To create a balanced anesthetic plan, Hugo’s unique physical characteristics, his breed, and the procedure to be performed were all considered. Brachycephalic breeds are predisposed to brachycephalic syndrome, characterized by an elongated soft palate, stenotic nares, and everted laryngeal saccules. Dogs with brachycephalic syndrome often have hypoplastic tracheas and pharyngeal and laryngeal collapse.1-5 In a retrospective study of 90 dogs with brachycephalic airway obstructive syndrome, 61% were English bulldogs; 94% of study dogs had elongated soft palates.1
Brachycephalic dogs have high negative airway pressure in the upper airway tract, which can cause the tissues of the soft palate to become stretched and contribute to upper airway obstruction.6 Hugo underwent soft palate resection 6 years prior, but his history of persistent snoring suggests that his soft palate continues to obstruct his upper airway. He is able to compensate for the obstruction when awake but not after sedation or induction because of relaxation of the pharyngeal and laryngeal muscles. In a retrospective study of 73 dogs, clinical signs returned to some degree in all dogs that underwent surgical correction for brachycephalic syndrome.2
Premedication agents that cause excessive sedation must be avoided in patients with brachycephalic syndrome to avoid worsening airway obstruction. Premedication drug effects on respiratory drive and normal respiratory function must also be considered. Opioid agents can cause hypoventilation by shifting the ventilatory response curve of the medullary chemoreceptors to the right, making them less sensitive to CO2 increases.7 Methadone is an ideal premedication for Hugo because it is a full μ-opioid agonist that provides appropriate analgesia for dental extraction but, unlike other opioids, is unlikely to cause vomiting when administered IM. Acepromazine, which can reduce respiratory rate, is also an appropriate premedication choice because it does not cause significant changes in arterial CO2 or O2 partial pressures.8,9
Brachycephalic dogs generally have higher vagal tone and may experience bradycardia during anesthetic procedures.10 Anticholinergic drugs (eg, atropine, glycopyrrolate) are often used in premedication protocols to prevent opioid-induced bradycardia; however, these drugs should be avoided in premedication combinations for brachycephalic patients. Anticholinergic drugs reduce the watery component of saliva but not the thick mucus, which can worsen airway obstruction. Once the airway is secured, anticholinergic drugs can be used if needed to treat bradycardia. Atropine has a relatively short duration of action; therefore, thickened saliva should not be a concern in the postoperative period.
Patients should be monitored continuously for worsening airway obstruction after sedative administration. Preoxygenation with 100% oxygen for 3 minutes has been demonstrated to increase the time to desaturation by nearly 5 times in patients experiencing postinduction apnea.11 Providing preoxygenation to brachycephalic patients is prudent when securing an airway rapidly may be difficult. The ability to gain rapid control of the airway via intubation is critical during induction. Propofol enables a controlled induction and, when given to effect, results in minimal cardiopulmonary depression. Alfaxalone also can be used, as it provides induction comparable to that of propofol with similar dose-dependent cardiopulmonary effects.
A laryngoscope facilitates endotracheal intubation in brachycephalic patients. Dogs with brachycephalic syndrome typically have an elongated (and often hyperplastic) soft palate; a hyperplastic tongue and pharyngeal tissue also are frequently present. These conditions combined can make visualization of the arytenoid cartilages challenging. The laryngoscope is used to depress the tongue and, if necessary, the epiglottis to improve visualization. In severe cases, an endoscope may be needed to facilitate endotracheal intubation. A hypoplastic trachea can make it difficult to determine the appropriate endotracheal tube size. Before starting intubation, tubes of multiple sizes should be available, and the veterinarian or veterinary nurse should attempt to place the largest diameter tube possible.
Brachycephalic patients should not be extubated until they clearly demonstrate airway control by swallowing vigorously. Surgical-site swelling can obstruct airflow and worsen breathing in brachycephalic patients; anti-inflammatory doses of steroids are often used to minimize swelling. Even after extubation, brachycephalic patients should be monitored closely for signs of respiratory difficulty. Continuous use of a pulse oximeter during the recovery period is ideal, but the pulse oximeter should be removed if it causes patient stress. Brachycephalic patients may require reintubation or tracheostomy if they are unable to ventilate adequately.
Many patients with brachycephalic syndrome continue to require oxygen supplementation following surgical correction. This can be provided via oxygen cages, facemasks, and nasal oxygen cannulas. In a retrospective study comparing use of nasotracheal tubes with other methods of postoperative supplementation in 20 dogs (19 of which had undergone palatoplasty), the authors reported that the nasotracheal tube was easy to place and suggested that it could reduce the incidence of respiratory distress postoperatively as compared with other methods of oxygenation.12