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ANESTHESIA AND ANALGESIA IN RUMINANTS

Description
LOCAL ANALGESIA


Local analgesia: Advantages
  • Inexpensive, minimal equipment
  • Eliminates risk of aspiration unless sedation included
  • Minimal organ depression



    Techniques



    1. Spinal block

    A. Epidural nerve block (perineal urethrostomy, flank laparotomy in sheep, goat). Addition of epinephrine to the local anesthetic solution significantly prolongs the duration of action.
    Injection of anesthetic at the lumbosacral junction blocks the sciatic nerve and results in hind limb paralysis. Injection of anesthetic solution at the sacrococcygeal or first intercoccygeal space may result in analgesia only of the perineum, so that the patient remains standing, or the solution may diffuse sufficiently forward to block the sciatic nerve and cause ataxia or recumbency.
    Advantages of this block are the low cost compared with general anesthesia, lack of a drug residue problem, excellent analgesia and muscle relaxation, minimal risk of regurgitation compared with general anesthesia.
    Complications of this block mainly relate to the vasodilation produced, which may result in hypotension. Decreased GI motility may result in bloat. Excessive cranial diffusion may cause respiratory muscle paralysis. Ataxia is not a major problem in ruminants but can be life-threatening in horses.
    Xylazine may be used as an alternative solution to lidocaine for epidural block. Xylazine causes analgesia but not paralysis.



    Advantages

    1. Cheap.
    2. Easy to perform.
    3. Minimal organ depression.
    4. Does not require equipment.



    Disadvantages

    1. Hypotension in some patients.
    2. Patient is awake and must be restrained/sedated.
    3. Lack of asepsis may result in meningitis.

    Injection of anesthetic at the lumbosacral junction blocks the sciatic nerve and results in hind limb paralysis. Injection of anesthetic solution at the sacrococcygeal or first intercoccygeal space may result in analgesia only of the perineum, so that the patient remains standing, or the solution may diffuse sufficiently forward to block the sciatic nerve and cause ataxia or recumbency.

    Advantages of this block are the low cost compared with general anesthesia, lack of a drug residue problem, excellent analgesia and muscle relaxation, minimal risk of regurgitation compared with general anesthesia.

    Complications of this block mainly relate to the vasodilation produced, which may result in hypotension. Decreased GI motility may result in bloat. Excessive cranial diffusion may cause respiratory muscle paralysis. Ataxia is not a major problem in ruminants but can be life-threatening in horses.

    Xylazine may be used as an alternative solution to lidocaine for epidural block. Xylazine causes analgesia but not paralysis.




    EPIDURAL BLOCK IN GOATS


  • Location of landmarks
    a. Goat is either standing or restrained on its side.
    b. To locate the lumbosacral junction: a line joining the cranial border of each ilium crosses the spinous process of the last lumbar vertebra. The caudal border of each ilium is on line with the sacrum. The needle should be inserted in the center of the depression between these two points.

  • Technique: same as for dogs.
    The meninges extend to mid sacrum in goats and calves and aspiration of CSF is common. The needle should be repositioned for epidural injection.

  • Drugs
    a. Lidocaine 2% with epinephrine 1 ml/5kg for laparotomy, 1 ml/7 kg for perineal urethrostomy. Onset may be immediate or take up to 15 min. Duration of analgesia 1.5 - 2 hours. Standing in 3.5-5 hours.
    b. Bupivacaine 0.75% (Marcaine®). Onset of action 40 min, duration of surgical analgesia 4-6 hours, standing 8-12 hours.
    c. Morphine diluted with saline (as for dogs) for postoperative analgesia.


    B. Spinal nerve block (flank laparotomy, but not commonly used)

    Local anesthetic solution injected at the lumbosacral junction into CSF in the subarachnoid space. Potential for cranial diffusion of anesthetic drug is greater.




    2. Nerve block
    - Local anesthetic solution is deposited on or near a nerve. Onset and duration of block depends on which agent is used.

    a.

    Paravertebral
    nerve block (flank laparotomy in adult cattle)

    Lidocaine is injected over the nerves either A. immediately adjacent to the vertebral column on nerves T13, L1, L2, and L3 = Proximal block, or B. at the tips of the transverse processes of L1, L2, L3, and L4 = Distal or Cornell block.







