Anesthesia

Canine castration and ovariohysterectomy/ovariectomy surgeries are linked to variable pain intensity contingent upon the degree of surgical trauma.

 

Devising effective anesthetic strategies for spay-neuter programs necessitates a comprehensive perspective, encompassing patient volume, procedural intricacies, and medication interactions. The goal is to achieve a balanced anesthesia, finely tuned by crafting a precise blend of analgesic and anxiolytic agents along with inhalant anesthesia. This orchestration ensures pain alleviation, stress reduction, muscle relaxation, and controlled central nervous system depression culminating in unconsciousness.

 

Analgesic Agents: A judicious fusion of opioids, NSAIDs, and alpha-2 adrenergic agonists ensures meticulous pain management. Multimodal analgesia, synergizing diverse agents, significantly enhances pain control.

 

Anxiolytics: Integrating tranquilizers (e.g., midazolam, diazepam) and alpha-2 adrenergic agonists mitigates stress, enhancing patient comfort when combined with analgesic interventions.

 

Inhalant Anesthesia: Overreliance on mask induction is cautioned against due to inconsistent loss of consciousness, heightened stress, and increased aspiration risk. While chamber induction is rarely warranted, it may be considered in exceptional cases. Regular mask maintenance, relevant for specific procedures, necessitates vigilant monitoring and protocol adjustments to minimize risks such as bronchial irritation and gas contamination.

 

Airway Management: Prudent airway management involving facemasks, endotracheal tubes, or supraglottic airway devices is pivotal. Proficiency and constant vigilance are vital to prevent complications.

 

Perioperative Thermoregulation: Maintaining patient normothermia is crucial to avoid hypothermia-related complications. Strategies like prewarming, minimizing contact with cold surfaces, and effective insulation techniques are recommended.

 

Tailoring anesthetic protocols meticulously to each patient's unique characteristics and requirements, and judiciously combining agents, ensures optimal pain control, stress mitigation, and safe anesthesia induction.

 

Canine and Feline Castration Protocol

Preoperative:

• Analgesia: Opioid administration.

• Sedation: Benzodiazepines (midazolam or diazepam at 0.25–0.4mg/kg IM); intravenous administration of diazepam is recommended due to the painful nature of IM administration; alpha2 adrenoceptor agonist.

• Induction of Anesthesia: A combination of intravenous propofol (3–5 mg/kg), ketamine (3–5 mg/kg) with diazepam or midazolam (0.25 mg/kg), or alfaxalone (1–2 mg/kg); or intramuscular administration of alpha2 adrenoceptor agonist along with ketamine (3–5 mg/kg) or tiletamine/zolazepam (3–4 mg/kg).

• Maintenance of Anesthesia: Inhalation anesthesia or propofol, alfaxalone, or ketamine (1/3 or 1/2 of initial dose) to effect; endotracheal intubation is recommended. Venous access is advised.

• Local Anesthetic Techniques: Employ intra-testicular and incisional blocks.

• Postoperative Analgesia: Administer NSAID.

• Protocol without Controlled Drugs: Administer a combination of NSAID and alpha2 adrenoceptor agonist, optionally supplemented with tramadol (2–5 mg/kg IM).

• Protocol with Limited Analgesic Availability: Employ alpha2 adrenoceptor agonist, optionally combined with NSAID. Intravenous or inhalant agents for induction and maintenance of anesthesia are recommended. Employ intra-testicular and incisional blocks for local anesthesia. Administer postoperative NSAID.

 

Feline and Canine Ovariohysterectomy.

A comprehensive approach to ovariohysterectomy is recommended to enhance analgesia at both ovarian and uterine surgical sites. The protocol involves the following steps:

Preoperative:

• Analgesia: Administer an opioid for preoperative pain management.

• Sedation: Employ benzodiazepines or an alpha2 adrenoceptor agonist for sedation.

