Anesthesia monitoring and surgery

  • Know how to prepare a patient for an anesthetic procedure and how to help him recover

  • Anesthesia is often challenging and more difficult than the actual diagnostic or surgical procedure conducted in exotic pets.
  • Anesthesia is required for:

–Grooming procedure

–Deepened clinical exam

–Diagnostic test

–Surgery

–Therapeutic procedure (ex: oesophagostomy tube)

  • Is anesthesia risky?

–Risk of anesthetic death is 1.4% in rabbits, 3.8% in GP, 1.7 to 3.7% in other exotics. Much more important than in dogs and cats (6-10x)

  • Complications occur faster and the time for intervention is shorter.
  • Blood loss are a significant stress:

–Do not exceed 5 to 10%, around 2 to 5ml/kg

–An average gauze sponge will absorb 7ml of fluids

–An average coton tip applicator will aborb 0,17ml of fluids

  • Is anesthesia risky?

–Factors to control:

–Species identification is mandatory, especially in birds and reptiles

–Stress (prey species!)

–Subclinical nutritional deficiencies (calcium, vitamin A, vitamin C)

–Subclinical diseases, esp. respiratory diseases (rabbits, rats) causing hypoxia. Thoracic Xrays and Bloodwork are advised.

–Small diameter of trachea: obstruction with fluids, edema or unadapted position

–Herbivores have usually smaller thorax compared to abdomen volume

–Peroperative complications: hypothermia (high surface area to body volume ratio)

–Postoperative complications such as digestive problem, infection, pain, electrolyte imbalances

–IV catheterization, IV fluids, tracheal intubation are not systematics

  • Anesthesia= CNS depression causing amnesia, loss of consciousness and immobility. Analgesia is not produced by anesthesia, it depends on the molecule used.
  • Sedation= Decreased response to environmental stimuli and muscle relaxation.
  • Analgesia= Absence of pain response after painful stimulation.

  • Usually, we use sedation and analgesia before obtaining anesthesia.
  • A same molecule can be used as an analgesic, sedative or anesthetic agent depending of the dosage and drug’s association.

  • Anesthesia monitoring begins before the anesthesia and finishes only when the patient has totally recovered (he’s eating, on a standing position and has normal reactions and reflexes)

Recovery from anesthesia is obtained when the patient is able to stand up on his legs, to move when stimulated, to maintain a sternal body position with normal respiratory, cardiac parameters. They require specific attention until they eat alone, and can maintain normally their body temperature.

  • It means that as soon as your patient comes into the vet clinic for an anesthetic procedure, you should have specific considerations:

–Should I keep the water bowl or water bottle in the cage?

–Does he need to eat? Should I let extruded diets? Hay?

–Provide secure and hidden area so the patient will not be too anxious

–What is the POTZ (or PBT=Preferred Body Temperature) of this Reptile?

–Was he examined by a vet of the structure recently?

What is required for a safe anesthesia?

1.Quiet environment

2.Prepare your material

3.Premedication

4.Preoxygenation

5.Induction

6.Maintainance

7.Recovery

What is our knowledge of anesthesia in exotic species?

  • It is really disparate.

–A lot of different species. Something that works and is weel-tolerated by rabbits may be toxic and dangerous in another species…

–A lot of publications and range of dosages,

–Not the same safety level when you are looking on anesthetic dosages used in experimentation and in clinical practice.

–How to chose? Respect the vet’s experience and the patients needs.

General information about Anesthesia

  • Duration of anesthesia

–Influenced by the drugs and species, strain, age, sex, body condition, type of procedure

–Very variable

–Always adjust to your patient: it is called TITRATION.

  • Depth of anesthesia

–Depends on the procedure (if painful, a deeper anesthesia is usually needed)

–Depends on the dosage of the anesthetic molecule (% of anesthetic gas or dosage of chemical anesthesia)

  • Anesthetic gas (halothane, isoflurane, sevoflurane)

–It only brings NARCOSIS (amnesia, loss of consciousness and immobility)

–The preferred way to anesthetize exotic pets. It does not mean that they are used alone. They are always associated to other drugs bringing analgesia, muscle relaxation or sedation (midazolam-morphine).

–Exotics: Isoflurane >> Sevoflurane. Don’t use Halothane (very toxic for humans and pets).

–% of anesthetic gas permits to adjust the depth and duration of anesthesia.

–Dose-dependent cardiovascular depression

  • Which anesthetic circuits?

–Non-rebreathing or pediatric circle

–Low dead space and low resistance

  • Bain crircuit or Ayre’s T-piece
  • Dead space= rebreathing of carbon dioxide

  • To deliver anesthetic gas

–Nose-cone, mask or tracheal tube

–Birds: Possible to use an air-sac catheter

–Protect yourself: do not breath that gas. Ventilate the room, reduce the loss of gas (mask’s size), adapt the % of oxygen and gas to the patient (do not overdose) and check the scavenging (outside or through activated charcoal canisters).

  • How to anesthetize?

–Induction: preferably in a sedated patient (otherwise, struggling and breath-holding), in a small box, a big mask or directly with towel handling. First, preoxygenation during several minutes, then 2 to 5 minutes with 3 to 5% isoflurane gas. Reduce gas % once the anesthetic state is obtained. Stress, apnea, hypotension and bradycardia can occur.

