Download PPT. Criteria for selection of anaesthetics and ancillary drugs

CRITERIA FOR SELECTION
OF ANAESTHESIA AND
ANCILLARY DRUGS IN FARM
ANIMALS
INTRODUCTION
The perfect anesthetic drug would induce
reversible unconsciousness, analgesia
& muscle relaxation without depression of
heart & lungs.
It would not require metabolism & would
be nontoxic to patient.
Careful preanaesthetic assessment
of patient for selection of
anaesthesia & ancillary drugs is
essential by identifying
physiological, pathological or drug
related factors which may
complicate the anesthetic
management or surgical procedure,
expected outcome of surgery or
management of patient and
consideration of drug residue effect.
CRITERIA OF SELECTION OF
ANAESTHESIA AND ANCILLARY
DRUGS IN FARM ANIMALS
Patient factors:
Species – Ruminants, Equine, Swine
Breed
Age – Neonatal, Geriatric
Reproductive status – Male, Female
(Pregnant)
Temperament of patient -Calm or
excited
Physiological status of patient –
Normal or diseased condition –
(Hepatic, Renal, Cardiovascular,
Respiratory
Surgical factors:
Nature of surgery
Duration of surgery –(short or long
duration)
Surgeon’s skill
Familiarity with proposed anaesthetic
technique
Equipments & personnel available
History of presenting problem
Physical
examination
Abnormality
identified
History of other
problems
Breed & age
Abnormality reported e.g.
exercise,intolerance,prolonged
hemorrhage after surgery
Further investigation
Definative or working
diagnosis
Knowledge of disease effect on
homeostatic mech.
Assesment of
physical status
Plan preoperative
stabilization
Plan patient
monitoring during
surgery
Drug & withdrawl time from meat & milk
Farm Animal Surgery,Fubini
Drug
Meat (days) Milk (days)
Triflupromazine
2
0.5
Diazepam
7
3
Midazolam
7
3
Xylazine
7
3
Acepromazine
7
2
Thiopentol
4
2
Butorphenol
3
3
Morphine
3
3
oxymorphone
3
3
Contd…
Drug
Meat (days)
Milk (days)
Lidocaine
3
2
Mepivacaine
3
2
Ketamine
2
2
Guaifenesin
2
2
Halothane
3
3
Isoflurane
3
3
sevoflurane
3
3
Ruminant Anaesthesia
General Considerations
Adult ruminants
Forestomach occupies 75% abdominal cavity
General anaesthesia
Decreases rumen function
Encourages bloat
Compromises cardiopulmonary function
due to body positioning
– Late term pregnancy significantly
compromises respiration
Promotes regurgitation and aspiration
Neonates
Preanesthetic Preparation
Adequate fasting decreases incidence of
regurgitation and bloat
Animal
Cattle
Feed
withholding
(hrs)
36-48
Water
with holding
(hrs)
12-18
Large bull
48-72
24
Sheep & goat
12-24
12
Horse
12
12
Pig
12
06
Premedications
Anticholinergics
Not routinely used in ruminants
Does not completely stop salivation
Saliva and respiratory secretions become more
viscous – harder to clear
Atropine has very short duration in cattle
Results in tachycardia which increases myocardial
work
Use reserved for intraoperative treatment of
bradycardia
< 25 bpm
Tranquilizers and sedatives
Butorphanol
Do not use alone – excitement is possible
0.025 – 0.05 mg/kg IV
Use in combination with xylazine for IV or
IM sedation for
– Examinations
– Standing procedures with local
anesthetic blocks
– Eg. Dehorn
Use in combination with diazepam
for IV or IM sedation
Diazepam 0.1 mg/kg IV
Suitable in goats with urethral
obstruction
Induction and Maintenance of
Anaesthesia
Diazepam– Ketamine
Usually used for short procedures in the
field
Can be used as induction for inhalation
anesthesia
Induction method of choice for both healthy
and sick patients
Can improve analgesia and anesthesia time
