Dialysis-induced hypoxemia: membrane dependent and membrane independent causes

Hypoxemia during hemodialysis may result from several differing processes. We initially studied patients undergoing standard acetate hemodialysis. At 15 minutes of dialysis, leukopenia (primarily neutropenia), a decline of platelet count, and hypoxemia occurred, but without a significant change in mean minute ventilation. Complement activation (V/A ratios of C5a greater than 1.0) persisted throughout dialysis. Leukocyte count returned to baseline by one hour. To separate the effects of solute and/or gas fluxes from those of blood-membrane interaction we studied changes in Po2, WBC, C5a, TxB2, and PGI2 during a period of blood membrane interaction without dialysis, and during subsequent acetate dialysis. Patients were studied with both polyacrylonitrile (PAN) and cuprophan membranes containing different priming solutions during membrane contact alone. Despite leukopenia and complement activation, hypoxemia failed to occur during membrane contact alone. At 15 minutes of subsequent acetate dialysis, significant hypoxemia occurred with both membranes. However, the degree of hypoxemia was twice as great with a cuprophan membrane primed with acetate (18.6 +/- 3.3 mm Hg) compared with air or bicarbonate (9.1 +/- 1.4 and 7.0 +/- 2.0 mm Hg, respectively), or compared with PAN (8 +/- 2.8 mm Hg). Changes in thromboxane B2, PGI2, and C5a did not correlate with changes in Po2. We conclude that there are two major components to dialysis related hypoxemia. One is membrane independent, and may relate to the metabolic effects of acetate or to dialyzer CO2 loss. The remaining portion is membrane dependent, occurring with cuprophan, but not with PAN, and is conditioned by an acetate dependent interaction between blood and membrane.