Anesthesia and Analgesia in Brachycephalic Dogs

Brachycephalic dogs (e.g., bulldogs, pugs, Shih Tzus) are extremely popular as pets, and their presentation for procedures that require anesthesia is common. This general review of anesthetic management of brachycephalic dogs focuses on dogs with components of brachycephalic obstructive airway syndrome (BOAS) but does not address specific procedures for airway surgery. Dogs with concurrent comorbidities or age-related physiologic changes may need drugs or dosages other than those discussed in this article. The overall health of the animal must be considered before choosing anesthetic protocols. The fundamental goals of anesthetic management in brachycephalic dogs are listed in BOX 1.

Physical Factors Affecting Anesthesia Management in Brachycephalic Dogs

Among other complications, the flattened features of the brachycephalic skull compress upper airway structures, which can cause a variety of medical problems and be particularly concerning for anesthetic safety. The main effect of narrowed airway structures in these animals is increased work of breathing. Any increase in respiratory effort, such as that caused by stress, excitement, pain, or hyperthermia, causes increasingly negative airway pressure and further airway narrowing with subsequent hypoventilation, hypoxemia, hypercarbia, and, potentially, airway collapse. Thus, a major goal of anesthetic management in these patients is avoidance of stressful situations.

Brachycephalic Obstructive Airway Syndrome (BOAS)

Many brachycephalic patients have components of BOAS. Airway components of BOAS and their impact on anesthesia are listed in TABLE 1.

Brachycephalic dogs with BOAS are twice as likely to have anesthesia complications as nonbrachycephalic dogs, with most complications, primarily dyspnea, regurgitation, and aspiration pneumonia, occurring in the postoperative period.^1,2 Prevention of aspiration pneumonia is also a main goal of anesthetic management,² and the author recommends antiemetics for all brachycephalic patients undergoing anesthesia.

In one study, the rate of postoperative complications in brachycephalic dogs undergoing anesthesia for imaging or surgeries other than airway surgeries was 13.9% versus 3.6% in nonbrachycephalic dogs.¹ In the same study, brachycephalic dogs were 1.57 times as likely to have intra-anesthetic complications and 4.33 times as likely to have postanesthetic complications. Although complications in recovery after surgery to correct BOAS are common, dogs that had a previous airway surgery to correct components of BOAS had fewer complications in the recovery period of a subsequent anesthetic event.³ Thus, surgical correction of BOAS components should be done at an early age to improve both quality of life and safety of subsequent anesthetic procedures.

Cardiovascular Concerns

Brachycephalics have higher vagal tone than dogs of other breeds,^4,5 and those with BOAS can have an exaggerated vagal response with rapid and potentially profound bradycardia when the upper airway is manipulated, as during surgery, intubation, or extubation. Anticholinergics may be indicated in some patients (see Potential Adjunct Drugs).

Gastrointestinal Disease

Esophageal and gastrointestinal (GI) tract lesions, including esophagitis, gastroesophageal reflux, gastritis, and hiatal hernia, are prevalent in brachycephalic dogs with upper respiratory dysfunction. A history of signs of GI abnormalities is highly linked to risk of aspiration pneumonia.^6-10 Stabilization or treatment of GI disease prior to anesthesia is recommended. However, correction of upper airway dysfunction is often the key to resolution of GI signs.

The presence of a hiatal hernia is a risk factor for gastroesophageal reflux, as is prolonged fasting.¹¹ Thus, prolonged fasting may not be appropriate for brachycephalic dogs. A fast time of less than 6 hours is recommended in the American Animal Hospital Association guidelines,¹² and a small meal 3 hours prior to anesthesia may be beneficial to decrease reflux.¹¹ However, ideal fasting times are still unknown and “standard” fasting times (i.e., no food after midnight the day before surgery) may still be appropriate.