• Induction of Anesthesia: Choose between intravenous propofol (3–5 mg/kg), ketamine (3–5 mg/kg) combined with diazepam/midazolam (0.25 mg/kg), or alfaxalone (1–2 mg/kg); alternatively, use an intramuscular combination of alpha2 adrenoceptor agonist and ketamine (5.0–7.5 mg/kg) or tiletamine/zolazepam (3–4 mg/kg).

• Maintenance of Anesthesia: Employ inhalation anesthesia, or adjust propofol, alfaxolone, or ketamine (1/3 or 1/2 of initial dose) to effect. Ensure venous access and apply local anesthesia via incisional and intraperitoneal/ovarium ligament blocks.

• Postoperative Analgesia: Administer NSAID for effective pain management.

 

Castration Procedures for Local Anesthesia (Felines and Canines) Step-by-Step Instructions:

• Choose the desired local anesthetic. Calculate the lower dosage range, which is 1 mg/kg (for cats) or 2 mg/kg (for dogs) of bupivacaine, ropivacaine, or 4 mg/kg (for cats) and 6 mg/kg (for dogs) of lidocaine.

• Conduct a preliminary surgical scrub around the testicles and the incision site, either scrotal (for cats) or prescrotal (for dogs).

• Insert a 22-gauge needle into the testicle's center, aiming the needle tip toward the spermatic cord.

• Aspirate and inject half of the calculated volume into each testicle, or inject until the testicle becomes turgid, whichever occurs first.

• The drug migrates along the spermatic cord, delivering pain relief for cord and vessel surgical manipulation.

• For incision-related pain relief:

•     a. For cats: Continue infiltration as the needle exits the testicular body, targeting the skin and subcutaneous tissue.

•     b. For dogs: Administer local anesthetic in the skin and subcutaneous tissue at the incision site.

While bupivacaine or ropivacaine offer longer duration than lidocaine, some practitioners lean towards lidocaine due to its higher safety margin if inadvertently administered IV, especially considering the testicles' vascularity. Thus, personal comfort with the drugs guides the final choice for this block.

 

Indications for Local anesthesia in Feline and Canine Ovariohysterectomies Step-by-Step Instructions:

(This approach may prove more efficacious than mesovarium block, as it provides analgesia at both ovarian and uterine surgical sites.)

• •     Choose and calculate the full dose of a local anesthetic, such as:

  •     Lidocaine (cats: 2–4 mg/kg, dogs: 4–6 mg/kg)

  •     Bupivacaine (cats: 1 mg/kg, dogs: 2 mg/kg)

  •     Ropivacaine (cats: 1 mg/kg, dogs: 2 mg/kg)

  •     If necessary, dilute the drug with saline; the total volume must be at least 0.4–0.6 mL/kg to lavage the entire abdominal cavity.

• Right after making the incision or upon completing the abdominal procedure (before closing the incision), gently instill the local anesthetic into the peritoneal cavity through the incision.

• Proceed with the incision closure, allowing the local anesthetic to remain within the abdomen.

 

Administering abdominal lavage immediately post-incision may enhance effectiveness (preemptive analgesia), but caution is needed to prevent absorption by blood-sponges. The objective is to retain the drug within the abdomen; therefore, lavage just prior to closure could be more efficient.

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REFERENCES:

• Griffin, B. The Association of Shelter Veterinarians 2016 Veterinary Medical Care Guidelines for Spay-Neuter Programs. JAVMA, Vol 249, No. 2. 2016.

• Mathews, K. WSAVA Guidelines for Recognition, Assessment and Treatment of Pain. JSAP, Vol 55, Issues 6. 2014.

• Grubb, T. 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats. Veterinary Practice Guidelines. J Am Anim Hosp Assoc, 56. 2020.  

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RECOMMENDED LINKS:

Spay / Neuter Programs. Association of Shelter Veterinarians. 

AAHA Guidelines. 2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats. 

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