by using xylazine + butorphanol as
premedication
Dosage
Diazepam 0.28 mg/kg IV
Ketamine 5.5 mg/kg IV
Drug combination is same as 1ml/20 lb
body weight
Two drugs combined in ratio 1:1 by
volume
0.5 ml of each drug per 20 lbs
Prolong anesthesia with small
increments as required
IV Anaesthesia
Guaifenesin + Ketamine
Guaifenesin 5% in D5
Ketamine 1.0 – 2.0 mg/ml
Usually used for short procedures in the field
May be used for both induction and
maintentance of anesthesia
May premedicate with xylazine to improve
analgesia
IV Anaesthesia
Guaifenesin + Ketamine + Xylazine –
“GKX” or “Triple Drip”
Add to Xylazine 0.1 mg/ml
Start at 0.5 – 1.0 mg/kg to induce
Then give to effect –
2.0 ml/kg/hour for adult cattle, sheep, and goats
1.5 ml/kg/hour for calves
Must be given IV
Positioning
If possible cranial thorax and neck should
be raised slightly
Facilitates drainage of saliva and regurgitation
from mouth
Positions abdominal viscera away from
diaphragm
Lateral recumbency in cattle
Down front limb should be pulled forward
Place in right lateral whenever possible –
rumen up
Dorsal recumbency in cattle
Place on padded surface
Limbs flexed in relaxed position
Complications
Regurgitation &
aspiration
Bloat
Salivation
Ventilation
perfusion mismatch
Lameness due to
myositis,radial
nerve paralysis
Prevention
Fasting
Intubation
Lowering mouth
from larynx
Washing of mouth
&nostril
Pull lower limb
forward
Inflated tyre is kept
under shoulder
Upper limb held
parallel to ground.
Since ruminant usually accept
physical restraint
Mild sedation with local or regional
nerve block often used in many
procedure
Goats are extremely sensitive to
Lignocaine. Dose above 10 mg/kg
never be exceeded.
Results: excitation ,convulsion
,opisthotonous, respiratory
depression,cardiac arrest ,death.
Equine Anaesthesia
General consideration
Hypoxemia (V:Q mismatch)
Obligate nasal breathers
Temperament, size – injuries
Myositis
MV 80 lts./min at rest
1500lts/min at race
Bradicardic & bradypnic
Premedication
Rapid inductions
Ketamine + Diazepam
GG + ketamine
Techniques for inhalation
anaesthesia:
After premeds, induction and intubation;
High oxygen flow (10 L/min) and high
vaporizer setting (4-4.5% isoflurane)
After 20-25 min lower isoflurane conc.
to 1.5 – 2% and lower the flow to 5-6
L/min
Start IV fluids
Monitoring (ECG, blood pressure, eye
signs)
"Triple Drip GKX"
Xylazine 1 mg/kg IV as premed 15 min
before.
Mix together:
Guaifenesin 1 liter of 5%
Ketamine 1 mg/ml (1000 mg/liter GG)
Xylazine
0.5 mg/ ml (500 m g/liter GG)
Induction - ketamine + midazolam
Maintenance 2.2 ml/kg/hour IV (to effect)
60 min max
Recovery after 1 hour anesthesia is
approx. 20-25 mins.
Hypoventilation/hypoxemia
Hypotension
Myopathy/neuropathy
Large body mass and nervous
temperament
Keep horse anaesthetized until in
the recovery stall
A dark, quiet stall with padded floor
and walls is recommended
Deflate cuff and tape tube to horse’s
head
Upper airway obstruction: patent
airway
Shoes, if not pulled, should be
covered with tape
Oxygen should be insufflated into
the endotracheal tube
Small dose of sedative such as
xylazine, 100 -150 mg, may be given
Assisted recovery may be
necessary:
Halter and tail ropes
Recovery
Swine Anaesthesia
Main considerations
Sloping down of larynx (acute angle
between posterior larynx & tracheal
opening)
Poor thermoregulatory mechanism
High body fat
Drug regimen for sedation
&anaesthetizing pig
Sedation
induction
Drug
Dose
(mg/kg)
Route
Onset
Duration
(minutes) (minutes)
ACP
0.2-0.5
i.m.
