Anaesthesia-Local analgesia or anaesthesia

ANAESTHESIA

The term anaesthesia is from Greek word Anaisthaesia, i.e., absence of sensation or insensibility- loss of sensation to the entire or any part of the body. This term was given by Dr.O.W.Holmes in 1886.

General anesthesia induces immobilization, relaxation, unconsciousness and freedom from pain. Anesthesia has contributes to humanitarian handling of surgical patients and protecting personnel while developing modern surgical science.

Reasons for anaesthesia are to decrease the pain and improve muscle relaxation, and other purposes are restraint, safer transport of wild animals, diagnostic and therapeutic procedures, euthanasia, humane slaughter(Co2 to pigs before slaughter).

A state of anaesthesia or absence of sensation by

1.Depression of CNS excitability leading to depression. Eg: Thiopentone/Halothane.

2.Increase the CNS irritability leading to hyper excitation. Eg: Ketamine, Nitrous oxide,Enflurane.

History of anaesthesia:

Ancients used opiates, alcohol, asphyxia, compression of carotid arteries.

In 1540, Paracelsus produced ether.

In 1800, Sir Humphrey Davy suggested nitrous oxide has anaesthetic property.

In 1824, pain decreased by mixture of nitrous oxide and Co2.

In 1844, Dr. Horace Wells discovered anaesthetic properties of Nitrous oxide.

Dr. C.P. Jackson used ether in animals.

In 1847, Chloroform for general anaesthesia in animals by Flourens.

In 1884, Kohler used cocaine for local anaesthesia of eye. Halstead used cocaine for nerve block anaesthesia. G.L. Corning cocaine in epidural anaesthesia.

In 1898 August Bier produced true spinal anesthesia.

In 1920 General anaesthesia by barbiturates, in 1930 by pentobarbital, in 1934 by thiopentone.

In 1950 Charpentier produced prenaesthesia by phenothiazine derivatives.

 

Types of anesthesia:

According to the type of drug used and method or route of drug administration, the types of anesthesia are as follows.

1.Inhalation Anaesthesia: Anaesthetic gases or vapours are inhaled in combination with oxygen.

2.Injectable Anaesthesia: Anaesthetic solution injected I/V,I/M,or S/C.

3.Oral/Rectal : Liquid oral anaesthetics/suppositories like by Chloral hydrate.

4.Local: Anaesthesia applied topically/injected locally into or around the surgical site (field block) or injected around a larger nerve trunk supplying a specific region (Regional nerve block). Nerve block is injecting agent perineurally and true spinal analgesia by injecting agent epidurally or into subarchnoid space.

5.Electronarcosis: Electric current passed through the cerebrum to induce deep narcosis.

6.Transcutaneous electric nerve stimulation(TENS): Local analgesia by low intensity, high frequency, electric stimulation of skin through surface electrodes.

7.Hypnosis: Non drug induced trance employed in rabbits and birds by inverting them.

8.Accupuncture: Chinese system, by long, fine needles to induce analgesia.

9.Hypothermia: Decrease of body temperature locally/generally to supplement anaesthesia or decrease the drug required, usually in neonates or cardiovascular surgery.

10.Regional Anaesthesia: Insensibility in a larger, though limited bodyarea (Eg: Paralumbar nerve block).

 

Some definitions:

Analgesia: It is loss of pain sensation.

Tranquilization:  Animal is relaxed and unconcerned with its surroundings, indifferent to minor pain stimulation. In behavioral pharmacology it is that state of tranquilization is the level of CNS depression just sufficient to produce loss of conditioned reflexes. Tranquilizers are also called as ataractic agents.

Sedation:  Degree of CNS depression in which patient is awake but calm and free from nervousness, unaware of surroundings, accompanied by drowsiness.

According to the level of CNS depression, Tranquilizer<Sedation<Hypnosis.

Hypnosis: State of trance resembling sleep due to moderate CNS depression, arousal by stimulation. Analgesia does not exist in sedation and hypnosis.

