Comparison of two methods of cervical plexus block for carotid endarterectomy
*Jarosław Wośko, Sławomir Sawulski, Wojciech Dąbrowski
Department of Anaesthesiology and Intensive Therapy, Medical University of Lublin
Background. Cerebral thromboembolism is one of the main risks of carotid artery occlusive disease. Carotid endarterectomy is a preventive operation to reduce the incidence of embolic stroke. Of prime concern during this surgery is protection of the brain during carotid cross-clamping. Since blood flow to the brain is provided via the non-affected carotid artery and collateral circulation, it is essential to maintain the consciousness of the patient during surgery in order to assess the effects of cross-clamping. Changes in speech or motor function indicate inadequate perfusion and the need for immediate bypass. Regional anaesthesia has therefore been regarded as the method of choice in this kind of surgery.
Methods. Seventy-five ASA I – III patients, scheduled for carotid endarterectomy, were randomly allocated to two groups to receive a combined cervical plexus block with two different techniques: according to either Winnie or to Moore. The quality of anaesthesia was compared using the Verbal Numeric Rating Score (VNRS) and the Visual Analogue Score (VAS).
Results. Both methods were safe and provided fair analgesia, with similar patient satisfaction and minimal cardiovascular side effects. Serious cerebral ischaemia requiring temporary bypass occurred in three cases. Additional local infiltration was necessary in both groups.
Conclusion. The cervical plexus block, regardless of the technique used, provides high satisfaction and safety during cervical endarterectomy.
Atheromatous stenosis of the carotid artery is one of the main risk factors of cerebral stroke. One of the treatment methods used is surgical restoration of carotid patency. Initially, carotid surgeries involved the ligation of carotid arteries due to haemorrhage or injury. In 1954, Eastcott and co-workers  successfully operated on a 66-year-old woman diagnosed arteriographically with internal carotid artery stenosis.
The key moment of the procedure is temporary, complete clamping of the common, internal and external arteries. Once the blood flow at the stenosis site is stopped, the artery is opened and atheromatous plaque removed. During surgery, the blood flows to the brain through the contralateral carotid arteries and vertebrobasilar circulation and thanks to the efficiency of the Willis’ circle, the blood reaches the areas supplied primarily by the artery operated on.
The efficiency of cerebral flow during artery clamping is assessed on the basis of abilities of awake patients to respond to simple commands. Continuous and thorough observation of a patient is the best way to prevent intraoperative cerebral hypoxia. For these reasons, block anaesthesia is a recognized method of management during surgical restoration of carotid artery patency.
The majority of authors believe that the most favourable conditions for restoration of carotid artery patency are provided during combined superficial and deep cervical plexus blockage. Superficial cervical plexus blockage is carried out by injecting the local anaesthetic solution into punctum nervosum . Deep cervical plexus blockage may be provided by a single injection of local anaesthetic at C3 or C4 level – according to the Winnie method (1976)  or by successive injections at C2, C3 and C4 levels – the Moore method .
The objective of the present study was to compare the efficacy of two techniques of cervical plexus blockage for carotid endarterectomy. The quality of intraoperative analgesia and anaesthesia–related satisfaction of patients were assessed.
The study was approved by the Bioethics Committee of Medical University of Lublin and involved all patients consecutively scheduled for carotid endarterectomy. During the anaesthestic visit on the day preceding surgery, the informed consent was obtained from each patient. Patients were randomly allocated to two study groups, both undergoing combined cervical plexus blockage. The superficial blockage was carried out in the same way in both groups; the deep blockage was performed according to the Winnie method (group W) or Moore method (group M).
The superficial blockage was provided with 1.5% lignocaine in 0.9% NaCl, in the total volume of 15 mL. The anaesthetic was administered in fractionated doses, 3mL, each. Before the administration of a successive dose, the direction of a needle was changed and the solution injected above the superficial lamina of the cervical fascia: at the skin puncture, bilaterally along the posterior border of the sternocleidomastoid muscle. After 5 min the deep cervical plexus blockage was initiated.
In group W, the needle was advanced until the resistance of the transverse process of the C3 was detectable and withdrawn by about 1-2 mm; the 0.375% bupivacaine solution in 0.9% NaCl (in the total volume of 15 mL) was injected. The injection was carried out in divided doses, 3 mL each.
