2.11 Cervical Plexus Flashcards
Relevance
The question of which of general or local anaesthesia for carotid endarterectomy is the better option was
not informed definitively by the GALA trial, not least because lack of funding meant
that this was discontinued before the planned 5,000 patients had been recruited and
because there was considerable criticism about aspects of its methodology.
Clinical
practice changed over the years during which patients were recruited, and neither
the general anaesthetic nor the regional anaesthetic techniques were standardized.
Nonetheless, in conjunction with other evidence it seems clear that in respect of
major perioperative outcomes, there is no difference between regional and general
anaesthesia, with mortality and stroke rates of around 5% in both groups.
Nerve supply to neck
nerves which supply the lateral aspect of the neck all derive from the ventral
rami of the second, third and fourth cervical spinal nerves (C2, 3, 4).
The first cervical nerve has no sensory distribution to skin.
Superficial cervical plexus anatomy
The cutaneous supply to the anterolateral aspect of the neck
is via the anterior primary rami of C2, C3 and C4.
These nerves emerge from the posterior border of the
sternocleidomastoid muscle midway between the
mastoid and the sternum.
The accessory nerve is immediately superior at this point.
The lesser occipital nerve (the first branch) supplies the skin
of the upper and posterior ear,
the greater auricular nerve (the second branch) supplies the lower
third of the ear and the skin over the angle of the mandible,
the anterior cutaneous nerve (the third branch) supplies the
skin from the chin down to the suprasternal notch and
the supraclavicular nerves (the fourth branch) supply the skin over the
lower neck, clavicle and upper chest
Superficial cervical plexus block
Superficial cervical plexus block:
all these nerves can be blocked at the midpoint of
the sternocleidomastoid by infiltrating up to
20 ml of local anaesthetic solution
between the skin and the muscle.
The external jugular vein crosses the muscle at
this point and can be a useful landmark.
Deep cervical plexus anatomy:
Deep cervical plexus anatomy:
The ventral ramus of the second nerve emerges from between the
vertebral arches of the atlas and axis and runs forwards between their
transverse processes to exit between
longus capitis and levator scapulae.
The ventral ramus of the third nerve exits the intervertebral foramen lying in a sulcus in the
transverse process, emerging between the
longus capitis and scalenus medius muscles.
The ventral rami of the fourth and remaining cervical nerves appear
between the
scalenus anterior and the scalenus medius.
Deep cervical plexus block:
Deep cervical plexus block in effect is a paravertebral block of C2, C3 and C4.
Needles are inserted at each of the three levels,
using as landmarks a line between the mastoid process and the prominent tubercle of the
sixth cervical vertebra
(which is palpable as Chassaignac’s tubercle at the level of the
cricoid cartilage).
The C2 transverse process is approximately one finger’s breadth
below the mastoid process along this line with C3 and C4 following at similar
intervals caudad.
After encountering the transverse process, 5–8 ml of local anaesthetic
can be injected with due precautions.
Because there is little resistance to the spread of solutions through the paravertebral space in the cervical region, adequate anaesthesia can also be obtained using a single needle technique and a larger volume
(15–20 ml) at a single level, usually C3.
Indications for cervical plexus blockade:
these include anaesthesia for carotid surgery under local anaesthesia,
clavicular surgery (typically open reduction and
internal fixation following trauma) and thyroid surgery.
Advantages of CEA under local anaesthesia
normal cerebration depends on adequate cerebral perfusion,
and in the awake patient it is usually obvious whether
this is being preserved.
In effect the patient acts as their own cerebral function monitor,
and signs of cerebral ischaemia are an indication for surgical shunt insertion.
Local anaesthesia does not interfere with cerebral autoregulation, and signs of
cerebral ischaemia are an indication for surgical shunt insertion.
Local anaesthesia does not interfere with cerebral autoregulation, and the requirement for vasoactive drugs is less.
Proponents of the technique claimed lower morbidity and mortality
rates, but there is no evidence to support that view.
Disadvantages of CEA under local anaesthesia
Disadvantages of CEA under local anaesthesia:
cerebral oxygen consumption does not fall
(the cerebral metabolic rate for oxygen, CMRO2, decreases under general
anaesthesia),
and a higher pulse and blood pressure during surgery results in higher
myocardial oxygen demand than would otherwise be the case.
It does also mean, however, that cerebral perfusion pressure is higher.
Cooperation can on occasion be a problem; immobility during extended surgery may be very uncomfortable for the
patient and, should their cerebration be obtunded by ischaemia, they may become
restless and agitated.
The nerve blocks may sometimes prove inadequate as surgery
proceeds, but local supplementation by the surgeon can circumvent this problem.
Advantages of CEA under general anaesthesia:
general anaesthesia allows more control,
can be extended indefinitely if necessary and during long procedures is more
comfortable for the patient.
At concentrations up to 1.0 MAC, sevoflurane decreases
cerebral blood flow and CMRO2.
Experimental evidence suggests that general anaesthetic
agents may confer a degree of neuroprotection, but the data are not robust
enough to mandate their use.
Disadvantages of CEA under general anaesthesia:
it is clearly more difficult to assess cerebral oxygenation,
and, although low concentrations of volatile agents do reduce CMRO2,
they may still impair dynamic cerebral autoregulation at MAC levels
below 1.0.
Monitors of cerebral oxygenation include near-infrared spectroscopy
(NIRS), electroencephalography (EEG), somatosensory evoked potentials (SSEPs)
and transcranial Doppler.
There are in addition the generic complications of general anaesthesia (in which the examiner will have little interest) and those of anaesthesia
for head and neck surgery, such as restricted access to the airway.
Complications:
Complications: superficial cervical plexus block risks mainly what can be described as
generic complications of local anaesthesia,
namely intravascular injection and systemic toxicity.
The complications of deep cervical block are much the same as those associated
with interscalene block,
which is not surprising given the anatomical similarities,
and include injection into the vertebral artery,
extension of the block either extradurally or intrathecally,
phrenic nerve block and cervical sympathetic block, which will
manifest as Horner’s syndrome (miosis, ptosis, anhidrosis and enophthalmos).
The recurrent laryngeal nerve may also be affected with resultant hoarseness
The GALA trial:
this multicentre trial was conducted over around seven years
between 2001 and 2007 and recruited 3.500 of the planned 5,000 patients, who were
randomized either to general or regional anaesthesia for carotid endarterectomy.
Thereafter, anaesthetists and surgeons were free to follow their routine practice.
Primary outcomes were death, stroke or myocardial infarction within 30 days of
surgery; secondary outcomes added death at 1 year, length of stay and quality of life.
There were essentially no differences between the groups.
Criticisms of the trial
included the fact that surgical and anaesthetic techniques were very variable; an
obvious example being the use or otherwise of shunts, and that both may have
changed during the relatively long period during which patients were recruited
(GALA Trial [Lancet 2008, 372: 2132–42]).
