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Objective: To compare the results of pleural fluid analysis for WBC counts and differential cell counts as follows: (1) counting performed manually vs that performed by an automated cell counter; (2) cells collected in different types of specimen containers; and (3) cell counts performed at 4 and 24 h postthoracentesis. Methods: Twenty-eight pleural fluid samples were each collected in five different containers (ie, ethylenediaminetetraacetic acid (EDTA)-treated glass, citrate-treated glass, heparinized glass, plain glass, and plain plastic tubes). The WBC counts and differential cell counts were obtained manually (on the EDTA tube) and with an automated counter on all tubes within 4 h of collection, and again after 24 h of refrigeration. Results: There was a close correlation between the WBC counts obtained manually and those obtained with the automated counter from the pleural fluid samples collected in the EDTA tubes (r = 0.92). With the automated counter, the pleural fluid WBC counts were similar among the three tubes containing anticoagulants, but the counts obtained from the tubes without anticoagulants were significantly lower. The differential cell counts obtained manually and those obtained with the automated cell counter differed substantially. Although the percentage of lymphocytes was similar, the automated counter was inaccurate in differentiating neutrophils from large monocytes or mesothelial cells. The WBC counts obtained within 4 h of collection and 24 h after collection were virtually identical. Conclusions: The WBC counts obtained manually and with the automated counter from pleural fluid samples in EDTA tubes correlated very closely. The pleural fluid WBC count was lower if the pleural fluids had been collected in tubes without an anticoagulant. Automated WBC counts from pleural fluid specimens were inaccurate, possibly due to difficulty in separating neutrophils from monocyte/mesothelial cells. Refrigerated storage for up to 24 h had no significant effect on the total WBC count or on the WBC count differential regardless of the tube utilized.

Study objectives To identify the typical duration ofpostoperative mechanical ventilation following coronary artery bypassgraft surgery (CABG), and to identify risk factors for prolongedpostoperative ventilation. Design Retrospective studyof 4,863 consecutive patients using univariate and multivariatesurvival analysis to identify independent risk factors. Setting Saint Thomas Hospital, Nashville, TN, a 575-bed, academically affiliated, regional referral hospital specializing incardiovascular diseases. Patients All patientsundergoing CABG in our hospital from January 1, 1996, to December 31,1997. Interventions None. Measurements andresults Duration of mechanical ventilation and mortality weremeasured. More than 94% of the patients were extubated in the first 3days following surgery, 4% more were extubated from postoperative days4 to 14, and almost 2% were receiving ventilation for > 14 days. Those risk factors that reflect preoperative medical instability, especially cardiac or respiratory insufficiency, were associated withthe highest incidence of prolonged postoperative mechanical ventilationand for operative mortality. The Society of Thoracic Surgeons-predictedmortality estimate was the best single independent predictor forprolonged postoperative ventilation. Conclusions Typically, patients can be expected to be extubated within 3 days after, CABG. Certain preoperative comorbidities, especially preoperativecardiac or respiratory instability, are predictive of prolongedpostoperative mechanical ventilation.