Page 467 - WSAVA2018
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fibreoptic or video bronchoscope is preferred over rigid endoscopes. While rigid endoscopes can be used for tracheoscopy, they are much less useful in feline practice as they do not allow examination beyond the carina and there is also risk of airway perforation in the hands of inexperienced operators. Flexible bronchoscopes will also have a ‘multi-use’ biopsy channel in which an adapter can be attached to allow for concurrent oxygen administration, passing biopsy forceps and saline for BALs. Bronchoscopes will usually only have two-way distal tip deflection (up and down). Ancillary equipment used in bronchoscopy includes cytology brushes/ aspiration catheters, foreign body retrieval forceps, transbronchial aspiration needles and biopsy forceps.
Often, animals that are candidates for bronchoscopy have compromised respiratory function. There is no such ‘one size fits all’ anaesthetic protocol and each case needs to be treated individually. Most cases tolerate a low-dose acepromazine (0.01 mg/ kg), an opioid (e.g. buprenorphine 0.02 mg/kg) and bronchodilator (e.g. terbutaline 1 mg/ml, 0.01 mg/kg IV, IM or SQ), the latter to help reduce bronchospasm and improve oxygenation. General anaesthesia is most easily maintained by total intravenous anaesthesia (TIVA) with incremental doses of propofol or alfaxalone, In cats, due to the sensitive nature of the larynx, topical anaesthesia with 1% lidocaine spray is required.
Technique
The bronchoscope should be sterilised before use, either by cold sterilisation in 2% glutaraldehyde solution such as Cidex (Johnson & Johnson) or Med- DisTM (Medichem International Ltd), F10 or using ethylene oxide gas sterilisation. If cold sterilisation is used, the instrument must be rinsed and channel flushed thoroughly with sterile water before use.
It’s essential for the operator to be familiar with endobronchial anatomy due to the limited amount of examination time spent within the airways between ‘re-oxygenation’ phases. Common examination method is to evaluate the larynx, trachea, entire right side, then entire left side in a standard order. Following a ‘roadmap’ will help with endobronchial orientation and ensures a more complete investigation of each lung lobe.5
The larynx (both structure and function) should be under a very light plane of anaesthesia. It is vital to have an assistant ‘announce’ phase of respiration to ascertain appropriate abduction on inspiration
and adduction on expiration. Unfortunately, cats have airways that are too narrow to allow for the passage of a bronchoscope through a T-adaptor and endotracheal tube. Instead, the bronchoscope is usually advanced directly into the airway under direct visualisation.
The trachea should then be examined down to the level of the carina. It should contain no mucus/ foam and should be a uniform pink colour with a smooth wall with easily visible submucosal capillary complexes.
The carina marks the bifurcation of the trachea into the left and right main stem bronchi. The right main stem bronchus is usually straight ahead of the bronchoscope and the left main stem bronchi usually require some manoeuvring to the operator’s right to facilitate entry. For this reason, airway foreign bodies (especially grass blades) are more commonly seen in the right main stem bronchi. Each segmental airway should be evaluated for changes in colour, shape, size, and signs of ‘bubbling’, purulent discharge, excessive mucus, or blood. If the operator becomes ‘lost’, the bronchoscope is retracted back to the carina (landmark) to re-establish position.
Airway sampling/bronchioalveolar lavage
Once the airways have been thoroughly evaluated, samples should be obtained for cytology and microbiology as gross changes are not pathognomonic for specific disease. Airway sampling is best achieved via directed BAL. Samples are obtained by ‘wedging’ the tip of the bronchoscope within a terminal bronchus. Warmed sterile saline is flushed through the biopsy port of the bronchoscope and immediately aspirated. BAL samples should be obtained from at least two sites (usually left and right side) as well as any focal abnormalities.4
The retrieved saline is submitted for both cytology, bacterial culture /sensitivity and mycoplasma PCR.
Postoperative management
The patient is intubated immediately post-procedure and maintained on 100% oxygen until stable and recovered from anaesthesia. It’s essential that patients are closely monitored on recovery and supplemental oxygen administered, either by flow- by or O2 tent, as required.
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