Rompum

Horses were sedated with xylazine (Rompum, Bayer, Mississauga, ON, Canada; 0.5 mg/kg, IV) and butorphanol (Torbugesic, Zoetis, Florham Park, New Jersey); 20‐30 μg/kg, IV) and tracheoscopy was performed with a 1.6 m videoendoscope (Evis Exera II CV‐180, Olympus Canada Inc., Richmond Hill, ON, Canada). Tracheal mucus score was evaluated during reviewing of video recordings by an investigator blinded to the treatment group.20 Bronchoalveolar lavage was performed as previously described.6 Briefly, after topical anesthesia with 0.5% lidocaine (Lurocaine; lidocaine hydrochloride 20 mg/mL, Vétoquinol N.‐A. Inc., , Lavaltrie, QC, Canada), two 250 mL‐boluses of warm sterile isotonic saline (0.9% Sodium Chloride Injection, USP, Baxter, Mississauga, ON, Canada) were sequentially instilled into a main bronchus through the videoendoscope and then aspirated with a suction pump. The samples were kept on ice until reaching the laboratory within 90 minutes. Cytocentrifuged preparations of BALF (400 μL, unfiltered) were made and cells were stained with a modified Wright–Giemsa solution (DiffQuick, Fisher Scientific, Waltham, Massachusetts). Differential leucocyte counts from 400 cells were performed by an investigator blinded to the treatment group.

Lung function was measured in standing unsedated animals, except for one horse that required sedation before each pulmonary function test (xylazine [Rompum, Bayer, Mississauga, ON, Canada], 0.4 mg/kg, IV).6 Briefly, esophageal pressure was measured as an index of the transpulmonary pressure (P_L) with a balloon sealed over the end of a polyethylene catheter placed in the distal third of the esophagus. Flow rates were obtained by the use of a heated pneumotachograph and a differential pressure transducer fitted to a mask placed over the horse's nose. The system (Flexiware 7.6, SCIREQ, Montréal, QC, Canada) allowed electronic integration of the flow signal to provide tidal volume. Before each experiment, the system was calibrated by forcing known flow of air through the pneumotachograph with a blower‐rotameter and by applying known pressure with a water manometer on the differential pressure transducer used to measure esophageal pressure. Values of pulmonary resistance (R_L) and elastance (E_L) were obtained by applying the data to the multiple regression equation for the single compartment model of the lung (P_L = E_LV + R_LV + K) where V is the volume, V the airflow, and K the transpulmonary end‐expiratory pressure. All the valid breaths were used for analysis.