Reptiles Anesthesia and Surgery Study Notes

REPTILES ANESTHESIA AND SURGERY

CONSIDERATIONS

ANESTHESIA MONITORING

  • Reflexes

    • Loss of Righting Reflex

    • Indicates loss of consciousness; a key sign during monitoring.

    • Palpebral Reflex

    • Reliable in species with eyelids; involves blinking when the eyelid is touched.

    • Corneal Reflex

    • Provides adequate indication of anesthetic depth; indicates the integrity of the nervous system.

    • Use a cotton swab moistened with ophthalmologic ointment for testing.

    • Loss of this reflex indicates too deep of a plane of anesthesia.

    • Tongue Withdrawal

    • Important for lizards and snakes; absence indicates too deep plane.

    • Toe Pinch Reflex

    • Positive withdrawal should not occur if the patient is properly anesthetized.

  • What Would We Use in Chelonians?

    • This point indicates a need for specific methods for tortoises and turtles but is left unanswered in the provided content.

ANESTHESIA THERMOREGULATION

  • Thermoregulatory Support

    • Essential during and following anesthesia to prevent prolonged recoveries and potential death.

  • Tools for Thermoregulation

    • Forced Air Warmers: Maintain body temperature.

    • Heating Pads: Provide warmth but require caution to avoid burns.

    • Heat Lamps: Effective in heating the reptile post-anesthesia.

    • Ceramic Heat Emitters: Alternative heating source.

    • Warm Fluid Bags: Used to maintain temperature.

    • Caution: prevent thermal burns during application.

    • Thermometers: Essential for monitoring temperature.

    • Flexible Temperature Probes: Allow for accurate temperature recording.

    • Esophageal Probes: Considered the most accurate method of measuring core temperature.

ANESTHESIA CARDIOVASCULAR MONITORING

  • Useful Equipment

    • Doppler Flow Device:

    • Monitors heart rate and rhythm.

    • Probe placement:

      • At the heart level in snakes and lizards.

      • Over the carotid artery in chelonians and lizards, directed caudally toward the heart.

    • Electrocardiography:

    • Can be performed in reptiles, using conventional lead placements.

    • Direct Arterial Blood Pressure Measurements:

    • Generally impractical due to the need for cut-down procedures for arterial access, usually in either the carotid or femoral artery.

ANESTHESIA RESPIRATION

  • Intubation: Options include cuffed versus uncuffed endotracheal tubes.

  • Positive Pressure Ventilation (PPV):

    • Following induction of anesthesia, all reptiles exhibit profound respiratory depression, necessitating assistance.

    • Essential to provide Intermittent Positive Pressure Ventilation (IPPV).

    • Small animal ventilators (either pressure-driven or volume-driven) can be useful.

    • Recommended Ventilation Rates: 4 to 8 breaths per minute.

    • Peak Airway Pressure: Should not exceed 10 to 15 cm H2O.

ANESTHESIA FOR SHORT NON-INVASIVE PROCEDURES OR INDUCTION

  • Dexmedetomidine and Ketamine:

    • Advantages:

    • Can be administered IM or IV.

    • Dexmedetomidine is reversible with atipamezole, allowing for faster recovery.

    • Low doses of ketamine enhance effects due to synergism with dexmedetomidine.

    • Disadvantages:

    • Risks include bradycardia, hypotension, hypercapnia, and hypoxemia.

    • Caution in debilitated animals with renal or liver impairments; start at lower doses until stabilization is achieved.

  • Propofol:

    • Must be diluted: 2 parts saline to 1 part propofol; administered IV over 2 minutes.

    • Caution is required as faster administration leads to more marked respiratory depression.

  • Alfaxalone and Midazolam: Additional anesthetic options explored.

ANESTHESIA FOR INVASIVE OR PROLONGED PROCEDURES

  • Inhalants:

    • Commonly used agents include Isoflurane and Sevoflurane.

ANALGESIA IN REPTILES

  • Anatomy Relevant to Pain Recognition:

    • Reptiles possess all anatomical structures capable of recognizing pain, including:

    • Peripheral nociceptors

    • Central nervous system structures and pathways for pain transmission.

    • Opioid receptors and endogenous opioids that interact with analgesics.

  • Pain Recognition:

    • Pain recognition is challenging in reptiles due to their stoic nature and subtle behavioral changes.

    • Common Signs of Pain:

    • Anorexia

    • Lethargy

    • Decreased mobility

    • Struggling during procedural interventions.

