Canine

Anesthesia for Dogs

Presented by:

• Jill Maney, VMD DACVAA

• Modified and delivered by Dr. Miguel Martinez, LV, Dip ECVAA

Objectives

• Describe appropriate premedication, induction, and anesthetic maintenance protocols for healthy dogs, emphasizing the importance of tailoring anesthetic approaches based on individual needs and circumstances.

• Discuss breed considerations, including unique aspects regarding brachycephalic dogs, which may affect anesthetic management.

• Address management techniques for anxious and aggressive dogs to ensure safety and comfort during procedures.

• Outline potential complications that can arise during anesthesia and strategies to mitigate these risks.

• Review newer FDA-approved drugs for dogs, incorporating the latest advancements in veterinary anesthetic practices.

Anesthesia Mortality Rates

• Dogs: 0.05-0.17%

• Cats: 0.11-0.24%

• Recent studies indicate a trend towards lower mortality rates in canine anesthesia, thanks to advancements in protocols and monitoring.

• These rates are significantly higher compared to humans, where mortality during anesthesia ranges from 1 in 100,000 to 1 in 1,000,000 (0.001% - 0.0001%).

Pre-anesthetic Evaluation

Key steps include:

• Comprehensive history and physical examination to gather vital information about the dog’s health.

• Conduct thorough pre-anesthetic evaluations, considering breed-specific concerns and known comorbidities.

• Implement tailored premedication protocols that align with the individual patient's needs.

• Develop induction and maintenance strategies that reflect the dog’s physiological status.

• Maintain awareness of potential complications and prepare contingency plans.

History Assessment

• Collect detailed history, particularly for patients with comorbidities or those on any medications.

• Common Concerns with Medications:

  • NSAIDs and Steroids: Potential adverse interactions during anesthesia.

  • Diuretics: Can lead to hypovolemia and electrolyte imbalances.

  • Cardiovascular Medications (e.g., ACE inhibitors, calcium channel blockers, beta-blockers): May cause hypotension.

  • Anti-epileptic Agents: Risk of additive sedation during anesthesia.

  • Serotonergic Drugs: Such as SSRIs, tricyclics, MAOIs, tramadol may increase the risk of serotonin syndrome and require careful management.

Systemic Disease Indicators

• Monitor for systemic disease signs, especially those related to cardiac and pulmonary function.

• Symptoms to note include: coughing, exercise intolerance, and syncope, which can indicate underlying conditions.

• Prior blood transfusions should be documented meticulously. Note that no naturally-occurring antibodies against RBC antigens are present until after a non-compatible transfusion; antibodies can develop within 5-7 days necessitating further typing and cross-matching.

Previous Anesthesia Records

• Always make a record of prior anesthesia and any severe complications as this information can significantly affect decisions in current procedures.

• Many adverse events in healthy patients are avoidable; thus, it is crucial to prevent repeating previous errors.

• In emergency situations, quick decisions may be essential, so obtaining as much information from the owner or previous veterinary staff is critical.

Signalment Factors

• Age: Pediatric and geriatric patients respond differently to anesthesia and may require adjusted dosages or techniques.

• Sex: Considerations during pregnancy that could impact anesthesia management.

• Breed/Size: Recognize different breed-specific concerns that require modifications to standard anesthesia protocols.

Brachycephalics

• Concern: Brachycephalic airway syndrome (BAS) poses significant risk during anesthesia.

• Anatomical issues such as stenotic nares, elongated soft palate, and hypoplastic trachea can lead to airway obstruction.

• These breeds often exhibit elevated PaCO2 and reduced PaO2 levels compared to their non-brachycephalic counterparts.

• Gastrointestinal issues may also heighten the risk of regurgitation and vomiting, which complicates the anesthetic process.

• Data shows that surgical correction of BAS can reduce post-anesthesia complications by 79% (Doyle et al. 2020).

Recommendations for Brachycephalics

• Minimize stress and avoid inducing vomiting during consultations and procedures; consider using anxiety-reducing measures.

• Closely monitor the dog post-premedication for any signs of distress or complications.

• Medications: Consider administering antiemetics, anticholinergics, prokinetics, and PRN steroids to manage potential airway swelling.

• Ensure preoxygenation and opt for rapid intravenous induction, ideally with agents like propofol or alfaxalone.

• Use appropriately sized endotracheal tubes based on the dog's weight to support airway patency.

• Strive for rapid recovery and late extubation; careful monitoring of analgesia is imperative, with readiness for re-intubation in severe cases of instability.

