Effect of lavage solution type on bronchoalveolar lavage fluid cytology in horses

Title: EFFECT OF LAVAGE SOLUTION TYPE ON BRONCHOALVEOLAR LAVAGE FLUID CYTOLOGY IN HORSES Authors: Cornélie Westermann1, de Bie A1, Olave C2, Teske E2, Couétil L3 1 Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 114, NL 3584 CM Utrecht, The Netherlands 2 Department of Clinical Science of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 114, NL 3584 CM Utrecht, The Netherlands 3 Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, Indiana, USA Purpose of the study: Equine bronchoalveolar lavage (BAL) is usually performed with 250-500 ml isotonic saline. Saline has a pH of 5.5 and causes an increase in neutrophil count (%N) 48 h after BAL. Other isotonic solutions such as Ringer’s solution, phosphate buffered saline (PBS) or Plasmalyte have a neutral pH of 7.4 and are thought to be a better choice for BAL. We hypothesized that performing BAL using neutral solutions would mitigate influx of neutrophils in airways. Methods used: BAL were performed in four different lung lobes of four healthy horses using four types of solution in a crossover design. BAL were performed twice at 48 h in the same lobe with 250 ml of solution and twelve days washout between solution types. Differential cell counts were determined by two investigators masked to treatments. Automated total cell count (TCC) were determined (n=128). Log-transformed data were analyzed using R and P<0.05 was significant. Summary of results: The mean BAL fluid volume return was 51%. Mean %N increased from 1.5 ± 0.9 % to 14.7 ± 9.6 % at 48h (P<0.0001) but there was no significant difference between solutions and lung lobes. Mast cell% decreased after BAL with saline (3.3 ± 2.5 vs 1.8 ± 1.2 %; P=0.0055) but not with other solutions. There was no significant change in TCC with solutions and lung lobes. Conclusions: We conclude that neutrophil influx after BAL procedure is independent of the type of isotonic solution and lung lobe. Solutions with neutral pH are recommended due to lesser effect on mast cells. Key words: bronchoalveolar lavage; lung lobes; equine; lavage fluids