Page 513 - ONLINE PROCEEDING BOOK WSAVA 2017
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that opioids cause respiratory depression, this is more
of a dose dependent issue. Opioids commonly used
for pre-medication include: methadone, morphine,
and buprenorphine. The premedication also frequently involves a sedative component in the form of an alpha-2 agonist such as medetomidine, a tranquilizer such as acepromazine, or a benzodiazepine such as diazepam or midazolam. Unlike phenothiazines and benzodiazepines, medetomidine will also provide analgesia. When combined with other medications in the premedication, dexmedetomidine may even provide suf cient analgesia and muscle relaxation for minor surgical procedures to be performed.
After proper premedication has been administered it is recommended that brachycephalic patients be “pre- oxygenated” prior to the administration of induction drugs. Administration of 100% oxygen before induction of anaesthesia prolongs the time to onset of arterial hypoxaemia. This technique increases the body’s oxygen stores, primarily in the functional residual capacity (FRC) of the lungs. Pre-oxygenation should only occur if it is not overly stressful to the patient.
When intubating a brachycephalic patient, expect to use a much smaller endotracheal tube than typically used for other similarly sized patients. Carefully select a wide variety of sizes, but be ready with 2 tubes smaller than what you estimate to be the right size. A laryngoscope is a necessary tool for intubation, as the amount of redundant tissue in the pharynx may reduce the visibility of the laryngeal opening.
While under anesthesia patients can be maintained with inhaled anesthetic such as iso urane or sevo urane in 100% oxygen. Sevo urane is metabolized faster than iso urane allowing for a faster recovery. This may be an attractive choice when anesthetizing a brachycephalic patient. All inhalant anesthetic agents produce an agent- and dose-dependent reduction in myocardial contractility, systemic vascular resistance, and cardiac preload with subsequent reductions in mean arterial pressure (MAP) and cardiac output in a dose-dependent manner, therefore vaporizer settings should be kept as low as possible, whilst maintaining an appropriate depth of anaesthesia.
Brachycephalic dogs have been shown to have a higher resting vasovagal tone than other breeds of dogs, which may predispose them to bradycardia. They are
at risk of an arrhythmias termed sinus arrest. A sinus arrest is a pause between two normal complexes that
is greater than two times the normal R to R interval due to lack of sinus node discharge. It will create on the ECG rhythm strip irregular pauses. These can be normal incidental  ndings, especially in brachycephalic breeds due to increased vagal tone associated with inspiration. Therefore, treatment is usually only started if the patient is clinical due to decreased cardiac output. Frequently, if the pauses are long enough the hearts natural defense
An Urban Experience
system will “escape” out of the normal pathway and initiate a beat from another region of the heart. These are then called “escape beats” or “escape rhythms” if it is a series of beats. These escape beats can either originate from around the AV node (called junctional escapes) or from the ventricles (called ventricular escapes). These beats can be differentiated from premature beats because they will occur AFTER the normal sinus beat would have occurred.
In addition, dogs with brachycephalic airway obstructive syndrome may also have functional and anatomic abnormalities of the gastrointestinal tract, which
may predispose them to regurgitation or vomiting in
the perioperative period. The postoperative surgical complication rate of brachycephalic dogs in the perioperative period has been reported to be as high as 12%, with 5% developing severe dyspnoea or death. Overall, the major concerns related to anaesthesia of the patient with brachycephalic airway syndrome are the development of airway obstruction (partial or complete) at any time in the anaesthetic period (from pre-operative sedation to full recovery) and the predisposition to bradycardia and regurgitation.
The recovery period is an important time for the anaesthetist to stay vigilant about patient monitoring. Appropriate post-operative medications should be administered, taking into account the level of pain anticipated from the surgery performed. Note that acepromazine has no analgesic properties and is not considered an adequate post-operative medication
if a painful procedure has been performed. We want recovery to be smooth and stress free. Because brachycephalics can sometimes desaturate during recovery, a portable pulse oximeter is a useful tool when in recovery. Brachycephalic patients should be recovered in sternal recumbency with their head slightly elevated. Avoid overly aggressive initial stimulation, as this may trigger swallowing only to be followed by a relapse into unconsciousness when the stimulation is removed.
It is important to have additional induction agent and additional endotracheal tubes ready in recovery in the event that airway obstruction occurs and re-intubation is needed. Recovering these patients with supplemental oxygen is advisable; an effective option is the placement of nasal oxygen catheter(s) during recovery. A nasopharyngeal tube can be placed and connected directly to an oxygen source to allow delivery of oxygen to the nasopharynx during recovery.
In summary, brachycephalic breeds have anatomical abnormalities that require the anaesthetist to carefully monitor breathing and any airway disturbances. However, proper premedication, vigilant monitoring in the pre-operative to recovery stages, as well as a stress-free induction and recovery, can make working with these patients less challenging and more rewarding.
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