Antacids and gastroprotectants, along with prokinetics, are often recommended for brachycephalics but can be overused (see Potential Adjunct Drugs). The American College of Veterinary Internal Medicine has published an in-depth review and consensus statement on the use of these drugs.¹³

Ophthalmic Concerns

Exophthalmos (proptosis) can increase ocular contact with blankets, scrub solution, cage doors, and other items, making corneal ulceration or other eye damage more likely. Patients should be carefully positioned to prevent any external pressure on the eye, and eye lubricant should be liberally applied before, during, and after general anesthesia.

Considerations in Drug Choice for Brachycephalic Anesthetic Protocols

Anesthetic and Sedative Drugs

Safe anesthesia for patients with upper airway dysfunction depends more on patient management than on drug choice. Both intubation and extubation can be difficult for the anesthetist and dangerous for the patient. Almost all anesthetic and sedative drugs are acceptable for use in brachycephalic patients, but the most appropriate drugs are those that are fast acting (for rapid intubation), have a short duration of action, and/or are reversible (for quick return to consciousness and normal breathing) (TABLES 2 AND 3). Although considered a longer duration drug, low-dose acepromazine can be a good option for sedation since it provides calming that lasts into recovery.

While there are no drug contraindications, deep sedation, if necessary, should be delayed until the anesthetist is prepared to quickly induce and intubate if sedation causes respiratory difficulty. Light sedation, on the other hand, is beneficial to prevent increased respiratory effort. Drugs and drug dosages that might cause prolonged recovery with subsequent delay to normal breathing are not ideal.

Most patients are anesthetized with inhalants (isoflurane, sevoflurane). These drugs cause dose-dependent respiratory and cardiovascular depression that can extend into the recovery period, especially if a high or prolonged dose of inhalants is administered. Use of robust and proactive analgesia is imperative to allow the lowest possible dose of inhalants.

Analgesic Drugs

Pain control throughout the entire anesthetic episode is critical, as pain is a major contributor to increased respiratory effort. Analgesic drugs and techniques should be incorporated into a balanced, multimodal protocol using knowledge of the drug(s) mechanism of action and site of action in the pain pathway (FIGURE 1).

Opioids are potent analgesics and should be included in most protocols; however, strong focus should also be on nonsedating drugs such as nonsteroidal anti-inflammatory drugs (NSAIDs) and local anesthetics. Analgesic choices are discussed in TABLE 4.

Potential Adjunct Drugs

Use of the following drugs/drug classes in anesthetic protocols for brachycephalic patients is somewhat controversial, with no strong expert consensus; however, they are commonly used adjuncts in clinical practice.

Anticholinergics

Based on the risk for bradycardia due to exaggerated vagal response, some veterinarians premedicate all brachycephalic dogs with an anticholinergic (atropine or glycopyrrolate), while others use anticholinergics for treatment of bradycardia if it occurs.¹⁹ The author does not routinely administer anticholinergics; however, routine anticholinergics can be considered in heart-healthy patients that have not received an α₂ agonist (e.g., dexmedetomidine), and some effects, such as mild bronchodilation, may be advantageous.

Steroids

Airway inflammation in brachycephalics with BOAS is often severe and may require steroids (e.g., dexamethasone-SP 0.1 mg/kg IV) for control. Due to steroid-mediated effects, many veterinarians recommend steroids for all airway surgeries and potentially for surgeries on other systems if preexisting inflammation is moderate to severe or intubation was difficult and potentially traumatic.

Steroids can be administered preoperatively if the presence of moderate to severe inflammation is known or expected, postintubation if intubation was traumatic or if moderate to severe inflammation is identified on visualization of the upper airway during intubation, or in recovery if the patient is having difficulty breathing after extubation. NSAIDs should not be administered preoperatively if steroid use is predicted and are often withheld for use in the recovery phase as long as steroids were not administered.

