3-Preanesthetic med

III-PREANESTHETIC MEDICATION

Definition:

It is the drug that usually administered prior to induction of anesthesia for sedation if the animal is to be operated under the effect of local or regional analgesia, or for sooth induction and smooth recovery from general anesthesia, and reduction of the anesthetic dose.

Aims:

1-Potentiation of anesthetic agent

2-Reduction and abolishing of pain

3-Soomth induction and smooth recovery of anesthesia

4-Avoiding harms to the animal and surgeon

5-Reducing the amount of anesthetic agent and its toxicity

6-Reduction of salivary and bronchial secretions and the subsequent possibility of asphyxia

7-Reduction of GIT motility

8-Stimulation of cardiac and respiratory functions

TYPES

1-Anticholenergic drugs

2-Muscle relaxants

3-Tranquilizers

1-Anticholenergic drugs (Atropine)

It is a water-soluble sulfate used as atropine sulfate. It is very safe drug with wide therapeutic margin except individual animals that have proved to be sensitive to the drug.

Uses:

Used as pre-anesthetic medication with wide safety margin for stimulation of cardiac and respiratory functions, and inhibition of salivary and bronchial secretions. Used prior to wide verity of anesthetic agents (barbiturates, or inhalation anesthetics), sedatives, and narcotics.

Effect on CNS: -

1-The clinical dose produces initial reduction of heart rate due to vagal stimulation, before its peripheral anticholenergic effect ensues

2-Over dose causes central cholenergic syndrome with fluctuations between hyper excitability and depression

Effect on eye: -

It causes mydriasis and it is contraindicated in cases of glaucoma

Effect on Respiration: -

It causes relaxation of bronchial musculature, dilates bronchi, prevents laryngeal spasm during intubation, and reduces bronchial secretion

Effect on Cardiovascular system: -

It prevents vagal inhibition induced by narcotics, or tranquilizers, accordingly it prevents bradycardia

Effect on GIT: -

It reduces muscle tone of GIT, inhibits motility, and reduces salivation

Side effects:

The use of this drug in equines is prohibited due to

1-Equine don't produce copious salivation

2-Posibility of formation of viscid bronchial secretion with subsequent occlusion of alveoli

3-Interfernce with vision and the animal becomes uncontrollable

4-Reduction of intestinal motility with subsequent intestinal distention, and colic

Dose and concentration:

Concentration is 0.6 mg/ ml (0.06%)

Rout of administration:

Injection by IV, IM, or SC

2-Muscle relaxant

A-Gallamine triethiodide (Gallamine-Flaxedil): -

1-Gallamine produces a non-depolarization block at the neuromuscular junction, vagal block, and tachycardia.

2-It does not produce histamine release in the dog, so it is the non-depolarizing relaxant of choice in dog.

3-It is not detoxicated in the body, but it is excreted unchanged in urine, so it shouldn't be given to animals suffering from renal insufficiency.

Uses:

1-Surgical application (muscular relaxation)

It is very useful in;

a-Abdominopelvic surgery                                         b-Thoracic and lung surgery

c-Tracheal intubation during anesthesia          d-Immobilizing wild animals.

e-Reduction of muscle spasm (help in reduction of dislocated joint)

f-Reduction of amount of general anesthetic agent

2-Obstitrical application

Especially during parturition in small animals at the stage of full dilatation (as the drug not pass via placental barrier) for relaxation of the perineum to avoid risk of injury or laceration.

3-Medical application

a-Reduction of traumatic and rheumatic  pain

b-Relief of myositis, and tetanus spasm

Side effect:

1-Tachycardia with increased arterial blood pressure with subsequent high incidence of hemorrhage

2-The drug has histamine-releasing effect except in dogs

3-The drug should be used cautiously, as it may cause respiratory failure, accordingly, it can't be used unless artificial respiration tools are available.

Dose and rout of administration:

Antidote:

Neostigmine

B-Succinylcholine: -

Advantages:

1-It is free from the usual complications of muscle relaxants like

a-Hypotension                        c-Tachycardia                        b-Histamine release and urticaria

2-It has a rapid rate of destruction due to hydrolysis by plasma cholinesterase (the later is inhibited by phenothiazine like chlorpromazine HCI), so it has no cumulative effect.

3-The myoneural action is intensified when procaine is injected after it.