Other Breed Considerations

• Sighthounds: Avoid thiobarbiturates due to their prolonged recovery periods, and prefer agents with shorter half-lives.

• Greyhounds: Be vigilant for anesthesia-induced hyperkalemia; they require ECG monitoring and potassium checks.

• Boxers: Monitor for a potential sensitivity to acepromazine; in some cases, collapse may be vagally-mediated, necessitating precaution.

Small Breed Considerations

• Commonly see tracheal collapse in small breeds, which poses risk during anesthesia.

• Avoid excitement as panting and coughing can exacerbate this condition; be strategic with sedatives to manage any anxiety.

• Have longer endotracheal tubes available to address complications like intrathoracic tracheal collapse.

• Administer supplemental oxygen judiciously if necessary.

Additional Breed-Related Concerns

• Be aware of various breed-related issues affecting anesthetic management, such as:

  • Cardiomyopathy: Common in Dobermans and Boxers.

  • Sick Sinus Syndrome: Notable in Schnauzers requiring special monitoring.

  • Mitral Valve Disease: Often seen in smaller breeds, demanding careful perioperative management.

  • Increased Vagal Tone: Commonly found in brachycephalics and dachshunds during anesthesia.

  • Von Willebrand Disease: Prevalent in Dobermans.

  • Hemophilia: Particularly observed in German Shepherds, necessitating awareness of potential bleeding risks.

  • The breed sensitivities noted by breeders can vary, and their relevance may not always be scientifically validated.

Multidrug Resistance Mutation (MDR1 / ABCB1)

• Focus on the gene coding for P-glycoprotein related to the blood-brain barrier; genetic testing is available to identify affected dogs.

• Mutation leads to increased sensitivity to various drugs, particularly in herding breeds.

• Consequence: Acepromazine can result in increased and prolonged sedation in homozygous dogs; a dose reduction of 30-50% is usually recommended for affected breeds.

Physical Exam Focus

• During physical examination, special attention should be directed to the cardiac and pulmonary systems; consider additional evaluation based on findings.

• Evaluate the dog’s temperament and behavior thoroughly to plan appropriate premedication drugs, dosages, and administration routes.

• Ensure thorough documentation of all aspects of evaluation and preparation to facilitate clear communication and medical records.

Premedications Overview

• Standard practice includes administering an opioid in combination with a sedative via IM injection before catheter placement. If an IV catheter is already in place, those premedications may be provided through that route.

• Opioid Options: Include pure mu agonists, partial mu agonists, and agonist-antagonists for pain management.

• Vomiting Risks: Certain drugs like fentanyl and methadone are least likely to induce vomiting, which is critical in scenarios where increased intracranial pressure, respiratory risks, or megaesophagus is present.

Premedication Specifics

• Benzodiazepines: Provide minimal sedation in healthy dogs, but their effect can be significantly enhanced in young, old, and sick patients; however, they do not provide analgesia.

• Acepromazine: Often causes mild to moderate sedation, does not provide analgesia, and can lead to hypotension, especially when combined with inhalant anesthetics.

• Dexmedetomidine: Offers marked sedation and analgesia but may induce hypertension and reflex bradycardia, requiring careful monitoring.

Non-anesthetic Premeds

• H1 Antihistamines: For conditions such as mast cell tumors or sensitivities to substances like chlorhexidine; Diphenhydramine is a common choice.

• NK1 Receptor Antagonists: Maropitant (Cerenia) can be used 60 minutes prior to administering opioids to significantly reduce the risk of vomiting while providing additional analgesia.

At-home Premeds for Anxious/Aggressive Dogs

• Sedative/Anxiolytic Options:

  • Trazodone acts as a serotonin antagonist and reuptake inhibitor; can help reduce anxiety.

  • Gabapentin is a GABA analog that blocks excitatory neurotransmitter release, useful for managing anxiety and increasing sedation.

  • Optional addition of acepromazine can provide enhanced sedation for dogs needing additional support.

OTM Administration Options

• Options for oral transmucosal administration for anxious/aggressive dogs can include Dexmedetomidine, combined forms with morphine, buprenorphine, or methadone.

• Dexmedetomidine oral gel (Sileo) is available through veterinary prescriptions, providing an easy administration option for managing anxiety.

Managing Aggressive Dogs

• Optimize patient arrival conditions, ideally ensuring dogs are muzzled and sedated to reduce risks during handling.

• Consider IM injections of ketamine, telazol, or alfaxalone paired with an alpha-2 agonist and an opioid for optimal comfort and compliance.

• Aim for deep sedation/general anesthesia to minimize potential risks; exercise caution with alpha-2 combinations when not followed by anesthetic drugs due to the potential for unexpected arousal.