Gastroprotectants and Prokinetics

Due to the strong association of BOAS and GI lesions, gastroprotectants and/or prokinetics have been recommended for brachycephalic dogs undergoing surgery.¹³ Histamine blockers, proton pump inhibitors, and promotility drugs (e.g., cisapride, metoclopramide) have all been used with varied success. However, there is no consensus on the routine use of these drugs in brachycephalics and indiscriminate use can be detrimental. The current recommendation is to administer the appropriate drug to dogs showing signs of GI disease, but there is evidence that not all dogs with GI lesions exhibit signs. The author uses protectants in dogs with GI signs and/or severe BOAS.

Step-By-Step Anesthesia Management of Brachycephalic Dogs

As for all patients, a plan should be developed prior to anesthetizing the patient and should address the needs and concerns for all 4 phases of anesthesia: preanesthesia, induction, maintenance, and recovery/discharge. For all phases of anesthesia, focus on airway management/oxygenation and dose drugs on lean body weight. Keys to successful anesthesia in brachycephalic patients are outlined in BOX 2.

Phase 1: Preanesthesia

Main concerns and potential complications: Increased inspiratory effort with potential for severe dyspnea/airway collapse leading to hypoxemia, hypercarbia, and hyperthermia.

Prior to the Day of Anesthesia

• Prepare the patient for safe anesthesia before the anesthetic event. This includes stabilization of any disease processes.
• The location, extent, and severity of airway compromise should be assessed before the day of anesthesia, if possible, to improve anesthetic safety by allowing the anesthesia team time to adequately prepare. Detailed airway examinations are described elsewhere.²⁰
• Tip: Take thoracic radiographs preoperatively. In one study, 40% of dogs with aspiration pneumonia postoperatively had evidence of pneumonia preoperatively.² Preexisting pneumonia should be treated prior to anesthesia if possible.
• Preexisting GI lesions should also be treated prior to anesthesia if possible.

The Day of Anesthesia at Home

• Tip: To decrease increased respiratory effort and work of breathing from fear/anxiety/stress (FAS) in patients already exhibiting FAS or expected to develop FAS at the hospital, have the pet owner administer oral anxiolytics (e.g., gabapentin 10 to 20 mg/kg or trazodone 3 to 5 mg/kg) 2 hours prior to leaving home.
• Tip: Have the pet owner administer an oral antiemetic (e.g., maropitant²¹) at home on the day of anesthesia to reduce not only in-clinic causes of vomiting (e.g., administration of emetic drugs like opioids) but also emesis that may occur during transportation to the hospital.

The Day of Anesthesia in the Hospital

• Prepare the anesthesia equipment before or immediately after the patient’s arrival at the hospital.
• One of the most important safety factors for anesthetizing patients, especially those with airway dysfunction, is to have the necessary anesthesia equipment ready in the event of an airway emergency.
• Ensure that the oxygen supply is open/connected, the appropriate breathing circuit is attached to the machine, and the machine/breathing circuit combination has been pressure-checked.
• Prepare for an emergency intubation.
• Choose several sizes of endotracheal tubes (ETTs), including several that are smaller than anticipated based on body size (FIGURE 2), pressure-check for cuff leaks, and place near the anesthetic machine along with tube lubricant.
• Arrange a laryngoscope, ETT stylet, lidocaine for the arytenoids, and gauze for holding the maxilla up to facilitate airway examination and/or intubation.

Patient Handling

• Begin the procedure as soon as possible after the patient arrives at the hospital to minimize the duration of hospital-induced stress.
• During the airway evaluation and/or preparation for anesthesia, handle the patient quietly and carefully with minimal restraint to avoid increased respiratory effort and hyperthermia.
• Monitor body temperature in stressed patients, especially those experiencing dyspnea.
• Supplemental oxygen should be administered to all patients during handling if breathing is impaired unless the patient resists oxygen delivery. In these patients, the examination should be stopped until the patient is calmer and breathing more normally or until sedatives are administered.
• Patients in respiratory distress should be placed in an oxygen cage if possible.
• Always be prepared for emergency induction and intubation.

