Large animal anaesthesia copy (3) pdf

VETERINARY
ANAESTHESIA
DR GYAN DEV SINGH
ASSISTANT PROFESSOR, BVC, BASU, PATNA-14

Introduction to anaesthesia
There are no safe anaesthetic agents; there are no safe
anaesthetic procedures; there are only safe anaesthetists
ROBERT SMITH
General consideration:
I. Anaesthesia and/or chemical restraint is a reversible
process; the purpose of anaesthesia is to produce a
convenient, safe, effective, yet inexpensive means of
chemical restraint so that medical or surgical
procedures may be expedited with minimal stress, pain,
discomfort and toxic side effects
II. criteria for selection of drugs and techniques
A. Species, breed, age and relative size of the patients
B. physical status and specific disease process of the
patient
c. concurrent medications,Demeanour of the patient and
severity of pain
E. personal knowledge and experience, availability and

Definitions
 Acupuncture: The stimulation of specific trigger points based on
traditional Chinese medicine
 Agonist: a drug that produces an effect by interacting with a
specific receptor site(e.g. opioid agonist)
 Akinesia: Loss of motor response (movement) usually caused by
blockade of motor nerves
 Allodynia: pain evoked by a stimulus that does not normally caused
pain
 Analgesia: loss of sensitivity to pain
 Anaesthesia: total loss of sensation in a body part or in the whole
body, generally induced by a drug or drugs that depress the activity
of nervous tissue either locally (peripherally) or generally (centrally).
 Phases of Anaesthesia:
I. preanaesthetic or preinduction period
II. Induction to anaesthesia
III. Maintenance
IV. Recovery
V. Post Anaesthetic period

Contd…..
 Local anaesthesia: Analgesia limited to a local area.
 Regional anaesthesia: Analgesia limited to a local area produced by
blocking sensory nerves
 General anaesthesia: loss of consciousness in addition to loss of
sensation: ideally includes Sedation, hyporeflexia, analgesia and
muscles relaxation (induced by single or combination of drugs).
 Surgical Anaesthesia: loss of consciousness and sensation
accompanied by sufficient muscle relaxation and analgesia to allow
surgery without pain or movement.
 Balanced Anaesthesia: produced by a combination of two or more
drugs or anaesthetic techniques, each contributing its own
pharmacologic effects like sedation, analgesia and muscles
relaxation.
 Dissociative anaesthesia: A CNS state charecterized by catalepsy,
analgsia and altered consciousness (Ketamine, Tiletamine).
 MAC: A term used to imply the minimum alveolar concentration of
inhalant anaesthetic required to prevent movement in response to a
noxious stimuli in 50% of anesthetized patients

Contd…..
 Antagonist: a drug that occupies a receptor site but produces
minimal or no effect (opiod anta gonist- naloxone)
 Catalepsy: state in which there is malleable rigidity of the limbs, the
patient is generally unresponsive to aural, visual or minor painful stimuli
 Central desensitization: An increase in the excitability and
responsiveness of nerves in the CNS particularly the spinal cord.
 Euthanasia: loss of consciousness and death without causing pain,
distress, anxiety or apprehension
 Hyperalgesia: an increased or exaggerated response to a stimulus that
is normally painful.
 Sedation: CNS depression in which the patient is awake but calm; a
termoften used interchangeably with tranquilization; with sufficient
stimuli the patient may be aroused
 Hypnosis: artificially induced sleep or a trance resemble sleep from
which the patient can be aroused from sufficient stimulus
 Narcosis: drug induced stupor or sedation with or without hypnosis
 Neuroleptanalgesia: hypnosis and analgesia produced by the
combination of a neuroleptic drug (i.e tranquilizer) and an analgesic
drugs

Contd….
 Tranquilization, ataraxia, neurolepsis: state of tranquillity and calmness in
which the patient is relaxed, reluctant to move, awake and
unconcerned with its surroundings and potentially indifferent to minor
pain.
CLINICAL JARGON:
Bag: ‘’The animal was bagged”. The rebreathing bag on the anaesthetic
machine was squeezed to inflate the animal’s lung during anaesthesia
Block: ‘’ the leg was blocked.” local anaesthesia was produced at a
specific site, locally or regionally.
Bolus: ‘’ A bolus of thiobarbiturate was administered.” a specific quantity of
drug was rapidly administered intravenously.
Breathed: ‘’ the animal was breathed six times a minute.’’ the lungs were
either manually or mechanically inflated.
Bucking: ‘’ the animal is bucking the ventilator.’’ the patient is resisting
being artificially (manually or mechanically) breathed. The patient breathes
out during inspiratory cycle or in during the expiratory cycle.
Crashed: ‘’ The animal crashed.’’ the patient demonstrated marked CNS
and cardiopulmonary depression after the administration of an anaesthetic
drug. The animal was crashed induced.

Contd…
Deep: ‘’ The animal is in deep stage of anaesthesia.”
Down: the animal was knocked down or put down.’’ (Euthanasia)
Dropped: ‘’ The animal was dropped.’’
Extubated: ‘’ The animal was extubated.’’ the endotracheal tube was
removed from he airways (opposite is intubated).
Preemptive: ‘’ The patient received preemptive analgesia.’’ the
deliberate administration of therapy before the event requiring therapy.
TIVA: Total intravenous anesthesia.
Topped-off: ‘’ The animal was topped off with a thiobarbiturate.’’ an
additional drug was administered to produce the desired effect.

Use of anaesthetics
I. Restraint
A. Diagnostic imaging (USG, radiography, MRI).
B. Cleaning, Grooming, Dental prophylaxis
C. Biopsy, radiation therapy, bandaging, splinting, cast application
D. Capture of exotic and wild animals
E. Transportation
F. Manipulation
1. Catheterization
2. Wound care
3. obstetrics
G. Assist or control Breathing
II. Anaesthesia: to facilitate or permit medical and/or surgical
procedures
III. Control of convulsions
IV: Euthanasia

Types of anaesthesia (according to route of
administration)
Acupuncture Infiltration* Intravenous*
Buccal Inhalation* Oral
Controlled Hypothermia Intramuscular* Rectal
Electroanaesthesia Intraosseous Subcutaneous
Epidural* Intraperitoneal Topical*
Spinal (subarachnoid) Intratesticular Transdermal*
Field Block Intrathoracic

Patient evaluation and preparation
General consideration
I. The preanesthetic evaluation history (history, physical condition and
physical examination) dictates the choice and dose of anaesthetic to
be used
II. The history and physical examination are the basis of patient evaluation
III. Laboratory tests are no substitute for a through physical examination
IV. A patient airway must be maintained in every patient
V. A patient intravenous route must be maintained for all risk patients
VI. Anticipate likely untoward events based on history and physical status
VII. An emergency cart with appropriate antidotes and antagonists should
be maintained.
Patient evaluation
I. Patient identification
A. CASE NUMBER OR IDENTIFICATION
B. SIGNALMENT
1. Species, breed, age, sex
C. BODY WEIGHT

Contd….
II. CLIENT COMPLAINT AND ANAMNESIS:
A. DURATION AND SEVERITY OF ILLNESS
B. CONCURRENT SYMTOMS OR DISEASE
1. DIARRHOEA, VOMITING, HAEMORRHAGE, SEIZURES, HEART FAILURE (COUGH,
EXERCISE INTOLERANCE), RENAL FAILURE
C. RECENT FEEDING
E. PREVIOUS AND CURRENT ADMINISTRATION OF DRUGS: ORGANOPHOSPHATES,
INSECTICIDES, ANTIBIOTICS(SULFONAMIDES, GENTAMICIN, AMIKACIN etc), digitalis
glycosides, beta-blockers, calcium channel blocker, diuretics, catecholamines
depleting drugs.
F. Anaesthetic history and reactions

Current physical examination
I. GENERAL BODY CONDITION: obesity, cachexia, pregnancy,
hydration, temperature, calm or excited, nervous or apprehensive.
II. Cardiovascular: heart rate and rhythm, arterial blood pressure,
pulse pressure quality and regularity, capillary refilling time(<1.5
second), auscultation (cardiac murmers).
III. Pulmonary: Respiratory rate, depth and effort (usually 15-25
breath/min for small animals and 8-20 for large animals), Tidal
volume (approximately 14 ml/kg), mucous membrane colour (pallor
in anemia or vasoconstriction), cyanosis (> 5g/dl of unoxygenated
hemoglobin), auscultation (breath sound), upper airway obstruction,
percussion
IV. Hepatic: jaundice, failure of blood to clot, comma, seizures
V. Renal: vomiting, oligouria/anuria, polyuria/polydipsia.
VI. GIT: Diarrhea, vomiting, distension, auscultation of intestinal sound,
rectal palpation.
VII. Nervous system and special senses: Aggression/depression,
seizures, fainting, coma.