    When performing the proximal block, 6 inch steel needles are inserted perpendicular to the cow's back, approximately 2" from midline. This block also includes block of sympathetic nerves to the splanchnic area, resulting in vasodilation, and block of nerves to the longitudinal muscles of the back, resulting in curvature of the spine (concave on the non-blocked side).

    When performing the distal block, 2 inch 18 ga hypodermic needles are inserted in a horizontal plane at the tips of the transverse processes. Splanchnic vessels and back muscles are not affected.

    b.

    Digital
    nerves, peroneal n. tibial n. median n., ulnar n. (lameness diagnosis, suturing lacerations, digit amputation)

    c.

    Cornual
    nerve block(s) (dehorning)

    d.

    Auriculopalpebral
    nerve block (prevents blinking during examination of eye). Motor effect only, no analgesia

    e.

    Peterson
    block (eye enucleation)

    f.

    Pudendal
    nerve block (relaxation of penis)

    g.

    Field block or L-block
    (flank laparotomy)

    Local anesthetic agent is infiltrated several cm proximal to the site of skin incision into skin and subcutaneous tissues (into muscle down to peritoneum when used for laparotomy)




    3. Terminal infiltration


    a. Local infiltration of incision site.

    b. Intravenous regional (Bier) block (amputation of a digit, suturing limb lacerations)
    A tourniquet is attached around the limb to occlude venous and arterial blood flow proximal to the surgical site. 2% lidocaine without epinephrine is injected into a vein. The lidocaine is distributed through the limb via the venous system. The lidocaine diffuses out of the vein into the tissues where it blocks nerve endings. Analgesia persists as long as the tourniquet is in place.





    Anesthetic agents


    1. Drugs used:
    a. Lidocaine (Xylocaine)
    b. Mepivacaine (Carbocaine)
    c. Bupivacaine (Marcaine)

    2. Contraindications to use:
    a. Inflammation at site of proposed injection
    b. Previous allergic reaction
    c. Specific clinical situations e.g. epidural nerve block and hypovolemia

    3. Toxic effects:
    a. CNS depression
    b. CNS excitation
    c. Decreased ventilation
    d. Decreased arterial pressure
    e. Decreased cardiac contractility





    SEDATION AND ANESTHETIC AGENTS




    Sedation

  • Xylazine > Behavioral effects
  • Detomidine > Respiratory effects
  • Acepromazine > Cardiovascular effects Other effects
  • Chloral hydrate
  • Diazepam in sheep / goats
  • Butorphanol in sheep / goats




    Xylazine in Ruminants:
    Other effects

  • Swallowing reflex depression > Risk of aspiration
  • Decreased motility > Bloat
  • Copious urination (x 6-8) > Do not use with urethral obstruction
  • Uterine contraction > Do not use in last trimester pregnancy
  • Profound hyperglycemia (200%)
  • ± Diarrhea 24 hours later




    General anesthesia in sheep, goats, calves


  • Ketamine > Premedication with xylazine, acepromazine, diazepam, and/or butorphanol
  • Telazol > Xylazine or butorphanol premedication and Expensive
  • Thiopental > Not if <3 months old and wide dose range



    CALVES, GOATS, SHEEP


    1.

    Thiopental


    a. Use of a thiobarbiturate in an animal less than 3 months of age cannot be recommended because it usually results in a prolonged or lethargic recovery.
    b. Thiopental provides an excellent induction of anesthesia for healthy adult goats and sheep. The dose rate required to provide relaxation for endotracheal intubation and anesthesia varies considerably between individuals. Preanesthetic sedation is optional.

    2.

