Trachea: transtracheal aspiration / washing
Synonym(s): Transtracheal wash or aspirate, Percutaneous transtracheal wash or aspirate, TTA / TTW
- Aseptic collection of samples from the lower respiratory tract for cytologic evaluation and bacteriologic analysis, by means of a catheter inserted percutaneously directly into the tracheal lumen.
- Useful in foals where transendoscopic collection of tracheal samples may not be feasible due to the size of endoscopes available.
- A useful and simple diagnostic test for investigation of infectious and non-infectious airway and pulmonary disease in the horse.
- Obtaining uncontaminated samples for bacteriological analysis, which may be difficult to obtain by endoscopic sampling.
- Can be performed in the standing adult horse with no sedation.
- Only minimal and simple equipment needed. Purpose made kits are available but are expensive and have few clear advantages.
- Is the most accurate way of collecting samples for bacteriology in the horse, without any contamination from the upper respiratory tract.
- Damage to the tracheal rings can occur if technique is not performed carefully.
- Breakage of the catheter in the tracheal lumen can occur, especially if a wide gauge hypodermic needle is used as the trochar.
- Is a surgical procedure (though very simple) and thus normal complications can occur, eg cellulitis at the site of puncture, local abscess formation, subcutaneous emphysema and pneumomediastinum.
- Direct visualization of the respiratory tract is not achieved and so ampling simply reflects the overall changes occurring within the airway.
- Sampling can sometimes be difficult if the catheter fails to engage a pool of fluid at the thoracic inlet, even following introduction of sterile saline.
- Transendoscopic tracheal aspiration Trachea: tracheal wash . This is the technique of choice in practice and visualization to the respiratory tract is achieved. It is less invasive and requires no surgical preparation. It may require sedation.
- However, an endoscope Respiratory: endoscopy , is needed (expense) and the samples are not as suitable for bacteriologic analysis due to some degree of contamination from the URT. It is possible to obtain sterile samples if a double protected sample system is used. This involves the use of a sterile endoscope and a shielded double catheter introduced via the biopsy channel.
- Bronchoalveolar lavage (BAL) Lung: bronchoalveolar lavage :
- This is the preferred technique for accurate cytologic analysis from defined parts of the bronchial tree.
- The technique requires the use of a long endoscope (2 m is a useful length).
- The procedure can be performed blindly without endoscopy using a BAL catheter but in this case sampling will be from a random location in the broncial tree.
- In both cases the horse needs sedation.
- Local anesthetic can be sprayed onto the carina to allow the catheter or scope to pass into the bronchial tree with less coughing.
- Bacteriological sampling is unreliable in view of the contamination from the upper airway during passage of the scope or catheter.
- 10 min.
- 5-30 min.
Criteria for choosing test
- Standard as for any pulmonary disease Respiratory: overview :
- History of airway disease/coughing.
- Clinical examination.
- Only significant if some severe infectious disease, or purulent, malodorous material is suspected or harvested, when care must be taken in managing the skin puncture, to avoid post-surgical infection.
- Standard care and adherence to details are needed but the overall procedure is very simple.
- Pair of clippers/razor.
- Twitch and/or equine sedative drugs Anesthesia: standing chemical restraint .
- Pair of surgical gloves.
- Stall or stocks.
- Local anesthetic solution Anesthesia: local - overview , eg mepivicaine/bupivicaine.
- Disposable hypodermic syringes. Sizes 2 ml, 20 ml and 50 ml.
- 12/14G over-the-needle catheter.
- Alternatives are:
- Purpose made sampling set
- Blunt teat cannula.
- 30 cm long Fr5 gauge sterile urinary catheter.
- Sterile bag of saline (lukewarm ideally).
- Containers to take samples.
- Some sort of preservative is needed in most cases unless cytologic anlaysis can be carried out in <4 h.
- Cellular deterioration and bacterial overgrowth can be minimized with a suitable product, eg an equal volume of 40% ethanol, or Cytospin preservation fluid (designed specially for cytocentrifugation).
- As many fixatives affect the morphology of cells on cytocentrifuge preparations it is always advisable to send both fixed and unfixed aliquots and also contact the lab for advice. Plain containers are required for samples being submitted for bacteriology (blood tubes can be used). Cytospin preservation fluid is a much better preservative than EDTA (purple tubes).
- Restraint is important although the technique is simple and minimally traumatic. Careful preparation beforehand and a competent assistant will help considerably.
- A 10 x 10 cm square is clipped off over the ventral aspect of the distal trachea.
- This area is aseptically prepared as standard, eg povidone-iodine scrub Povidone-iodine , rinsed (twice) and surgical spirit spray to finish.
- 2 ml of local anesthetic is injected in a bleb subcutaneously at a midline site between two subcutaneous tracheal rings .