Contd….
VIII. Metabolic and endocrine: temperature (hypothermia,
hyperthermia), hair loss, hyperthyroidism/hypothyroidism,
hyperadrenocorticism/hypoadrenocorticism, diabetes.
IX. Integument: Hydration, Neoplasia (pulmonary metastasis),
subcutaneous emphysema (fractured ribs), parasites (fleas, mites):
anemia, hairloss, burns (fluid and electrolyte loss), trauma.
X. Musculoskeletal: muscle mass (fat %), weakness, electrolyte
imbalance (hypokalemia, hyper kalemia, hypocalcemia), ambulatory or
non ambulatory, fractures
Presurgical laboratory workup:

Local anaesthetics
PRODUCE DESENSITIZATION AND ANALGESIA OF SKIN SURFACES (TOPICAL
ANAESTHESIA), TISSUES (INFILTRATION AND FIELD BLOCKS), REGIONAL
STRUCTURE (CONDUCTION ANAESTHESIA)
CLASSIFICATION:
1. ESTER LINKED DRUGS: A. COCAINE,
B. PROCAINE (NOVOCAINE): PROTOTYPE OF ALL LOCAL ANESTHETICS,
HYDROLYSED IN PLASMA BY PSEUDOCHOLINESTERASE, LESS POTENCY AND
SHORTER DURATION THAN MOST LOCAL ANESTHETICS BUT MINIMAL TOXICITY,
POOR ABSORPTION (NOT RECOMMENDED TOPICALLY).
C. TETRACAINE HYDROCHLORIDE (PENTOCAINE): 10-15 TIMES MORE POTENT
THAN PROCAINE, 1.5-2 TIMES LONGER DURATION THAN PROCAINE,
RELATIVELY TOXIC, PROLONGED ANESTHETIC EFFECT, USEFUL FOR TOPICAL
ANAESTHESIA.
D. BENZOCAINE/BUTAMBEN/TETRACAINE (CETACAINE): BENZOCAINE BLOCKS
SODIUM CHANNELS WITH PRESSURE CAUSED BY MEMBRANE EXPANSION, NOT
BY DIRECT INHIBITION OF THE CHANNEL, RAPID ONSET AND SHORT DURATION,
USE ON LARYNX OR PHARYNX MAY CAUSE METHEMOGLOBINEMIA,
METABOLIZED BY PLASMA CHOLINESTERASE, USED FOR SURFACE
ANAESTHESIA, LOCALIZED ALLERGIC REACTIONS MAY OCCUR

Contd…..
Amide linked drugs:
A. Lidocaine hydrochloride (xylocaine,
lignocaine,lidoderm): most stable drugs in this group, not
decomposed by boiling, acids or alkali, superior
penetration compared with procaine, spread over a
wider field
- Minimal tissue damage or irritation, no allergy or irritation,
mild sedative effects when given IV (Anaesthetic sparing),
antiarrhythmic, GI promotility effects, antishock effect but
potentially can induce hypotension when given IV in some
animals, metabolized in liver, can be infused IV continuously
with inhalation anesthesia to augment analgesia.

Contd..
B. Mepivacaine hydrochloride (carbocaine): similar to
lidocaine, no irritation or tissue damage, metabolized in liver,
avoided in pregnant animals.
C. Bupivacaine (marcaine): longer time of analgesic effects
than lidocaine, anesthesia longer than procaine (3-10
hours), may produce CNS and cardiac toxicity
TOPICAL ANASTHETICS: butacaine, tetracaine, piperocaine,
proparacaine (ophthane), benzocaine (cetacaine), EMLA
cream (lidocaine and prilocaine mixture).
NOTE: local anesthetic drugs are local and occasionally
systemic vasodilators except cocaine (vasoconstrictor).
Toxicity: seizures, hypotension, arrhythmia, apnea,
methemoglobinemia (benzocaine and prilocaine), allergic
reaction.

Ruminants: Local anaesthesia for standing laparotomy
I. PARALUMBAR FOSSA: FOUR TECHNIQUE
a. INFILTRATION ANAESTHESIA B. PROXIMAL PARAVERTEBRAL
ANAESTHESIA C. DISTAL PARAVERTEBRAL ANAESTHESIA D.
SEGMENTAL DORSOLUMBAR EPIDURAL ANAESTHESIA
INDICATION: RUMENOTOMY. CECOTOMY, CORRECTION OF
GASTROINTESTINAL DISPLACEMENT, INTESTINAL OBSTRUCTION,
VOLVULUS, CESERIAN SECTION, OVARIECTOMY, LIVER OR KIDNEY
BIOPSY.
a. INFILTRATION ANAESTHESIA: A. LINE BLOCK: ADVANTAGE IS EASIEST
TECHNIQUE, USE OF ROUTINELY SIZED NEEDLES (2.5 CM, 20 GUAGE OR
SMALLER FOR SKIN BLOCK; 7.6 TO 10.2 CM, 18 GUAGE FOR INFILTRATING
THE MUSCLES LAYERS AND PERITONEUM)
DISADVANTAGES: LARGE VOLUME OF ANAESTHETICS, LACK OF MUSCLE
RELAXATION, INCOMPLETE BLOCK OF DEEPER LAYERS OF ABDOMINAL
WALL, FORMATION OF HAEMATOMAS ALONG THE INCISION LINE,
INCREASED COST DUE TO LARGER AMOUNTS OF ANAESTHETIC USE AND
TIME REQUIRED.
COMPLICATIONS: TOXICITY IF 2% LODOCAINE (250 ML OR 5G) ADMINISTERED
INTRAPERITONEALLY TO 450 KG COW OR 10 ML (200MG) TO ADULT GOAT.

Inverted L block (flank caudal and ventral to site of injection)
Site: a line along the caudal border of
the last rib and along a line ventral to
the lumbar transverse processes from
the last rib to the fourth lumbar
vertebra
Method: inject drug into the tissues bordering the
dorsocaudal aspect of the last rib and ventrolateral aspect
of the lumbar transverse processes, creating a wall of
anaesthetic enclosing the incision.

Specific Nerve anaesthesia
Proximal paravertevral nerve block
Farquharson, Hall or
cambridge technique: dorsal
and ventral branch of T13, L1
AND L2. Analgesia of the
caudalmost part of the
paralumbar fossa for cesarean
section or ipsilateral fore teat
and mammary gland.
2.5-5.0 cm from
mid line
Palpate the lumbar tranverse process, starting from L5 and moving forward.
L1 may be difficult to feel, measure 5cm from midline, palpate the lumbar
dorsal processes, injection site is at 90 degree angle to the spaces between
the dorsal processess. Pass the needle vertically down untill hitting the
cranial edge of the transverse processess and proceed down through the
intertransverse ligament. Inject 10 -15 ml of 2% lidocaine below the ligament
to block the ventral branch of the nerve. Withdraw thw needle 1-1.5 cm
sufficiently to inject 5 ml of lidocaine above ligament, level with dorsal
surface of transverse process to block the dorsal branch.

Contd........advantage over nerve block
 Advantage: 1. anaesthesia of skin, musculature and perotoneum,
wide and uniform area of analgesia and muscle relaxation, no
additional restrain required.
2. Large quantities of local anaesthetics not required
Disadvantags: 1. produce difficult in fat cattle and some beef cattle
2. Arching of the spine caused by paralysis of back muscles
3. No anaesthesia of abdominal viscera
4. Bowing out toward the area of incision (after unilateral blockade),
making the closure of the incision more difficult
Complications: 1. possible penetration of the aorta
2. Possible penetration of the thoracic longitudinal vein (posterior) or
vena cava.
3. Loss of motor control of the pelvic limb caused by caudal migration of
drug (femoral nerve block).

Contd.....
Distal paravertevral nerve block
Dorsal and ventral rami of
T13, L1, AND L2 nerve is
blocked.
Magda, cakala or cornell technique: Insert the needle ventral to the tips of
the respective transverse process, inject anaesthetic (upto 20 ml) in a fan
shaped infiltration pattern, withdraw the needle a short distance, reinsert it
dorsal and caudal to the transverse process and inject approximately 5 ml of
the anaesthetic.

Advantages and disadvantages
Advantages: use of routinely sized needle, minimizes risk of penetrating a
major vessel, lack of scoliosis, minimal ataxia or weakness in the pelvic
limb.
Disadvantages: larger volume of anaesthetic is required, variations in
efficacy, particularly if the nerves follow a variable anatomic pathway.
Segmental dorsolumbar epidural block (Arthur block): insert the spinal
needle 8-12 cm ventral and cranial at an angle of 10-15 degrees from
vertical, piercing of the inter-arcuate ligament is felt as slight resistance
during the insertion process, no blood or cerebrospinal fluid can be
aspirated, and also no resistance to the injection of anaesthetic results
after correct needle placement.
Advantages: only one injection, small quantity of anaesthetic used, uniform
anaesthesia and relaxation of skin, musculature and peritoneum.
Disadvantages: difficult technique to perform, potential for trauma to the
spinal cord or venous sinuses.
Complications: loss of motor control of the pelvic limbs caused by overdose
or subarachnoid injection, potential for trauma to the spinal cord or
venous sinuses.

