General anaesthesia is an essential component of modern medicine. It
is a drug induced reversible condition that includes
specific behavioral and physiological traits - unconsciousness, amnesia,
analgesia, and akinesia- with concomitant stability of the
autonomic, cardiovascular, respiratory, and thermoregulatory systems.
General anesthesia in ruminants has inherent risks such
as regurgitation of ruminal contents, excessive salivation and the
possibility of pulmonary aspiration; therefore it is not always
recommended and local or regional techniques may be used instead.
Epidural anaesthesia is a central neuraxial block technique
which is used regularly in veterinary practice for treatment of
different obstetrical and surgical interferences in the perineal,
sacral,
lumbar, and caudal parts of the thoracic region of domestic animals.
There have been several scientific researches on the use of
epidural anesthesia in ruminants and other species for various surgical
and laboratory procedures. In conclusion, the disadvantages
of general anaesthesia outweigh the advantages especially in ruminant
specie. Therefore, epidural anaesthesia is the most preferred.
Anaesthesia is an indispensible prerequisite for most surgical
interventions both in humans and in animals Muhammad [1] It
is supposed to provide reversible unconsciousness, amnesia/
analgesia, muscle relaxation, and immobility with minimal
adverse effects, rapid and smooth recovery of protective reflex and
psychomotor function Bajwa [2] Hemming. General anaesthesia
is the controlled and reversible loss of consciousness for many
surgical procedures that warrant effective control of pain and
movement.
General anaesthesia is an essential component of modern
medicine. It is a drug induced, reversible condition that includes
specific behavioral and physiological traits - unconsciousness,
amnesia, analgesia, and akinesia- with concomitant stability of
the autonomic, cardiovascular, respiratory, and thermoregulatory
systems (Brown [3]. In the practice of medicine (especially surgery
and dentistry), anaesthesia is a state of temporary induced loss of
sensation or awareness. It may include analgesia (relief from or
prevention of pain), paralysis (muscle relaxation), amnesia (loss
of memory), or unconsciousness A patient under the effects of
anesthetic drugs is referred to as being anesthetized. Anesthesia
enables the painless performance of medical procedures that
would cause severe or intolerable pain to an unanesthetized
patient. Three broad categories of anaesthesia exist: General
anesthesia suppresses central nervous system activity and results
in unconsciousness, total lack of sensation and loss of protective
reflexes. Sedation suppresses the central nervous system to a lesser
degree, inhibiting both anxiety and creation of long-term memories
without resulting in unconsciousness.
Regional anesthesia and local anesthesia, which block
transmission of nerve impulses between a targeted part of the
body and the central nervous system, causing loss of sensation in
the targeted body part. A patient under regional or local anesthesia
remains conscious, unless general anaesthesia or sedation is
administered at the same time. Two broad classes exist:
a) Peripheral blockade inhibits sensory perception in an
isolated part of the body, such as numbing a tooth for dental
work or administering a nerve block to inhibit sensation in an
entire limb.
b) Central, or neuraxial, blockade administers the anesthetic
in the region of the central nervous system itself, suppressing
incoming sensation from outside the area of the block. Examples
include epidural anaesthesia and spinal anaesthesia.
To achieve the goals of anesthesia, drugs act on different but
interconnected parts of the nervous system. Hypnosis, for instance,
is generated through actions on the nuclei in the brain and is similar
to the activation of sleep. The effect is to make the patient less aware
and less reactive to noxious stimuli Miller and Ronald [4].
Loss of memory (amnesia) is created by action of drugs on
multiple (but specific) regions of the brain. Memories are created
as either declarative or non-declarative memories in several stages
(short-term, long-term, and long-lasting) the strength of which
is determined by the strength of connections between neurons
termed synaptic plasticity. Each anesthetic produces amnesia
through unique effects on memory formation at variable doses.
Inhalational anesthetics will reliably produce amnesia through
general suppression of the nuclei at doses below those required
for loss of consciousness. Drugs like midazolam produce amnesia
through different pathways by blocking the formation of long-term
memories.
Tied closely to the concepts of amnesia and hypnosis is the
concept of consciousness. Consciousness is the higher order process
that synthesizes information. For instance, the “sun” conjures
up feelings, memories and a sensation of warmth rather than a
description of a round, orange warm ball seen in the sky for part
of a 24 hour cycle. Likewise, a person can have dreams (a state of
subjective consciousness) during anesthetic or have consciousness
of the procedure despite having no indication of it under anesthetic.
