veterinary anesthesia

1. Veterinary
Anaesthesia & Analgesia
Dr./ Elhussein E. Mahmoud
Lecturer of animal surgery, SVU, Egypt.
Postdoctoral Research Fellow, Stanford University, USA.

2. Preanesthetic Preparation
 No grain is to be fed 24 hours before anesthesia. No hay is to be fed 12 hours before anesthesia.
 Water is OK .
 Laboratory evaluation (minimum are PCV, BUN, glucose).
 Do a physical examination to determine any abnormalities. Auscultate for cardiac dysrhythmias and
murmurs, or abnormal lung sounds..
 Pick the feet and clean the debris and dirt or cover the shoes .
 Rinse the mouth with warm water prior to induction .

3. Pre-anaesthetic medication
Premedication implies administration of sedatives, tranquilizers
and analgesics before anesthetic induction.
Premedication is aimed to
o Relieve anxiety thus apprehension, fear and resistance to anesthesia.
o Counteract unwanted side effects of agents used in anesthesia.
o Reduce the dose of anesthetic.
o Provide extra analgesia.

4.  Tranquillizer: Predominant action is relieving anxiety without causing major sedation.
 Sedative: A drug which relieves tension and anxiety thereby allowing sleep.
 Hypnotic: Hypnosis is a drug-induced sleep.
 Hypnotics will not induce sleep in the presence of severe pain.
Definitions of anesthetic terms

5. Pre-anaesthetic medication
Anticholinergics Muscle relaxants Tranquilizers

6. The main purposes are:
1. To reduce salivation and bronchial secretions.
2. To block the effects of impulses in the vagus nerves.
3. To block certain of the effects produced by drugs which stimulate the
parasympathetic system.
Anticholinergics
Atropine Glycopyrrolate Hyoscine

7. 1- Atropine
- Dilate bronchi --- prevent laryngospasm
- Reduce in motor activity of GIT.
- Decrease bronchial and salivary secretions.
- It is contra-indicated in case of tachycardiac patients.
- Necessary with drugs induce salivation.
Dogs: 0.04 mg/kg.
Large animals: 0.005 mg/kg

8. 3- Hyoscine
2- Glycopyrrolate (Robinul-V® (0.2 mg/ml)):
Large synthetic quarternary ammonium molecular size prevents easy crossing of the blood-brain
barrier and placental barrier. Therefore, it may be a better choice for CNS diseased patients or in
pregnant animals than atropine.
• The mechanism of action is similar to atropine and duration is longer, lasting 90 – 180 minutes.
• Typical dose is in the range of 0.005 – 0.01 mg/kg, IV, IM, and SC.
• Tachycardia is not as prevalent as seen with atropine.
• It is more expensive than atropine.
• It is more potent but its effect on heart rate is less than that of atropine.
• Dose of hyoscine 0.2 to 0.4 mg.

9. Muscle relaxants
To relax skeletal muscles for easy accessibility of surgical procedures.
To facilitate control of respiration during intrathoracic surgery.
To assist dislocated joints.
To limit amount of general anaesthetic used.
For easier inducing performance of endotracheal intubation and endoscopy.
Muscle relaxants may be indicated for intraocular surgery to ensure an
immobile eye, during controlled ventilation to prevent ‘bucking’ of the
ventilator, for reduction of displaced fractures, and during certain abdominal
procedures (e.g. ovariectomy) to improve surgical exposure.
To recognize that the usual indicators of anesthetic depth are abolished
(nystagmus, palpebral response, limb movement).

10. Termination of effects
• Is due to hydrolysis by plasma cholinesterase.
• Prolonged duration of action of SCh occurs with decreased plasma cholinesterase
activity.
– Organophosphate treatment, malnutrition, anemia, pregnancy, and hepatic disease have
been shown to decrease plasma cholinesterase activity.
1- Succinylcholine
Free from usual complications of muscle relaxants such as hypotension,
tachycardia, histamine release, urticaria, and cumulative effects.
Succinylcholine (SCh) has a rapid onset and duration of action.

11. 2- Gallamine triethiodide (Flaxedil)
Gallamine block of cardiac muscarinic activity can be useful during halothane anaesthesia
since halothane tends to produce bradycardia via the vagus nerve. Tachycardia occurs within
1.0 to 1.5 min after i.v. injection in dogs. It is not detoxicated and is excreted unchanged in the
urine.
Gallamine does not give rise to histamine release so that it is a useful non-depolarizing
relaxant in dogs.
Gallamine is given intravenously in doses of :
Dogs: 1.0 mg/kg.
Horses: 0.5 mg/kg.
Cats: 1.0 mg/kg.
Young lambs and calves: 0.5-1.0 mg/kg.
Pigs are very resistant to Gallamine and doses of 4mg/kg are needed to produce complete
relaxation.