Contd......
Segmental dorsolumbar nerve
block
Skin area caudal
to the T13 or L1
spinal process
and flank on both
sides
8 ml of 2%
lidocaine in an
500 kg cow,
1ml/50 kg of 2%
lidocaine in
sheep and goat.
Site is epidural
space
between L1
and L2
vertebrae

Anaesthesia for obstetric procedures and rectal tenesmus
Co1-Co2 and S5-
Co1
Area blocked: anus, perineum, vulva
and vagina
Advantages: minimal effect on cardiovascular and respiratory systems, little
effect on organ systems, little problem with toxicity, good muscle relaxation,
good post-operative analgesia, rapid recovery, relatively simple,
inexpensive.
Disadvantages: technically difficult if Co1-Co2 interspace is not identified,
technically difficult if the sacrococcygeal interspace is ossified in older cows.

Internal Pudendal nerve block
Indication: analgesia and relaxation
of the penis for examination, relief
of tenesmus associated with
vaginal and uterine prolapse.
Nerve blocked: internal
pudendal(fibers of the ventral
branches of S3 and S4), caudal
rectal (fibers of the ventral
branches of S4 and S5), and pelvic
splachnic nerves.
Method: use rectal palpation to locate the lesser sciatic foramen, a soft,
circumscribed depression in the sacrosciatic ligament; find the nerve a finger’s
width dorsal to the pudendal artery present in the fossa; pass the needle through
the disinfected skin in the ischiorectal fossa; deposit up to 25 ml of 2% lidocaine
around the nerve; withdraw and direct the needle 2-3 cm caudodorsally and
inject another 10 ml of the anaesthetic in the area of the pelvic splachnic nerve;
repeat the procedure on the opposite side of the pelvis
Advantages: no loss of tail tone, no sciatic nerve involvement, ballooning of the
vagina may aid in retention of the vagina after it is repositioned in a cow with
prolapse.
disadvantages: technical difficulty and necessity of identifying the injection sites

Anterior epidural anaesthesia
Calves, sheep, goat & pigs: lumbosacral
space.
Cattle: sacrococcygeal or first
intercoccycegeal
Area blocked: perineal region, inguinal
region, flank and abdominal wall
caudal to the umbilicus.
Contraindication: severe cardiovascular disease, bleeding disorders,
shock or toxemic syndromes because of sympathetic block and resulting
depression of blood pressure.

Local anaesthesia for dehorning: Cornual branch of
zygomaticotemporal (lacrimal nerve) and a portion of the opthalmic division of
trigeminal nerve.
Area blocked: horn and base
of horn
B. Cornual branch of
infratrochlear nerve
Advantages: minimal systemic effects on CVS and relatively simple
procedure.
Diaadvantages: 1. cornual anaesthesia does not result if the anaesthetic is
injected too deeply in the aponeurosis of the temporal muscle
2. A second injection posterior to the horn may be required in adult cattle
with well developed horns.
3. Anaesthesia of a fractured horn involving the frontal bone or sinuses may
require a peterson eye block
Goat site: halfway between lateral canthus of eye and lateral base of the
horn (lacrimal nerve) and halfway between medial canthus of eye and
medial base of horn (cornual branch of infratrochlear nerve).

Local anaesthesia for eye
1. Auriculopalpebral branch of
facial nerve: akinesia of eye
2. Peterson technique: for
immobilization of eye globe
Area blocked: eye and orbit,
orbicularis oculi muscle except
the eye lids.
Nerves blocked: occulomotor,
trochlear and abducens nerves
and the three branches of the
trigeminal nerve (ophthalmic,
maxillary and mandibular).
Site: the points at which these nerves
emerge from foramen
orbitorotundum
Method: fully extend cow’s head in a standing position with frontal and nasal
bones parallel to the ground. Inject several mililiters of anaesthetic with a
small guage needle into the skin and subcutaneously into the notch formed
by the zygomatic and temporal process of the malar bone (where the supra
orbital process of the frontal bone meets the zygomatic arch). Place a 14
guage, 1.3 to 2.6 cm needle(to serve as a canula) through the skin as far
anterior and ventral as possible in the notch. Direct a straight, 18 guage, 12.7
cm needle with no suringe attached (to feel the bony landmarks) through the
canula in a horizontal and slightly posterior direction, untill it strikes the
coronoid process of the mandible.

Contd......
 Reposition the point of the needle anteriorly untill it passes medially around
this bone. Advance needle slightly posteriorly and somewhat ventrally untill it
strikes a solid bony plate, which is at e depth of between 7.6 to 10.2 cm.
Inject 15 ml of 2% lidocaine anterior to the foramen orbitorotundum
 Auriculopalpebral nerve block: fill a 10 ml syringe with local anaesthetic,
attach it to the needle and partially withdraw the canula, withdraw the
needle untill it almost leaves the skin and direct it posteriorly for 5-7.5 cm
lateral to the zygomatic arch while injecting lidocaine. If upper lid is involved
in the surgical procedure make a line of infiltration with local anaesthetic
subcutaneously approximately 2.5 cm from the margin of the lid.

Local anaesthesia of the foot: 3 methods
I. Infiltrating the tissues around the limb with local anaesthetic solution
(ring block).
II. Desensitizing specific nerves A. Brachial plexus block B. Epidural
anaesthesia
III. Injecting local anaesthetic solution into an accessible superficial vein in
an extremity isolated from circulation by placing a tourniqet on an
animal’s leg (intravenous regional anaesthesia).
A. Common dorsal metacarpal
vein
B. The radial vein
C. The planter metacarpal vein
D. The cranial branch of the
lateral saphenous vein

Teat and udder anaesthesia of cattle
Most surgical procedures on the
teat(e.g. Repair of a stenotic teat
sphincter, repairs of teat fistulae,
lacerations, and injuries) are
generally performed with the
animal under local anaesthesia.
Needle: 25-guage, 1.3 cm or teat
cannula.
Anaesthetic: 4-10 ml of 2%
lodocaine.
A. Inverted V block B. Teat ring
Block C. Tourniquet and canula
placement for teat cistern infusion.
Methods: 1. Inverted V block: line infusion of the anaesthetic using an
inverted V pattern, which encloses the teat skin defect
2. Ring Block: local anaesthetic infused into the skin and muscular tissue of
base of the teat, after through cleaning of the external surface of the teat
and quarter.
3. Teat infusion block: teat opening is cleaned, tourniquet is placed at the
base of the teat. 10 ml of 2% lidocaine is infused into the teat cistern.
Mucous membrane of the teat cistern is anaesthetized within 5 minutes: the
muscular and skin layers remain sensitive, thereafter the remaining lidocaine
is milked out and the tourniquet is removed.

REGIONAL ANAESTHESIA OF HEAD (HORSES)
The most frequently desensitized
nerves of the head:
A. SUPRAORBITAL(frontal)
B. AURICULOPALPEBRAL
C. INFRAORBITAL
D. MANDIBULAR ALVEOLAR
A. Anaesthesia of the upper eyelid and forehead (supraorbital or frontal
nerve)
AREA BLOCKED: upper eyelid except medial and lateral canthi. Site is
supraorbital foramen.
METHOD: Palpate the supraorbital foramen approximately 5 to 7 cm above
the medial canthus where it perforates the supraorbital process of the frontal
bone; insert the needle into the foramen to a depth of 1.5 to 2.0 cm; inject 2
ml of lidocaine into the foramen; 1ml as the needle is withdrawn and 2ml
sucutaneously over the foramen.

Akinesia of the eyelids (AURICULOPALPEBRAL)
AREA BLOCKED: Paralysis of orbicularis oculi muscles; no desensitization. Site is caudal
to posterior ramus of the mandible
METHOD: insert the needle into the depression caudal to the mandible at ventral
edge of the temporal part of the zygomatic arch; inject local anaesthetic
subfascially as the needle is withdrawn
USE: examination of the eye; successful blockade of the motor nerve supply prevents
the horse from closing the eyelids.
AKINESIA OF THE UPPER LIP AND NOSE (infraorbital foramen)
AREA BLOCKED: Upper lip and nostril, roof of nasal cavity and related skin upto the
infraorbital foramen. Site is external opening of the infraorbital canal.
METHOD: Halfway along the bony lip of the infraorbital foramen, about 2.5 cm dorsal
to a line connecting the nasomaxillary notch and the rostral end of the facial
crest; push the flat levator labii superoris muscle, which runs over the
foramen,upward with the fingertips and place the needle at the foramen
opening USE: simple lacerations in quiet or sedated horses.
Akinesia of lower Lip and Premolars: Area blocked is lower lip, all parts of
mandible rostral upto and including the third premolar tooth (Mandibuloalveolar
nerve block)
Method: palpate the lateral border of the mental foramen as a ridge along the
lateral aspect of the Ramus in the middle of the interdental space; insert the
needle into the foramen as far as possible in a ventromedial direction; injection
requires pressure, and fluid might partially drain back from the canal under the
skin

Regional anaesthesia of the limb
A. Palmer B. Abaxial sesamoidean c.
Low palmar D. High palmar
The palmar (volar) digital nerves of the fore limb or the plantar digital nerves
of the hind limb branch dorsal to the fetlock at the level of the sesamoids,
forming three digital nerves. A. Dorsal digital nerve supplies sensory fibres to
the anterior two thirds of the hoof B. Medial digital nerve (relatively
unimportant) C. The low palmar or plantar digital nerve, which is most
important clinically, supplies sensory fibres to the distal palmar or plantar
third of the hoof, including portions, if not all, of the navicular area.

