- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- TA of fluid may be performed by two commonly used methods
- In the percutaneous technique, fluid is aspirated from the tracheal lumen using sterile polyethylene tubing, a catheter inserted through a cannula, or a large-bore needle inserted between the sterilely prepared tracheal rings. The site is infiltrated with 2% lidocaine and a small skin incision made prior to passing the needle or cannula. With this method, a sterile sample from the airways is more easily obtained, but complications can occur
- Another method for obtaining samples is via passage of an endoscope through the nostrils and pharynx into the trachea. A catheter is then advanced through the endoscope biopsy channel beyond the tip of the endoscope and into the trachea. This method is less invasive than the percutaneous technique, but the sample is more likely to be contaminated as the endoscope passes through the nares and pharynx. The use of dedicated double lumen catheters decreases the level of contamination
- With either method, sterile saline (10–60 mL) or lactated Ringer's solution is instilled and immediately recovered by applying suction with a syringe. If the attempt to recover fluid is not successful, the tubing or catheter may be moved a few centimeters in either direction, and additional fluid may be injected
- The sample is aliquoted into a sterile tube for culture and into a tube containing EDTA for cytology
- Direct smears, sediment preparations, or cytocentrifuged slides are made for cytologic examination. Making slides soon after collection of fluid avoids artifactual changes in cells and limits the confounding overgrowth of bacteria that can occur when there is contamination of the sample
- Most commonly, air-dried slides are stained with Wright's or Diff-Quik. Diff-Quik is a non-metachromatic stain and it may fail to stain mast cell granules, making identification of mast cells problematic
- Cell counts are not typically performed because the amount of fluid infused and recovered is variable and the presence of mucus can lead to irregular distribution of cells
- Protein content is not commonly determined because wash fluids usually are low in protein
- In aspirates from normal horses, columnar epithelial cells, which may appear ciliated or nonciliated, are the most common cell type. Macrophages are also present in moderate numbers, along with small numbers of nondegenerative neutrophils and occasional eosinophils and lymphocytes. Multinucleated macrophages may be seen in low numbers
- Mucus is present in many samples and appears as strands of purple fibrillar material. NETs have a similar appearance and are generally confused with mucus in the presence of activated neutrophils
- Squamous epithelial cells, organisms, and debris from the oropharynx or skin may be present and indicate contamination
- Samples from normal horses have a wide range of cell types and generally do not contain the same cell types as those obtained using BAL. This reflects differences in cell populations in the trachea compared with those lining alveolar spaces. Tracheal aspirates contain cells from all areas of the lung and may be useful in detecting focal lung lesions
- Acute inflammation of the respiratory tract often causes migration of inflammatory cells to the trachea
- Other conditions (e.g. severe equine asthma) may not be diagnosed as readily by TA as by BAL
- Chronic inflammation or irritation causes increased mucus production by epithelial cells of the airways. This is a feature of equine asthma. The presence or amount of mucus may or may not be associated with increased numbers or percentages of neutrophils in these conditions
- With suspected septic conditions, sterile collection of material by TA is preferred over BAL; however, bacteria in the trachea without cytologic evidence of neutrophilic inflammation suggests nonpathogenic colonization of the trachea
- Any breed, age, or sex
- Foals 1–6 months of age are susceptible to pneumonia caused by Rhodococcus equi
- Pneumonia
- Equine asthma
- EIPH
- Parasitic inflammation (lungworms)
- Idiopathic eosinophilic pneumonia
- Neoplasia
- History of R. equi previously on premises; see Signalment
- Young performance horses (e.g. racehorses) are at higher risk for developing upper respiratory tract viral infections, secondary bacterial pleuropneumonia, mild and moderate equine asthma (inflammatory airway disease), and EIPH
- Long-distance transportation
- Proximity to donkeys (lungworms)
DIAGNOSIS
TREATMENT
FOLLOW-UP
MISCELLANEOUS