12. Tranquilizers
Phenothiazines
Chloropromazine
Acepromazine
Promazine
Promethazine
Thiazine
Detomidine
Medetomidine
Romifidine
Xylazine
Benzodiazepines
Chlordiazepoxide
Diazepam
Midazolam
Butyrophenones
Major
Minor

13. Phenothiazines
 Phenothiazines, although still used in equine anesthesia, have largely been
replaced by alpha agonists.
 Acepromazine is the most commonly used phenothiazine.
Physiological effects of phenothiazines
 Mild tranquillizing effect.
 Anti-emetic effect (not relevant in the horse).
 Decrease gastrointestinal motility (transient).
 Flaccid penis.
 Onset of effect is slow.. within 20–30 minutes.
 Administered at doses of 0.02–0.05 mg/kg.

14.  Xylazine
 Onset of action following IV injection at 2 min, reaching peak effect in 5 minutes.
 Duration for sedative effect lasts about 30 minutes.
 0.5 - 1 mg/kg IV (Equines), 0.05-0.2mg/kg (Ruminants).
Other side effects
o Diuresis
o Sweating
o GIT motility depression
o Depressed intestinal motility will last longer than the sedative effects of the drugs. Do not
feed the horse until intestinal motility returns, otherwise the horse may become colicky.
o Uterine contractions in cows (Ecbolic effect). The incidence of abortion in pregnant mares
has not been established. Detomidine in this regard has been regarded better alternative
both in cows and mares.

15. • Duration of sedation longer acting than xylazine (twice), lasting at least 45 min.
• 5 - 20 mcg/kg IV
• Similar side effects in all other aspects with xylazine
• Precautions are similar to those given for xylazine. Sedation may be inadequate if horse was
excited before administration of detomidine.
 Detomidine
 Medetomidine
• It is the most potent and replacing the use of xylazine in case of dogs and cats because of less
vomition.
• It causes marked ataxia in the horse even in low doses. It is more potent 10 times than
xylazine.
• Dose is approximately 5-30 mcg/kg IM, IV, SQ.

16. Conclusion
There is no premedicants or combination of drug protocols that can be
safely and routinely administered to all patients.

17. Forms of anaesthesia:
1. Local---- nerve endings.
2. Regional---- nerve trunk.
3. General---- CNS.

18. Anaesthesia
Local analgesia
Surface
Infiltration
Intravenous regional analgesia
(IVRA) (Bier's block)
Intrasynovial
Regional
General
anaesthesia
premedication
Subarachnoid Analgesia
Cranial (anterior)
Epidural Analgesia
Head (Eye and Dental surgery)
-Supraorbital N., Infraorbital N., Mandibular N.,
Mental N., Auriculopalpebral N., and Retrobulbar N.
Body (Trunk) Paravertebral analgesia
(Farquharson, Cambridge, and Magda)
Limb
(Diagnosis of lameness, operation
management at the desensitized area)
Linear, Field block
Inhalation anaesthesia
Injectable anaesthesia
Narcosis – Chloral
hydrate
Anticholinergics.
Muscle relaxants.
Tranquilizers.
An= Without
Aesthesia= Sensation
Perineural analgesia Spinal analgesia
Caudal (posterior)
Epidural Analgesia
Epidural Analgesia

19. Perineural analgesia of head
(Nerve Block)

20. Definition of nerve block
• Nerve course & type.
• Supplying area.
• Site of injection.
• Technique of injection.
• Indication(s).

21. Applied anatomy of trigeminal nerve (5th cranial nerve)
• Ophthalmic
• Maxillary
• Mandibular

22. 1- Supra-orbital nerve block

23. 2- Infra-orbital nerve block

25. 3- Mandibular nerve block
4- Mental nerve block

26. 5- Auriculopalpebral nerve block

27. 6- Retrobulbar nerve block

28. 7- Cornual nerve block
A, Cornual branch of the lacrimal nerve.
B, Cornual branch of the infratrochlear nerve.

29. Anaesthesia
Local Analgesia General Anaesthesia
Preanesthetic
medication
An= Without
Aesthesia= Sensation

30. Local Analgesia
Injection of the local analgesic drug at the area of the surgical field through
desensitization of the nerve endings.
Advantages of local analgesia
* Many operations can be performed in standing positions.
*Easy to learn this technique.
* No need for any assistance.
* Local analgesia can be useful to reduce depth of anesthesia.
* Quick safe recovery.
* Economic.

