responses (27-42 mm Hg), three lesser responses (7-9 mm Hg), and two no response. Similar changes were found in the alveolar-arterial oxygen gradient and the ratio of PaO2 to fractional inspired oxygen concentration. In two responders studied further, PaO2 had fallen to baseline values 4-6 h later and a repeat indomethacin challenge again increased PaO2 by greater than 25 mm Hg with concomitant changes in pulmonary shunt. There were no significant changes in the other gas-exchange or haemodynamic variables measured and there was no clear reason for the variability in response to indomethacin. These results suggest a role for products of the cyclo-oxygenase pathway of arachidonic acid metabolism in the pathogenesis of hypoxaemia in patients with severe bacterial pneumonia.