    • Assessing the effects of analgesia is difficult; a balance must be struck to avoid sedation side effects in critically ill patients.

  • Methods to Study Analgesic Drugs:

    • Pharmacokinetic Studies: Evaluating drug levels at various times post-administration.

    • Efficacy Studies: Utilizing subjective ethograms and applied stimuli (thermal/electrical) to measure response accurately.

  • Challenges in Extrapolation:

    • Drug levels effective for managing pain in mammals do not necessarily correlate with those in reptiles due to physiological differences.

ESTABLISHING A SPECIES ETHOGRAM FOR PAIN ASSESSMENT

  1. A detailed ethogram is essential for distinguishing between normal and abnormal pain behaviors.

  2. Observers should be adequately trained to identify subtle behavioral differences; staff should be well-versed in reptile behavior and husbandry practices.

EXAMPLE OF BEHAVIORAL ETHOGRAM

  • Evaluation of pre-operative and post-operative behavioral responses in reptiles after a unilateral orchidectomy:

    • Groups: Morphine group, Butorphanol group, and Saline group.

    • Results: Morphine group returned to normal behavioral patterns more rapidly than other groups.

EXPERIMENTAL PAIN INDUCTION AND ASSESSMENT IN OTHER REPTILES

  • Large patient size complicates practical research.

  • Ethical concerns with threatened/endangered species impact study feasibility.

  • Behavioral assessments through ethograms remain subjective but practical in current research contexts.

EXTRAPOLATION CHALLENGES IN ANALGESIC RESEARCH

  • Diversity of Reptilian Class: Variability makes it difficult to determine universal analgesic efficacy.

    • Example 1: Meloxicam effective for 24 hours in mammals.

    • Example 2: Loggerhead sea turtles require 0.4 mg/kg IV/IM/SQ but likely do not maintain efficacy for 24 hours and has poor oral absorption.

    • Example 3: Green iguanas may require 0.2 mg/kg orally or intravenously every 24 hours.

  • Opioid Drugs: Most effective for pain control in mammals, classified by receptor subtypes:

    • Mu (ยต)

    • Kappa (ะš)

    • Delta (ฮด)

    • Opioid receptors must be present to facilitate pain reduction.

    • Opioid receptor genes are conserved across vertebrate taxa; documented in two snake species and various reptiles.

MORPHINE IN REPTILES

  • Preferred analgesic for various reptiles including bearded dragons, RES (Red Eared Sliders), crocodilians, and anoles, shown effective by thermal noxious stimulus method.

  • Risks: Respiratory depression observed with use.

MULTIMODAL ANALGESIA

  • May represent the best approach for managing pain effectively:

    • Involves the concurrent administration of multiple analgesic agents providing effects at different levels in CNS and PNS.

    • Example: Combination of Dexmedetomidine, NSAIDs, and Tramadol.

TRAMADOL IN REPTILES

  • Administration results in significantly increased withdrawal latencies up to 96 hours following a 10 mg/kg PO (per os) remedy.

  • Notably less respiratory depression than morphine, with pharmacokinetic studies indicating effects last up to 96 hours.

COMMON SURGICAL PROCEDURES

  • Lizards:

    • Orchidectomy

    • Ovariectomy with salpingectomy

    • Chelonians (Turtles/Tortoises):

    • Abscess treatments

    • Aural and integumentary procedures

    • Cloacal/rectal/oviductal/phallus prolapse repair

    • Plastron osteotomy

    • Gastrotomy/Enterotomy

    • Cystotomy

    • Ovariohysterectomy

    • Prefemoral fossae approach

    • Liver and renal biopsy

    • Egg removal

  • Snakes:

    • Removal of foreign bodies via gastroscopy

    • Enterotomies

    • Repair of fractures and lacerations

  • Crocodiles: Specific procedures left open for details.

WOUND THERAPY

  • Common causes of wounds include:

    • Boat strikes

    • Amputations

    • Machete injuries

    • Mating injuries

    • Live prey injuries

    • Burns

    • Abrasions

  • Assessment Considerations:

    • Determine what requires treatment.

    • Assess neurological state (stable vs unstable).

    • Differentiate between contaminated and uncontaminated wounds.

WOUND CARE FIRST RESPONSE

  • First Steps:

    • Stop hemorrhage by applying digital pressure.

    • Wound packing may be necessary.

    • Electrocautery or ligation could be indicated if bleeding persists.

