Thromboxane and prostacyclin in clinical acute respiratory failure.

Plasma levels of thromboxane A2 and prostacyclin have been elevated during experimental acute respiratory failure (ARDS). The present study evaluates the relationship of plasma levels of thromboxane A2 and prostacyclin, measured by radioimmunoassay as the stable metabolites thromboxane B2 (TxB) and prostaglandin 6-K-F1 alpha (PGI) to the incidence of clinical ARDS. Sixty-seven consecutive patients at risk for ARDS were studied prospectively. TxB, PGI, platelet, and leukocyte counts were measured daily for up to 5 days. Of 55 patients without cerebral injury, 25 (45%) developed ARDS, and 30 did not. Of 12 patients with cerebral injury, none developed ARDS. This difference was highly significant (P less than 0.01). TxB was increased and age lower with head injury (P less than 0.05). PGI was significantly lower in ARDS (110 +/- 32 vs 227 +/- 211 pg/ml, P less than 0.05), and mean TxB was unchanged. TxB was increased in age greater than 60 and decreased with prostaglandin inhibitors. ARDS was significantly associated with TxB greater than 70 pg/ml, PGI below the detectable level of 103 pg/ml, TxB/PGI ratio greater than 0.7, and age greater than 60 years. Peak TxB occurred before or simultaneously with onset of ARDS in 68%. Leukocytes were decreased in ARDS (8.6 +/- 4 vs 11.1 +/- 4.4 X 10(3)/mm3) and platelets were unchanged. ARDS was decreased with steroid therapy. Elevated TxB is related to a high incidence of ARDS. Elevated PGI may protect against ARDS. Cerebral injury patients in this study were resistant to ARDS in spite of increased TxB.