    Ketamine


    a. Ketamine is a useful drug in small ruminants. Given alone it causes immobilization, muscle rigidity and opisthotonos, but does not appear to cause convulsions or excitement as observed in dogs or horses.
    b. Usually ketamine is given after or concurrently with xylazine, diazepam, or acepromazine. Addition of these sedatives provide better conditions for surgery.
    c. Duration anesthesia from diazepam - ketamine is 15 min and from xylazine-ketamine is 30 min. Anesthesia can be prolonged by additional injections of ketamine and xylazine. Prolongation of anesthesia with injectable drugs > 1.5 hours results in prolonged recovery.
    d. Swallowing reflex is abolished or decreased and the trachea should be intubated to avoid aspiration of rumen contents. Slight jaw movements may be present during anesthesia; an increase in vigor of these movements is an indication for additional drug administration. Bradycardia may develop and require treatment with atropine. Rectal temperature usually decreases. Goats have difficulty regaining normal body temperature after anesthesia when rectal temperature decreases to 97oF during anesthesia.

    3.

    Telazol


    a. Xylazine - Telazol will provide about 65 min anesthesia.
    b. Arterial PO2 usually low with this combination.


    4.

    Propofol


    Provides satisfactory anesthesia, but is costly.


    5.

    Halothane, Isoflurane


    a. These anesthetics agents produce satisfactory anesthesia in small ruminants.
    b. Anesthesia is easily induced in calves and young goats/sheep with halothane or isoflurane administered initially by facemask.
    c. Anesthesia can be induced with any of the injectable drugs discussed and then maintained with halothane or isoflurane.
    d. A circle circuit used for dogs is suitable for small ruminants up to 140 kg bodyweight. The vaporizer settings are similar to those used for dogs, e.g. halothane 1 - 2% for maintenance of anesthesia.


    6.

    Nitrous oxide


    N2O is rarely used because it freely enters the rumen and causes bloat.


    7.

    Atropine and glycopyrrolate

    a. Not used routinely because ileus potentiates bloat and cattle are slow to resume eating after anesthesia.
    b. Atropine premedication may be advisable in Llamas because some may develop bradycardia abruptly during anesthesia.




    DRUG COMBINATIONS FOR ANESTHESIA IN CALVES, GOATS, SHEEP


  • Diazepam (0,2 to 0,3 mg/kg IV) and Ketamine (6 to 7.5 mg/kg IV) gives anaesthesia duration of 10 - 15 min. (Comments: Can include butorphanol 0.1 mg/kg)
  • Xylazine (0.1 mg/kg IM) and Ketamine (6 mg/kg IV or 10 mg/kg IM) gives anaesthesia duration of 30 min. (Comments: Additional xylazine can be added if depth of anesthesia not adequate)
  • Thiopental (7 to 20 mg/kg IV) gives anaesthesia duration of 10 min. (Comments: Not when <3 mo, individual dosages varies; initially inject 5 mg/kg IV and titrate additional drug 'to effect')
  • Xylazine (0.1 mg/kg IM) and Telazol (4 mg/kg IM) gives anaesthesia duration of 45 - 60 min. (Comments: Higher xylazine dose may cause apnea)
  • Butorphanol (0.2 mg/kg IV) and Telazol (4 mg/kg or more) Comments: Satisfactory dose rates still being worked out
  • Propofol (About 4 mg/kg IV) gives short anaesthesia duration but can be maintained by incremental injections or infusion




    DRUG COMBINATIONS FOR ANESTHESIA IN CALVES 200 - 350 KG BODYWEIGHT


  • CALVES 200 - 350 KG BODYWEIGHT > Xylazine (0.1 mg/kg IM) and Ketamine (4 mg/kg IV or 6 mg/kg IM) gives anaesthesia duration of 20 min duration. For prolongation see below
  • ADULT CATTLE: Xylazine (0.1 mg/kg IM ) and Ketamine (2.2 mg/kg IV) gives anaesthesia duration of 15 - 20 min duration. For prolongation see below
  • Prolongation ketamine anesthesia: Add 1g (10 ml) ketamine to 1 liter 5% guaifenesin > Infuse 2 ml/kg/hr IV. Tracheal intubation recommended
  • All cattle: Guaifenesin 5% (100) Thiopental (4,4) > Up to 600 kg bodyweight, then dose rate decreases. Tracheal intubation recommended. Premedication with acepromazine or xylazine
    decreases dose required




    ADULT CATTLE


    The increased concern for the use of sedatives or anesthetics in food animals that are to be shipped to market should be recognized. If a residue is found in such animals, the individual administering the drugs can be prosecuted.

