general consideration in lage animals in anesthesia

1. CONSIDERATIONS FOR
GENERAL ANESTHESIA
IN LARGE ANIMALS
Zaid bashir
J-17-MV-
511

2. introduction
Large Animals
Ruminants Equines
• Cattle
• Buffaloe
s
• Sheep
• Goat
• Camel
• Horses
• Ponies
• Mules
• Equine anesthesia is a challenge when compared with ruminant anesthesia.
• 95% of Equine surgeries are done under General anesthesia whereas 80-
90% of surgeries in ruminants are done under Local or Regional
anesthesia.

3. Considerations for equine surgical
patients
 Horses are difficult to anesthetize.
 A thorough knowledge of the appropriate use of anesthetic
agent and equipment is necessary for high quality equine
anesthesia.
 Since, perioperative period is relatively complicated in
horses, animal handling techniques should be effective and
well planned.
 The size and the mass make induction and recovery
dangerous to both animal and personals, causing

4. Cont…
 This necessitates the need of sufficient padding to
prevent Myositis and Neuropathy or both.
 The equine temperament rarely tolerates
immobilization, so inadequate anesthesia may lead
to violent reaction.
 Also anesthetics frequently induce hypoxemia or
hypotension
Knowing these possibilities, the anesthetist must be
prepared to deal with horse that is too deep or too
light; finding the correct balance is sometimes the
elusive goal.

5. Considerations should include:

6. Preanaesthetic preparation
PHYSICAL EXAMINATION:
 A preoperative physical examination is critical but need not be time
consuming.
 In emergencies, the examination may be abbreviated but not
omitted.
 Auscultation of heart: to obtain a baseline heart rate (attention to
presence of murmurs and arrhythmias).
 Auscultation of lung and trachea, observation of nostrils and
thorax: for signs of respiratory disease or distress.
 The temperament of horse should be assessed to decide induction
and recovery techniques to be followed.

7. Cont…
 A horse with visual deficit may require special handling
to avoid approaches from the blind side during
induction and recover, whereas a horse with long bone
fracture may require sling support for induction and
recovery.
 Signs of underlying disease should be noted
 In case of dehydration or electrolyte imbalance, fluid
therapy and electrolyte therapy is indicated before
induction of anesthesia.

8. Cont…
 Medical history :
 The actual owner?
 The insurance status?
 Patients recent history?
 Whether any depressants given?
 current problems?
 Treatment already been given?
 Any known behavioral problem?
 Any history of “tying up”?
 Normal diet of the animal?
Generally, a good history provides a significant amount of data and
may provide information that may alter anesthetic management.

9. Cont…
Preanesthetic patient preparation:
 For elective surgery under ideal circumstances,
preanesthetic preparation should include withholding
of grain and hay for 12 hours with access to water
allowed until the time of premedication.
 Accurately weighing the horse, removing shoes,
bathing or completely grooming the horse, washing out
mouth, and placement of a catheter in jugular vein.
 Its important to have an accurate weight for calculation
of drug dosages, if the scale is not available, a weight
tape may improve the accuracy of estimated weight.

10. Cont…
 Preanesthetic tranquilizers or sedatives aid induction
by decreasing apprehension.
 Excitement can lead to higher drug requirements and
increased endogenous catecholamine release.
 In some cases, premedicants improve recovery.
 The choice of premedication depends on certain
factors: Health and disposition of horse.
Medications previously administered.
Induction drugs to be used.
Types of surgical procedures planned
Facilities and personals available.

11. Preparations for induction and
maintenance

12. Endotracheal intubation
 Usually endotracheal intubation is easily accomplished
in the horse.
 Common causes of difficult intubation are improper
positioning of the head and neck, an improperly sized
endotracheal tube, insufficient depth of anesthesia and
less commonly, partial laryngeal paralysis.
 A 30mm internal diameter endotracheal tube will fit the
average adult (450kg )horse.
A small horse (350-400) may require smaller diameter
(26mmID) tubes.
Foals and ponies require tubes ranging in size from
12-22mmID.
If laryngeal paralysis is present or in case of unsuccessful repeated
attempts ,a sterile stomach tube may be positioned into the trachea to act
as “guide tube ”,over which the endotracheal tube can be passed.

13. Positioning, padding during
anesthesia
 Attention to patient positioning, padding and limb support is critical for the
prevention of Postoperative Myopathy or Myositis and Neuropathy.
 Prevention of myositis accomplished by meticulous attention to padding
and positioning.
 If in lateral recumbency, the shoulder and hip should be padded(inner
tubes, dunnage bags, air mattresses or foam padding can be used).
Halters removed to prevent facial nerve paralysis.
 Postoperative myositis has been linked to hypotention therefore monitor
blood pressure.
Facial, Radial, and Peroneal nerve paresis may occur by even short periods of
recumbency on hard surfaces.
In lateral recumbency, plaques and edema and areas of myositis can occur
on the
downside as a result of hard surface and on upper side, usually, following
prolonged periods of hypotention.

