Preservation of normal gas exchange with hemodilution in patients with pulmonary hypertension.

The relationship between the plasma colloid osmotic pressure/pulmonary capillary wedge pressure difference (PCOP-PCWP) and the development of gas exchange abnormalities was examined prior to, during, and after cardiac operations in 13 patients with pulmonary hypertension owing to mitral and/or aortic valvular disease. Alveolar-arterial oxygen tension gradient [P(A-a)DO2] and pulmonary shunt fraction (Qs/Qt) were used as indices of gas exchange impairment owing to accumulated lung water. During the baseline period, PCOP-PCWP was -8.5 +/- 2.6 mm Hg; P(A-a)DO2, 352.5 +/- 30.1 mm Hg; and Qs/Qt, 17.0% +/- 1.5%. There were no significant correlations between PCOP-PCWP and P(A-a)DO2 or Qs/Qt at any time during the study. Thus PCOP-PCWP does not predict susceptibility to lung water accumulation reliably in patients with pulmonary hypertension, and other protective factors may contribute to unimpaired gas exchange, even in the setting of profound hemodilution and low PCOP.