• Be prepared to intubate if necessary, providing 100% oxygen during stabilization to ensure adequate oxygenation.

Induction Protocols

• The choice of induction agent is influenced by the dog's cardiovascular stability and the planned length of the procedural intervention. Common agents include:

  • Propofol

  • Alfaxalone

  • Ketamine combined with benzodiazepines

  • Etomidate

  • Thiopental is rarely used due to limited availability and potential complications.

Induction Administration

• Drug administration should be performed based on the sedation level after premedications; it’s crucial to titrate to effect.

• Initiate administration slowly, ideally over a 30-60 second interval, to minimize the risk of overdose or adverse reactions.

• Note that ketamine possesses a higher therapeutic index than other agents; slow administration is advised to avoid rapid onset of effects that may compromise airway management.

Intubation Techniques

• Proper intubation involves using a laryngoscope gently placed at the base of the tongue while avoiding trauma to the epiglottis

• Choose the largest endotracheal tube (ETT) that passes easily; ensuring lower resistance enhances airflow and reduces chances of obstruction during maintenance.

• Applying sterile lubricant to the ETT cuff can minimize the risk of tracheal trauma during placement.

Intubation Challenges

• Dogs are generally easier to intubate due to their large mouths and proportionately sized tracheas; however, brachycephalic breeds require careful handling and adjustment due to potential long soft palate obstructions.

• Advance the tube towards the thoracic inlet, ensuring to mark pre-measurements to avoid mainstem bronchus intubation errors.

Anesthesia Maintenance

• Common inhalant anesthetics used throughout the maintenance phase include Isoflurane and Sevoflurane, selected based on the patient's needs and procedure specifics.

• Injectable anesthetics used for continuous rate infusion (CRI) include Propofol or Alfaxalone, whereas Etomidate is generally not recommended due to its potential for adrenal suppression.

• Administer adjunct medications such as opioids, lidocaine, or ketamine through CRI depending on pain management needs.

• Monitor IV fluids diligently; the average blood volume for dogs is ~90 mL/kg; use balanced, isotonic crystalloid fluids, and target a rate of 5 mL/kg/hr to maintain hydration and overall stability during anesthesia.

Managing Regurgitation Risks

• The primary goal throughout anesthesia is to prevent esophageal damage from occurring, which could lead to complications like esophagitis or esophageal strictures.

• Aspiration often occurs silently, posing significant risks for pulmonary complications; thus, safeguarding against this is paramount.

• Mitigate these risks through appropriate management of the ETT cuff and ensuring adequate inflation during maintenance.

Regurgitation Contingencies

• If regurgitation occurs during anesthesia, implement postural drainage while the animal remains anesthetized, positioning them with their nose down.

• Use suctioning techniques on the caudal oropharynx before extubation to clear any aspirated material or debris.

• Maintain cuff inflation during extubation to prevent aspiration of any remaining material from the pharynx.

• Position the patient in sternal recumbency as soon as feasible after regurgitation to support optimal recovery.

• Consider protective medications for high-risk patients post-anesthesia (e.g., proton pump inhibitors, prokinetics) to manage complications stemming from regurgitation.

Recovery Monitoring

• The recovery phase represents the most critical period for anesthetic-related mortality.

• Vigilant monitoring of physiological parameters is essential; continued stability during recovery, particularly until achieving sternal recumbency, is vital for patient safety.

• Addressing pain and anxiety post-operatively is necessary, utilizing clinical observations to tailor management strategies specific to each dog’s conditions and responses.

Recently FDA Approved Drugs - Sileo

• Dexmedetomidine Oral Gel (Sileo): Approved for managing canine noise aversion, providing a valuable treatment option for anxious dogs. It is administered orally via the transmucosal route, indicating significant utility in both anxiolysis and sedation management.

Recently FDA Approved Drugs - Zenalpha

• Medetomidine-vatinoxan (Zenalpha): Approved as a sedative-analgesic agent—not for premedication. This IM injectable preparation reduces cardiovascular side effects typically associated with medetomidine, such as vasoconstriction and reflex bradycardia; caution is advised as hypotension may occur post-inhalation anesthesia.

Recently FDA Approved Drugs - Librela

• Bedinvetmab (Librela): Anti-NGF monoclonal antibody approved for managing pain associated with osteoarthritis. It is administered monthly through injection and targets joint pain relief by binding to nerve growth factor and blocking the transmission of pain signals.

Questions?

• Open forum for questions regarding the presented material to ensure understanding and address concerns either related to this topic or other anesthetic practices.