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Anesthesia Protocol for Cat Neutering (Male Castration & Female OVH/OVE)

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1. Pre-Anesthetic Assessment

• Body weight (dosing is weight-based)
• Cardiovascular and respiratory auscultation
• Mucous membrane color and CRT
• Hydration status
• Temperature
• Assessment of temperament and stress level

• Adults: withhold food 4-6 hours pre-op; water can generally be allowed up to the time of premedication
• Neonates/kittens (< 8 weeks): limit fasting to 1-2 hours to avoid hypoglycemia
• Geriatric cats: reduce fasting time; monitor glucose

• Immature P450 enzyme system - variable drug metabolism until ~5 months
• Highly susceptible to hypothermia during anesthesia
• Use lower end of all dose ranges

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2. Equipment Preparation

• Endotracheal tubes (2.5-4.5 mm ID for most adult cats)
• Laryngoscope
• Oxygen source and breathing circuit (T-piece/Bain circuit for cats < 10 kg)
• Monitoring equipment: pulse oximeter, capnograph, blood pressure monitor, ECG, thermometer
• IV catheters (22-24 G), flush, tape
• Emergency drugs ready: atropine, epinephrine
• Warm environment/heat mat to prevent hypothermia
• Anesthesia machine checked and leak-tested

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3. Premedication (Phase 1)

Route and Timing

• IM or SC injection, in a quiet environment
• Allow 15-30 minutes (IM) for full effect before induction
• After giving premedication, place the cat in a quiet, warm, dark cage to minimize stimulation

A. For Calm/Easy-to-Handle Cats (Light-Moderate Sedation)

• Butorphanol 0.2-0.4 mg/kg IM + Acepromazine 0.01-0.05 mg/kg IM
• Buprenorphine 0.02 mg/kg IM or OTM (oral transmucosal)

• Butorphanol 0.2-0.4 mg/kg IM + Medetomidine 0.01-0.04 mg/kg IM OR
• Butorphanol + Dexmedetomidine 5-20 mcg/kg IM

B. For Fractious/Nervous/Unsocialized Cats (Moderate-Heavy Sedation)

• Medetomidine (0.04-0.08 mg/kg) + Butorphanol (0.2-0.4 mg/kg) + Ketamine (2-5 mg/kg) IM
• Dexmedetomidine (10-20 mcg/kg) + Butorphanol (0.2 mg/kg) + Ketamine (5 mg/kg) IM

• Alfaxalone 5-10 mg/kg IM - note: provides NO analgesia; additional analgesics are mandatory

• 3-4 mg/kg IM - provides restraint and anesthesia; recovery can be prolonged

C. Pre-op Analgesia - Always Include

• NSAID (meloxicam 0.2 mg/kg SC or PO, once-only) at or before premedication
• Opioid as part of premedication (see above)
• Together these form multimodal analgesia

Notes on Drug Classes

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4. Induction of Anesthesia (Phase 2)

IV Induction Options

Dose reduction rule: If an alpha-2 agonist was used in premedication, reduce all IV induction drug doses by 30-50%.

IM Induction (when IV access is not possible)

Intubation

• After induction, endotracheal intubation is strongly recommended for:
  • Procedures > 5 minutes
  • Cats maintained on inhalant
  • Airway protection
• Cats have a narrow glottis - apply topical lidocaine to the larynx (1-2 sprays of 2% lidocaine) 30-60 seconds before intubation to prevent laryngospasm
• Use the smallest tube that allows adequate ventilation (2.5-4.0 mm ID typical)
• Confirm placement by capnography (CO2 waveform) and bilateral chest auscultation

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5. Maintenance of Anesthesia (Phase 3)

Inhalant (Gas) Anesthesia - Preferred for Longer Procedures

• Isoflurane: 1.5-2.5% in oxygen (most common)
• Sevoflurane: 2.5-3.5% in oxygen (faster induction/recovery, good for mask induction in kittens)
• Delivered via a T-piece or Bain breathing circuit (for cats < 10 kg)
• Oxygen flow: 200-500 mL/kg/min for non-rebreathing circuits

For male cat castration: In many cases the procedure is brief (5-10 min) and no maintenance drugs are needed - the premedication + induction agent provides sufficient duration. Always have a plan ready to extend anesthesia if needed.

Injectable Maintenance (if inhalant not available)

• Ketamine IV: 1/3 to 1/2 of initial induction dose as boluses as needed
• Propofol CRI: 0.1-0.4 mg/kg/min IV infusion
• Alfaxalone CRI or boluses: 1-3 mg/kg IV as needed

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6. Local Anesthetic Techniques (Highly Recommended)

For Male Castration:

• Intratesticular block: Lidocaine 1-2 mg/kg per testis, injected directly into the testicular parenchyma before incision
• Incisional infiltration: Lidocaine SC along the incision line, pre- or post-surgery

For Female OVH/OVE:

• Incisional (line) block: Lidocaine SC along the flank/midline incision
• Intraperitoneal/ovarian ligament block: Lidocaine 1-2 mg/kg dripped onto the ovarian pedicle and ligament before clamping

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7. Monitoring During Anesthesia

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8. Supportive Therapies

Fluid Therapy

• Healthy cats undergoing brief elective procedures: fluids are optional but recommended
• Rate: 3-5 mL/kg/hour IV crystalloid (e.g., Hartmann's/LRS or 0.9% NaCl)
• Increase if hypotension detected

