Recently, alteplase, a recombinant tPA, has been used for loculated parapneumonic effusions in humans. In rabbits with empyema, the administration of alteplase leads to the production of large amounts of pleural fluid with no effects on the empyema. To analyze the characteristics of the increased volumes of pleural fluid seen after tPA is administered to rabbits.
A chest tube was inserted into the right pleural cavity and empyema was induced by administering Pasteurella multocida intrapleurally in 2 subgroups of rabbits, with each subgroup receiving 6 doses of tPA 1mg (n=2) or 4mg (n=4) for 3 days. The pleural fluid volume, pH, glucose, protein, LDH, WBC count of pleural fluid were measured. After 10days, the rabbits were sacrificed and an empyema score and a pleural thickening score were recorded.
The total amount of pleural fluid drained was significantly greater in tPA 4mg group than tPA 1mg group (204.5 ml vs 104.3 ml p<0.05). The protein, glucose, pH, LDH, and WBC counts did not differ significantly between tPA 1mg and 4mg group (p>0.05). But in both groups, the WBC counts were markedly increased to approximately 100,000/mm3, the pH was consistently below 7.10 and the LDH levels were markedly increased to 20x the upper normal limit for serum. The Gram stains were positive only for 1day after induction of empyema.
The intrapleural administration of tPA in rabbits with empyema markedly increases the volume of pleural fluid. The pleural fluid is highly inflammatory as evidenced by very high WBC and LDH and reduced pH.
The results of this study suggest that the increased drainage seen with fibrinolytics may be the result of augmentation of the pleural inflammatory response rather than facilitated drainage.
Moon Jun Na, Grant monies (from sources other than industry) supported by Saint Thomas Foundation.