A Nimmo

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Biography

A_NimmoDr Alastair Nimmo
Consultant Anaesthetist, Royal Infirmary of Edinburgh, Scotland.
Dr Nimmo trained in anaesthesia in Newcastle (where he also worked in Accident and Emergency and General Medicine) and in Edinburgh before working as an anaesthetist in the Charité Hospital in Berlin. He came back to Edinburgh in 1995 to take up the post of Consultant Anaesthetist with a special interest in Vascular Anaesthesia. He is co-editor of the textbook Core Topics in Vascular Anaesthesia.
Dr Nimmo’s clinical and research interests include blood transfusion, blood conservation and the diagnosis and treatment of coagulation abnormalities during surgery, regional anaesthesia and total intravenous anaesthesia. He is currently the President of the Society for Intravenous Anaesthesia, whose annual meeting will be held in Edinburgh this year:  http://www.edinburgh2012.org
Between 1996 and 1998, he anaesthetised over 100 patients for carotid endarterectomy using a combination of regional and general anaesthesia before he was able to persuade one of his surgical colleagues to agree to operate under regional anaesthesia alone! However, within a few months of the first CEA performed under regional anaesthesia, the hospital’s practice changed in 1999 to using regional anaesthesia alone for almost all cases.

Abstract

Regional anaesthesia for carotid endarterectomy
Carotid endarterctomy (CEA) under locoregional  anaesthesia in an awake or lightly sedated patient has the advantage of permitting clinical assessment of the adequacy of cerebral perfusion when the carotid artery is clamped. The GALA trial, a mulicentre randomised trial of general against local anaesthesia for CEA, found no significant difference in the incidence of stroke, myocardial infarction and death, but that surgery under local anaesthesia was more cost-effective.

The most commonly used regional anaesthetic technique is cervical plexus block. Three variants of the block may be used, alone or combination:

  • Superficial cervical plexus block – a subcutaneous injection along the posterior border of the sternocleidomastoid muscle.
  • Intermediate cervical plexus block – injection posterior to the sternocleidomastoid and deep to an apparent fascial layer.
  • Deep cervical plexus block – single or multiple injections in the region of the transverse processes of the C2, C3, C4 vertebrae.

Randomised trials have not shown any difference in the effectiveness of the different types of cervical plexus block but superficial and intermediate blocks are associated with a lower risk of serious complications than deep blocks. Ultrasound may be used to assist the performance of cervical plexus block but is not yet clear whether this improves analgesia or reduces complications.

Cervical plexus block usually provides good anaesthesia for the skin incision and initial dissection, but dissection within the carotid sheath and cross clamping of the artery may produce pain, sometimes  referred to the teeth. Carotid pain may be prevented or reduced if the surgeon injects 1 ml of local anaesthetic around the artery. This should be done very cautiously with repeated aspiration to reduce the risk of inadvertent intra-arterial injection. Topical application of local anaesthetic to the artery has also been advocated.

Some anaesthetists avoid supplementary analgesia or sedation because they may mask a change in conscious level or make the patient uncooperative. However, the block does not always provide complete pain relief, and both anxiety and discomfort from lying still with the neck extended for a long period are common. Heavy premedication, and long-acting sedative and analgesic drugs, should be avoided, but careful titration of short-acting agents can improve the patient’s comfort without impairing assessment. The level of sedation should be light enough to allow identification of a change in conscious level or in power in the contralateral arm, and detection of dysphasia or dysarthria. For the past twelve years we have used low-dose target-controlled infusions of propofol (0-1 µg/ml) and remifentanil (0-1 ng/ml) which are started before the block is performed and adjusted to ensure that the patient is appropriately lightly sedated during surgery. I will describe our experience with this technique.

Other measures which improve patient comfort during surgery include use of a transparent surgical drape to prevent claustrophobia, placing a pillow under the knees to prevent back pain, the use of a fan to cool the face, wetting the lips with water and restricting administration of intravenous. fluids to avoid a full bladder.