Effect of Lavage Solution Type on Bronchoalveolar Lavage Fluid Cytology in Clinically Healthy Horses

SIMPLE SUMMARY: One of the most valuable methods to diagnose lower airway disorders such as equine asthma is broncho alveolar lavage (BAL), whereby a solution, usually saline, is inserted in a distal part of a lung lobe. The solution is then collected and contains cells present in the deeper airways. It is a safe procedure, but saline can cause local inflammation (neutrophilia). This study aimed to investigate if there are better solutions for the procedure, for example, less acidic ones, to avoid causing inflammation, and whether the BAL fluid retrieved from one lung lobe is representative for the whole lung. Since it is not necessary to use horses with respiratory disorders to answer these research questions, healthy horses were used. Four horses were used (using four lung lobe locations and four different solutions per horse twice with an interval of 48 h) and generated enough data to answer the questions. The findings were that the BAL composition is not affected by either the solution used or the lung lobe sampled. These findings are positive because they support keeping the procedure easy and practical. ABSTRACT: Equine bronchoalveolar lavage (BAL) is usually performed with 250–500 mL of isotonic saline at pH 5.5. The acidic pH of saline may cause an increase in airway neutrophil count 48 h after BAL. Other isotonic solutions such as Ringer’s solution, phosphate-buffered saline (PBS) or Plasma-Lyte 148(®) have a neutral pH of 7.4 and might be a better choice for BAL by not provoking inflammation and the influx of neutrophils into airways. BAL was performed in four healthy horses in four different lung lobes using four different solutions in a randomized crossover design. In each lobe, BAL was performed twice with a 48 h interval using 250 mL of solution. Automated total nucleated cell counts (TNCs) were recorded, and differential cell counts in lavage fluid were determined by two investigators blinded to treatments. The mean volume of BAL fluid retrieved was 51 ± 14%. The mean neutrophil percentage (%N) increased from 1.5 ± 0.9% to 14.7 ± 9.6% at 48 h (p < 0.001) but was not significantly affected by the solution used or the lung lobe sampled. In conclusion, in this study, the influx of neutrophils into airways after BAL was independent of the type of isotonic solution used and the lung lobe sampled. Saline remains an appropriate solution for BAL in horses.