Effects of cervical plexus block on lung ventilation
*Jarosław Wośko, Sławomir Sawulski, Wojciech Dąbrowski, Andrzej Nestorowicz
I Department of Anaesthesiology and Intensive Therapy, Medical University of Lublin
Background. Carotid endarterectomy is a preventative operation to reduce the incidence of embolic stroke. The prime concern during surgery is the protection of the brain during carotid artery cross-clamping. Since blood flow to the brain is provided via the non-affected carotid artery and collateral circulation, it is essential to maintain consciousness in the patient during surgery, in order to assess the effects of cross-clamping. Regional anaesthesia has therefore been regarded as the method of choice for this kind of surgery.
Cervical plexus analgesia can be achieved at two levels: superficial – when skin branches of the plexus are blocked, and deep – when short and long nerves are blocked. Successful block of the cervical plexus depends of effective analgesia achieved at both levels. This can be achieved by a single injection as described by Winnie, or multiple injection at C2, C3 and C4 as described by Moore. Among possible complications, the most common is transient phrenic nerve block with diaphragm dysfunction.
Methods. We have compared the effects of cervical plexus block performed according to Winnie (group W), or Moore (group M) on spirometry, arterial oxygen saturation and carbon dioxide tension, in seventy-five patients scheduled for endarterectomy.
Results. Group W consisted of 44 patients, and group M – of 31 patients. VC, FVC, FEV1 and PIF decreased in all patients. There were no statistically significant differences between the groups. Transient paralysis of the diaphragm, confirmed by chest x-ray, occurred in 8 (19.5%) patients of group W, and in 4 (14.3%) patients of group M. Gas exchange remained unchanged.
Conclusions. We proved that cervical plexus block is associated with moderate depression of respiratory function without impairment of gas exchange. The block may be complicated by transient unilateral diaphragm paralysis.
Besides neoplastic diseases, atherosclerosis is currently the main factor determining the quality of life and life span of man. Its most tragic course is associated with atheromatous damage to the vessels supplying the brain. Sudden closure of blood flow in the supplying vessels causes irreversible neuronal damage and subsequently leads to their complete dysfunction. In the majority of cases, atherosclerosis develops at the site of bifurcation of the common carotid artery into internal and external carotid artery. In over 50% of cases, changes are bilateral .
The disease aetiopathogenesis is complex and includes both the physical and chemical factors, with the inflammatory reaction likely to be involved in both . Several risk factors of atherosclerosis have been identified: age > 75 years, male gender, arterial hypertension, diabetes mellitus, tobacco smoking, hypercholesterolemia, and obesity (BMI >25 kg m-2) [3, 4, 5].
There are three management options for atheromatous carotid artery stenosis: endovascular angioplasty of the carotid artery with stent implantation, if required, carotid endarterectomy or conservative treatment.
Block anaesthesia for surgeries to restore the carotid artery patency is considered to provide a bigger margin of safety for patients than general anaesthesia. The surgical procedure can be performed in an awaken patient, in whom all abnormalities in the brain blood supply related to temporary, intraoperative closure of blood flow in the affected artery will immediately manifest themselves in the form of less or more severe symptoms of focal brain ischemia.
Early identification of patients at risk of intraoperative cerebral ischemia enables immediate institution of emergency rescue procedures, including temporary bypasses. At present, according to the majority of authors, combined carotid plexus block is the method of choice.
Conduction of nervous stimuli within the carotid plexus may be blocked at two levels - superficial with the skin nerves blocked and deep, in which the short and long nervous branches are blocked. The essence of carotid plexus block is simultaneous blockage of nervous conduction in its both layers.
Deep carotid plexus block is achieved by a single injection of local anaesthetic solution at the level of C3 or C4 – as described by Winnie  or by multiple injections at the level of C2, C3 and C4 – as described by Moore .
Irrespective of the method used, deep carotid plexus block is associated with the risk of complications and side effects, including blocked conduction in the diaphragmatic nerve leading to unilateral paralysis of the diaphragm.
The objective of the present study was to compare the effects of both carotid plexus blocks on lung ventilation parameters.
The study, approved by the Bioethics Committee in Lublin, involved all patients consecutively scheduled for carotid endarterectomy. All patients underwent combined cervical plexus block. Patients were randomly assigned to two study groups. In both groups, superficial block was performed in the same way using 1.5% lignocaine in 0.9% common salt up to the total volume of 15 mL. Deep block was carried out according to Winnie in group W or Moore in group M; in each case, 0.375% bupivacaine solution in 0.9% common salt, total volume of 15 mL, were used.
The assessment involved monitoring of SpO2, PaCO2 and selected spirometric parameters. Moreover, radiographic examinations were performed – a series of two A-P chest X-ray pictures.
Spirometric tests were based on the American Thoracic Society protocol . During the anaesthetic visit on the day preceding the anaesthesia and surgery, patients were instructed about the test. The following parameters were recorded:
- inspiratory vital capacity (IVC),
- forced vital capacity (FVC),
- forced expiratory volume in 1 sec (FEV1),
- Tiffeneau ratio – FEV1/FVC,
- peak inspiratory flow (PIF).
Spirometry was carried out using the portable SpiroPro five times at successive procedure stages. Each measurement was repeated three times, the highest value was considered the final result. The measurement on the day preceding the procedure was considered the baseline and the successive ones were recorded as a decimal fraction of the baseline value.
The arterial blood samples were examined every 20 min throughout the procedure, immediately after its completion and after the first postoperative day. Changes in PaCO2 values were assessed.
Chest X-ray pictures were taken in all patients on the day preceding the procedure and immediately after it. Both examinations were performed in the A - P projection and in the inspiratory phase of spontaneous respiratory cycle.