Palmar (volar) or plantar digital nerve block
Area blocked: distal palmar or plantar third of the foot including the
navicular bursa.
Site: palmar (volar)/plantar region of the pastern joint
Method: palpate the palmar (volar) or plantar nerve just palmar/plantar to
the digital vein and artery, dorsal to the flexor tendon; insert the needle in
the palmar/plantar region of the pastern joint, medially and/or laterally
with the leg elevated or bearing weight.
Use: diagnosis of equine lameness
ABAXIAL (BASILAR) SESAMOIDEAN NERVE BLOCK:
Area blocked: entire foot distal to the injection site, including the back of
the pastern area and distal sesamoidean ligaments (anterior and
posterior digital nerves).
Site: palmar region of the fetlock joint over abaxial surface of proximal
sesamoid
Method: palpate the digital nerve in the palmar region of the fetlock joint
over the abaxial surface of proximal sesamoids, just palmar/plantar to the
digital artery and vein; insert the needle subcutaneously at this site

Low palmar (volar) or plantar nerve block
Area blocked: almost all structures distal to the fetlock and fetlock joint, except for a
small area dorsal to the fetlock joint supplied by sensory fibres of the ulnar and
musculocutaneous nerves.
Site: medially and laterally at the level of the distal enlargements of metacarpals II
and IV and metatarsals II and IV.
Method: A. location is just distal to the buttons of the splint bones.
B. Desensitize the palmar nerves (medial/lateral) by injecting the anaesthetic
between the flexor tendon and suspensory ligament.
C. Desensitize the palmar metacarpal and metatarsal nerves (medial/lateral) by
injecting the anaesthetic between the suspensory ligament and the splint bone
HIGH PALMAR (VOLAR) OR PLANTAR NERVE BLOCK
Area blocked: palmar (volar) metacarpal or plantar metatarsal region and all of the
digit distal to the fetlock. Site is proximal quarter of the metacarpus or metatarsus
proximal to the communicating branch of the medial and lateral palmar (volar) or
plantar nerves.
Method: desensitize the medial and lateral palmar and plantar nerves by injecting
anaesthetic subfascially into the groove between the suspensory ligament and
the deep flexor tendon on both the medial and lateral sides

Contd...........
Ulnar nerve block
Median nerve
block
Ulnar nerve block: area blocked is lateral or dorsal and palmar skin areas.
Site: 10 cm proximal to the accessory carpal bone
Method: the nerve is desinsitize 1.5 cm deep beneath the fascia between the
flexor carpi ulnaris and ulnaris lateralis muscles
Median nerve block: area blocked is lateral, medial, palmar and dorsal skin
areas.
Site: medial aspect of the forelimb 5cm ventral to the elbow joint
Method: the median nerve is desensitized between the posterior border of the
radius and the muscular belly of the internal flexor carpi radialis

Musculocutaneous nerve block
Musculocutaneous nerve block: area blocked is medial, palmar and
dorsal skin areas.
Site: anteromedial aspect of the forelimb halfway between the elbow
and carpus
Method: the musculocutaneous nerve is desensitized subcutaneously,
where it is easily palpated just cranial to the cephalic vein
Musculocu
taneous N.

Intraarticular injection
A. Podotrochlear(navic
ular bursa)
B. Coffin Joint
C. Pastern joint
D. Fetlock joint
E. Distal flexor tendon
sheath
A. Radial carpal joint
spaces
B. Inter carpal joint
spaces
A. Cunean bursa
B. The
tarsometatarsal
joint spaces
C. Intertarsal joint
spaces
D. Tibiotarsal joint
spaces

Premedication
Aims of premedication
 To reduce fear and calm the patient.
 To reduce distress during restraining and minor
manipulations like placement of catheters.
 To produce pre, intra and post operative analgesia.
 To reduce salivary secretion and airway secretion.
 To decrease the total quantity or amount of the
major anaesthetic drug.
 To reduce the deleterious side effects of the major
anaesthetic drug, To provide smooth induction.
 To reduce intra operative complications like
vomiting and regurgitation and To provide safe and
smooth recovery.

Classification of premedicaments
S.No. Premedicaments Examples
1. Anticholinergics Atropine sulphate, Glycopyrrolate
2. Transquilizers or neuroleptics
Phenothiazine derivatives
Butyrophenones
Benzodiazepines
Chlorpromazine, Acepromazine,
triflupromazine, promethazine
Droperidol, Azaperone
Diazepam, Midazolam,
Zolazepam, clonazepam
3. Sedatives
Alpha 2 adrenergic agonist
Chloral hydrate
Xylazine,
Detomidine,Medetomedine
Romifidine
4. Opioid agents
Agonists
Partial Agonists/Antagonists
Morphine, Meperidine
buprenorphine
.

CLINICAL PROPERTIES AND USES
 Contraindicated in ruminants ( salivary and bronchial
secretions will become more viscid, ruminal atony.
 Cause excessive salivation and bradycardia (e g. Xylazine).
 Preexciting bradycardia they increase the cardiac out put.
 Increase the heart rate by blocking vagal tone on S.A node.
The increase in heart rate is associated with increased
myocardial oxygen consumption, contraindicated in animals
with pre exciting tachycardia, heart failure and
cardomyopathies.
 Large dose of atropine may cause dilatation of cutaneous vessels
due to the effect on the cholinergic receptors of the vascular smooth
muscles (Atropine flush).
 Decrease glandular secretions, increase gastric PH, decrease
GI motility
 Bronchial dilation and mydriyasis ( due to the cholinergic
blockade of iris and ciliary body and paralyze
accommodation reflex (cycloplegia) resulting in photophobia
and blurred vision).

CONTD…..
 eye surgeries (prevent oculo-cardiac reflex).
 Relax the urinary tract smooth muscles(cause urinary
retention).
 Excessive dose of atropine and scopolamine may
induce hallucination, excitement and seizures and
this central stimulation is not noticed after
administration of glycopyrrolate, as it does not cross
the blood-brain barrier. Due to this property
glycopyrrolate is considered as a useful premedicant
in equine anaesthesia.
 Undesirable effects of atropine and glycopyrrolate
reversed with neostigmine or physostigmine

CLINICAL DOSES, ADVANTAGES AND
DISADVANTAGES(anticholinergic)
Species Atropine Glycopyrrolate
Horses 0.02 – 0.05 mg/kg S.C/I.M 0.02 mg/kg S.C/IM
Goats 0.20 mg/kg I.M 0.01 mg/kg I.M
Pigs 0.3—1.8 mg total dose
Dogs
0.02—0.05 mg/kg S.C/I.M 0.01—0.02 mg/kg S.C/I.M/I.V
0.02 – 0.02 mg/kg I.V
Cats
0.02 – 0.1 mg/kg S.C/I.V 0.02—0.02 mg/kg S.C/I.M./I.V
0.01 – 0.02 mg/kg I.V
Atropine: advantages: less expensive, tachycardia is not extreme,
indicated in animals required quick response for bradycardia.
DISADVANTAGES: may induce variety of arrhythmia if myocardial oxygen
demand is less. I/V use for caeserian section is contraindicated in bitches
(induces bradycardia initially due to stimulation of vagal nuclei in the
medulla)
Glycopyrrolate: Advantages: less dose (0.44 mg atropine =0.11 mg of
glycopyrolate), controls bradycardia effectively, indicated in caeserian
section as it does not cross the placental barrier and causes excessive
increase in the heart rate of neonates, effectively controls gastric acidic
PH and avoids aspiration of gastric acid secretion, less intestinal stasis (

Phenothiazine derivatives
 Phenothiazine derivatives are three ring structures in
which two benzene rings are linked by a sulphur and
nitrogen atom.
 Structurally phenothiazine derivatives is similar to
epinephrine, norepinephrine and dopamine.
 Act on the CNS by depressing the brain stem and
connections of the cerebral cortex.
 Increase the dopamine and norepinephrine turn over in
the brain and block the peripheral actions of
catecholamines at alpha 1 receptors, weak
anticholinergics and have extrapyramidal stimulating
properties.
 Acepromazine maleate, triflupromazine hydrochloride,
chlorpromazine, promazine, promethazine and
methotrimeprazine commonly used phenothiazines.
acepromazine, triflupromazine and chlorpromazine are
used in veterinary anaesthesia

