TOPIC Common Anaesthetics and anaesthesia in dogs Lecture 1 introduction local anaesthetics and premedicaments Introduction to anaesthesia There are no safe anaesthetic agents there are no safe anaesthetic procedures there are only safe anaesthetists ID: 913677
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Slide1
VMD-513
Pet/Animal Breeding, Management, Nutrition and Health Care
TOPIC: Common Anaesthetics and anaesthesia in dogs
Lecture: 1 (introduction, local anaesthetics and
premedicaments
)
Slide2Introduction to anaesthesia
There are no safe anaesthetic agents; there are no safe anaesthetic procedures; there are only safe anaesthetists
ROBERT SMITH
General consideration:
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
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 training of
assistants,Length
and type of operation or procedure to be performed
III. Patient responses can vary because doses and techniques are for the ‘’Average, normal, healthy’’ animal: thus it is essential that the
practioner
knows how to modify anaesthetic techniques.
Slide3Definitions
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 (
centrall
y).
Phases of Anaesthesia:
I.
preanaesthetic
or
preinduction
period
II. Induction to anaesthesia
III. Maintenance
IV. Recovery
V. Post Anaesthetic period
Slide4Contd
…..
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
Slide5Contd
…..
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
Slide6Contd
….
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.
Slide7Contd
…
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.
Slide8Use 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
Slide9Types 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
Slide10Patient evaluation and preparation
General consideration
The
preanesthetic
evaluation history (history, physical condition and physical examination) dictates the choice and dose of anaesthetic to be used
The history and physical examination are the basis of patient evaluation
Laboratory tests are no substitute for a through physical examination
A patient airway must be maintained in every patient
A patient intravenous route must be maintained for all risk patients
Anticipate likely untoward events based on history and physical status
An emergency cart with appropriate antidotes and antagonists should be maintained.
Patient evaluation
Patient identification
CASE NUMBER OR IDENTIFICATION
SIGNALMENT
1. Species, breed, age, sex
C. BODY WEIGHT
Slide11Contd
….
II.
CLIENT COMPLAINT AND ANAMNESIS:
DURATION AND SEVERITY OF ILLNESS
CONCURRENT SYMTOMS OR DISEASE
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
Slide12Current physical examination
GENERAL BODY CONDITION:
obesity, cachexia, pregnancy, hydration, temperature, calm or excited, nervous or apprehensive.
Cardiovascular:
heart rate and rhythm, arterial blood pressure, pulse pressure quality and regularity, capillary refilling time(<1.5 second), auscultation (cardiac
murmers
).
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
Hepatic:
jaundice, failure of blood to clot, comma, seizures
Renal:
vomiting,
oligouria
/anuria, polyuria/polydipsia.
GIT:
Diarrhea
, vomiting, distension, auscultation of intestinal sound, rectal palpation.
Nervous system and special senses:
Aggression/depression, seizures, fainting, coma.
Slide13Contd
….
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:
Slide14Local anaesthetics
Produce desensitization and analgesia of skin surfaces
(topical anaesthesia),
tissues (infiltration and field blocks), regional structure (conduction anaesthesia)
Classification:
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
Slide15Contd
…..
Amide linked drugs:
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.
Slide16Contd..
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.
Slide17Premedication
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.
Slide18Classification 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 agentsAgonistsPartial Agonists/AntagonistsMorphine, Meperidinebuprenorphine
.
Slide19CLINICAL 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).
Slide20CONTD…..
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.
Undesirable effects of atropine and
glycopyrrolate
reversed with neostigmine or
physostigmine
Slide21CLINICAL DOSES, ADVANTAGES AND DISADVANTAGES(anticholinergic)
Species
Atropine
Glycopyrrolate
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:
advantage
s: 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 ( indicated in equine anaesthesia to reduce post anaesthetic colic due to Ileus).
Slide22Thanks