Narcosis:  Drug induced deep sleep from which animal can be aroused with great difficulty but it again relapses. Eg: Opium alakaloids/Morphine derivatives.

General Anaesthesia: It is drug induced reversible loss of sensory and motor functions with unconsciousness due to depression of CNS.

Dissociative Anaesthesia: It is the loss of sensation of whole body due to functional disruption or dissociation of various CNS systems by marked stimulation. It is to dissociate thalamocortical  and limbic systems. It is characterized by a cataleptoid state in which eyes remain open, with functional swallowing reflexes. Eg: Ketamine will produce muscle relaxation and dissociative anaesthetic to catch monkeys.

Local anaesthesia: It is transient, reversible, paralysis of sensory nerves and nerve fibres in a local area. It is temporary loss of sensation in a circumscribed area of the body due to inhibition in the conductive process of peripheral nerves without impairment of consciousness.

Local Analgesia: Temporary pain stimulation alleviation in a circumscribed area without loss of consciousness.

Basal Anaesthesia: State of CNS depression produced by preanaesthetic agents which serves as a basis for general anaesthesia.

Surgical Anaesthesia: It is the state of anaesthesia in which surgery can be performed painlessly without any physical response on the part of the animal. Animal is unconscious, muscles relaxed with analgesia.

Balanced Anaesthesia: (Mixed Anaesthesia)

It is the combination of two or more drugs or techniques used to produce unconsciousness, analgesia, muscle relaxation, attenuated autonomic reflexes and moderation of undesirable effects of any drugs used with an object of avoiding the  toxic effects of one single agent otherwise required in larger doses.

For example:

Atropine premedication for thiopentone induced salivation and cardiac depression of xylazine.

Nitrous oxide to keep minimum thiopentone dose.

Gallamine to relax muscles to avoid excessive general anaesthetic dose.

Balanced anaesthesia was described by Lund in 1942, and popularized by L.W.Hall in veterinary practice.

Neuroleptanalgesia: Neuroleptic drug in combination with analgesic  for surgical pain relief.

 

Classification of Anesthesia:

Anaesthetics are substances for inducing anaesthesia.

Four main types of anaesthesia.

Local Anaesthesia	Regional Anaesthesia	Sedation & Narcosis	General Anaesthesia
Surface Application	Nerve Blocks	Before Local and Gen.Anaesthesia as Preanaesthetics
Local Infiltration S/C or I/D	Epidural Injection	Narcotics-Depress CNS Tranquilizers-Sedation without drowsiness Hypnotics-Induce Sleep

 

Local analgesia: 

Applied around nerve terminals and nerve fibres to prevent conduction of nerve impulses by nerves.

Drugs used are called as local analgesia/local anaesthetics.

Field block/field anaesthesia—Desensitization of an area by injecting analgesics around its borders.

Local anaesthetics:

1.Cocaine:

• Extracted from Erythroxylon coca.
• Irritant and toxic in small doses.
• Toxic symptoms are clonic convulsions, loss of consciousness and medullary paralysis.
• Cocaine as doping agent in horses.
• The lethal dose is 15mg/kg.
• The maximum dose is 780mg in horses, 45-120mg in dogs depending on size,15mg in cats.
• It is withdrawn due to toxicity, only 4% eye solution and 10-20 % for nasal and laryngeal areas.
   

2. Procaine Hcl (Novocaine):

• Ester derivative of cocaine, which is short acting.
• 2-2.5 % solutions for local infiltration/Nerve block.
• Preferably with adrenaline 1:100000 for potentiating.
•  Non irritating, quickly detoxified by liver.
• Decomposed in alkaline solution.

3. Amethocaine Hcl (Anethaine):

• 5-10 times more powerful than procaine.
• 1 % for local infiltration, 2 % for surface application.
• More toxic compared to procaine.

