50. Local anaesthesia for carotid endarterectomy

Question 1

You are asked to anaesthetise a 76-year-old man for a carotid
endarterectomy. What are the indications for this operation?

Answer 1

The indication for carotid endarterectomy is symptomatic carotid stenosis of
>70%.

For these patients there is a 16% absolute risk reduction in the combined
risk of post-operative death and stroke over more than 5 years giving a
number needed to treat of 6.3 (Rothwell et al.).

Evidence is weaker for lesser degrees of stenosis.

Question 2

Complications of carotid endarterectomy

Answer 2

1. Peri-operative stroke.
   The incidence of peri-operative stroke is
   approximately 2.2%, but is higher in those with a history of previous
   stroke (4.2%).
2. Peri-operative myocardial infarction.

Co-existing ischaemic heart disease is a significant cause of peri-operative morbidity and mortality in patients undergoing carotid endarterectomy.

The 30-day risk of MI is 2.2%.
In one study 13% of patients had a ‘silent’ Troponin I rise,
which has prognostic implications.

3. Other co-morbidity.
   Patients presenting for carotid endarterectomy
   are frequently elderly with significant co-morbidities such as chronic
   obstructive pulmonary disease, hypertension (∼70%), and diabetes.
4. Cranial nerve injury – usually transient
5. Airway compression

Question 3

Which nerves are blocked to perform carotid endarterectomy under
local anaesthesia?

Answer 3

Lesser occipital nerve
Greater auricular nerve
Transverse cervical nerve
Supraclavicular nerve

the ventral rami of C2–4 and are sensory only,
radiating from the posterior border of sternocleidomastoid just inferior to the
accessory nerve.

Question 4

Block

Answer 4

These nerves lie on the transverse processes of their corresponding vertebra
and
may be blocked here
(deep cervical plexus block).
or
at the level of their cutaneous branches
(superficial cervical plexus block).

The accessory nerve is the 11th cranial nerve and,
together with the ventral ramus of C2,
supplies sternocleidomastoid and trapezius
(together with ventral rami of C3–C4).

Branches of the trigeminal nerve supplying the submandibular area may
also be required to block the discomfort of surgical retraction.
Local infiltration of the carotid sheath is needed because it has a cranial
nerve supply.

Question 5

How do you perform a deep cervical plexus block?

Answer 5

Draw a line from the tip of the mastoid process to the anterior tubercle of
C6 at the level of the cricoid cartilage.

Intervals of 1.5 cm below the mastoid process on this line indicate the
position of the transverse processes of C2–C4 (feel C2 tubercle just below
mastoid; C6 tubercle is Chaissaignac’s).

Three injections are directed medially and downwards onto the transverse
processes at these points.

5 ml of local anaesthetic is injected after the needle is directed laterally off
the transverse processes through each.

Question 6

What are the potential complications of this technique?

Answer 6

Vertebral artery injection

Phrenic nerve runs just below mastoid and is frequently blocked too

Horner’s syndrome

Recurrent laryngeal nerve block

Intrathecal injection

Hypoglossal nerve block

Question 7

How do you perform a superficial cervical plexus block?

Answer 7

The injection point is given by drawing a line laterally from the cricoid
cartilage to the point where it meets the posterior border of
sternocleidomastoid.
Insert a 22 g short bevelled ‘block’ needle perpendicular to the skin until it
‘pops’ through the cervical fascia.
Inject 10 ml of local anaesthetic. It should track up and down if the needle is
in the right plane.

An additional 10 ml of local anaesthetic may be infiltrated along the middle
third of the posterior part of the sternocleidomastoid up and down the
posterior border of the sternocleidomastoid between the skin and muscle.

Supplementation by the surgeon is often needed (this is also the case when
the deep block is used). Patients are also less likely to require supplementary
analgesia in the 24 hours after surgery with the deep cervical plexus block.

Question 8

What alternative regional technique may be used for carotid
endarterectomy

Answer 8

Cervical epidural is an alternative technique and does provide good operating
conditions. However, it is associated with a significant risk of major anaesthetic
complications including dural puncture, epidural venepuncture and
respiratory muscle paralysis.

Question 9

What are the advantages and disadvantages of local anaesthesia vs.
general anaesthesia for carotid endarterectomy?

Answer 9

Advantages of local anaesthesia

There is preservation of autoregulation, the patient acts as his own cerebral
monitor, there may be a lower incidence of BP variation and there is less need
for drugs to control BP post-operatively

A large-scale study of general anaesthesia vs. local anaesthesia (GALA),
however, recently concluded that there is ‘no reason to prefer LA or GA’.

A meta-analysis of the non-randomised studies showed that the use of local
anaesthetic was associated with significant reductions in the odds of death
from all causes, stroke, myocardial infarction and pulmonary embolism
within 30 days of surgery.

A meta-analysis of the randomised studies showed that the use of local
anaesthetic was associated with a reduction in the risk of local
haemorrhage within 30 days of surgery, but there was no evidence of a
reduction in the odds of operative stroke. However, the trials were small
and in some studies intention-to-treat analyses were not possible.

Question 10

Disadvantages of local anaesthesia

Answer 10

1. No fall in cerebral metabolic rate due to GA.
2. Discomfort due to a fixed posture held for a protracted period.
3. Need for co-operation.3
4. If there is cerebral ischaemia, the patient may not cooperate.