29 Feb 2016
Anna Bryla discusses one-year-old bulldog Arnie, who presents with 3 out of 10 right pelvic limb lameness in the latest in the Case Notes series.
Anna Bryla
Job Title
Figure 2. A bulldog sedated with medetomidine 5μg/kg and butorphanol 0.3mg/kg IV for tibial-plateau-levelling osteotomy x-rays. Note the tongue pulled forward, sand bag under the chin, cohesive bandage wrap in the mouth and oxygen using flow-by.
Arnie, a one-year-old male bulldog weighing 21kg, has been presented with 3 out of 10 right pelvic limb lameness and you have admitted him for x-rays.
Arnie is, otherwise, well in himself and is a typical, excitable puppy, so will need some form of chemical restrain to enable you to take x-rays. However, you have noticed Arnie has stenotic nares and increased respiratory noise, and his rectal temperature is 39.2°C.
Heavy sedations should be avoided in brachycephalic breeds, such as pugs and bulldogs – especially those with signs of brachycephalic obstructive airway syndrome. Heavy sedation can exacerbate respiratory obstruction due to relaxation of the pharyngeal muscles.
Hyperthermia can further worsen breathing problems, so body temperature should be monitored and active cooling introduced, if required.
Although sedation is an option, in this case the risks can be greater than the benefits. GA should be recommended for brachycephalic patients as a safer option and chosen over sedation, whenever possible.
Prior to anaesthesia for a brachycephalic patient, it is useful to complete a checklist to make sure nothing has been missed (Figure 1). A selection of endotracheal tubes should be available from as small as 5mm.
Even though Arnie weighs 21kg, he may have a hypoplastic trachea.
Preanaesthetic oxygen supplementation for five minutes before induction is always good practice, especially for brachycephalic patients, to help prevent hypoxaemia during induction. During recovery, late extubation is recommended, as well as close monitoring post-extubation.
If GA is not an option and you have to sedate a dog such as Arnie, some tips are available to save unnecessary stress.
Brachycephalic patients should be kept in sternal recumbency, whenever possible. It is important to have the head and neck extended to prevent obstruction from the pharyngeal soft tissues.
Pulling a patient’s tongue forward and keeping its mouth open with cohesive bandage wrap (Figure 2) are simple ways to encourage mouth breathing and help keep airways open.
Attention should be paid to oxygenation using a pulse oximeter. Make sure the mucous membrane is pink and arterial oxygen saturation stays above 92%. Oxygen should be provided using flow-by or a mask at all times, if saturation falls below 92%.
Be prepared to intubate in case of sudden desaturation. Having propofol and endotracheal tubes handy may save time and stress. Having IV access is also a good idea. Finally, make sure the dose of atipamezole is drawn up before sedating the patient with medetomidine.
Medetomidine sedation is profound and dose-dependent, and can lead to the upper airway obstruction in brachycephalic dogs. Combining medetomidine with an opioid, such as butorphanol, means the dose of medetomidine can be reduced due to the synergistic effects.
While most clinicians use 10μg/kg to 20μg/kg of medetomidine as a “standard dose”, with brachycephalic dogs this can be reduced to as low as 2μg/kg to 5μg/kg IV or IM and still be effective.
The addition of butorphanol 0.2mg/kg to 0.3mg/kg can give an excellent effect with minimal impact on the cardiorespiratory system.