In group M, once the transverse processes of the C2, C3 and C4 vertebrae were identified, the 0.375% bupivacaine solution in 0.9% NaCl was injected in the doses of 5 mL per each of the three spinal nerves blocked.
Each successive dose of a local anaesthetic was preceded by the check-up aspiration test. The surgical procedure was initiated 20 min after the local anaesthetic administration.
Once pain sensations develop, the blockage was supplemented with infiltration anaesthesia with 1% lignocaine. Moreover, intraoperative blockage of the carotid glomus was routinely performed with the same agent. Supplementary intravenous analgesia with fentanyl in boluses of 0.05 mg each was administered if need be.
Pre- and intra-operatively, the following parameters were recorded in each patient: ECG, HR, SAP and DAP. Arterial blood pressure was determined indirectly (Korotkow) and directly (using the arterial line and transducer system). To standardize the data, SAP and DAP values recorded indirectly were used. During anaesthesia, ECG and HR were continuously measured; SAP and DAP were recorded every 10 min.
Intraoperative changes in SAP, DAP and HR by more than 20% of baseline values were considered significant; those exceeding 40% as requiring therapeutic intervention. Urapidil was used to reduce SAP and DAP whereas ephedrine to elevate them. Decreased or increased HR was treated with atropine or metoprolol, respectively.
The values were recorded at the following procedure stages: 1 – directly before cervical plexus blockage (baseline), 2-20 min after anaesthesia, immediately before the onset of surgery, 2-1 – at the surgery onset, 2-2 – at 10 min, 2-3 – at 20 min, 2-4 – at cervical carotid artery clamping and 2-5 – during the skin suturing.
The efficacy of blockage was assessed on the basis of additional requirements of intraoperative pain management. In both groups, the total volume of 1% lignocaine solution administered during surgery in the form of infiltration anaesthesia and total fentanyl dosage used during anaesthesia were recorded.
Twenty-four hours after surgery, patients were asked to assess subjectively the quality of blockage; two scales were used – the verbal numeric rating score (VNRS), in which 0 denotes – lack of pain and 10 – the strongest pain and visual analogue score (VAS) for assessing personal satisfaction (from 1 pts to 10 pts).
Statistical analysis was conducted using Statistica 6.0 software (Statsoft, USA). All numerical data were presented as mean and standard deviation (x±SD). The distribution of numerical data was assessed using the Shapiro-Wilk W test. The Student’s t-test was applied for normal distribution; inter-stage analysis for nonparametric distributions was carried out using the Wilkinson’s and sign tests whereas the inter-group analysis was performed using the Mann-Whitney U test. P<0.05 was considered significant.
Eighty ASA I-III patients were included. Four of them, despite initial qualification were excluded from the study, mainly due to lack of spirometry-related cooperation. In total, the study population consisted of 75 patients, 23 women and 52 men; one patient underwent procedures of both carotid arteries at the interval of 4 weeks.
Group W consisted of 44 patients, 14 women (31.1%) and 30 men (68.9%); their mean age was 67.6±9.3 years and BMI 26.2±3.5 kg m-2. Twenty (45%) patients were treated due to arterial hypertension and 12 (27%) because of coronary disease.
Group M encompassed 31 patients, 9 women (29%) and 22 men (71%); their mean age was 66.8±9.2 years and BMI 26.3±4.2 kg m-2. Arterial hypertension was diagnosed in 17 patients (55%) and coronary disease in 7 (23%). There were no significant inter-group differences in demographic parameters.
In all cases, cervical plexus blockage enabled surgical restoration of carotid artery patency. In both groups, no anaesthesia-related complications were observed. In group W, the volume of intraoperative lignocaine was 5.0±4.17 mL and in group M – 3.98±3.39 mL. Fentanyl was administered to 12 patients in group W and 10 in group M. Its mean dose was 0.032±0.06 mg and 0.031±0.05 mg, respectively. In all patients, pre-anaesthesia blood pressure measurements (stage 1) were considered as the baseline values.
In group W, SAP values at successive measurement stages were comparable and ranged from 149±19.8 mm Hg to 153.5±27.1 mm Hg (Fig. 1). The intraoperative SAP increases exceeding the baseline value by 20% (stage 1) were noted in 9 (20%) patients whereas decreases in 8 (17.8%) individuals. In 4 cases, urapidil was required to reduce the arterial pressure; in the other 4 patients, ephedrine was administered to increase pressure.