3. Lignocaine Hcl (Xylocaine):

• Amide derivative of cocaine,fast acting.
• Widely used , 2 % for local infiltration and 4 % for surface application.
• Not decomposed by boiling, strong alkalies/acids.
• Convulsive dose in cats is 15mg/kg.
• Goats sensitive to it, max dose 10mg/kg body weight, toxic effects are excitation, tonic and clonic convulsions, opisthotonus,respiratory distress,cardiac arrest and death.
• Often combined with thiopentone for dysarhythmia and cardio protective action.
• Combined with adrenaline at 1:200000.

4. Bupivacaine:

• It is fast and long acting amide derivative.
• Less safety margin.
• Convulsive dose in cats is 3-5mg/kg.
• Intravenously induces myocardial depression.
• Not combined with thiopentone.

 Regional Anaesthesia:

Analgesic injected over main nerve trunk in nerve block.

Epidural Anaesthesia:

Anaesthetic solution at spinal nerve origin in sub archnoid space.

INFRA ORBITAL NERVE BLOCK Indications:                     Continuous twitching of upper lip and nostrils, temporary relief by blocking the nerve. Nerve Infra orbital nerve is the division of trigeminal nerve. It supplies sensory nerve to the first and second molar (PM 1 & 2), canine and incisors as it passes the canal. After emerging from the canal it supplies sensory fibres to the upper lip, cheek, nostrils and lower part of the face. Site and technique The infra orbital foramen is located at the level of bisection of a line connecting the facial tuberosity and the naso-maxillary notch. The nerve can be blocked either as it passes the canal or after emerging from the canal using a 19 G x 5 cm needle. In dogs the infra orbital foramen is situated in front of the anterior margin of the PM 4 where it can be palpated. Area desensitized The skin of the lip, face of the side upto the level of the foramen is desensitized if blocked at the level of the foramen.  If it is blocked in side the canal in addition to the above structures PM 1 & 2, canine, and incisors with their alveoli and gum and the skin upto the inner canthus of the eye.

 

MANDIBULAR NERVE BLOCK

Indications:

 Desensitising teeth alveoli and gum of lower jaw and lower lip.

Nerve

• Mandibular nerve is the alveolar branch of mandibular division of the 5^th cranial nerve. It enters the mandibular foramen at the medial aspect of the vertical ramus of the mandible. Then it passes through the mandibular canal and supplies sensory dental and alveolar branches to the side. After emerging out it is called as mental nerve and it supplies to the lower lip.

Site and technique

• The nerve can be blocked as it enters the mandibular foramen or as it emerges out from the mental foramen.
• Mandibular block: The mandibular foramen is located opposite to the point of intersection of a line passing vertically downwards from the lateral canthus of the eye and another line extending backward from the tables of the mandibular teeth. The site is selected medially 3 cm below the temperomandibular articulation on the posterior boarder of the mandible. 4 to 6 ml of the solution is deposited using along spinal needle.
• Mental block: Mental foramen is easily located on the lateral aspect of the jaw below the angle of the lip (in the middle of the interdental space) 3 to 5 ml of the solution is deposited.

SUPRA ORBITAL NERVE BLOCK

Indications:

                  Upper eyelid operations.

Nerve

• Supra orbital nerve (frontal nerve) is a sensory terminal branch of the ophthalmic division of 5^th cranial nerve. It emerges from the orbit through the foramen accompanied with the artery. It supplies sensory fibres to the upper lip and part of the skin on the forehead.
  Site and technique

• The foramen is palpated as a pit like depression midway between the upper and lower borders of the supra orbital process close to the frontal bone.
•  Successful block desensitizes the upper eyelid and the frontal region.
• Dogs do not have supra orbital foramen.
   

CORNUAL NERVE BLOCK

Indications:

                   Horn core analgesia and skin around the base of the horn.