CLINICAL DOSES
Drug Dose
Acepromazine Dogs = 0.03 – 0.05 mg/kg I.V, 0.03 – 0.05 mg/kg I.M.
Cats = 0.03 – 0.05 mg/kg I.V, 0.03 – 0.1 mg/kg I.M.
Horses = 0.02 – 0.05 mg/kg I.V, 0.04 – 0.09 mg/kg I.M.
Cattle = 0.02 – 0.05 mg/kg i.V, 0.04 – 0.09 mg/kg I.M.
Pigs = 0.1 mg/kg I.M.
Chlorpromazine Dogs = 0.55 – 4.4 mg/kg I.V, 1.1 – 6.6 mg/kg I.M.
Cats = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M
Horses = 1.1 – 2.2 mg/kg I.M.
Cattle = 0.2 – 1.1 mg/kg I.V, 0.2 – 2.2 mg/kg I.M.
Sheep = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M.
Goats = 0.55 – 4.4 mg/kg I.V, 2.2 – 6.6 mg/kg I.M.
Pigs = 1.0 – 2.0 mg/kg I.M.
Promazine Horses = 0.44 – 1.1 mg/kg I.V/I.M.
Cattle = 0.44 – 1.1 mg/kg I.V/I.M.
Goats = 0.44 – 1.1 mg/kg I.V/I.M.
Sheep = 0.44 – 1.1 mg/kg I.V/I.M.
Pigs = 0.44 – 1.1 mg/kg I.V, 0.44 – 4.0 mg/kg I.M.
Triflupromazine Dogs = 1.00 mg/kg

CLINICAL PROPERTIES AND USES
 Sedation, general calming and reduction in motor activity,
Antagonize dopamine excitatory chemoceptors and suppress
vomiting.
 High doses and some times in clinical doses induce extrapyramidal
signs such as rigidity, tremors and catalepsy. Hence contraindicated
in patients with the previous history of epilepsy, Undergoing
myelographic procedures, With the history of recent intake of
organophophorus drugs or toxicity.
 Slight depression in respiratory rate, suppression of antidiuretic
hormone(induce urine production)
 Animals undergoing intradermal allergic tests should not be
administered with phenothiazines as they are potent antihistaminics.
 Contraindicated in animals undergoing epidural, spinal or segmental
anaesthesia. Following induction of regional anaesthesia there will be
vasodilation in the anaesthestised part of the body and this effect is
compensated by the vasoconstriction in the un-anaesthetized parts
of the body to maintain cardiac out put.

BUTYROPHENONES (Droperidol, fluanisone, azaperone and lenperone)
 Similar properties like phenothiazines, block the central actions of
dopamine and norepinephrine.
 Produce extrapyramidal signs like tremors, rigidity and catalepsy in
clinical doses hence not popular.
 Potent antiemetics and even prevent drug induced
vomiting produced by opioid analgesics by acting on
the chemo-emetic trigger zone( neurolept-analgesics in
anaesthetic regimen).
 Less cardiac depressive effects and the hypotension
produced by the agents can easily be reversed with
phenylephrine, minimal changes in respiratory
parameters.

DRUGS AND DOSES
 Droperidol: combination with an opioid analgesic, fentanyl citrate.
(0.4 mg of fentanyl citrate and 20 mg of droperidol per ml = Innovar
vet), profound analgesia for 30 minutes and sedation for a
considerable time in dogs (neuro-leptanalgesia: combination of a
tranquilizer or sedative and analgesic drugs).
 In cats it may induce undesirable central nervous system
stimulation.
 Other effects noticed after administration are panting, aggression
upto 48 hours after recovery, defecation and salivation. Naloxone
- 0.04 mg/kg mixed with 4- aminopyridine - 0.5 mg/kg intravenously
reverse the side effects of droperidol-fentanyl combination.
Clinical dose
 Dogs 0.05 – 0.1 mg/kg I.M
 Cats 0.10 – 0.11 mg/kg S.C
 Pigs 0.10 – 0.4 mg/kg I.M

CONTD…..
Azaperone: widely used in pigs for control and transportation. In
pigs it is administered prior to metomidate. (not used in
equine)Clinical dose - Pigs = 0.4 – 1.2 mg/kg I.M (low dose),2.0
mg/kg I.M (medium dose), 4.0 mg/kg I.M (high dose)
Fluanisone: combination with fentanyl citrate. (0.315 mg of
fentanyl and 10 mg of fluanisone = Hypnorm).
contraindicated in patients with respiratory, renal and
hepatic diseases.
Naloxone is the reversal agent for this combination.
 Clinical dose - Dogs = 5 mg/kg along with 0.1 mg/kg of
fentanyl citrate (neuroleptanalgesia)

Precautions: phenothiazines, butyrophenones (important)
 Hypotension
 Hypothermia
 Inhibit platelets aggregation
 Not analgesics
 Phenothiazines may lower seizures threshold in animals
with epilepsy
 Excessive doses of phenothiazines or butyrophenones can
cause apparent involuntary musculoskeletal effects and
hallucinatory activity, particularly in horses.
 Occasional bradycardia (e.g. Boxer dogs).
 Long duration of action (e.g. intrahepatic and
extrahepatic shunts)

BENZODIAZEPINES(GABA receptor) Diazepam, midazolam,
climazolam and zolazepam
 NO analgesic property, good anxiolytics, hypnotics and anticovulsants, minimal
respiratory and cardiovascular depression, muscle relaxation.
 DIAZEPAM: To treat status epilepticus in dogs, cats and human.
 In horses produces excitation if used as a sole sedative premedicant hence
combined with xylazine.
 It decreases the release of catecholamines and act as anti-dysrhythmic agent.
 Appetite stimulant in dogs and cats at the dose of 0.05 – 0.40 mg/kg Oral/I.M.
 Storage in plastic syringes, infusion bags and infusion tubes are not advisable.
 Rapid intravenous injection may cause thrombosis.
 Dogs 0.1 – 0.5 mg/kg I.V, 0.3 – 0.5 mg/kg I.M.
 Cats 0.05 – 0.4 mg/kg I.V, 0.3 – 1.0 mg/kg I.M.
 Horses 0.02 – 0.04 mg/kg I.V
 Foals 0.1 – 0.2 mg/kg I.V
 Cattle 0.1 mg/kg I.V
 Goat 0.1 – 0.1 mg/kg I.V
 Pigs 1.0 mg/kg I.V

Contd…
 Midazolam: twice as potent as diazepam, as premedicant to
thiopentone, ketamine and propofol anaesthesia, metabolized in the
liver rapidly hence less cumulative can be stored in aquous solution
in plastic container upto 100 hours without loss of potency.
 Dose - Dogs & cats = 0.07 – 0.22 mg/kg I.M/I.V
 Climazolam: potent benzodiazepine, In horses the
drug is combined with other premedicants and
anaesthetics as it may produce excitement and
muscle weakness.
 Dogs = 1.0 – 1.5 mg/kg in combination with 5.15 mg/kg of fentanyl I.V
 Horses 0.05 – 0.2 mg/kg I.V
 Cattle 0.5 – 1.1 mg/kg I.M
 Sheep & goats 0.5 – 1.1 mg/kg I.M
 Pigs 0.5 – 1.0 mg/kg I.M
 Chicken 5.5 – 11.0 mg/kg I.M

ZOLAZEPAM AND FLUMAZENIL
Zolazepam: It is marketed in combination with dissociative
drugs like tiletamine (250 mgs of tiletamine and 250 mgs of
zolazepam in lyophilized form). For dose calculation the two
drugs are considered as one product (500 mg).
Dogs 6.6 - 9.9 mg/kg I.M, 2.0 - 43 mg/kg I.V and Cats 6.0 -
11.9 mg/kg.I.M.
Flumazenil: The actions of all benzodiazepines can be
reversed or antagonized with flumazenil at the dose of 0.1
mg/kg I.V.

Important facts about benzodiazepines
 Enhance the activity of CNS inhibitory neurotransmitters:
GABA, glycine, combine with CNS benzodiazepines
receptors
 Muscle relaxation
 Anticonvulsants effects
 Mild calming effect: may produce apprehension and
nervousness in dogs and cats.
 Minimal cardiopulmonary effects in dogs, cats and horses
 Stimulate appetite and produce pica
 Midazolam and zolazepam are wter soluble
 Antagonized by flumazenil
 May cause disorientation and agitation, particularly in
cats.
 Diazepam painful if administered IM.

ALPHA 2 ADRENERGIC AGONIST sedative analgesics
 xylazine hydrochloride, detomidine, medetomidine and
romifidine.
 Xylazine: dose-related depression of the central nervous system.
analgesic activity is 15 – 30 minutes and the sedation is for 1-2 hours.
 One tenth of the dose used in horses and dogs induce sedation and
recumbency in cattle.
 In horses it is a reliable sedative and the horse will be in standing
position in clinical doses. Drooping of head and buckling of hind
limbs are commonly noticed in horses.
 The clinical dose through intravenous route is 1.1 mg/kg. Further increase
in the dose will not increase the intensity of sedation, only the duration
will be increased.
 Emesis is common in dogs & cats ( stimulation of central emetic
center).
 Produces muscle relaxation, which is attributed to decrease in
intraneural and synaptic transmission in the central nervous system.