    1.

    Xylazine-Guaifenesin-Ketamine or Xylazine-Ketamine


    a. Produce satisfactory anesthesia. Ketamine dose is much less (2 mg/kg IV) in cows than in small ruminants (6 mg/kg IV, 10 mg/kg IM).
    b. Anesthesia can be maintained by a continuous infusion of GG/ketamine (Total Intravenous Anesthesia, TIVA).


    2.

    Guaifenesin or Guaifenesin-Thiobarbiturate


    a. Guaifenesin alone or mixed with barbiturate produces excellent immobilization in cattle. Premedication is not essential, but may be used if needed for restraint for IV puncture. If complete anesthesia is induced, the trachea should be intubated. If available, oxygen should be provided.
    b. A 5% solution of guaifenesin is used.




    PROBLEMS IN RUMINANTS during anaesthesia


  • Regurgitation and pulmonary aspiration > Always a risk
  • Hypoxemia > Dorsal recumbency all ruminants and Large ruminants and recumbency
  • Radial nerve paralysis > Adult bovine; inhalation anesthesia




    Monitoring during anesthesia


  • Eye signs > Eye rolls more ventrally
  • Ventilation > Rate is faster than other species
  • Heart rate, CRT, blood pressure > Heart rate 60 - 100 and auricular, median, coccygeal arteries and bulls may be hypertensive




    Recovery from general anesthesia


  • Problems > Hypoxia and Aspiration
  • BEFORE extubating trachea > Sternal position and wait until tongue withdrawal is present
  • Usually these are not problems > Excitement and standing




    ADMINISTRATION OF ANAESTHETICS


    1.

    Preparation of patient


    a. Physical examination
    b. Lab tests?
    c. Withhold food 24-36 hours (small ruminants) or 36-48 hours (adult bovine). No water 6-12 hours. Note that after starvation, animal's temperature, heart rate, and serum calcium may be decreased.
    d. Correct hypovolemia, if present


    2.

    Restraint for drug administration


    a. Chute
    b. Halter and body ropes to induce recumbency first.
    c. Neck rope to restrain for IM injection.
    d. Manual restraint in small ruminants.


    3.

    Catheters


    a. Jugular vein catheter most common (14 gauge)
    b. Cephalic or saphenous vein also available in small ruminants.


    4.

    Endotracheal intubation


    a. Animals up to 300 kg.
    A laryngoscope is very useful. May be easier with the patient in sternal position. Head and neck fully extended. A stilette inside the endotracheal tube may be helpful in sheep/goats. May have to rotate the tube a quarter or half turn to facilitate entrance into the larynx.

    b. Adult cattle
    Insert your hand into the pharynx and palpate the epiglottis and laryngeal entrance. Use your fingers to depress the epiglottis and help to guide the tube into the larynx. Alternatively, insert a nasogastric tube into the trachea, remove your hand, and feed the endotracheal tube over the nasogastric tube.


    5.

    Monitoring


    a. Depth of anesthesia
    Palpebral reflex and eyeball position, pupil size. Lack of movement

    b. Ventilation
    Rate and depth, membrane color

    c. Circulation
  • Peripheral pulse strength and rate (coccygeal, median, auricular, femoral)
  • Mucous membrane color and CRT
  • Heart rate
  • Arterial pressure if available: Indirect measurement on forelimbs of small ruminants. Tail of adult bovine may not be accurate. Catheter in auricular artery for direct BP measurement.

    d. Rectal temperature


    6.

    Adjunct treatment


    a. Oxygen if possible; resuscitator bag for small ruminants in absence of anesthesia machine
    b. Balanced electrolyte for major surgery.
    c. Glucose containing solution for newborns and pediatric.


    7.

    Recovery


    a. Support patient in sternal position as soon as surgery is finished.
    b. Prevent aspiration - leave endotracheal tube in until patient chewing vigorously and can pull its tongue back into its mouth. Pull tube only when patient is sternal.
    c. Continue to monitor rectal temperature.
    d. Problems with excitement and struggling early to stand are not usually a feature of ruminant anesthesia.













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