20-30
30-60
Azaperon
e
1.0
i.m.
5-15
60-120
Xylazine
+
0.5
i.m.
5-10
5-15
Ketamine
5.0
i.m.
Short duration anaesthesia
Drug
Dose
(mg/kg)
Route
Onset
(minutes)
Duration
(minutes)
Thiopentone 10-20
i.v.
immediate
15-45
Diazepam
+Ketamine
1-2 +10-15
i.m.
10
20-40
Xylazine
+Ketamine
4.0+ 4.0
i.m.
5-10
15-30
For long procedure
Medetomidine +Xylazine +Ketamine
@ 0.08+ 0.2+ 2.0 mg/kg i.m. (60-120
minutes)
Azaperone+ Xylazine +Ketamine @
2.0 + 0.2 + 2.0 mg/kg i.m. (40-60
minutes)
Post anaesthetic complications
Malignant hyperthermia
Torn muscle condition
Fighting at time of reintroduction in
herd
Neonatal anaesthesia
6-8 weeks gradual develops normal
physiological function & respiratory
function
12 weeks-well developed
circulatory,respiratory,hepatic renal
thermoregulatory
CVS
Rate dependent
Cardiac output
increase 30% only
Slowing heart rate
is fatal
Respiratory
system
High oxygen
demand
High BMR
Less functional
residual capacity
Less oxygen
reservoir
Uptake &
elimination of drug
faster
Blood brain
barrier
Open tubocisternal
E.R of cerebral
endothelial &
choroid plexus epi.
Cell
Anaesthesia has
greater acess to
brain
Use lower dose
Renal function less
Hepatic
microsomal enz
less.
Body fat less
Large body surface
area
Skeletal muscle
activity less
Functions and Properties of the
BBB
General Properties of the BBB
1.
2.
3.
Large molecules do not pass through the BBB easily.
Low lipid (fat) soluble molecules do not penetrate into the
brain. However, lipid soluble molecules rapidly cross the BBB
into the brain.
Molecules that have a high electrical charge to them are
slowed.
Therefore:
The BBB is selectively permeable to :Oxygen, Carbon dioxide
and glucose
The BBB is not permeable to
hydrogen ions
Geriatric patient anaesthesia
70 – 75% life is completed
Horse greater than 19 – 20 years
age( normal life span 35 years)
Basic physiology
Cardiovascular
system
Atrophy of
myocardial fibers
Decrease coronary
perfusion
Loss of elasticity,
fibrosis &
calcification of
myocardial fiber
Ventricular
hypertrophy
Nervous system
Loss of neurons
Delay in central
processing
Decrease
receptors activity
Loss / altered
neurotransmitters
Respiratory
system
Fibrosis & decreased
elastin content of lung
parenchyma
Increased residual
volume
Wasting of intercostals
& diaphragmatic
muscle
Functional negative
pressure of thorax
reduced
Renal system
Decreased tubular
function
RBF & GFR reduced
Renin-angiotensin
function decreased
Half life of anaesthetic
drugs increased
Liver
Decreased hepatic blood flow
Hypoproteinemia
Impaired blood clotting
Hypoglycemia
Capacity of drug detoxification
delayed (plasma half life of drug
increases)
Anaesthetic selection
Anticholinergic drugs
Not used indiscriminately
Preexisting Cardiac diseased patient
not tolerate increase myocardial
oxygen demand
Alpha 2 agonist causes bradycardia
Opioids cardiovascular & respiratory
depress
Butorphanol (agonist & antagonist) –
minimal cardiovascular & respiratory
depression
Barbiturate – high protein bound,
depend on redistribution & hepatic
metabolism ( use lowest possible
dose)
Ketamine Improves cardiovascular
functions, depend on renal & hepatic
clearance ( t1/2) , not use in
preexisting cardiovascular disease
Caesarian section
anaesthesia
Caesarian section anaesthesia
Basic goal
No danger for foetus and dam
No fetal depression
No decrease in uterine circulation
Good analgesia and muscle
relaxation
Physiological alteration
Cardiovascular system
cardiac output ,blood volume ,plasma
volume increase & hemoglobin ,PCV
decrease
Decrease cardiac reserve result in
hypoventilation,hypoxia,hypercarbia
Reduced hepatic detoxification
Increase renal perfusion
Fetal
Circulation
Anaesthetic selection for C.S.