14. Horses have thin
skin with more
blood supply.
As the horse is
casted for more
than an hour
The blood vessels press
leading to lack of blood
supply.
This leads to
anaerobic
metabolism of
muscles resulting in
lactic acid formation
Anoxia leads to
rhabdomyolysis
leading to
muscle damage
and fibrous
tissue formation.
Never cast a Horse for more than one hour?

15. Monitoring and support
 Regular accurate assessment of anesthetic depth is
essential, but perhaps this is more difficult in horse than in
other species.
 Jaw tone cannot be used to assess muscle relaxation as it
is in small animals, and heart rate varies less with depth of
anesthesia than in other species.
 The anesthetist should evaluate as many body systems as
possible, especially central nervous, cardiovascular, and
respiratory systems, and make the best possible judgment
about depth of anesthesia.

16. Eye signs
 Evaluation of eye signs provides information about the
central nervous system.
 With inhalants, a surgical plane anesthesia is usually
achieved if the palpebral reflex is absent or slow, while the
corneal reflex is maintained.
 Eye rotates from the central to the rostro-ventral position
as the horse passes from light to moderate anesthesia
then back to central position in deep anesthesia.
 Although, the presence of nystagmus indicates light
anesthesia levels, many horses show a periodic
nystagmus while showing no other signs of insufficient
anesthesia.

17. Cont…
 Tear production usually occurs
when horse is lightly
anesthetized.
 Eye reflexes may also be
affected by induction drugs; a
strong palpebral and central
position of eye are maintained
by ketamine as primary

18. Skeletal muscle relaxation
 Muscle relaxation also provides
information about the CNS varying
with kinds of drugs used.
 If Guaifensin is used, muscle
relaxation may be good without
adequate analgesia.
 Ketamine may produce little muscle
relaxation, even when the horse is
sufficiently anesthetized.

19. Heart rate and rhythm
 Changes very little with changes in depth of
anesthesia in horse.
 In fact, ECG may appear normal when mechanical
function is totally inadequate, making it an unreliable
indicator of horse’s condition.
However, any sudden change in heart rate should be
investigated immediately, because it may indicate a
major problem.
 Most likely occurances:
Sudden bradycadia due to
increased vagal tone (asso. with
surgical stimulation).
Sudden tachycardia due to
overzealous administration of

20. Respiratory rate and rhythm
 Respiratory rate and rhythm usually are consistent during
anesthesia; therefore any change should be investigated.
 Slow, deep breaths usually indicate adequate ventilation,
but it is almost impossible to evaluate how effectively a
horse is ventilated or oxygenated without measuring
arterial blood gas.
 Hypoxemia may occur when injectable anesthetics are
used if supplemental oxygen is not provided.
 Its very important to be sure that the horse is breathing
regularly and to monitor mucous membrane.

21. Recovery from anesthesia
 Recovery from anesthesia is a critical time for a
horse.
 Complications while recovery include:
 Precautionary measures:
 Limb fractures.
 Myositis .
 Laryngospasms.
 Quiet, padded area free from hazards
should be chosen.
 Large recovery room for allowing horse
to stand and move (size 5m*5m).
 If recovery to occur outside, clean grassy
area with safe fencing and without
obstacles should be chosen.

22. Cont…
 Ideally horse regain consciousness within 10-20minutes of
anesthetic discontinuation, roll on sternal recumbancy for a brief
period and then rise.
 Most horses return to standing within 1 hour of anesthetic
discontinuation.
 Attempts to speed the recovery process usually causes horse to
have prolonged period of unsteadiness once they stand.
 Recovery should only be prompted if a horse had cardiopulmonary
embarrassment while anesthetized.in this instance, rolling the
horse into sternal recumbency during recovery improves
oxygenation.

23.  Insufflation or the use of demand valve can also support
oxygenation.
 Horses that try to rise too quickly can be sedated with
small doses of intravenous xylazine (0.2mg/kg).
 Laryngospasm is infrequent in horse . Some prefer to
leave endotracheal tube in place until a horse is standing.
Otherwise remove the ET when horse begins to swallow in
lateral recumbency.
 Occasionally, particular after dorsal recumbency,
congestion of nasal passage can cause snoring.

24.  Congestion can be alleviated by:
Intranasal administration of phenylephrine
prior to recovery passage of 30-40cm long, 10-
14mm internal dia Et into nasopharynx via ventral
meatus.
 Tube is removed after horse stands. Horses that fail to rise within 90 min of the end of anesthesia should be evaluated
further.
 Potential causes include weakness, rhabdomyolysis, or neurogenic paralysis.
 Treatment includes intravenous fluid administration to promote perfusion and
assure urine formation to minimize the chances for myoglobinuria renal failure.
 Acepromazine is given is small doses to calm the horse and promote peripheral
perfusion.

25. Ruminants
 Ruminants usually accept physical restraint well and that in
conjunction with local or regional anesthesia is sufficient to enable
completion of any procedure.
 The diagnostic or surgical procedures that are more complex
require general anesthesia.
 Preanesthetic preparation include:
 Domestic animals have a multicompartmental stomach with a
large rumen that does not empty completely.