- The operator's hands are then scrubbed and gloved.
- A stab incision is made with a No. 11 blade.
- Twitch Restraint methods .
- Some degree of chemical standing restraint may be needed depending on the horse's temperament and operator experience Anesthesia: standing chemical restraint .
- Sedation is mandatory in foals.
Step 1 - Catheter insertionDo not use the needle method, the IV cannula approach is preferred.
- A sterile 12G over-the-needle catheter is inserted through the anesthetized stab incision site; carefully between two tracheal rings into the tracheal lumen . Using one hand to stabilize the trachea and the other to guide the catheter .
- Once in the tracheal lumen the catheter is immediately directed caudally.
- The trochar is removed and a 30 cm Fr5 sterile urinary catheter is inserted carefully via the catheter and passed caudally towards the tracheal base .
Step 1 - Sample aspiration
- While slowly advancing the catheter caudally suction is applied with a 20 ml syringe until high resistance is felt. This suggests that the catheter tip is in a pool of respiratory secretions at the most dependant point of the trachea just distal to the thoracic inlet. Suction should produce a sample of tracheal secretions in the syringe .
- If the catheter is introduced until coughing occurs it is likely to be close to the carina and should be withdrawn. If repeated catheter relocation and suction is unsuccessful then a transtracheal wash is performed.
- 20-30 ml of saline is introduced through the catheter .
- Once all the fluid has been introduced the urinary catheter is gently withdrawn as suction maintained on the syringe.
- As soon as resistance is felt the position is fixed and fluid is aspirated into the syringe.
- If repeated suction is unsuccessful a further 20 ml of lukewarm saline should be flushed into the trachea and the process repeated as needed to obtain a sample.
- Sometimes several attempts are required to obtain a meaningful sample.
- It can be useful to lower the horses head to aid sampling.
- Many horses cough during the above procedure.
Step 2 - Sample preservation
- The sample is then either analyzed immediately or some is placed in a fixative (as discussed earlier) for cytology Respiratory: lower airway cytology and some in a sterile container for bacteriology.
- Samples should be sent to a suitably equipped and experienced laboratory for analysis.
- The catheter is removed followed by the cannula and digital pressure is applied to the stab incision for a minute or so.
- There is no need to suture the stab incision and a dressing is not required, although an antiseptic ointment might be sensible.
- Antibiotics Therapeutics: antimicrobials and/or anti-inflammatory drugs Therapeutics: anti-inflammatory drugs can be given on rare occasions when infection is a high risk (see earlier).
- Antiseptic ointment, adhesive dressing or tissue adhesive can be used to close the wound.
- See earlier if infectious or purulent material is suspected.
- Local wound infection with cellultis is a very rare complication tat can arise 2-4 days after the procedure. Standard treatment includes hot packs, local DMSO, antibiotics, anti-inflammatories.
- Subcutaneous emphysema is rarely seen, as the appearance of air trapped under the skin extending from the stab wound, with the characteristic crackling feel. This will usually settle on its own with no intervention needed in most cases, unless associated with infection (see above).
- Abscessation can occur at the surgical site and is treat as standard.
- Coughing seldom occurs during the procedure but may be encountered.
- If a needle is used as the cannula there is a serious risk of cutting the catheter. If this occurs the catheter fragment is usually coughed up, but on occasion may require endoscopic removal.
- Careless technique can result in a local tracheal ring, granuloma/chondroma. This is usually only a local blemish and is avoided by good technique.
- Pneumomediastinum can occur in theory, but is a really unfortunate occurrence and usually indicates other problems.
Reasons for treatment failure
- In a small number of horses it can be very hard to obtain a suitable sample.
- Very simple technique with few complications, but superseded in many cases by transendoscopic sampling Trachea: transendoscopic aspiration / washing with more generalized use and availability of the flexible fiberoptic endoscope Respiratory: endoscopy .
- Recent references from PubMed and VetMedResource.
- Rendle D (2012) Making the most of samples from the equine respiratory tract - a clinician's perspective on clinical pathology. UK Vet 17 (4), 4-9 VetMedResource.
- Dixon P (1995) Collection of tracheal respiratory secretions in the horse. In Pract 17 (2), 66-70 (a very good practical review of this subject) VetMedResource.
- Wood J L N & Chanter N (1994) Can washing help to keep the lungs clean? Equine Vet Educ 6 (4), 220-222 (interesting background reading on the significance of bacteria isolated from tracheal washes, essential for any vets involved in racing practice) VetMedResource.
Other sources of information
- Rose R J & Hodgson D R (1993) Manual of Equine Practice. W B Saunders Co. pp 140-141. ISBN: 0-7216-3739-6 (useful overview of this technique from a different perspective).