Influence of the Concentration of the Local Anesthetic Ropivacaine on the Quality of a Ultrasound Guided Intermediate Cervical Block.

Carotid endarterectomy is commonly performed under cervical plexus block. This is presumed to offer advantages over general anesthesia in terms of monitoring neurological function during cross-clamping of the carotid artery since, in conscious patients, speech, cerebration, and motor power provide early measures of inadequate cerebral perfusion. Some studies also claim lower shunting requirements, lower cardiovascular morbidity, and shorter hospital stay.

Traditionally, the common methods of cervical plexus block are termed 'deep' or 'superficial'. The deep block, as described by Moore or Winnie and colleagues, consists of identifying the transverse processes of upper cervical vertebrae C2 - C4 and injecting local anesthetic directly into the deep (prevertebral) cervical space. This may be achieved either as separate injections or as a single injection. The superficial block incorporates a variety of procedures. The simplest is a s.c. infiltration of local anesthetic along the posterior border of sternocleidomastoid muscle by either the surgeon or the anesthetist.

An 'intermediate' block is one where the injecting needle pierces the investing fascia of the neck, deep to the s.c. layer, but superficial to the deep cervical (prevertebral) fascia. It is also possible to use a 'combined block', consisting of a deep injection and a superficial or intermediate injection.

Practitioners may prefer one block to another, but no consensus exists on the efficacy of one block when compared with another. However, it has been suggested that complications of the technique are related to the deep injection and not the superficial (or intermediate) injection. These complications include intrathecal or intravascular injection, respiratory problems related to phrenic nerve paralysis, or local anaesthetic toxicity.

In this study the Influence of the concentration of the local anesthetic ropivacaine on the quality of the intermediate cervical plexus block for carotid endarterectomy will be evaluated. For this purpose two different concentrations of ropivacaine will be compared (3,75% vs 7,5%). The primary endpoint of the study will be the quantity of the additional needed local anesthetic to achieve adequate operative analgesia. Furthermore we will record the frequency of the most common side effects as well as the patient satisfaction with a standardized questionnaire.