31. Ideal characters of local analgesic drugs
 Stable in solution.
 Rapid onset of action
 Prolonged duration of action
 Minimal irritation and swelling especially in horses.
 Low toxicity.
 Spreading properties.
 Easy to be sterilized without any toxic changes.
 Economic.
NO ONE meets all required characters

32. Adjunctive agents:
These agents may Increase anesthetic effect and/or duration of action of local anesthetic.
1. Hyaluronidase: allow the anaesthetics for better diffusion. Its concentration (1500 IU/100 ml).
Adding enzyme to a local anesthetic solution to break down hyaluronic acid which
functions as extracellular matrix of the tissue and leading to increase tissue penetration in
the region of infiltration and hasten the onset of action.
2. Epinephrine: resulting vasoconstriction increase anesthetic residence time in the infiltrated
area (1:100000 and 1:200000). These effects of epinephrine will be delay absorption, increase
safety margin, reduced toxicity. While, it is contra-indicated for its using in case of
?

33. Examples of the local analgesic drugs:
Procaine Hcl (Novocaine)
Proparacaine Hcl
Lidocaine Hcl (lignocaine):
Mepivacaine Hcl
Bupivacaine Hcl
Classification of analgesic drugs
- Short (30-45min): Procaine.
- Intermediate (1-2h): Lignocaine, Mepivacaine.
- Long (3-6h): Bupivacaine.
Levobupivacaine Hcl
• Extreme stability.
• More rapid diffusion.
• Somewhat longer duration of action.
• Good surface analgesia on mucous
membranes and cornea.
• Economic

34. Systemic and toxic effect of local analgesic drugs:
- Accidental I/V administration of the local anesthetics is the most common cause of
adverse reaction associated with local anesthetic administration. In severe cases, it
can cause cardiac arrest.
For avoidance false I/V injection, syringe aspiration must be performed before
injection of the local anaesthetics.
- Signs of overdose are seizures, convulsions, coma, and death.
- Some respiratory depression.
- Using of excessive amounts of anesthetics with vasoconstrictors in wounded area
may delay healing.
- Bupivacaine is more cardiotoxic than lidocaine.

35. How to avoid toxicity
Limiting the total quantity of drugs.
Dilute solution.
Retarding absorption.
Repeated aspiration before injection.

36. Methods of Producing local analgesia
 Surface (Topical).
 Intrasynovial.
 Infiltration.
 Intravenous regional local anaesthesia (Bier's block).

37.  Surface (Topical) analgesia
Simple from ----- Ice , volatile substances such as ethyl chloride and carbonic
acid snow.
 Intrasynovial analgesia.
Used for diagnosis of lameness and relief of the pain
Mepivacaine is the drug
of choice for intra-articular
injection.
Technique:
- Aseptic preparation of the site of injection.
- Insertion of the needle intra-articularly.
- Aspiration of the excessive synovial fluid.
- Local analgesic is injected into synovial cavity, then dispersed
throughout the cavity by manipulation of the limb.
- Analgesia develops within 5-10 min after successful injection
and persists for about 1 hr.
The drug of choice for topical corneal analgesia is
Proxymetacaine Hcl (Proparacaine) (ophthaine) ?
?

38. B. Field block.
• Inverted L (7 block).
• Circular block.
• Ring block.
Infiltration analgesia
A. Linear infiltration.
Before injection of local analgesic drug, aspiration must be attempted to ascertain
needle point not entered blood vessel. If blood is aspirated into the syringe, the
needle is partially withdrawn and reinserted in slightly different direction.
Injection site is the same incision site.

39. Intravenous regional local anaesthesia (Bier's block).
In the thoracic limb ---- common dorsal metacarpal vein on the dorsal surface, palmar metacarpal
vein on the palmar surface, and radial vein on the medial surface.
In the pelvic limb ---- cranial branch of the lateral saphenous vein and lateral plantar digital vein.

40. Perineural analgesia of the body
Paravertebral analgesia
Paravertebral anesthesia refers to the perineural injection of local anesthesia about the
spinal nerves as they emerge from the vertebral canal through the intervertebral foraminae.

41. Indications:
 This block is done to enable a surgical incision in the paralumbar fossa (flank) of a
standing animal (laparotomy).
 Caesarean section.
 Rumenotomy.
 Abomasal displacement.

42. Advantages:
 Easy to perform operations in standing position.
 Induce complete uniformly desensitization of the flank region.
 Relaxation of the abdominal wall of the flank region.
 Safe and easy to be performed.

43. Applied anatomy of the paralumbar fossa:
Boundaries.
Layers of the flank region.
Nerve supply. (last thoracic, 1st , 2nd lumbar nerve.)

44. Techniques of paravertebral analgesia:
Farquharson.
Cambridge.
Magda.

45. Perineural analgesia of the limb
Incision = otomy -------- Surgical opening.
Ostomy ------ Permenant fistula.
Excision= ectomy ------- Surgical removal.
Examples:
Rumenotomy ----- Opening of the rumen.
Enterotomy ------- Opening of the intestine.
Neurectomy ------ Removal of the nerve.

