Spinal Anaesthesia
Description:
An injection of anaesthetic agent, typically Diamorphine or 0.5%
Heavy Marcaine, into the intrathecal space and the
cerebrospinal fluid of the subarachnoid space, around the lower spinal nerves,
below L2, so as to avoid piercing the spinal cord. This produces a temporary
block of the
sensory,
motor,
and
autonomic nerves, which come into contact with
the anaesthetic.
The
sensory block gives the
required
analgesia, but the associated
motor block causes
weakness or
paralysis, whilst the
autonomic block
causes
vasodilation of blood vessels within the
distribution of the block. Because of this vasodilation, blood pressure may fall,
and
vasoconstrictor
drugs must be made available to counter this fall.
A 'spinal' is suitable
for procedures below the umbilicus. Onset is a few minutes, and duration is 2-3 hours.
Injection point:
The vertebral level of the injection influences the rate of spread of the block, as
does the amount of local anaesthetic injected, and the position of the patient.
Injection is usually made below the 2nd Lumbar vertebra, as this is the
level at which the spinal cord terminates, and there should be less risk of nerve
damage from the needle below this level.
Fine bore needles are used, with "pencil" point and smallest gauge being least likely
to cause post-spinal headache, which is caused by CSF leakage through the hole in the dura, made by the needle.
Description:
High spinal block: Local anaesthetic depression of the cervical spinal cord and brainstem,
which may result from excessive spread of an intrathecal injection of local anaesthetic,
or inadvertent spinal injection of an epidural dose of local anaesthetic.
Symptoms:
- Hypotension
- Bradycardia
- Breathing difficulties
Prior to the above symptoms, the patient may complain of nausea, or tingling in the
fingers, which may be due to a high block at the level of T1.
Treatment:
Hypotension can be treated with:
- Volume infusion
- Vasopressors
- Raising the legs
Bradycardia treatment is by anticholinergics, such as Atropine, or β-adrenergic
agonists, such as ephedrine.
Breathing difficulty should be managed with proper ventilation and vasopressors (eg Ephedrine).
If treatment is ineffective, the patient may have to be induced by rapid sequence, and
ventilated by
IPPV.