Anticholinergic drugs---reduces vagal
tone during traction & manipulation
Glycopyrollate is preferred
GGE+ketamine
Alpha-2 agonist contraindicated
Inhalation rapidly cross placental
barrier
Most preferred is
Regional anaesthesia (epidural
anaesthesia)
Adv-minimal exposure to foetus
Animal remain awake
Optimum muscle relaxation &
analgesia
Disadv — hypotension due to
sympathetic nerve block
Anaesthesia in cardiovascular
disease
Patient with cardiovascular disease
Prone to fluid overload,
dysarrythemia, heart failure
Lack of sufficient cardiac reserve
Physiology
Myocardial cell for pumping action
Action of actin, myosin, tropomyosin
troponin
Free calcium around myofibrill result
in heart muscle contraction
Blood pressure
Product of peripheral vascular
resistance & cardiac output
Cardiac output = heart rate X stroke
volume
Phenothiazine, alpha 2 agonist,
barbiturate alters peripheral
resistance
Narcotic, alpha 2 agonist dissociate
anaesthesia & inhalant alters heart
rate
Impaired cardiac
output
Hypertrophy
Congestive heart
failure
Pericardial
tampnode
Mitral valve
insufficiency
Preoxygenate for 5
– 7 min. prior to
anaesthesia
Avoid
anticholinergic &
dissociate
anaesthesia
Tranq. ACP (min.
myocardial
depression)
Avoid alpha 2
agonist ( severe
disarrythemia)
Patient with hypotension or
hypovolemia
Stabilize the patient with fluid or
whole blood prior to anaesthesia
Avoid drug that increase preexisting
hypotension
Patient with anemia &
hypoproteinemia
Less Oxygen carrying capacity
Less tolerate to fluid administration
Fluid overload & pulmonary edema
Whole blood transfusion PCV is less
than 25% & protein 3.5 gm/dl
Preoxygenate before anaesthesia
Anaesthesia in renal disease
Patient with renal disease
Basic physiology
Gomerular filtration, reabsorption &
secretion
Renal blood flow regulated by
Extrinsic – nervous ( sympathetic
constrictor fiber of T4-L1) &
hormonal; control
Intrinsic - autoregulation
All anesthetics decreases rate of GFR
& RBF
Directly affect RBF or indirectly alter
renal function via cardiovascular or
neuroendocrine change
Anaesthesia that cause
catecholamine release – effect on
RBF
Xylazine suppress ADH release –
diuresis (contraindicated in
obstruction)
Nephrotoxic drug
Methoxyflurane
Amino glycosides
Amphotericin B
Iodinated radiographic contrast agent
NSAIDS
oxalates
Anaesthesia For Patient with
Respiratory Dysfunction
General considerations
Lack ability to properly expand the lung
(extra pulmonary dysfunction)
Lack ability to exchange gas (intra
pulmonary dysfunction)
Extrapulmonary
dysfunction
Intrapulmonary
dysfunction
D.H.
Pneumothorax
Hydrothorax
Thoracic lesion
Pneumonia
Pulm. edema
Intraplm.
hemorrhage
Interstitial disease
Atelectasis
BASIC PHYSIOLOGY OF
VENTILATION
• Sensors
• Controllers
• Peripheral carotid
body chemoreceptor
• Central
chemoreceptor(m.o.)