WOUND CARE DEBRIDEMENT

  • Key Concepts:

    • Contaminated wounds must not be closed immediately.

    • Remove dead tissue and bone; focus on developing a healthy granulation bed.

    • Techniques include wet-to-dry bandaging, sugar, honey application; may take weeks to months.

    • Adequate nutrition, water quality, and reduced stress are crucial for healing.

WOUND THERAPY

  • Preliminary Steps:

    • Perform blood cultures and sensitivities upon identifying an infection.

    • Select appropriate antibacterial and antifungal therapies based on culture results.

TOPICAL PRODUCTS FOR WOUND CARE

  • Compounds used include:

    • Dilute Betadine or Chlorhexidine: common antiseptics;

    • Silver Products: SSD (Silvadene);

    • Antibacterial and Antifungal options;

    • Honey & Collasate: known for their healing properties;

    • Tegaderm, Duoderm: types of wound dressings.

HONEY AND HONEY COMB IN WOUND THERAPY

  • Honey properties include:

    • Hyperosmotic nature kills bacteria and fungi by drawing moisture from their cells.

    • pH around 4, aiding in bacterial growth inhibition.

    • Hydrogen peroxide produced when glucose is broken down by glucose oxidase enzyme.

  • Benefits of Honey:

    • The unique composition enhances immune system responses, demonstrates anti-inflammatory effects, and stimulates cell growth.

    • Application: Coat tissue with honey or use honeycomb applied directly to the wound; can be secured with bandages for up to 10 days.

WOUND VAC THERAPY

  • Benefits:

    • Creates negative pressure to remove bacterial contamination.

    • Assists in reducing edema and increases blood flow.

    • Promotes granulation tissue formation while speeding healing processes.

    • Less labor-intensive, involving infrequent bandage changes (every 48 hours to every 5 days); reduces painful procedures.

REPTILE EUTHANASIA

  • Challenges in Euthanization:

    • Discomfort for veterinary staff and clients due to the attachment many owners have to their pets and limited euthanasia drug options.

    • Difficulty confirming death through traditional means (e.g., lack of full anesthesia).

  • Veterinary/Staff Comfort:

    • Planning is crucial; ensure rapid transfer into examination areas to minimize public discomfort during euthanasia discussions.

  • Client Comfort: Involves empathetic communication regarding their bond with the reptile and the grieving process.

EUTHANASIA PROTOCOLS

Step 1 - Sedation/Anesthesia

  • Optimal Temperature Management: Warm reptiles to their preferred temperature range before administering euthanasia drugs.

  • Key Indicators: Loss of pedal reflex, righting reflex, and muscle tone are critical before proceeding.

  • Drug Choices for Sedation:

    • Tiletamine/Zolazepam: 15-30mg/kg IM or SQ for lizards/chelonians; 5-10mg/kg IM for snakes.

    • Alfaxalone: 20-30mg/kg IM for lizards and chelonians.

    • Isoflurane: 2.5% in oxygen via chamber or mask.

Step 2 - Primary Euthanasia

  • Drugs for Euthanasia:

    • Sodium Pentobarbitol: Administer IV preferred, dosage 100-150 mg/kg.

    • Routes of Administration:

      • IV access usually involves the ventral coccygeal vein for lizards/snakes and the jugular vein for chelonians.

    • Additional Notes: If given IV, no secondary method is necessary to confirm death but is recommended when given via IC route (Intracoelomic). Oral, SQ (subcutaneous), or IM (intramuscular) are not recommended.

  • Inhalants: CO2 and Isoflurane/Sevoflurane are present but not recommended as sole euthanasia methods, often requiring extended exposure and secondary methods.

Step 3 - Ancillary Methods (if necessary)

  • Methods Not Considered Humane: Freezing condemned by AVMA.

  • Considerations for Other Ancillary Methods:

    • Decapitation: Can be pursued but requires follow-up methods (pithing) for humane death confirmation due to potential for prolonged neural activity post-decapping.

  • Pithing: Involves insertion of a rod or syringe through the foramen magnum to destroy brain tissue for ensured death.

DETERMINATION OF DEATH

  • Key Consideration: Heart activity can continue after brain death.

    • Confirmation of death requires cessation of heartbeat through auscultation or Doppler monitoring; any heartbeat indicates the reptile is still alive.

BODY DISPOSAL/RETURN TO OWNERS

  • Post-Determination Considerations: Ensure all aspects of disposal align with ethical and client preferences after confirming the reptile's death.