ANION GAP IN TURPENTINE-INDUCED PLEURAL EFFUSIONS - CORRELATION WITH PH AND PROTEIN LEVEL

Since the pleural fluid proteins and lactate are unmeasured anions, th e pleural fluid anion gap (Na+K-Cl-total CO2) should vary with the pro tein level and should be high in acidic effusions (which have high lac tate levels). The anion gap is also convenient and inexpensive to meas ure, and less subject to artifact than the pH measurement. To test the hypothesis that the anion gap correlates with the pH, protein level, and other traditional pleural fluid measurements, we used a well-descr ibed model of turpentine-induced effusions in nine New Zealand white r abbits. Nonacidic exudative effusions were induced by an intrapleural injection of turpentine; acidic exudative effusions were induced by a second injection. Pleural fluid and blood were obtained just before (0 h) and 9, 24, 48, and 72 h after the second injection. We found the a nion gap correlated with pH, the glucose, protein, and lactate dehydro genase levels, pleural-fluid/plasma protein and lactate dehydrogenase ratios, and WBC count (all p<0.001). The pH and protein ratio together accounted for 95% of all anion gap variation within individual subjec ts. We also found the influence of the Pco(2) level on pH was not sign ificant after taking into account the influence of the anion gap. Thes e results suggest the anion gap may be useful in the clinical evaluati on of pleural effusions and could potentially replace the pH measureme nt.