 Fasting
 Estimation of body
weight
 Hematologic values.

26. • Each species is susceptible to complications
associated with recumbency and anesthesia
• Complications include:
• To reduce this calves, sheep, goats should be fasted
12 to 18 hrs and deprived of water for 8-12 hrs. Adults:
fasted for 12-24hrs and deprived of water for 12-18hrs.
 Tympany
 Regurgitation
 Aspiration pneumonia

27. • Fasting of neonates is not advisable because
hypoglycemia may result.
• Fasting and water deprivation will decrease the
likelihood of tympany and regurgitation by
decreasing volume of fermentable ingesta.
• Fasting can cause bradycardia in cattle.
• Additionally, pulmonary functional residual capacity
may be better preserved in fasted animals.

28. Cont…
For accurate drug administration, the
animal must be weighed.
Anticholinergics are usually not
administered to domestic animals prior to
induction of anesthesia.
They do not consistently decrease
salivary secretions unless used in higher
doses given frequently.
Anticholinergics, while decreasing the
volume of secretion, make them more
viscus and difficult to clear from trachea.

29. sedation
 Acepromazine is most commonly used phenothiazine
derivative tranquilizer used in veterinary anesthesia.
 It is not commonly used in ruminants however can be
used in a manner similar to its use in horse:
Lower doses of acepromazine are required in ruminants
than in horses.
 Acepromazine should not be injected into the
coccygeal vein.
Produces calming effect with minimal muscle relaxation or ataxia.
Does not produce analgesia but may potentiate other drugs such as
opiods that are analgesics.
Close proximity to coccygeal artery makes risk of intrarterial injection
possible with subsquent loss of tail.

30. Considerations at the time of
induction
 Ruminants are not always sedated prior to induction of
anesthesia.
 Atraumatic physical restraint can be used to lieu of
sedatives in some circumstances.
 Because ruminants seldom experience emergence
delirium, sedation during recovery period is nor required.
 In some instances, primarily adult bulls, sedation is
required for safer handling during induction period.
 Sedation tends to lengthen the recovery period from
general anesthesia and increase likelihood of regurgitation.

31. Cont…
 General anesthesia can be induced by either
injectable or inhalation techniques.
 Anesthesia can be induced in large animals either
by intravenous or intramuscular techniques.
 It can also be induced with halothane, isoflurane,
or servoflurane by masks in small or debilitated
camelids or camelids restrained with xylazine-
ketamine etc.
Mask in healthy untraquilized adult camelids is usually not attempted because
application of mask may provoke spitting.
Addition of nitrous oxide(50%of total flow) to the inspired inhalant gas mixture
will speed induction.

32. INHALENT ANESTHETIC
MACHINE

33. INTUBATION

34. INTUBATION OF COW BY
PALPATING LARYNX

35. Inhalant anesthesia:
 • For prolonged or painful
 procedures
 • Isoflurane - most common
 inhalant anesthetic utilized and may
 be administered after an injectable
 induction agent
 • Sevoflurane - required in
 higher doses than Isoflurane

36. Cont…
 In cattle: jugular furrow is present making IV administration
easy.
 However, in case of camels, Jugular Furrow is absent
which makes IV administration difficult.
 Rostral part of the jugular vein is covered with carotid
sheath, which can lead to faulty administration into carotid
artery.
 In long necked animals, valves in veins are present to
check the backflow of blood, needles may get stuck in

37. maintenance
 Tracheal intubation is recommended all ruminants and
camelids because it provides a secure airway and prevents
aspiration of salivary and ruminal contents if active or
passive regurgitation occurs.
 As rumen contents contain more solid material than do the
monogastric animals, there is greater potential for ingesta
to block the larynx while the more fluid portion drains from
mouth.
 Consequently, patients that are not intubated are at higher
risk of aspiration of rumen contents.
 Treatment includes removal of ingesta from buccal cavity
or buccal lavage prior to extubation

38. Supportive therapy
Patient
positioning
• Adult cattle may suffer from postanesthetic myopathy or
neuropathy due to improper positioning and padding.
• Post anesthetic myopathy does not occur in sheep; goat.
Fluid
administration
• Is important during anesthesia to correct preexisting dehydration.
• A balanced electrolyte solution is preffered.
Respiratory
supportive
therapy
• Domestic animals tend to hypoventilate while anesthetized
• Mechanical ventilation should be considered when the procedure
exceeds 1.5hrs and is indicated to prevent hypoventilation.

39. recovery
 Ruminants recover well from general anesthesia and
seldom experience emergence delirium, make
premature attempts to stand or sustain injury.
 When α2 agonist is used as part of the anesthetic
regimen, an α2 antagonist can be used to hasten
recovery.
 Domestic animals should not be extubated before the
laryngeal reflex has returned.
 Although ruminants recover well from GA with minimal