• Receptors sensing—
stretch,irritation,prop
rioception,of lung
,airway ,muscle of
diaphragm
• Cortex
• Medulla
• Effectors
• Respiratory Muscles
Anaesthetic effects
Alter ventilatory pattern by
Alter threshold of respiratory center to
CO2
Alter sensitivity of respiratory center
to CO2
Relaxing muscle of ventilation
Anaesthetic considerations
Careful examination of patient
If any abnormality then delay surgery
Before surgery Preoxygenation 7-9
minutes
Mild preanaesthetic dose
Rapid induction for quick airways
controll
Rapid &accurate intubation required
Maintain with inhalation anaesthesia
& IPPV
ANAESTHETIC AGENTS
USED
[email protected]/kg i.m.(max total dose
1mg)
[email protected]/kg i.m. (max
total dose 20 mg)
[email protected] mg/kg i.m.
Induction with thiopentone, propofol,
ketamine
Maintenance by inhalation
Nitrous oxide contraindicated
increases pneumothorax severity
Anaesthesia For Hepatic
Patient
considerations
Liver blood supply by hepatic artery&
portal vein
Anaesthesia effect on both H.A. &
P.V.
Hypoproteinemia
Hypoglycemia
Alter coagulation factors
Excessive wt. of ascitic fluids
Most anaesthesia metabolized by
liver, if liver disorder t1/2 increased
Remove ascitic fluid before
anaesthesia
Local anaesthesia (amide or esters)
prolonged generalized effects.
Anaesthesia for ocular patient
Anaesthesia for ocular patient
Basic goal
IOP maintenance
Immobilization of eye ball
Hemorrhage control
Prevention of activation of
occulocardiac reflex
Dilation of pupil
analgesia
Oculocardiac reflexes
 Triggers: Muscle traction / globe pressure
Effects: Bradycardia / sinus arrest /
resp. arrest / nausea
Prevention
Lidocain 1.0 mg/kg body wt.
Avoid hypercapnia (sensitises the reflex)
Prophylactic anticholinergic
Normal IOP horse 28-38 mm hg
Increased IOP
Decreased IOP
-Straining
-Endotracheal
intubatiuon
- Arterial pressure
- Hypoventilation
- Airway obstruction
- Hypercapnia
Drugs :
- Ketamine
- Succinyl choline
- Etomidate
Drugs:
- Barbiturate
- Propofol
- Alpha 2 agonist
- Benzodiazepam
- ACP
- Opioids
- Pancuronium
- Vacuronium
- Atracurium
Anaesthetic selection
Topical anaesthesia
Premedication
Atropine / Glycopyrollate
ACP
Diazepam
Midazolam
Induction by thiopentone/ propofol
Maintenance by halothane / isoflurane
/ sevoflurane
Nitrous oxide contraindicated (diffuse
in anterior chamber, increased IOP)
Muscle relaxant
Pancuronium, vacurinium, atracurium
( but require IPPV )
Antagonist atropine followed by
neostigmine
Anaesthesia in Thoracic
surgery
Indications
Evaluation of patient
Preoxygenation to patient
Induction by thiopentone propofol
E.T. intubation
Quick connection to anesthetic circuit
Controlled ventilation
maintenance
IPPV
only oxygen by circuit&
anaesthesia by i.v.
both oxygen & anaesthesia by
circuit
Complications
Hypothermia
Fluid loss
Pneumothorax
Submitted to
Dr. B. Justin William, Ph.D.
Dept of Veterinary Surgery
and Radiology
Madras veterinary college
Chennai-07
Submitted by
Abhishek Kumar Mishra
MVM 08052 (VSR)
REFERENCES
Lumb & Jones
veterinary Anaesthesia (3rd edition)
Farm Animal Surgery by Fubini
THANK YOU