–Maintenance: 1,5 to 3,5% depending of the preanesthetic drugs, the type of procedure, the species…

–Recovery: only oxygen until complete recovery. Check breathing pattern, cardiac frequency and temperature. Hypotension and hypothermia are common. Be sure of airways patency.

  • Injectable anesthesia (ketamin, medetomidine, alfaxalone, propofol…)

Never use an injectable molecule alone. Associate it to other injectable anesthesia or to gaseous anesthesia (Combination drug= cocktail anesthesia).

–Difficult to adjust: once injected, it can not be removed. Some molecules (alpha2 agonist like medetomidine and dexmedetomidin) can be reversed with atipamezole. If needed, can be re-administered (20 to 30% of the initial dosage) but it decreases the safety level (however, we can not finish the procedure if the animal is not properly anesthetized).

Analgesic drugs

  • Injectable drugs

The first injection must be done before surgery, it is called « pre-emptive analgesia ». It permits to block the painful stimuli.

  • Frequency of administration depends on the species (individuals, age, breed, sex, body score) and the type of procedure.
  • Difficult to assess pain in exotics. Always presume they are in pain following the surgery.
  • Opioid analgesics have usually a short duration. They can be combined to NSAIDs so duration and efficiency of analgesia will be increased.

–What about atropine and glycopyrrolate?

  • They are not normal premedication
  • They should not be associated to α2 agonists
  • Many rabbits possess atropinesterase. Use glycopyrrolate first.
  • Use it if your patient develops bradycardia during anesthesia

How to secure anesthesia?

  • No stress in the vet clinics. Premedicate and isolate in a quiet environment without excessive handling. Provide hiding boxes, chewing material
  • Weigh accurately your patient on the day of the procedure
  • Premedicate
  • Preoxygenation (even if injectable anesthesia is used)
  • Tracheal tube when possible.
    • –Always check airways patency (extend the neck so the trachea is straight)

      –Air sac catheterization is possible in birds

    • Venous access & IV fluids depending on the duration of procedures. Intraosseous catheterization is also advised.
    • Keep your emergency resuscitation kit close
      • Remove food, not too early
        • –They are very sensitive to food deprivation (hypoglycemia, transit slow down).

          –If anesthesia is required for a short duration and non invasive procedure (grooming, diagnotic, dental): remove food only 1h before anesthesia to ensure there is no more food in the oral cavity and crop.

          –If anesthesia is required for a longer duration and more invasive procedure (abdominal surgery): remove food only 3h before anesthesia in rabbits and rodents.

        Prepare all the material needed for the anesthesia, the procedures and a potential emergency

        Check particularly the anesthetic circuit (level of isoflurane, open-circuit, production of oxygen)

        • Always check

        –Cardiac parameters:

        • Cardiac rate, arrythmia, bradycardia, via stethoscope or ECG or Doppler probe
        • If available, blood pressure
        • –Respiratory parameters:

          • Respiratory rate and pattern, airways patency, membrane color, capnography & capnometry (if intubated), pulse oxymetry
          • Easy if transparent surgical fields are used
          • –Body temperature:

            • Heating mat, hot water bottles, warm filled gloves (!), warm IV fluids
            • Avoid heat stroke, burn (protect your patient) & hypothermia
            • Use rectal thermometer or oesophagal probe

        –Depth of anesthesia:

        • Pedal withdrawal reflex is lost when surgical plane of anesthesia is achieved
        • Too depth anesthesia will provoke bradypnea, bradycardia

        –Pain:

        • The pain felt can be seen as tachycardia, tachypnea…
        • Ask the surgeon if he is doing something painful
        • Renew analgesic drugs as needed
        • Add several molecules: local anesthesia, opioïds, constant rate infusion of ketamin…

        –Cornea should be lubricated to prevent drying out

        –IV line when possible and fluids i possible

        • Keep your emergency resuscitation kit close to you

        –Atropine, adrenaline, glycopyrrolate, doxapram, diazepam should be ready to use with syringe, needles and tables showing dosage by species and weight

        • Keep your emergency resuscitation kit close

        –Laryngeal mask are great, if weel-inserted, to oxygenate patients. They permit to realize positive-pressure ventilation if needed.

        –It is also possible to ventilate via the mask if adequately sealed or to blow gently into the nose

        Gastric tympanism may develop

        • Check your patient until complete recovery

        –In 1 survey, more than half the anesthetic mortalities occurred after the surgery!

        –Heart rate, Respiratory Rate and Airways patency, Body temperature should be monitored regularly.

        –The patient must benefit of oxygen delivery until his complete recovery (except Reptiles!)

        –When recovered: appetite and feeding, fecal output, pain, behavior should be supervised

        –Painkiller should be used in a pre-emptive manner

        –Assisted feeding are required in birds and small mammals

        –Prokinetics drugs should be used in herbivores species

        –Do not forget social contact when they need it

        • You are the guarantors of anesthetic safety
        • Always think about patient’s admission, pre-anesthetic, peranesthetic and postanesthetic period
        • You are only relieved when the patient comes back 15d later and everything is OK