Contd….xylazine
 Used in the treatment of equine colic for pain relief. But it may mask the
clinical signs and may aggravate ileus.
 Xylazine induce profound Bradycardia (reversed with atropine),
decreased cardiac out put, hypotension and increase in central venous
pressure are noticed, A.V block, transient increase in blood pressure (I/V).
 Contraindicated in brachycephalic breeds, older dogs and in intestinal
obstruction.
 Increases the sensitivity of myocardium to the circulating
catecholamines hence cardiac dysrhythmias with halothane.
 In ruminants it reduces the gastrointestinal and ruminal motility with
relaxation of cardia oesophageal sphincter. This favours ruminal tympany
and regurgitation.
 Oxytocic property and increase the intrauterine pressure (induce
abortion). Increase in intrauterine pressure may cause embryo/ovum
ejection if administered in embryo/ovum transplantation.
 Thermoregulation is depressed following xylazine administration and
the animal may become hypothermic or hyperthermic depending on
the ambient temperature.

Contd…..
 Xylazine is used as epidural anaesthetic ( alpha receptors
in the spinal cord and structural similarity with lidocaine).
 Excessive urine production ( suppression of antidiuretic
hormone), Salivation,Hyperglycemia
 Dose: Horse 1.1 mg/kg I.V/IM
 Dogs & cats 0.2 --- 1.1 mg/kg I.V/I.M/.S.C
 Cattle, sheep & goats
 0.05 – 0.08 mg/kg I.M. standing restraint
 0.1 – 0.3 mg/kg I.M. recumbency and prolonged
 0.1 – 0.2 mg/kg I.V recumbency
 Pigs
 1.0 – 2.0 mg/kg I.V
 Upto 4.0 mg/kg I.M.
 Epidural 0.07 – 0.17 mg/kg in 5.0 to 10.0 ml of saline

Other agents
Detomidine (horses and cattle):
 Advantages of these drugs: Does not stimulate pituitary
adrenocortical axis hence stress is less, Can be administered in
pregnant animals, Can be administered in animals which are not
fasted, very effective in relieving pain from colic in horses.
 Provides standing restrain in cattle at the dose of 10 to 20 µg/kg I.V.
Horse, Cattle, Sheep & Goats 10 - 40 µg/kg I.V
 Medetomidine: Dogs 0.01 - 0.04 mg/kg I.V/I.M/S.C, Cats 0.04 - 0.08
mg/kg I.V/I.M/S.C, Cattle 0.01 - 0.02 mg/kg I.V
 Romifidine (Sedivet). It is developed from clonidine and has
alpha 2 adrenergic agonistic action. Used in horses and maximum
sedation is achieved at the dose of 80 µg/kg I.V

IMPORTANT FACTS ABOUT ALPHA-2 AGONISTS
 Pronounced sedation, muscle relaxation and analgesia.
 Can be used for epidural or subarachnoid analgesia
 Antagonized by yohimbine, tolazoline, and atipamezole
 Sinus bradycardia, first or second degree AV-block
 Xylazine may transiently increase cardiac sensitivity to
catecholamine-induced arrhythmias (ventricular arrhythmias) in
dogs
 Decrease cardiac output (and tissue perfusion), increase
peripheral vascular resistance
 Ileus and bloat in dogs; colic in horses.
 Pale mucous membrane caused by vasoconstriction
 Respiratory depression and ataxia
 Cause vomiting in dogs and cats.
 Suppress insulin release
 Oxytocin like effects in ruminants

Reversal of alpha-2 antagonists
Yohimbine hydrochloride: Specific reversal agent for xylazine
and detomidine ( 0.1 mg/kg I.V). Often combined with 4-
aminopyridine (0.04 mg/kg) for better results. Used in the
treatment of equine colic due to ileus and reverses the
gastrointestinal stasis produced by xylazine.
Atipamezole: Used to reverse the effects of medetomidine
( 0.04 – 0.5 mg/kg I.V).
Doxapram: It is not a specific reversal agent to alpha 2
adrenergic agonists but offer certain beneficial effects due
to its central nervous system stimulation and respiratory
stimulation

Opioids:
 Acts by reversible combination with specific receptors (µ, ₭,
delta).
Classification: pure agonists: binds to one or more types of
receptor and causes certain effects (e.g. morphine).
Agonists-antagonists: cause less pronounced effects than that of
a pure agonists (e.g. butorphanol, pentazocine)
Partial agonists: binds to more than one ype of receptor and
causes an effect at one but no effect or a less pronounced effect
at another (e.g. buprenorphine)
Antagonists: binds to one or more types of receptor but causes no
effect at those receptors. By competitively displacing an agonist
from a receptor, the anta gonists effectively reverses the agonist’s
effect (naloxone).
Analgesic potency:
fentanyl>remifentanil>buprenorphine>oxymorphone>hydromorph
one>butorphanol>morphine=methadone>meperidine

Important facts about opioids
 Produce analgesia without loss of proprioception or
consciousness.
 Produce excellent sedation in dogs, but excitement occurs in
some species, especially in cats and horses
 Metabolized by liver and eliminated in the urine
Cautions:
1. Morphine and meperidine IV can produce histamine release
2. Bradycardia, hypotension.
3. Dose dependent respiratory depression
4. Vomiting, salivation, nonpropulsive GI hypermotility (ropy gut),
increases in sphincter tone.
5. Defecation
6. Increase ADH release.
7. Tolerance can occur

Injectable anaesthetic drugs
General consideration: Dose: on the basis of lean body mass
I. Increasing intensities of CNS depression
II. Factors that can determine rate of onset, amount of depression, and
duration of anaesthesia are potency of anesthetic drug, dose, rate of
drug administration when administered IV and route of administration,
drug pharmacokinetics and protein binding (barbiturates), animals level
of consciousness, acid base and electrolyte balance (acidosis
enhances barbiturate anesthesia), animals cardiac out put and drug
tolerance.
III. Almost all injectable anesthetic drugs shows unconconsciousness by
CNS Depression (barbiturates and propofol for seizure control) and
barbiturates also used for strychnine poisoning clinically by depressing
spinal reflexes.
IV. Routes of administration: dissociatives and neurosteroids (IM OR IV),
Barbiturates (IV only due to alkaline nature: if administered
subcutaneous or IM it causes sloughing of skin that is known as
barbiturate slough),
 Intralipid diluent for propofol supports bacterial growth and can
interfere with some biochemical tests
 Ketamine formulations having pH in between 3.5-5.6 (avoid IM
administration), etomidate causes perivascular irritation and hemolysis
due to high osmolality.

Barbiturates
 Short and ultrashort acting barbiturates are used for anesthesia
 Long or intermediate acting barbiturates are used as anticonvulsants
 CNS depression due to interaction with GABA A receptor and poor
analgesics.
 Respiratory depression and apnoea, coughing, sneezing, hiccoughing
and laryngospasm (cat), cardiovascular depression (transient
hypotension). Thiobarbiturates increase both parasympathetic and
sympathetic tone lead to atrial and ventricular arrhythmia, first and
second degree heart block.
 Tissue toxicity when greater than 2.5% IV is administered, intraarterial
injection may cause severe pain, vasoconstriction and tissue necrosis
 Minimal effects on liver or kidney function at anesthetic doses
 Methohexital can cause excitement and myoclonus during induction
and recovery from anesthesia.
 Barbiturates contraindicated in pregnant animals because it readily
diffuses across the placental barrier and causes respiratory depression
of fetus (45 sec).
 Drug concentration in muscles and skin peak approximately 15-30
minutes and drug concentration in fat peak after several hours
(repeated dose- have cumulative effect)

Contd……
 Extremely thin, heavily muscled animals demonstrate prolonged
recovery (3-5 hours) from thiopental.
 Obesity delay drug elimination because of high lipid solubilty of
barbiturates.
 Barbiturates excretion occurs by oxidative activity of hepatic
enzymes and by renal excretion.
 Nonionized and nonprotein bound barbiturates concentration
increases by acidosis and low plasma protein and alkali
administration potentiate drug elimination.
 Dose: pentobarbital: 10-50 mg/kg body weight and thiopental
sodium 3-12 mg/kg body wt IV. Methohexital: 6-10 mg/kg in small
animals, 6mg/kg in horses and adult cattle, 3-5 mg/kg in calves.
NOTE: duration of anaesthesia can be prolonged by administration of
50% glucose IV (glucose effect).
methohexital is used in grey hound and whippet because it has short
duration of action and it also has less cumulative effect and readily
metabolized.

