Deterioration of gas exchange in patients with severe thrombotic thrombocytopenic purpura with respiratory failure during therapeutic plasma exchange

Therapeutic plasma exchange (TPE) is a procedure performed on patients suff ering from various disorders, including thrombotic thrombocytopenic purpura (TTP). As we noted a frequent transient deterioration in respiratory funct ion when the procedure was performed on intensive care unit (ICU) patients, we studied retrospectively the incidence of respiratory deterioration duri ng and shortly after TPE and looked for a probable correlation with a chang e in the white blood cell (WBC) counts. Over a period of 10 months six pati ents with TTP, five of whom had parenchymal lung disease due to different m edical reasons, underwent TPE. The oxygen saturation was measured continuou sly before, during, and after TPE; additionally, the WBC and differential c ounts were measured pre- and post-TPE. The ratio of the oxygen saturation b y pulse oxymetry (SpO(2)) to the fraction of inspired oxygen (FiO(2)) was c alculated before, during and after TPE. In these five patients with lung di sorders, there was a consistent trend of a decreasing SpO(2)/FiO(2) quotien t during and within 2 h post TPE compared to the pre-TPE value. The decreas e in SpO(2)/FiO(2) range was 0.20-0.89 with an average of 0.56. In the same 5 patients there was an increase in the WBC count in the range of 2.3-19.7 x 10(9)/L with an average increase of 9.3 x 10(9)/L. The percent neutrophi ls of the total WBC counts also increased following most of the sessions, t his increase was in the range of 1-15% with an average of 7%. The effect of TPE on the SpO(2)/FiO(2) ratio and the correlation to the WBC count and to a possible neutrophil activation has not been previously reported. We post ulate that TPE can accentuate respiratory deterioration in patients with TT P who already have acute lung injury. This may be due to the priming and ac tivation of the leukocytes that could lead to the release of cytokines and inflammatory mediators during the procedure. Thus, it is important to be aw are of the possible deterioration in respiratory function and gas exchange while administering TPE to patients with pre-existing parenchymal lung inju ry. (C) 2001 Wiley-Liss, Inc.