Blue Cross Veterinary Clinic
Quite often in our practice we have to sedate or keep under anaesthesia brachycephalic dogs and cats. This is associated with some stress for us, given the peculiarities of the breed. In this article I will try to briefly present the main key points in the anesthesia of brachycephalic breeds, which has gained great popularity in recent years. Will pay attention to their anatomical and physiological features, which are a prerequisite for complications during anesthesia, and how to avoid them and reduce the risk.
The main specificity of them is the so-called brachycephalic syndrome ( BOAS). It may include narrowed nostrils, a long soft palate, a hypoplastic trachea, or an inverted laryngeal sac. It can be re-applied and used for prolonged trauma to the pharyngeal soft tissues and trachea, which can cause soft tissue outflow or tracheal collapse. This trauma most often occurs when the animal is intubated. Gastroesophageal reflux should not be forgotten, also high vagal tone.
In severe cases of BOAS, airway obstruction may benefit from the development of pulmonary edema. The pathophysiology of post-obstructive pulmonary edema includes the effect of negative intrathoracic pressure on fluid distribution and subsequent hypoxia. High negative intrathoracic pressure causes an increase in venous return to the right atrium, which increases the pulmonary artery, while left ventricular function is reduced and afterload is increased. The end result is increased hydrostatic pressure, which aids in the movement of fluids from the capillaries in the interstitium and thus causes pulmonary outflow. Rapid recognition of this condition and taking temporary measures, such as maintaining airway patency, adequate oxygen supply and, if necessary, PPV administration. Diuretics may also be used, but it should be anticipated that hypovolaemia and hypoperfusion may occur during anesthesia and clinical delivery should be considered. And because of the risk of soft tisuue and pulmonary oedema, it’s beneficial to add an corticosteroid in low dose, as prevention. Unless there are a serious contraindications. There are different anaesthesia protocols with dexamethason or methylprednisolon, it’s a matter of personal choice.
Deep sedation in these patients is performed with excessive relaxation of the pectoral muscles and aggravation of airway obstruction. Even if the patient is aggressive, it is good to adhere to lower doses of premedication. The most commonly used combination is of a sedative component, for example an alpha-2-agonist and an opioid. A tranquilizer such as acepromazine and benzodiazepines such as diazepam or midazolam may also be used. Accordingly, the doses are at the discretion and according to the desired effect and treatment. In the table below I quote some of the most commonly used pre- anaesthetic drugs with the value of the dose. There are no restrictions and contraindications to the use of narcotic drugs in this breed. For induction you can use a different combinations, as benzodiazepine+ propofol or benzodiazepine+ ketamine. Your choice mainly depends on what the end result you whant. In brachycefalic breeds it is recommended the induction to be smooth and fast, so the most suitable drug in this case is propofol.
Given the peculiarity of the birth, it is very important to monitor the brachycephalic patient during the pre-aesthetic period, as relaxation of the pectoral muscles further complicates breathing, reduces the number of respiratory movements and the appropriate patient does not fall into hypoxia. It is recommended that the patient be preoxygenated during the pre-anesthetic period. The administration of 100% oxygen before induction of anesthesia prolongs the time to the onset of arterial hypoxemia.
When intubating a brachycephalic patient, prepare several tube sizes, apparently up to two sizes smaller than you think would be appropriate. It will be useful if you use a laryngoscope, especially when your patient has a long soft palate, as it will help ensure good visibility to the airways.
It is common practice to maintain the patient under inhalation anesthesia during the operation. Isoflurane is most commonly used for this purpose. It should be borne in mind that, like other inhaled anesthetics, it produces a dose-dependent reduction in myocardial contractility, systemic vascular resistance and cardiac preload, followed by a reduction in mean arterial pressure (MAP) and cardiac output in a dose-dependent manner; therefore, the evaporator settings should be kept as low as possible while maintaining an adequate depth of anesthesia.
In brachycephalic breeds, there is a very strong vasovagal tone, which can cause bradycardia, which in turn can lead to AV block or even cardiac arrest. The most common reason for increased vagal tone is severe pain. Advice on this reason for good pain relief of this breed is extremely important. However, if the patient develops severe bradycardia, a use of anticholinergic in an appropriate emergency dose is indicated.
As mentioned earlier, another common complication is gastroesophageal reflux, which can occur at any stage of anesthesia. This can lead to airway obstruction and aspiration pneumonia. Advice for this reason is recommended in the anesthesia protocol to include antiemetics, unless there are serious contraindications. It is recomended to be applied proton pump inhibitors as omeprasole, 4 hours before the planed anaesthesia.
The recovery period is also not to be underestimated. Here it is important to constantly monitor the patient and be extubated, when we are sure that all reflexes have returned. Especially the swallowing one. The best time to extubate is when our patient has muscle tone in the lower jaw and tries to cough up the endotracheal tubus itself or even better if the patient is tring to chews it. It is important to be positioned in a sternal position with appropriate continuous monitoring.
The anaesthesia of these specific breeds is not so complicated, if know their features and for what to watch out for. With more carefulness and knowinge there is nothing to be afraid of.
Tabl. Most commonly used pre- anaesthetic drugs
|Drug||Benefit||Side effects||Peak onset/duration of action||IM dose|
|Profound sedation, reversible, some analgesic properties, drug sparing (reduction in induction drugs needed)||Dose dependent bradycardia||5-15 min IM
2- 3 min IV
|Dexmedetomidine 5-15 µg/ kg
3- 10 µg/ kg
|Butorphanol||Mild analgesia, good sedation||Poor analgesia and should not be used for surgical patients||10–15min/lasts for 60–90min||0.1–0.4mg/kg|
|Buprenorphine||Moderate analgesia, mild sedation||Moderate analgesia||10- 15 min IV
/can be given q 6–8 h
|Methadone||Good analgesia||If given too fast, IV can cause bradycardia and respiratory depression||30min/can be given q 4 – 6 h||0.1–0.4mg/kg|
|Acepromazine||Good anxiolytic, sedation improved when administered with an opioid||Hypotension, unreliable sedation when used alone, not reversible||35–40min IM
10- 15 IV
/can be given q 4–6h