Preanesthetic Medication

• Choose and administer the appropriate premedicant sedative and dose from TABLE 2 and analgesic from TABLE 4.
• Sedation is often crucial to prevent dyspnea exacerbation and to promote use of lower doses of induction and inhalant drugs in an effort to avoid drug-related dose-dependent respiratory depression.
• Preemptive analgesia is part of a balanced analgesic protocol and also promotes decreased induction and inhalant drug dosages.
• Intramuscular administration is generally preferred to reduce the need for restraint compared with intravenous administration. However, patients in severe respiratory distress should have an IV catheter in place prior to administering any drugs.
• If not administered at home, maropitant should be administered IV or SC at least 60 minutes prior to anesthesia. Maropitant should be stored in the refrigerator to decrease “sting” on subcutaneous injection and delivered slowly if administering IV (over 1 to 2 minutes) to prevent maropitant-induced hypotension.²²
• Anticholinergics are not necessarily recommended as routine premedicants for all patients, but a dose of either atropine (0.04 mg/kg) or glycopyrrolate (0.01 to 0.02 mg/kg) should be calculated in case sudden bradycardia occurs.
• GI protectants may be necessary or recommended.

Phase 2: Induction and Intubation

Main concerns and potential complications: Difficult intubation or prolonged time to intubation with subsequent hypoxemia and/or airway collapse and decreased tissue oxygen delivery. See BOX 3 for tips for a difficult intubation.

• Choose appropriate induction drug and dose (TABLE 3).
• Be prepared to intubate.
• Preoxygenate to support tissue oxygen delivery (FIGURE 3). Administration of 100% oxygen for as short as 3 minutes increases the time to desaturation (oxygen saturation [SpO₂] <90%) from approximately 1 minute to approximately 5 minutes.²⁵
  

  Figure 3. Preoxygenating a brachycephalic dog while the IV catheter is placed. The flange of the mask has been removed to avoid pressure on the eyes.

• Administer the induction drug and intubate when the jaw tone is decreased and no swallowing occurs if the pharynx/larynx is touched with the tube. Do not attempt to intubate if the patient is still swallowing. This could cause trauma to an already potentially inflamed/edematous upper airway.
• The anesthetist should visualize the larynx using a laryngoscope or other light source both to assist with intubation and to evaluate the degree of upper airway pathology, which is important for the anesthetic recovery plan.
• Following intubation, immediately inflate the ETT cuff and connect the ETT to the breathing circuit with oxygen flowing.
• Lubricate the eyes.

Phase 3: Maintenance

Main concerns and potential complications: Excessive anesthetic depth due to inadequate analgesia and difficulty breathing if obese.

The inhalant dose should be kept as low as possible to decrease the negative effect on blood pressure and ventilation and to decrease inhalant effect on prolonged recovery. The procedure should be kept as short as possible, as increasing anesthetic duration has been associated with anesthetic complications.³

Anesthesia

• Choose appropriate maintenance drug and dose.
• Very short procedures may be completed using injectable anesthesia (e.g., ketamine/benzodiazepine, tiletamine-zolazepam bolus, propofol or alfaxalone infusion), but intubation is required. The procedure time should be kept to an absolute minimum and repeat or prolonged dosing avoided, as drug accumulation could delay recovery, especially if drug metabolism is slowed for any reason. Propofol and alfaxalone cause more respiratory depression than the 2 dissociatives listed but also have shorter duration of action.

Analgesia

• Choose appropriate analgesic drug, technique, and dose (TABLE 4).
• Provision of analgesia is necessary not only for pain control but also to allow use of the lowest possible inhalant dose.
• Use local anesthesia blockade whenever possible. Local anesthetics are very potent analgesics that have numerous benefits for the patient. Local anesthetic blocks are not sedating and so do not compromise return to consciousness. Blockade of the maxillary nerve desensitizes structures often involved in upper airway surgery (e.g., nares, sinuses, soft palate); for surgery in other areas, use appropriate local/regional blocks. More information on blocks and on local anesthetic drugs is published elsewhere.^16,17
• Constant-rate infusions are also strongly recommended, and an open-access infusion calculator is available.¹⁸ Infusions are administered at very low dosages and can provide analgesia with minimal to no sedation. In addition to, or instead of, opioids, which can cause some degree of respiratory depression, ketamine and/or lidocaine (ketamine 10 µg/kg/min; lidocaine 25 to 50 µg/kg/min) should be considered.