It is estimated that 22% of people dream during general anesthesia
and 1 or 2 cases per 1000 have some consciousness termed
“awareness during general anesthesia” Miller and Ronald [5].
Starter cultures
General anesthesia in ruminants has inherent risks such as
regurgitation of ruminal contents, excessive salivation and the
possibility of pulmonary aspiration; therefore it is not always
recommended and local or regional techniques may be used
instead (Hall and Clarke [5]) Sheep and goats are ideally suited to
local analgesic techniques under manual restraint with or without
sedation (Taylor [6]).
Local anesthesia is any technique to induce the absence of
sensation in a specific part of the body, generally for the aim of
inducing local analgesia, that is, local insensitivity to pain, although
other local senses may be affected as well. It allows patients to
undergo surgical and dental procedures with reduced pain and
distress. In many situations, such as cesarean section, it is safer and
therefore superior to general anesthesia. It is also used for relief
of non-surgical pain and to enable diagnosis of the cause of some
chronic pain conditions. Anesthetists sometimes combine both
general and local anesthesia techniques.
However, there are other important reasons for using epidurals,
including a reduction in the incidence of perioperative pulmonary
and cardiac complications in certain settings Ballantyne [7] Beattie
[8]. The evidence that epidurals offer better postoperative analgesia
than systemic opioids is unequivocal, Block [9] and the risk of major
complications from epidurals inserted in the perioperative period
is low Cook [10].
Regional anaesthesia certainly provides high quality pain
relief Popping [11]. However, it may carry a risk of neurological
deficit. A systematic review of neurological complications after
regional anaesthesia cited incidences of neuropathy of 1.48:100
for axillary block and of 2.84:100 for interscalene block, Brull [12]
but permanent neurological injury is very rare. The balance of risks
and benefits has to be considered in the context of the particular
patient, operation, and regional block.
Epidural Anaesthesia
Epidural anaesthesia is a central neuraxial block technique
which is used regularly in veterinary practice for treatment of
different obstetrical and surgical interferences in the perineal,
sacral, lumbar, and caudal parts of the thoracic region of domestic
animals. Epidural anesthesia using local anesthetic drugs has been a
common technique used in veterinary medicine to perform surgical
procedures since the 1950s in North America and Europe. With the
advent of safer injectable and inhalational anesthetic drugs and
accessibility to anesthetic equipment, the use of epidural anesthesia
became less frequent in the following years. In the late 1980s,
however, with the recognition of opioids’ analgesic actions on the
spinal cord, the use of epidural analgesia became an important tool
that has re-emerged in intra- and postoperative epidural techniques
to provide analgesia and anesthesia in veterinary medicine Valverde
[13]. Epidural administration (from Ancient Greek ἐπί, “on, upon” +
dura mater) is a medical route of administration in which a drug or
contrast agent is injected into the epidural space of the spinal cord.
Techniques such as epidural analgesia and epidural anaesthesia
employ this route of administration. The injection can result in a
loss of sensation, including the sensation of pain by blocking the
transmission of signals through nerve fibers in or near the spinal
cord. Injecting medication into the epidural space is primarily
performed for analgesia. This may be performed using a number of
different techniques and for a variety of reasons. Additionally, some
of the side-effects of epidural analgesia may be beneficial in some
circumstances (e.g., vasodilation may be beneficial if the subject
has peripheral vascular disease). When a catheter is placed into the
epidural space a continuous infusion can be maintained for several
days, if needed. Epidural analgesia may be used:
a) For analgesia alone, where surgery is not contemplated.
An epidural injection or infusion for pain relief (e.g. in
childbirth) is less likely to cause loss of muscle power, but has
to be augmented to be sufficient for surgery.
b) As an adjunct to general anaesthesia. The anaesthetist
may use epidural analgesia in addition to general anaesthesia.
This may reduce the patient’s requirement for opioid analgesics.
This is suitable for a wide variety of surgery, for example
gynaecological surgery (e.g. hysterectomy), orthopaedic surgery
(e.g. hip replacement), general surgery (e.g. laparotomy) and
vascular surgery (e.g. open aortic aneurysm repair).
c) As a sole technique for surgical anaesthesia. Some
operations, most frequently Caesarean section, may be
performed using an epidural anaesthetic as the sole technique.