Nonbarbiturates anesthetic drugs
I. Etomidate:
1. Rapid acting, ultra-short acting, imidazole compound, non-cumulative
2. Produces hypnosis by binding to GABAA Receptors, primary site of action is
RAS, Myoclonus (by enhancing monosynaptic reflex activity).
3. Not a good analgesic at subhypnotic doses, crosses the placenta but effects are
minimal (due to its rapid clearance)
4. Produces adequate muscles relaxation and not used in equine and food animals
(expensive).
5. Regurgitation and vomiting
6. Pain on IV injection (dose: 0.5-3 mg/kg IV in dogs and cats)
7. Transient (>3 hr) adrenocortical suppression in dogs and cats

Contd…..
I. Propofol: Rapid active, ultrashort, nonbarbiturate, noncumulative IV anaesthetic.
1. Produces sedation-hypnosis similar to other hypnotics by binding to GABA
receptors and acting as a sodium channel blocker.
2. Dose dependent depression of the cerebral cortex and CNS polysynaptic reflexes,
may enhance the effects of non-depolarizing neuromuscular blocking drugs.
3. Minimal analgesia at subhypnotic doses and produces anticonvulsant and
antiemetic effects, minimal drug carry over effects.
4. Solubilized in a lecithin containing emulsion (10% soyabean oil and 1.2% lecithin).
5. Nanodroplet formulations and specialized solubilizing diluents (2-hydroxyl β-
dextrin HPCD) are being investigated for clinical use to limit storage and bacterial
growth issues with intralipid.
6. Dose dependent respiratory depression and initial periods of apnea, dose dependent
decreases in arterial BP transiently caused by decreases in cardiac output and
systemic vascular resistance.
7. Crosses the placenta and can induce dose dependent fetal depression
8. Short duration of action are due to the drug’s large volume of distribution, which
allows redistribution from the brain to muscle and fat, rapid clearing from the body
by hepatic and extrahepatic metabolism compared with thiobarbiturates.
9. Produces good to excellent muscle relaxation
10. May induce oxidative injury to feline RBCs resulting in hemolysis (Heinz body

Contd….
Dose of propofol: 2-8 mg/kg IV in dogs and cats for induction, 0.2-0.6
mg/kg/min IV for dog and cats (maintenance).
Alphaxalone: Rapid, short acting, nonbarbiturates steroids anesthetic,
complexed with HPCD (previously solubilized in polyethoxylated castor oil
causing histamine release).
1. Crosses the placenta and can induce fetal depression (dose
dependent), rapidly metabolized by liver, some metabolites are
eliminated in urine.
2. Nonlinear pharmacokinetics in cats suggesting that drug effect and
persistence of effects are not predictable at different doses
3. Minimal analgesia at subhypnotic doses, good to excellent muscles
relaxation.
4. Rapid and uneventful onset and recovery from anesthesia in dogs and
cats.
5. Relatively noncumulative, excellent for induction to anesthesia and short
term medical or surgical procedures, minimal drug carry over effects.
6. Dose and rate of administration rate dependent respiratory depression
7. Hypotension and animals may become hyporesponsive to sound during
recovery.
Dose: 2-5 mg/kg (induction IV), repeated dose 2mg/kg (maintenance IV),
0.07-0.1 mg/kg/min or 4-7mg/kg/hr IV for maintenance. 12-15mg/kg IM

Guaifensin (glyceryl guaiacolate ether):
 white, finely granular powder, soluble in water, decongestant and antitussive and
a centrally acting muscle relaxant.
 Blocks impulse transmission at internuncial (inter) neurons of the spinal cord and
brainstem; centrally acting muscle relaxant, produces minimal sedation and
analgesia.
 Produces skeletal muscle relaxation but minimal effects on respiration at relaxant
doses, relaxes laryngeal and pharyngeal muscles, facilitating intubation of the
trachea.
 Respiratory rate may increase initially, tidal volume decreases, excessive dose
produces apneustic pattern of breathing
 Crosses placental barrier but does not produce significant respiratory depression
in the foetus. Excreted in urine after conjugation in the liver to glucuronide.
 Used in combination with thiobarbiturates and ketamine for anaesthetic
procedure upto 60 minutes. Dissolve in water or 5% dextrose as 5 % to 10%
solution.
 High concentration (>6%) may cause hemolysis and hemoglobinuria in cattle,
greater than 15% causes hives in horses and cattle.
 Dose varies from 50-100 mg/kg IV. Ketamine (500 mg) and xylazine (250 mg)

CHLORAL HYDRATE
 Used as a reliable sedative hypnotic in cattle and horses, less
expensive and still perfectly acceptable sedative agent, aromatic
odour and is bitter in taste. CNS depression is due to its metabolic
product namely 2,2,2 trichloro ethanol, hence the sedative effect is
prolonged even after cessation of administration, no analgesia.
 Trichloro ethanol combined with glucuronic acid and excreted as
urochloralic acid.
 Chloral hydrate depresses the motor and sensory responses at
sedative dose and produces cerebral and medullary center
depression at anaesthetic dose resulting in muscle relaxation and
depression of cardiac and respiratory system.
 In cattle it can be drenched preferably through stomach tube, at the
dose of 30 to 120 grams dissolved as 1 in 20 solution in water.
 Bullls can be controlled by water deprivation for brief period
and allowing them to drink chloral hydrate dissolved water (90
to 120 grams in 12 litres of water).
 Chloral hydrate is administered as 10% solution intravenously in
cattle at the dose of 80 to 90 mg/kg.

Contd…
 Chloral hydrate combined with magnesium sulphate at 2:1 or 3:1
ratio (weight) and administered in cattle.
 It is combined with magnesium sulphate and pentobarbital and
administered to horses (Equithesin mixture).
Disadvantages of chloral hydrate: Prolonged hangover
with ataxia and stupor, Perivascular administration causes pain, swelling
and necrosis, Induces abortion in mares
 Chloral hydrate alone 5 to 10 mg/kg for mild sedation and hypnosis,
20 to 40 mg/kg for moderate sedation and hypnosis, 50 to 75 mg/kg
for profound sedation and hypnosis and 150 to 250 mg/kg for
anaesthesia

DISSOCIATIVE ANAESTHESIA
1. Noncompetitive NMDA receptor antagonists
2. Profound amnesia, superficial analgesia (lack of visceral pain)
catatonia and catalepsy, Involuntary spontaneous movements,
Persistence of reflexes like swallowing, pharyngeal palpebral and
corneal, Large dose may induce convulsions, Lack of muscle
relaxation, salivation and lacrimation are common and may
become copious. Swallowing may take it difficult to place an
endotracheal tube.
3. Some animals develop hyperreflexia and hyperresponsiveness to
physical stimulation and sound. Ataxia following recovery from
anesthesia may persist for hours and “emergence delirium” may
develop.
4. Ketamine increases CBF and causes no change or an increase in
CMRO2 ratio increases, arterial BP and intracranial pressure increase,
cerebral perfusion pressure decreases.

contd
5. Resp rate may be increased, apneustic pattern of breathing, arterial PO2
generally falls after IV administration, possible increase in PCO2 and decrease in
arterial Ph (irregular pattern of breathing)
6. Increased HR, increased BP, increase in heart rate and myocardial oxygen
requirement and decrease in cardiac contractility may induce pulmonary
oedema or acute heart failure with pre-existing cardiac disease
7. Ketamine (by liver) via N-methylation to norketamine (active metabolite).
8. Telazol: A 1:1 drug combination of zolazepam and tiletamine (50mg/ml of
each)
Dose: IM, IV, SC, buccally, rectally and nasally.
IV dose: 1-5 mg/kg but may use 10 mg/kg or larger in non domesticated or
exotic species. IM: 5-20 mg/kg
Dose of Telazol: dogs, cats, cattle, sheep, goats: 2-5mg/kg IV and 1-8mg/kg IM.
Horses: xylazine 1mg/kg followed by 1-1.5/kg telazol IV. Telazol powder can be
solubilized using detomidine (1ml) and ketamine (4 ml of 100mg/ml). The resulting
solution is administered to achieve sedation in horses (xylazine, 0.6 mg/kg, IV) at
dose of 0.007 ml/kg IV (1ml/150 kg). Duration: 30 minutes.
Pigs: 500 mg of telazol powder with 2.5 ml of xylazine (100 mg/ml) and 2.5 ml of
ketamine (100 mg/ml); administer 1-2ml/50 kg IM

Inhalant anaesthesia
Nitrous oxide: Oldest anaesthetic gas available as liquid at room
temperature in cylinders (See anaesthetic equipment). MAC is
more than 100% in animals (Dogs 188%, Cats 255%).
 good analgesic property and combining narcotics, which
interact selectively with opiate receptor endorphin system,
potentiates the analgesia.
 It helps in additional uptake of the inhalant agent and
potentiate the desirable effects at a minimal concentration of
the inhalant agent (Second gas effect).
 Eliminated rapidly from the body because (low partition
coefficient).
 diffuses into the closed cavities filled with gas such as
pneumothorax and distended intestinal loops due to
obstruction or strangulation.
 Diffuse into the rumen and In horses prolonged administration
induce distension of bowels and increase in
transdiaphragmatic pressure.