Cattle

• Cornual nerve is a branch of lacrimal division of ophthalmic division of trigeminal nerve.
• It supplies sensory fibres to the horn corium and the skin around the base of the horn.
• The nerve passes through the periorbital tissues dorsally and then runs along the frontal crest to the base of the horn.
  Goats

• In goats the horn is supplied by the corneal branch of lacrimal nerve and corneal branch of infratrochlear nerve.
• The infratrochlear nerve emerges from the orbit dorsomedially.
   

SITE AND TECHNIQUE

Cattle

• As the nerve runs from the orbit to the base of the horn it becomes more and more superficial.
• The block is done more easily 2 to 3 cm below the base of the horn with 5 to 10 ml of 2% lignocaine.
  Goats

• The lacrimal branch can be blocked half way between the lateral canthus and the lateral base of the horn.
• The infratrochlear branch can be blocked half way between the medial canthus and the medial base of the horn.
• To amputate the horn at the base it is better to provide sedation, as this block will not desensitize the perostium and sinus mucous membrane.
   

RETROBULBAR NERVE BLOCK

• Auriculopalpebral branch of the facial nerve  (VII)

SITE AND TECHNIQUE This nerve passes  through foramen orbital. Anaesthetic solution is deposited anterior to the foramen. The notch formed by the supraorbital process, zygomatic arch and the coronoid process of the mandible is located and a 18G x 7 to 11 cm needle is inserted directed until it reaches the pterygopalatine fossa. Deposit 15 ml of the solution. An additional 10 to 15 ml can be deposited slightly caudodorsally as the needle is withdrawn. This block does not provide desensitization of eyelids, hence for extirpation of eye ball in addition to this the auriculopalpebral nerve block and infiltration of eyelids mut be carried out.

PARAVERTIBRAL NERVE BLOCK

• This regional anaesthesia is very important for bovine laparotomy.
• The dorsal and ventral nerve roots of last thoracic (T13) and first and second lumbar (L 1 & 2) spinal nerves are blocked as they emerge from the intervertebral foramen.
• If analgesia of caudal paralumbar area is required additionally the third lumbar (L3) is blocked which result in weakness of the hind limb.

SITE AND TECHNIQUE

• Each nerve is blocked immediately in front of the cranial border of the transverse process of the succeeding lumbar vertebra.
• The last thoracic nerve is blocked half way between the last rib and the transverse process of the first lumbar vertebra about 5 cm from mid line.
• The first and second lumbar nerves can be blocked at the posterior edge of the transverse process of the corresponding vertebrae about 5 cm from the mid line.
• The needle pricks are made through the subcutaneous wheals, to penetrate the intertransverse ligaments and 15 ml of local anaesthetic is deposited below the ligament and another 5 ml above the ligament.
• Successful block shows analgesia of flank, paralysis of flank muscles, increase in the temperature of flank, and scoliosis towards the desensitized side.
• In horses the block is performed on T 18, L1 and L2.

EPIDURAL ANALGESIA

• Epidural space is that compartment between the duramater and the bony and ligamentous wall of the spinal canal.
• This space is filled with extradural fat, internal vertebral plexus of veins and the spinal nerves.
• Injection of local anaesthetics will desensitize the nerves.

SITE OF INJECTION IN DIFFERENT SPECIES

• Bovine - Sacrococcygeal junction between I & II coccygeal vertebrae
• Equine - Between I & II coccygeal vertebrae
• Canine - Lumbosacral space
• The terms high (anterior) and low (posterior) are often used to describe the level of block.
• If the block extends the segment from where the sciatic nerves arises (second sacral and more cranial segments) the block is termed as anterior epidural.
• The anterior epidural is achieved by increasing the volume of local anaesthetic injected.
• In high epidural or anterior epidural the animal will be recumbent and the motor functions will be lost.