Monitoring and Support

Physiologic monitoring and support during maintenance are not specific for BOAS but might include specific monitoring and support for underlying disease. The anesthetist should address all organ systems (e.g., cardiovascular and respiratory systems) and make any corrections necessary to support normal physiologic function (e.g., correction of hypotension and/or hypoventilation).

Although the clinical relevance is unknown, brachycephalic animals can have inherently decreased arterial oxygen saturation, increased carbon dioxide levels, and hypertension,²⁶ potentially increasing the likelihood of anesthesia-related adverse events and emphasizing the need for diligent anesthetic monitoring and support.

Many brachycephalic patients are also obese, necessitating intermittent or continuous ventilatory support. Ventilation must also be supported if the ETT is significantly smaller than the trachea to avoid excessive work of breathing. Ventilate to an end-tidal CO₂ of 35 to 45 mm Hg and SpO₂ greater than 95% in patients receiving 98% to 100% supplemental oxygen. More on ventilation of brachycephalics is published elsewhere.²⁷

Body temperature monitoring is critical as hypothermia can contribute to respiratory depression and delayed recovery.

Phase 4: Recovery and Discharge

Main concerns and potential complications: Hypoxemia, dyspnea/apnea, airway collapse/obstruction in the extubated patient.

Recovery

• Have a recovery plan for the patient that includes timing of extubation. Recovery is generally the most critical part of the entire anesthetic episode with the highest incidence of adverse effects.
  • The patient should be kept calm and pain-free for optimal recovery. Specific drugs for the recovery period might include:
  • Dexmedetomidine (0.0005 to 0.002 mg/kg) or acepromazine (0.005 to 0.01 mg/kg). IV administration for fast onset may be beneficial and is necessary in patients experiencing respiratory distress.
• Opioids administered at equal to or half of the premedication dose, depending on the level of pain and other analgesics administered.
• The patient should be kept warm for optimal recovery. Hypothermia will prolong recovery time and return to normal breathing. Shivering increases oxygen consumption, which may not be met by oxygen delivery if the patient cannot breathe, and oxygen debt (inadequate tissue oxygenation) may occur.
• Use the pulse oximeter to monitor adequacy of oxygenation, especially after extubation. If the tongue is not accessible, alternative sites of pulse oximeter probe placement can be used (FIGURE 4).
  

  Figure 4. Variety of sites for pulse oximeter probe placement. (A) Tongue.

  

  Figure 4. (B) Prepuce (shown) or vulva.

  

  Figure 4. (C) Lip.

  

  Figure 4. (D) Toe web.

• Ensure the patient is fully awake but calm and that pain is alleviated prior to extubating.
• Brachycephalic patients often still tolerate the ETT when completely conscious and can be carefully extubated at this point (FIGURE 5).
  

  Figure 5. Fully conscious brachycephalic dog with the endotracheal tube still in place.

• See Box 4 for tips on treating airway complications after extubation.

Discharge

• Discharge with analgesic drugs and, if needed, anxiolytics.
• NSAIDs are nonsedating and surgical pain is primarily caused by inflammation; therefore, NSAIDs are an excellent choice for pain relief for this group of patients. If perioperative steroids were administered, initiation of NSAID therapy should be delayed as appropriate for the duration of action of the steroid.
• Minimally sedating opioids can be used (e.g., buprenorphine).
• Gabapentin, trazodone, or other anxiolytics should be administered if the patient experiences FAS at home.