Contd….
 Prolonged exposure causes bone marrow depression
(depletion of Vit.B12). Administered at 66 to 70% of the total
inspired air. Oxygen is given at 30% concentration
DIETHYL ETHER: It is a colourless, highly volatile and inflammable
liquid with a boiling point 35oC. MAC is 1.92%.
 It gives an irritating vapour and may cause salivation, In low
concentration the vagal activity is decreased and at higher
concentration it induce arrhythmia.
 Catecholamine level increases following ether administration.
METHOXYFLURANE: It does not alter the cardiac function much
except slight hypotension, which is associated with reduction in
cardiac contractility, and cardiac out put.
 Concurrent use of epinephrine and adrenaline are
contraindicated as methoxyflurane sensitizes the myocardium
to the actions of catecholamines. Compared to halothane the
sensitization and cardiac arrhythmia are less.
 Methoxyflurane reduce the minute volume and induces
respiratory acidosis.

Contd……methoxyflurane
 It does not alter the cardiac function much except slight
hypotension, which is associated with reduction in
cardiac contractility, and cardiac out put.
 Methoxyflurane sensitizes the myocardium to the actions
of catecholamines (less than halothane).
 Reduce the minute volume and induces respiratory
acidosis.
 Soluble in fat (prolong recovery in obese patients).
 Methoxyflurane is contraindicated in patients with renal
disease (release of fluoride ions as by product and further
aggravated by the concurrent use of tetracycline).
 Use is restricted to small animals.

HALOTHANE
 The MAC is reduced when combined with agents like
morphine (reduced 84%), alfentanil (48%), xylazine and
nitrous oxide.
 Halothane reduces cerebrospinal fluid production and
pressure (brain and spinal cord surgeries and patients with
increased intracranial pressure).
 It suppress adrenal cortical hormone release by 50% due
to its action and inhibition on the carrier - mediated
transport system of choline.
 Halothane depress cardiac out put,mean arterial pressure
and coronary blood flow. Decreases arrhythmogenic
thresholds and sensitizes the myocardium for the actions
of catecholamines.
 Exogenous administration of epinephrine or adrenaline
induces cardiac arrhythmia and ventricular stand still.

Contd……
 It induces AV shunts (arterio-venous shunts) and is further
aggrevated by hypoxia. (21 to 22%) thus resulting in
ventilation perfusion mismatch. Oxygen exchange is
further reduced in patients with pulmonary diseases.
 The minute volume decreases during halothane
anaesthesia due to the decreased contractility of
inspiratory muscles.
 Halothane induces hepatic hypoxia. In ponics following
halothane anaesthesia 138% increase in plasma bilirubin
excretion, 16% reduction in plasma bilirubin and 46%
reduction in biliary bile acid concentration. Centrilobular
necrosis is the toxic manifestation induced by halothane
in liver. The incidences of hepatic necrosis are higher in
goats following halothane anaesthesia

Contd….
 Halothane undergoes biotransformation in the liver. The
metabolic products or the intermediary products induce
allergic and toxic responses similar to autoimmune
diseases. The metabolic intermediary products bind with
the bivalent genes responsible for self-protein synthesis in
the liver. Following binding the genes will alter the coding
and non-self protein will be synthesized which may result in
allergy, anaphylaxis or autoimmune like diseases.
 Teratogenic and mutogenic properties.
 Halothane suppress the number and activity of natural
killer cells (NK cells) and produce immune suppression,
thus favouring higher incidences of post anaesthetic
infection( prefer in tissue transplantation).
 It’s better to revaccinate horses with tetanus toxoid
following halothane exposure.

ISOFLURANE
 Its vapour pressure is almost equal to halothane hence
halothane vaporizers can be used after cleaning thymol,
pungent odour.
 It provides cardiac stability. Reduction in blood pressure is
noticed during isoflurane anaesthesia due to the reduction in
peripheral vascular resistance (unlike myocardial depression in
halothane. It increase the myocardial perfusion by reducing
the coronary vascular resistance. It has little or no action on
sensitizing the myocardium for the actions of catecholamines (
used in patients with cardiac diseases).
 It does not interfere with of central autoregulation of blood
pressure, (indicated in patients with head injures).
 Better muscle relaxation property than halothane and does
not promote convulsions.
 It induces more respiratory depression than halothane and
results in hypoventilation.
 Only 2% are metabolized in the liver due to its relative
insolubility (can be used in patients with liver diseases).

Sevoflurane
 Respiratory depression similar or greater than isoflurane.
Does not sensitize heart to catecholamine induced
cardiac arrhythmias.
 Good muscle relaxation and can trigger malignant
hyperthermia.
 Rapidly crosses the placenta, producing fetal depression.
 Induction and recovery from anesthesia is generally faster
than isoflurane (due to low blood gas partition
coefficient).
 Recovery may be rapid especially following short duration
anesthesia; emergency delirium may occur.
 Dose: mask induction 5%-7% and maintenance: 3%-4%

Desflurane
 Similar in structure to isoflurane with fluorine substituted for
chlorine
 Rapid induction and recovery (low blood gas partition
coefficient) less potent (high MAC: 7.2%).
 Requires a special, electrically heated vaporizer for safe
administration and produces airway irritation, provoking
coughing and breath holding (induction of anesthesia is
difficult unless preceded by adequate preanesthetic
medication and also have poor mask induction
property).
 CVS effect is similar to isoflurane and can cause
sympathetic activation “ sympathetic storm in some
animals.
 Good muscle relaxation and analgesia.
Dose: mask induction: 10-15% and maintenance: 6-9%

PROPERTIES OF INHALANT ANAESTHETICS
PROPERTIES OF INHALANT ANAESTHETICS
Property Halothane Isoflurane Sevoflurane
Formula CBrCIH-CF3 CF3-CHCl-O-CF2H CFH2-O-(CF3)2
Type Halogenated Ether Ether
Molecular weight 197.4 184.5 187.0
Sp.gr. 1.86 1.50
Preservative Thymal Not required Not required
Reaction
Soda lime Yes No Yes
U.V. Light Yes No
Metal Yes No No
Boiling point C@ 760 mm Hg 50.2 48.5
-Vaplour pressure (mm hg) 243, 32% 239, 31%

Monitoring of anesthesia
PRE OPERATIVE PATIENT MONITORING:
 To prepare the patient for safe administration of
anaesthesia,
 To assess the cardiovascular, pulmonary, hepatic, renal
functions and haemato biochemical and electrolyte
balances (eg. In diabetic patients half of the insulin dose is
administered after stabilization).
 Physically examination general body condition, palpation, percussion,
auscultation, measurement of heart, pulse and respiratory rates,
examination of lymph nodes, rectal temperature, appearance of the
mucous membrane, reflex status, integument, location of the lesion and
weight of the animal.
 Systemic examination
 Systemic examination includes the assessment of cardiovascular,
pulmonary, hepatic, renal gastrointestinal, central nervous system,
endocrine and musculoskeletal functions.
laboratory examination: CBC, Protein, ECG, X-rays and other special
examinations

Contd….CNS
Pedal reflex: abolished in stage III anaesthesia, reliable in barbiturate
anesth.
Palpebral reflex: abolished in light plane of anesthesia in cats and
sluggish in surgical plane of anesthesia in horses.
Corneal reflex: corneal reflex deep plane of anaesthesia in
horse,not reliable in dogs and in cattle may be abolished by
repeated stimulation.
Lacrimation: In horses and cattle reduced in deep plane of
anesthesia.
Yawning: seen in light plane of anesthesia.
Swallowing reflex & Laryngeal reflex:disappears at the light plane of
anaesthesia
Anal reflex: Abolished in the middle of III stage of anaesthesia in dogs
and cats.
Pupillary reflex: dialate then constricts upto surgical stage, again pupil
dialate in IV stage of anesthesia followed by resp and cardiac arrest.
Eyeball position:
Hearing sense:

monitoring
Ventilation and respiratory system: frequency, pattern and changes in tidal
volume by observing thorax and rebreathing bag, capnometry, spirometry (measures
the volume of a single breath or minute volume)…………….non-invasive method.
Invasive method: arterial and/or venous blood gas, pH and lactate analysis.
SpO2: % saturation of oxygen in arterial blood.
Cardiovascular system: heart rate, capillary refilling time, CVP (in shock falls, in heart
failure CVP rises and in anaesthesia CVP rises), Cappillary refilling time.
ABP: Oscilometric method, ultrasonic Doppler method (non-invasive), catheterization
of artery (invasive).
ABP: CO X TPR (total peripheral resistance); CO: SV (stroke volume) X HR
NOTE: Decreases in HR, SV OR TPR individually or in any combination can decrease
ABP.
MAP in mm of Hg = Diastolic + ((Systolic – diastolic)/3).
difference of systolic and diastolic is pulse
pressure.
Pulmonary artery pressure and wedge pressure: functional capacity of left side of
heart. Baloon catheter inserted in right atrium-----right ventricle……..pulmonary artery
bifurcation.

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