Table 1 presents the types of examinations and successive stages of the procedure in which they were performed.
Results were statistically analysed. Intergroup changes caused by the carotid plexus block were evaluated using the Wilcoxon test. Differences between measurement stages 1-2, 1-4, 2-3, 4-5 and 1-5 were compared. Possible intergroup differences were identified using the Mann-Whitney U test. Results obtained at stage 2, 3, 4 and 5 were compared. P<0.05 was considered as statistically significant.
The study encompassed 75 patients, 23 females and 52 males fulfilling the ASA I-III criteria. One patient underwent procedures of both carotid arteries within 4 weeks. Group W included 44 and group M 31 patients. Demographic characteristics of both groups were comparable (Table 2).
In all cases, carotid plexus block enabled the restoration of carotid artery patency. No severe anaesthesia-related complications were observed.
In both groups, once patients were placed in the supine position, the values of spirometric parameters were slightly lower (3-10%) compared to baseline values. After carotid plexus blocks, successive significant decreases in the following values were observed : VC - by 10.6% in group W and 11% in group M (Fig. 1), FVC - by 12.9% and 11.7% (Fig. 2), FEV1 -by 12.2% and 12.1% (Fig. 3) , and PIF by 11.7% and 11.7% (Fig. 4), respectively.
Significant decreases in FVC considered as a sensitive marker of diaphragm dysfunction were noted in 40 % of group W patients and in 35% of group M patients.
Irrespective of the anaesthesia method used, the spirometric parameters normalized within 24 postoperative hours.
In both groups, no significant changes in the Tiffeneau ratio resulting from the carotid plexus block were demonstrated. No significant intergroup differences in spirometric parameters were found. Moreover, there were no significant changes in SpO2 and PaCO2 observed in both groups.
Chest X-ray pictures were taken in 42 (93.3%) patients of group W and in 28 (90.3%) patients of group M. In the immediate postoperative period, the elevated diaphragmatic dome on the affected carotid plexus side was observed in 8 (19.5%) patients of group W and in 4 (14.3%) of group M (Fig. 5). The intergorup differences in the incidence of such events were not significant.
Analysis of our findings demonstrates that both methods of deep carotid plexus anaesthesia have similar effects on lung ventilation parameters. The severity and incidence of changes are also comparable; after 24 h, ventilation parameters normalize.
Lung ventilation is properly assessed once the circumstances of spirometric tests are accounted for [9, 10]. It is known that the supine position, particularly in the elderly, changes the parameters of ventilation and gas exchange, which increases the Tiffeneau ratio, decreases FVC and facilitates the retention of CO2 [11, 12]. Our findings do not confirm such observations – the changes observed were not significant.
After carotid plexus blocks, the values of spirometric parameters in both study groups substantially decreased compared to baseline recordings; the biggest changes concerned VC, FVC, FEV1 and PIF.
A decrease in FVC below 75% of the normal value is the most sensitive marker of diaphragm dysfunction. It was demonstrated that FVC changes were strictly correlated with diaphragmatic pressure changes, which is still the gold standard for the diagnosis of abnormalities in diaphragm dysfunction .
The results of studies in patients with the diaphragmatic nerve surgically removed showed that FVC decreased by 20%, FEV1 by 19% and VC by 21% . Similar changes were recorded in our patients suspected of significant dysfunction of the diaphragm due to reduced FVC values.
Reduced VC, FVC and FEV1 at maintained or increased Tiffeneau ratios are characteristic of restrictive lung diseases. One of the causes of such abnormalities is the weakened respiratory muscle force, including the diaphragm . Similary, unilateral diaphragmatic paralysis resulting from carotid plexus block is likely to induce such ventilation changes [15, 16, 17]; the normalization of spirometric parameters 24 h after carotid plexus block evidences the relation between ventilation disturbances and the block performed.
There are only a few studies comparing the methods of carotid plexus anaesthesia according to altered values of lung ventilation parameters. The results of those studies are diverse or even conflicting. Michałek and co-workers  observed decreased values of FVC comparable to our results when 0.5% of bupivacaine in the total volume of 16 mL was given to selectively block C2 and C3 nerve roots. Otherwise, Kulkarni and colleagues  who performed bilateral deep carotid plexus blocks with 0.375-0.5% bupivacaine did not note any relevant FVC changes.
However, assessment of the incidence of diaphragmatic nerve paralysis and of diaphragmatic disorders due to deep carotid plexus anaesthesia cannot be exclusively based on spirometric parameters. Additional data are provided by chest X-rays.
The radiographic diagnosis in the present study consisted of two A-P chest X-ray pictures. The first examination was to exclude coexisting lung pathologies and was used as a baseline for comparative evaluation of the diaphragmatic dome position on the affected side. In both groups, no markers of severe lung pathologies were observed before anaesthesia, although chronic, circulation- or inflammation-related changes were noted. The second X-ray taken immediately after the procedure showed unilaterally elevated diaphragm in some patients. Once the diaphragm paralysis is suspected, the diagnostic value of chest X-ray is limited [19, 20], yet radiographic results combined with spirometry demonstrate explicitly the cause of this complication since the sole significant medical event between the two imaging examinations was the carotid plexus block and carotid endarterectomy.
1. Carotid plexus block causes transient changes in lung ventilation, mainly of restrictive nature; the severity and incidence of changes are independent of the method of anaesthesia used.
2. Ventilation changes do not induce significant abnormalities in lung gas exchange.
3. In some patients, chest A-P X-ray pictures confirm the unfavourable effects of carotid plexus block on the diaphragm function on the affected side.
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