Low Concentration Silver Nitrate Pleurodesis in Rabbits: Optimal Concentration for Rapid and Complete Sclerosing Effect

Abstract

Pleurodesis is a useful therapeutic tool when local treatment of a recurrent malignant pleural effusion or pneumothorax is needed. We have previously demonstrated that the intrapleural injection of 0.5% silver nitrate (SN) produces a significant pleurodesis, while 0.25% SN has no sclerosing effect in a rabbit model. The objective of this study was to determine the minimum concentration of SN needed to induce pleurodesis in our experimental model. One hundred twenty male New Zealand white rabbits received 0.3, 0.4, or 0.5% SN (40 animals per group) in a total volume of 2 mL instilled intrapleurally. These animals were sacrificed 3, 7, 14 or 28 days after the intrapleural injection (n = 10 animals per group), and the pleural spaces were then assessed grossly for evidence of pleurodesis and microscopically for evidence of fibrosis and inflammation. By 28 days, all concentrations of SN had produced a pleurodesis. There was evidence of a gross pleurodesis 7 days post-injection in animals that received 0.5% SN (score of 2.8 +/- 0.2 on a scale of 0-4). After 14 days, significant pleural adhesions were evident in the groups that received 0.4 or 0.5% SN. We conclude that SN concentrations as low as 0.3% can effectively produce a pleurodesis within 28 days of intrapleural injection. However, the precocious pleurodesis development observed 7 days after the intrapleural injection of 0.5% SN suggests that this concentration may be optimal when a fast result is necessary.

Evidence that mesothelial cells regulate the acute inflammatory response in talc pleurodesis

“…The experimental finding that mesothelial cells may play a major role in the mechanism of pleural inflammation and contribute to an effective sclerosis in talc-induced pleurodesis may help explain why malignant pleural effusions with a high tumour burden and a low pleural fluid pH and glucose concentration may be less responsive to talc-pleurodesis than malignant effusions with less malignant involvement of the pleural space [18][19][20][21][22]. However, this is not absolute because effective pleurodesis can be achieved using talc by thoracoscopy despite the findings of low pleural fluid pH [23].…”

“…The talc was suspended under sterile conditions in an endotoxin-free saline solution. The protocol of pleural injection has been described in detail previously [17,18]. After 6, 24 or 48 h, the animals were sacrificed and, after exposure of the diaphragm via a midabdominal incision, the pleural fluid was aspirated and processed for cytokine measurements.…”

Experimental Pleurodesis Induced by Antibiotics (Macrolides or Quinolones)

“…Table 1 also shows the scores used to quantify collected fragments of pleura and parenchyma; these were processed and stained with hematoxylin and eosin. Similarly to the macroscopic assessment, we based our microscopic analysis on previously validated scores, [13][14][15][16] quantifying the degree of inflammation and fibrosis (0 to 4).…”

“…Such scores were established in order to macroscopically quantify the degree of pleural adhesion (0-4), atelectasis (0-2), and fluid collection (0-4). Pleurodesis was considered effective when the degree of pleural adhesions was equal to or greater than a score of 3 [11][12][13][14][15][16] and no presence of atelectasis or fluid collection. Table 1 also shows the scores used to quantify collected fragments of pleura and parenchyma; these were processed and stained with hematoxylin and eosin.…”

“…The thorax was removed en bloc, and the lungs were expanded with 60 mL of 10% formalin and immerged in this solution for at least 48 h. After this period, each pleural cavity was exposed using the method previously described by our group. [13][14][15][16] Then, with the thorax opened, we evaluated the presence of macroscopic pleural adhesions and collected fragments from the pleura and pulmonary parenchyma for later microscopic analysis. Table 1 summarizes scoring scheme for adhesion, atelectasis, and fluid collection.…”