TECHNIQUE

Cattle and horse

• The exact position of the sacro coccygeal junction or the space between the first and second coccygeal vertebrae can be located by palpating the borders with simultaneous pumping of the tail.
• 3 ml of 2% lignocaine with epinephrine is injected in cows for low epidural which will induce paralysis of tail, and analgesia of perineum rectum, and the inner aspect of the thigh.
• Higher dose upto 120 ml of 2% lignocaine is administered in adult cow to achieve high epidural in which the cow will be recumbent for more than 4 hours.
  Dogs

• The local anaesthetic is administered between sacrococcygeal or I and II coccygeal vertebrae for docking.
• The complications of epidural anaesthesia includes hypotension, respiratory collapse due to the block on higher levels, clonic spasms, convulsions (goats are more sensitive), pareses or paralyses.

INTERNAL PUDENTAL NERVE BLOCK

• This block is commonly done to induce relaxation and analgesia of penis to aid in examination and treatment in cattle.
• The lesser sciatic foramen is located by rectal palpation as a circumscribed depression in the sciatic ligament.
• The internal pudental nerve is found a finger width dorsal to the pulsating pudental artery.
• The block is done bilaterally on both the sides.
• The ischorectal fossa is prepared aseptically and an 18G x 8 to 10 cm needle is inserted and directed towards the nerve under rectal guidance 20 to 25 ml of local anaesthetic is deposited and the process is repeated on the other side.
• Penile relation and cutaneous analgesia over the anus, perineum, posterior medial thigh and urethral opening are achieved.
   

ANALGESIA FOR CASTRATION

• Analgesia can be provided by injecting local anaesthetic into the spermatic cord or directly into the testicle. The incisional site must be infiltrated subcutaneously on the scrotum.
   

BRANCHIAL PLEXUS BLOCK

• This block is mainly induced in dogs.
• Successful analgesia will show all the symptoms of radial paralysis.
• The brachial plexus in the dog is best blocked on its lateral recumbancy.
• First the costo chondral junction of the first rib is located by moving the upper limb.
• An 8 to 10 cm long needle is inserted towards the costochondral junction.
• If the leg is held, as in the normal position the correct site of needle insertion will be medial to the shoulder joint directed parallel to the vertebral column.
• After reaching the costochondral junction the needle is withdrawn 0.5 to 1 cm, then aspirated to ascertain that no blood vessel is punctured.
• 1 to 10 ml of 2%lignocaine is injected depending on the size of the dog.
   

MEDIAN AND ULNAR NERVE BLOCK

• Median and ulnar nerve block will desensitize the carpus and structure distal to it.
• Median nerve is blocked at the caudomedial border of the radius just distal to the superficial pectoral muscle.
• The nerve lies cranial to the median artery and vein. Skin desensitization involves only the medial aspect of the pasern.
• Ulnar nerve is blocked in the groove on the palmar aspect of the antebrachium between the ulnaris lateralis and the flexor carpi ulnaris muscles, 10 cm proximal to the accessory carpal bone at a depth of 1 to 2 cm.
• Skin desensitization occurs on the dorsal aspect of the proximal metacarpus.
• Needle and volume 20G x 1”, 10 to 15 ml on each site.
   

TIBIAL AND PERONEAL NERVE BLOCK

• Tibial and peroneal nerve block will eliminate deep sensation from the hock and structures distal to it.
• Tibial nerve is blocked just caudal to the deep digital flexor tendon and cranial to the Achilles tendon about 10 cm proximal to the top of the tuber calcis on the medial aspect of the limb beneath the fascia.
• Skin sensation is usually lost between the bulb of the heel.
• Peroneal nerve is blocked between the long and lateral digital extensor tendons on the lateral aspect of the crust, 10 cm proximal to the lateral malleolus.

PALMAR/PLANTAR DIGITAL NERVE BLOCK

• The palmar/plantar nerve is desensitized in the palmar region of the pastern joint medially and laterally.
• Palmar nerve is formed by the fusion of the terminal branch of ulnar nerve and the terminal branch of median nerve
• Plantar nerve is the result of bifurcation of the tibial nerve.
• Needle and volume 20 to 25 G x 2.5 cm, 2 ml on each site.
• The area of desensitization includes pastern and one third of the hoof with portions of navicular area.