In group M, the lowest SAP value was 152.6±22 mm Hg and the highest one 161±26.9 mm Hg. Increases and decreases in SAP exceeding the baseline value by 20% were observed in 5 (16.1%) and 3 (9.7%) patients, respectively. Ephedrine was used in 2 and urapidyl in 1 patient. A significant increase in SAP was found between stage 1 and 2-1 (p<0.01) (Fig. 1).
There were no significant inter-stage differences in DAP in group W. Increases by over 20% were noted in 5 (11.1%) patients whereas decreases in 6 (15.6%) (Fig. 2). In group M, DAP ranged from 90.3±10.1 to 97.2±11.7 mm Hg (Fig. 2). In 5 (17.2%) patients, DAP increased by over 20% of the baseline value. Significant changes in DAP were observed in stages 2-1(p<0.05), 2-3 (p<0.05) and 2-4 (p<0.01) (Fig. 2).
The values of HR ranged from 77.4±16.4 min-1 to 85.5±20.4 min-1. HR was accelerated by more than 20 % of the baseline value in 7 (15.6%) and slowed down in 4 (8.9%) patients in group W. Similar effects were observed in 5 (16.1) and 3 (9.7%) patients in group M, respectively (Fig. 3).
There were no significant inter-group differences in the quality of surgical procedures. In group W, the severity of intraoperative pain according to VNRS was 3.2±1.65 whereas in group M – 3.0±1.32; satisfaction according to VAS was 8.35±1.64 and 9.0±1.11, respectively.
During anaesthesia, 4 patients (two in each group) developed hoarseness; in 3 of them, symptoms subsided spontaneously within 24 h and in 1 – were still observed at postoperative day 14. In all these cases, the laryngological examination disclosed unilateral paralysis of the vocal cord on the operated and anaesthtised side. Three patients developed intraoperative symptoms of severe focal cerebral ischemia requiring temporary bypasses. In 1 case, ischemic symptoms developed in the early postoperative period and were related to decreased arterial pressure. In 3 patients, transient, mild intraoperative manifestations of cerebral ischemia were observed, which subsided as a result of treatment. Moreover, 2 intraoperative undesirable cardiac events occurred: in one patient – pulmonary oedema in the course of acute left ventricular failure and in another one – anginal episode. The symptoms subsided once appropriate therapeutic management was instituted. In 2 patients, the operative wound revision was necessary in the early postoperative period due to symptoms of a progressing haematoma.
Superficial cervical plexus blockage is relatively simple and the anatomical landmarks clear. In both groups, the 1.5% lignocaine solution was used in the total volume of 15 mL, which provided anaesthesia before identification of anatomical landmarks of the deep layer. Other authors used 20 mL of 2% lignocaine yet in some patients the plasma lignocaine levels exceeded 6 µg mL-1, which is regarded as the potential toxic value . Another argument in favour of reduced doses of the agent used was its infiltration administration during surgery.
The dosage of lignocaine used in both study groups for superficial cervical plexus blockage was 225 mg (2.3-3.7 mg kg-1). Higher doses exceeding 3-4 mg kg-1 are likely to result in overdosage. According to the literature data, however, the dose of 300 mg or even 400mg was often exceeded [4, 5, 6, 7].
In our study, it was accepted that the time necessary to stabilize the blockage was 20 min; after such a period, the surgery was started. In cases of pain sensations, the patient reported them to the anaesthesiologist, who informed the surgeon about the necessity to administer supplementary infiltration anaesthesia. The volume of the local anaesthetic administered was not fixed in the protocol. Thus, the use of lignocaine for superficial cervical plexus anaesthesia and supplementary infiltration anaesthesia could have resulted in overdosage. In both study groups, the overdosage symptoms were not observed. The literature data indicate that plexus blockage has to be supplemented with infiltration anaesthesia in about 53% of cases . Our experiences are less optimistic, 77.2% and 71.8% of patients in group W and M respectively required extra local anaesthetic agent for carotic glomus infiltration.
The supplementary anaesthesia is required due to anatomical conditions as the vessel operated on is often supplied with afferent autonomic innervation, which is not blocked due to cervical plexus anaesthesia. Moreover, location of the atheromatous lesion and division of the cervical artery may require a wide surgical access or the use of retractors, which may irritate the sensory endings of the adjacent dermatomes .