Hypothermia Prevention

• Cats lose body heat rapidly under anesthesia
• Use: warm IV fluids, heat mat (never electric on direct contact - use circulating warm water), forced-air warming blanket
• Target temperature: maintain > 37°C throughout

Eye Care

• Cats often lose the blink reflex under anesthesia
• Apply ophthalmic lubricant (artificial tears/eye ointment) to both eyes immediately after induction and repeat every 20-30 minutes

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9. Standard Protocol Summary Tables

Male Cat Castration - Full Protocol (Preferred, with Controlled Drugs)

Male Cat Castration - Without Controlled Drugs

Female Cat OVH/OVE - Preferred Protocol

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10. Recovery Phase

• Place cat in a quiet, warm, padded cage with sternal recumbency positioning
• Extubate when the swallowing reflex returns (cat attempts to chew the tube)
• Monitor continuously until standing and alert
• Maintain body temperature - provide warm bedding/heat source
• Assess pain score on recovery (2-3 hours post-op and before discharge)
• Use validated feline pain scoring tool (e.g., UNESP-Botucatu, Glasgow Composite Pain Scale)
• If pain score is elevated: administer rescue analgesia (buprenorphine 0.02 mg/kg OTM or IV fentanyl 1-3 mcg/kg)

Pain indicators in cats:

• Orbital tightening / squinting
• Muzzle/whisker pad tension
• Ear position (flattened)
• Head position (lowered, tucked)
• Body posture (hunched, reluctant to move)
• Vocalization
• Guarding the surgical site

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11. Drug Reversal

Acepromazine has no reversal agent. Atimuscarinic drugs (atropine, glycopyrrolate) are NOT routinely given but may be used intra-operatively for opioid-induced bradycardia causing hypotension (atropine 0.01-0.02 mg/kg IV).

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12. Common Complications and Management

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1. Multimodal analgesia (NSAID + opioid + local block) is the standard of care - never rely on a single drug class.
2. Dose reduction is essential when combining drugs - premedication significantly reduces induction requirements.
3. Temperature monitoring and active warming are as important as the drug protocol.
4. Local anesthetic blocks (intratesticular for males; incisional/intraperitoneal for females) should be used in every case.
5. Atipamezole reversal of alpha-2 agonists should be delayed until the procedure is complete to avoid pain/excitation.

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Ivermectin Dose Rates in Dogs - Complete Guide

1. Overview & Mechanism

• Goodman & Gilman notes: "the drug causes significant neurotoxicity in some species such as the beagle dog" and penetration across the BBB is normally prevented by ABCB1/MDR1/P-glycoprotein.

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2. Dose Rates by Indication

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3. Dose Escalation Protocol for Demodicosis (Important)

• Stop escalation immediately if any neurological signs appear (ataxia, mydriasis, tremors, depression)
• Duration: continue until 2 negative skin scrapings taken 1 month apart - this often means 3-6 months total

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4. Available Formulations

For off-label use of 1% injectable solution orally in dogs: at 0.1 mL/kg = 1 mg/kg = 1000 mcg/kg (far too high). Always dilute carefully. Many clinicians dilute 1% solution to 0.1% (1 mg/mL) in propylene glycol for easier dosing.

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5. MDR1/ABCB1 Gene Mutation - Critical Safety Warning

• Collie (Rough and Smooth) - highest prevalence (~70%)
• Shetland Sheepdog (Sheltie)
• Australian Shepherd
• Old English Sheepdog
• Border Collie
• McNab
• White Swiss Shepherd
• Silken Windhound
• Long-haired Whippet
• German Shepherd (low prevalence ~5%)
• Mixed breeds with any of the above

• Heartworm prevention doses (6-12 mcg/kg) are generally safe
• Doses ≥ 100-200 mcg/kg can cause severe toxicity
• Daily demodicosis doses (300-600 mcg/kg) are CONTRAINDICATED

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6. Signs of Ivermectin Toxicity in Dogs

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7. Contraindications and Precautions

• MDR1-mutant breeds at high doses (see above)
• Puppies < 6 weeks - immature BBB; avoid or use with extreme caution
• Pregnant/lactating bitches - generally considered safe at heartworm doses; caution at higher doses
• Microfilaremic dogs - administering ivermectin at microfilaricidal doses can trigger a severe anaphylactoid/shock reaction due to rapid microfilarial death; pretreat with corticosteroids/antihistamines and keep under observation for 4-8 hours
• Concurrent drugs - P-glycoprotein inhibitors (spinosad, ketoconazole, cyclosporine) can increase ivermectin CNS penetration and increase toxicity risk even in normal dogs

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8. Quick Reference Summary Card

IVERMECTIN DOSE RATES IN DOGS
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Heartworm prevention:      6-12 mcg/kg  PO monthly
Microfilaricide:          50-200 mcg/kg PO single dose
Sarcoptic mange:         200-400 mcg/kg PO/SC q1-2wk x 3-4 doses
Intestinal nematodes:    200 mcg/kg    PO single dose
Otodectic/Cheyletiella:  200-400 mcg/kg PO/SC q2wk
Demodectic mange:        300-600 mcg/kg PO daily (escalate slowly)
                         treat until 2 neg scrapings 1 month apart

MDR1 mutation breeds: AVOID doses > 100 mcg/kg