46. General indications:
 Operative surgery in the desensitized area.
 Diagnosis of lameness.
 Before neurectomy.

47. I. Fore limb
II. Hind limb
Median, Ulnar, and musculocutaneous nerve block.
Tibial, Superficial and deep perineal nerve block.
 Palmar/plantar nerve block.
 Abaxial nerve block.
 Palmar/ plantar digital nerve block.

48. Applied anatomy of the limb:

49. Median, Ulnar, and musculocutaneous nerve block.

50. Tibial, Superficial and deep perineal nerve block.

51. High Palmar/ plantar nerve block
Medial and lateral palmar/ plantar nerves.
Medial & lateral palmar metacarpal/ plantar metatarsal nerves.

52. Low Palmar/ plantar nerve block

55. Epidural analgesia
Definition.
Anatomy.
Types.
Common sites.
Desensitized area.
Indications.
Techniques.
Complications.

56. Spinal Cord is a cylinder of nerve tissue
within the vertebral canal.
(Function: locomotion, conduction)
3 meninges:
 Pia mater
 Arachnoid
 Dura mater

57. • Spinal anesthesia is the injection of local anesthetic around the spinal
cord.
Types::
1.Caudal (posterior) epidural analgesia: it is the preferred and most commonly used technique
in the horse as it is easier and safer to perform, resulted in analgesia of the perineal region
without risk of the spinal injection. It can performed through either sacrococcygeal, 1st
intercaudal or 2nd intercaudal space.
1.Cranial (anterior) epidural analgesia: Injection of local analgesic drug through lumbosacral,
sacrococcygeal, and intercaudal space, with increasing anaesthetic dose in comparison with
caudal analgesia to facilitate its rostral spread inside spinal canal with affecting motor function
of the hind limb.

58. Termination of spinal
cord
Common sites Doses
Dogs & Cats In dogs L6/L7 junction - In cats S3 L7-S1 Lumbosacral space for anterior
epidural.
1ml/ 4.5 kg Post.
Equine S2 – midsacrum Sacrococcygeal / 1st-2nd intercaudal space 10ml 2% lignocaine, 5ml 2%
mepivacaine, Post.
Cattle Last lumber – S1 S5-Co1 Sacrococcygeal /First intercaudal
space
5-10ml Post. & 100-120ml Ant.
Small
ruminants
S1 S4-Co1 Sacrococcygeal / First intercaudal
space
1ml/7kg
Dangers of spinal and epidural block
 Infection- Careful sterile precautions (good clipping and scrubbing)
 Irritation causing spinal damage (most likely with subarachnoid).
 Hind limb motor paralysis (problem in large animals, acceptable in small).
 Respiratory paralysis (only if massive overdose of local analgesic used).

59. Desensitized area of caudal epidural analgesia:
It is performed to produce regional anaesthesia of the pelvic viscera, genitalia, perineum, urethra,
tail, anus and rectum in standing position.
Desensitized area of cranial epidural analgesia:
It desensitizes the hind limbs, mammary tissue, flank region, and abdominal wall till navel region.
Indications:
Rectal prolapse, perineal laceration, urethrostomy, tail docking, atresia ani, relief of tenesmus, fetotomy,
correction of the uterine torsion, and any operation at the desensitized area can be performed. In case of
anterior analgesia, abdominal and pelvic surgery especially for small ruminants.

60. Techniques:

61. Anesthesia of Laboratory Animals.
• Premedication
1.Reduce fear, stress free induction of anaesthesia.
2.Decline amount of anaesthetic drug needed.
3.Reduce salivary and bronchial secretions.
4.Smooth induction and recovery.
1- Anticholinergics:
Ex. Atropine sulphate, glycopyrrolate.
2- Tranquilizers.
Ex. Xylazine, Diazepam, Midazolam, and medetomidine

62. • Local analgesia. It is usually poor used.
• General anaesthesia.
¶ induced and maintained with volatile agents.
¶ induced with injectable drugs and maintained with volatile agents.
¶ maintained with injectable drugs alone.

63. ANAESTHESIA WITH VOLATILE AGENTS
The most popular agents:
Halothane
Isoflurane.
Sevoflurane.
Ether. (not recommended) ?

64. ANAESTHESIA WITH INJECTABLE DRUGS

65. Injectable anaesthetics:
1. Ketamine. The best choice.
Rabbits: xylazine 3mg/kg + ketamine 3mg/kg. i.v.
Rats: Ketamine 40-87mg/kg + xylazine 5-13mg/kg i.p., i.m.
2. Chloral hydrate. Neuropharmacology

66. Assessment of anaesthetic depth.
1- Respiratory rate.
2. Pedal reflex.
3. Ear Pinch.
4. Tail pinch.
5. Palpebral reflex.
6. Cornea.

67. Thank you
https://pubmed.ncbi.nlm.nih.gov/?term=Mahmoud+EE