Fentanyl was part of intraoperative supplementary analgesia and was administered when infiltration anaesthesia failed to relieve pain sensations. Pain most commonly occurred when, due to high location of the atheromatous lesion, surgeons had to expose the tissues directly near the mandible branch or angle and press the periosteum with instruments. Additionally, in 3 cases fentanyl was administered because of severe back pain resulting from immobilization on the operating table. Fentanyl was injected in boluses. Some authors [4, 5, 7] used fentanyl in 33-70% of patients and its doses varied. In all the studies mentioned, there was no uniform protocol of fentanyl administration.
The comparative analysis between two groups did not demonstrate significant differences as to the methods of supplementary intraoperative analgesia. The mean volume of lignocaine used in both groups was comparable or even lower than that reported by other authors . It is worth stressing that during the surgical procedure intraoperative blockage of the carotid glomus was almost routinely carried out, which is not standard management. Moreover, the use of fentanyl was moderate in both groups. The overall analysis demonstrated high efficacy of the anaesthesia administered. None of the methods was shown to provide significantly better intraoperative analgesia.
When planning the study, it was accepted that arterial pressure would be measured directly after cannulation of the radial artery of the limb opposite the operated side. Despite various opinions about its usefulness, the Allen test was routinely carried out in all patients. When the result was negative or inconclusive, the radial artery cannulation was abandoned and arterial pressure monitored indirectly. Another problem associated with radial artery cannulation was the necessity to perform the procedure on the dominating limb as well (45% of patients); in total, direct arterial pressure measurements were carried out in 31 patients. In order to unify the methods, the results of indirect arterial pressure measurements were used for analysis.
Deep cervical plexus blockage leads to impairments of autonomic regulation of the circulatory system. Impaired conduction of impulses by the vagus and glossopharyngeal nerves to the brain stem nuclei is implicated. Under such conditions, the effect of the vagus nerve on the circulatory system is inhibited, baroreceptor reactivity impaired and the sympathetic system activated . This results directly in elevated systolic blood pressure and accelerated heart rhythm. A similar clinical effect is induced by the surgical procedure itself: incision of the jugular artery bulb, i.e. the most common location of atheromatous lesions, leads to “denervation” of baroreceptors and reflex impairment.
At successive stages, the elevations in diastolic and systolic blood pressures were observed in both groups, significant in group M. Under similar conditions, Young-Kug and co-workers  recorded comparable effects. They carried out the blockage according to the Moore method using the 0.75% solution of ropivacaine with adrenaline 1:200 000. It is possible that elevated systolic arterial pressure after deep cervical plexus blockage observed by them was associated with the action of adrenaline, however, this amine affects mainly the frequency of heart rate. Our study did not show significant changes in heart rhythm before and after cervical plexus blockage, which was reported by the authors cited.
Subjective assessment of intraoperative pain severity was based on the verbal numeric rating scale and not on visual analogue pain scale as the former is much simpler and easier for patients. Both scales are widely recommended and used for assessment of acute pain, both are characterized by high correlation of the results, however, their differences are also underlined [10, 11, 12]. According to Holdgate , the results of VNRS assessment of pain severity are likely to be slightly overestimated compared to VAS. Our findings demonstrate low intraoperative pain severity in anaesthetized patients. Only a few reported pain sensations exceeding 5 according to VNRS.
One of the key elements of comparative assessment of the methods of cervical plexus blockage is the patient’s satisfaction. A variety of methods is used: analogue scales, numeric scales and 3, 5, or 7-item categorical scales . The prevailing opinion is that only multimodal scales assessing satisfaction enable comparative analysis. We used the 10 cm visual analogue scale [10, 11]. The satisfaction was assessed retrospectively (as in the case of pain severity) – 24 h after surgery, which is the commonest method used-even after 72 h or longer periods by mail . The results in both our groups show high anaesthesia-related satisfaction of patients.
1. Cervical plexus blockage according to Winnie or Moore provides effective anaesthesia in patients undergoing procedures to restore patency of atheromatous carotid arteries.
2. In some patients, irrespective of the method of block anaesthesia, supplementary intraoperative analgesia is required.
3. Both methods of anaesthesia have only slight effects on circulatory parameters.
4. Cervical plexus blockage for carotid artery surgery ensures patient highsatisfaction.
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