This can allow the patient to remain awake during the
operation. The dose required for anaesthesia is much higher
than that required for analgesia.
d) For post-operative analgesia, after an operation where
the epidural technique is employed as the sole anaesthetic,
or in conjunction with general anaesthesia. Analgesics are
administered into the epidural space typically for a few days
after surgery, provided a catheter has been inserted. Through
the use of a patient-controlled epidural analgesia (PCEA)
infusion pump, a person can supplement an epidural infusion
with occasional doses of pain medication through an epidural
catheter.
e) For the treatment of back pain. Injection of analgesics and
steroids into the epidural space may improve some forms of
back pain.
f) For the treatment of chronic pain or palliation of
symptoms in terminal care, usually in the short- or mediumterm.
The epidural space is more difficult and risky to access as one
ascends the spine (because the spinal cord gains more nerves as it
ascends and fills the epidural space leaving less room for error),
so epidural techniques are most suitable for analgesia anywhere in
the lower body and as high as the chest. They are (usually) much
less suitable for analgesia for the neck, or arms and are not possible
for the head (since sensory innervation for the head arises directly
from the brain via cranial nerves rather than from the spinal cord
via the epidural space).
The epidural space is the space inside the bony spinal canal
but just outside the dura mater (“dura”). In contact with the inner
surface of the dura is another membrane called the arachnoid
mater (“arachnoid”). The cerebrospinal fluid that surrounds the
spinal cord is contained by the arachnoid mater. In adults, the
spinal cord terminates around the level of the disc between L1 and
L2 (in neonates it extends to L3 but can reach as low as L4), below
which lies a bundle of nerves known as the cauda equina (“horse’s
tail”). Hence, lumbar epidural injections carry a low risk of injuring
the spinal cord. Insertion of an epidural needle involves threading
a needle between the bones, through the ligaments and into the
epidural potential space taking great care to avoid puncturing the
layer immediately below containing CSF under pressure.
There have been several scientific researches on the use of
epidural anesthesia in ruminants and other species for various
surgical and laboratory procedures. Olaifa [14] reported the
physiological and biochemical effects of epidural lidocaine with
adrenaline in pregnant West African dwarf goats and this will serve
as reference point for surgeons when operating on pregnant animals
under epidural anaesthesia especially during caesarean section
and rectal tear repairs. Olaifa [15] used epidural anaesthesia with
plain lignocaine in naturally PPR infected WAD goats to produce
effective anaesthesia which can be used for surgical procedures in
such animals. Kisani and his colleagues [16] compared the effects of
duration of epidural anaethesia in West African dwarf goats using
ketamine Hcl, lidocaine Hcl and xylazine Hcl; lidocaine-distilled
water and lidocaine-magnesium sulfate mixture Sadegh 17] Also,
comparing the efficacy of medetomidine HCl and lignocaine HCl as
epidural anesthetic in Buffalo Calves Akbar [18] Epidural morphine
improves analgesia in goats undergoing hindlimb3 and abdominal2
surgery Pablo [19]; Hendrickson et al. [20]. Lumbosacral epidural
lidocaine-epinephrine, lidocaine-xylazine and bupivacaine provide
prolonged anaesthesia that may contribute to pain relief in the
immediate postoperative period in animals undergoing surgical
procedures involving the flank, perineum and hindlimb Rostami
and Vesal [21]. The combination of bupivacaine (0.25mg kg-1) plus
ketamine (1.25mg kg-1) has been used safely for epidural analgesia
in sheep without any marked side effects Dadafarid and Najafpour
[22]. Epidural administration of tramadol alone provided good
anti-nociception in the perineal region, with a prolonged duration
of effect with no ataxia, however, tramadol-lidocaine combination
resulted in a rapid onset time and prolonged duration which may be
useful in clinical practice for a single-dose epidural administration
to enable surgical and obstetrical procedures of long duration to
be completed Dehkordi. Epidural injection of lignocaine produced
a longer duration of antinociception with lower frequency of pain
associated behavioural changes in goat subjected to castration with
the use of high tension band Ajadi [23]. Thoracolumbar epidural
technique also promotes satisfactory analgesia in the animal’s
flank, and a larger anaesthetized area. The combination of 0.5%
bupivacaine and methadone was shown to be more effective in
promoting analgesia, with a short-lasting ataxic period and no
undesirable effects when compared to bupivacaine alone Silva
[24,25].
In conclusion, from the scientific literatures and information
gathered, the disadvantages of general anaesthesia outweigh the
advantages especially in ruminant specie. Therefore, epidural
anaesthesia is the most preferred.