Dose and rout of administration:

3-Tranquilizers or Ataractics, and Sedatives

They are drugs used to depress the CNS, and are useful in wide verities of conditions in animals

Classification:

A-Weak acting drugs: -

Like meprobamate derivatives (Equinal) and used for human only

B-Strong acting drugs: -

1-Phenothiazine derivatives: -

a-Acepromazine (Acetylpromazine)

b-Chlorpromazine (Largactil or Neurazine)

c-Promazine (Sparine)

d-Propionylpromazine (Comblen)

2-Thiazine derivative: -

a-Xylazine HCl (Rompun or Xylaject)

b-Detomidine

3-Benzodiazepine derivative (Diazepam, or Valipam): -

a-Short acting (Valium, Neuril, Diazepam or Valipam)

b-Very long acting (Lorazepam)

Clinical use:

1-Preanesthtic drug

2-Relief anxiety of hospitalized animal

3-Restrain of refractory animal during examination

4-Prevention of animals from licking wounds or chewing bandage and splints

5-Used in minor surgical operations like abscess incision

6-Used in conjunction with local or regional analgesia

Clinical effect:

1-The ear drops with sluggish response

2-The eyes close or become semi-closed with protrusion of third eyelid

3-The tongue protruded in some cases

4-In cattle, the muzzle becomes dry with excessive salivation and reduced deglutition, that may cause dehydration and disturbance of acid base balance as a result of excessive loss of bicarbonate of the saliva

5-In cattle the head and neck drop and deviate to lateral side

6-Stugering gait of animal that becomes unconscious to the surrounding and try to lie down, and finally the animal lies down

7-Protrosin of penis and dilatation of anal and vulval sphincter

8-Reduction of temperature, pulse, and respiration

Advantages:

1-Easier handling of the animal during induction of anesthesia

2-Reduction of the required amount of anesthetic agent with subsequent reduction of toxicity

3-Smooth induction and recovery from anesthesia (reduction of struggling)

4-Inhibition of vomiting by the anti-emetic action of the drug

5-Phenothiazine derivatives help in prevention of shock

Warning:

1-Tranqulizer doesn't produce true analgesia

2-Occisionally severe or fatal reactions may occur

3-Not economical as the cost is high in many occasions

4-When administered to shocked animal, alpha-blockage may produce fatal hypotension

STRONG ACTING DRUGS: -

1-Phenothiazine derivatives: -

a-Acepromazine (Acetylpromazine): -

Dose:

0.1-0.2 mg/ Kg B. wt. in pets and large animals

b-Chlorpromazine (Largactil or Neurazine): -

Preparations:

Suppositories, tablets, drops, and vials for injection.

Effect and properties:

1-Produces state of calmness with reduction of motor activity, but it doesn't interfere with responses to unconditioned stimuli such as needle pricks and painful manipulations

2-It has potent anti-emetic, anti-adrenaline, and vagolytic properties.

3-It causes vasodilatation and should be used cautiously in shocked animals, but its use prior to operation counteracts tendency of tissue hypoxia, and prevents the onset of shock.

4-It has a wide safety margin and animals will recover from the effects of very large doses, but it should be used cautiously if there is severe depression of the heart or central nervous system, or if there are extensive liver or lung lesions.

5-The liver is the main site for detoxication so the action enhanced in during liver damage.

Uses:

1-Preanesthetic medication, to potentate the anesthetic agent

2-Long acting strong tranquilizer

3-Antiemitic, and used in cases of uremia or gastroenteritis in pets, or with drugs causing nausea and vomiting.

4-In case of tetanus to control titanic spasm and convulsions, and to diminish pain.

5-Its use in the horse ensures that the animal will recover quietly from anesthesia

6-Its use in dog ensures absence of narcotic excitement during recovery from barbiturate, and doesn't suppress respiration of puppies or labour of bitch.

Dose and administration:

c-Promazine HCl (Sparine 5%): -

Use and indication:

Like chlorpromazine HCl

Dose and administration:

d-Propionylpromazine (Combelen 1%): -

It is one of phenothiazine derivatives, yellow crystalline, and soluble in water. The solution used for injection contains 1% of active principle propionylpromazine.

Uses:

1-Sedation

a-Prior to drug administration                    b-Examination                            c-Minor operations

d-Radiographic examination                     e-Dressing of wounds

2-Preanesthtic medication for induction of general anesthesia

3-Potentiation of anesthetic agents by deepening and prolongation of its effect, and reduction of 10-40% of anesthetic dose

Disadvantages:

Should be used cautiously in case of cardiac disorders, and in case of severe lung, liver, or kidney problems.

Antidote:

Caffeine or nor-adrenaline

Duration:

1-8 hours according to rout of administration, dose, and age

Recovery:

Effect disappears completely within 24 hours

Dose:

2- Thiazine derivative (Sedatives): -

a-Detomidine: -

Stills under investigation

b-Xylazine HCl (Rompun or Xylaject): -

It is used in concentration of 2%

Properties:

a-It is sedative (depressant effect on CNS), analgesic, anesthetic, and muscle relaxant.

b-Ruminants are 5-10 times sensitive than equine.

c-It has emetic effect in pets.

d-Reduces dose of anesthetic

1-Sedation:

This effect is of clinical importance for;

a-Transportation of animals,

b-Changing environment and familiarization with new surrounding

c-Examination and treatment of claw, or shoeing of horse

d-Surgery                           e-Artificial examination of less domesticated cattle

Duration of sedation:

2-Analgesia:

This effect is of clinical importance for;

a-Management of udder and teat injury

b-Dehorning, fitting of nose ring, flushing of nasolachrymal duct

c-Bloodless castration                    d-Treatment of foot affections

Duration of analgesia:

3-Anesthesia:

a-It has local analgesic effect on the cornea of rabbit several times higher than that of procaine HCl  (0.2%)

b-Local anesthetic effect in dogs by 0.1-0.2% with induction of local insensibility for 60 mins

c-Used for epidural analgesia

4-Muscle relaxation:

Used in surgical operations to avoid tetany and to capture the animal

Duration of muscle relaxation:

According to the dose it varies from 20-120 mins

Side effect:

1-Cardiovascular system:

It causes bradycardia, in a manner resembles that of atropine

2-Respiratory:

No great changes with recommended doses

3-GIT:

It depresses GIT and ruminal motility and may cause tympany in ruminants but this reduction of motility is helpful in case of equine colic.

4-Uterous:

It increases intra-uterine pressure in pregnant cows in a manner resembles that of oxytocin, accordingly it shouldn't be used in the last trimester. This is not the same in mares that can be given xylazine along the all gestation period with no harm

Dose and rout of administration:

3-Benzodiazepine derivative: -

a-Short acting (Valium, Neuril, Diazepam or Valipam): -

Uses:

1-Preanesthetic medication          2-Sedative and hypnotic            3-Control of convulsions

4-Produces muscular relaxation                       5-Epidural analgesia

Dose and administration:

b-Very long acting (Lorazepam): -

It is 4 times potent than diazepam, with shorter on set of action and prolonged duration and recovery, and used as pre-anesthetic medication prior to ketamine HCl especially in cat

IV-BASAL NARCOSIS

Definition:

It is a stage during which the animals losses consciousness but still responding to painful stimuli, so it is of clinical importance for performing operations in horses and cattle under local or regional analgesia. Its administration should be limited to avoid interference with vital processes. The most common drug is chloral hydrate.

1-Chloral hydrate: -

1-It is a white crystalline, easily soluble in water, and has penetrating odor

2-Mainly used for equine and may be used for cattle

3-Detoxicated in liver and excreted by kidney

4-Can be used in different doses to induce three stages of narcosis

5-Can be used strictly IV, orally, or rectally

6-Hypnotic dose doesn't affect respiration, but over dose predisposes to respiratory failure via affecting the respiratory center

Stages of narcosis, doses, and effect:

Routs of administration:

Advantages:

1-Easily dissolved in water

2-Wide safety margin

3-Detoxicated by liver and excreted by kidney

4-Easily absorbed from mucous membrane of GIT

5-The animal able to stand under effect of light and medium narcosis

Disadvantages:

1-Very irritant, and can't be injected IM or SC

2-Over dose causes hypotension and respiratory failure

2-Morphine: -

It is used either as morphine sulfate or HCl, and mainly used in dogs

Dose,  rout, on set, and duration:

Action:

1-It depresses the higher functions of the brain

2-Stimulates then depresses medullary functions, and stimulates spinal reflexes

3-Produces depression, analgesia, and sleeping in dogs, but in large doses cause coma. Also it Produces pin-point pupil

4-Produces delirium or 'maniacal excitement in cat

5-Produces unreliable effect in horses, cattle, and pigs (narcosis or excitement). Also it may cause sufficient excitement to dilate the pupil.

Side effects:

1-It is advised that the dose of morphine as a preanesthetic should not exceed 15 mg even in the large dogs because larger dose causes respiratory depression.

2-It crosses the placenta and reaches the fetus, depressing its respiratory center and making the initiation of breathing difficult after birth, but the analgesic doses of morphine do not affect normal uterine contractions at parturition, accordingly it shouldn't be used for caesarian section.

3-The stimulant effect on the vagal center

a-Increases gastro-intestinal activity

b-Increases the tone of the visceral muscle (especially pyloric, ileo-colic and anal sphincters). c-Increases segmenting contractions

d-Diminishes the truly propulsive movements.

e-Delays intestinal contents in the large bowel and allows an increased absorption of water

f-Inhibits the normal defecation reflex because the distended rectum no longer produces the usual discomfort.

4-In species with developed vomiting center, it stimulates then suppresses vomiting, and when vomiting occurs, it is not associated with the usual unpleasant emotional reactions, so that animals do not appear distressed.

5-Morphine also produces retention of urine, distension of the bladder

6-It affects respiratory system through the central nervous system and decreases respiratory activity (respiration becomes slow and deep), however the analgesic effect of morphine improves respiration when it is fast, shallow, and inefficient due to pleural pain or trauma, or when lungs are edematous, as in left ventricular failure.

7-Therapeutic doses have negligible effects upon the heart rate and blood pressure, but larger doses slow the heart by depressing conduction in the myocardium and stimulation of the vagal center.

References: Hall, C.W. and Clarke, K.W. (1983), Veterinary anesthesia, 8th edition; Hall, L.W. (1978), Wrights veterinaray anesthesia and analgesia, 7th edition