Effectiveness of Bilateral Superficial Cervical Plexus Block as Part of Postoperative Analgesia for Patients Undergoing Thyroidectomy in Empress Zewditu Memorial Hospital, Addis Ababa, Ethiopia

Introduction The pain after thyroid surgery is considered of moderate intensity and short duration. Most trials showed significant reduction in pain intensity and severity of pain in patients for whom bilateral superficial cervical plexus block (BSCPB) was done. Objective To assess the postoperative analgesic effect of BSCPB for thyroid surgery. Methods Sixty six euthyroid patients were recruited and assigned to two groups (33 patients each). Group 1 BSCPB and Group 2 standard analgesia. The unpaired Student's t-test and Mann–Whitney test were used for comparison. Statistical significance was stated at p value < 0.05. Results The median postoperative pain score (NRS) was 3 in the BSCPB group and 5 in the control group (p=0.002). There was also statistically significant difference at 6th, 12th, and 24th hour showing a lower median pain score in the BSCPB group compared to the control group. The median time was (360 minutes) in the treatment group and (180 minutes) in the control group (p=0.0006). The median tramadol consumption within 24 hours is 0 mg in the BSCPB group compared to 100 mg in the control group (p=0.001). Conclusion and Recommendation BSCPB done for thyroidectomy under general anesthesia decreases the postoperative pain score, total analgesia consumption, and time to first analgesia request.


Background
e total goiter prevalence in the global population is estimated to be 15.8%, and the highest prevalence of 28.3% is observed in Africa [1]. It is estimated that half of the Ethiopian population faces iodine de ciency, where 14 million or 40% of those at risks are believed to have goiter. e proportion of Addis Ababa households who consume iodized salt is 30%, which is higher compared to that in rural areas (13%). ough goiter with iodine de ciency is treated with iodine supplementations, goiter that does not regress in size, rebound growth, and presence of pressure symptoms are among indications for surgical treatment [2].
Anesthesia for thyroid surgeries is commonly done under general anesthesia. A mean postoperative pain score of 69 mm was reported on a 100 mm Visual Analogue Scale (VAS). It has also been reported that the morphine consumption in the rst postoperative day is 90%. Studies also show that the proportion of patients with a pain score greater than 40 mm is 70% on the VAS scale [3,4]. Cervical plexus block, either super cial or deep or combinations given bilaterally, could easily lead to adequate block appropriate for thyroid surgery without any signi cant side e ects [5,6]. It is associated with decreased requirement of opioids and lesser complications like postoperative nausea and vomiting, postoperative pulmonary complications, and longer hospital stay. Cervical plexus block has also been effectively used in other surgeries like carotid endarterectomy and lymph node biopsy/excision [7,8].
BSCPB is also known for decreasing intraoperative analgesic requirements when given before surgery [3,9]. By reducing analgesic requirements, the block yields stable operative conditions compared to general anesthesia alone. Studies have gone as far as recommending to use BSCPB as a sole anesthetic technique for smaller anterior neck surgeries for patients with comorbidities. BSCPB is also easier and safer than the combined super cial and deep cervical plexus block [10,11]. It has also showed increased analgesic quality when compared with local in ltration [12].
Besides decreasing cost and side e ects of opioids, the use of BSCPB also supports the principle of multimodal analgesia where a variety of analgesic medications given together might have additive or synergistic e ects and more e ective pain relief when compared with single-modality interventions. e objective of this study is hence to assess analgesic e ectiveness of bilateral super cial cervical plexus block (BSCPB) for postthyroidectomy pain control.

Methodology
After ethical approval was obtained from Addis Ababa University Ethical Committee, all patients who underwent thyroid surgery from December 20, 2016, to May 30, 2017, were included in the study. Patients with substernal goiter, age <18, emergency reoperation, and preexisting neck pain and patients with respiratory disease were excluded from the study. Sampling for each group was done based on two independent sample size formulae relying on the mean di erence of the VAS score, time to rst analgesia request, and total analgesia request among the two groups. A total of 35 ASA I and ASA II euthyroid patients were assigned to each group. Afterwards, all patients who were scheduled for elective thyroidectomy were enrolled in the study and assigned to either the BSCPB or control group randomly. Four patients were found to have incomplete data and were removed from the study.

Super cial Cervical Plexus Block.
e cervical plexus is derived from the C1, C2, C3, and C4 spinal nerves and supplies branches to the vertebral muscles, strap muscles of the neck, and phrenic nerve. Blockade of this distribution results in anesthesia of only cutaneous branches. e block is relatively easy to perform and provides anesthesia in the areas innervated with C2-C4-like lymph node dissections and carotid endarterectomies. If used bilaterally, it can also be used for thyroidectomies.
After preoperative preparation, all patients who were scheduled for elective thyroidectomy, who ful lled inclusion criteria, and who volunteered to take part in the study were instructed on how to self-report pain using the eleven-point NRS score 0 to 10 in the morning of the operation day at ward with a trained nurse. On the day of the surgery, all anesthesia management was carried out by the assigned bachelor's and master's anesthetists.
Patients were sedated with 2 mg midazolam and 10 mcg fentanyl before the procedure. After cleaning the skin with an antiseptic solution, a hypodermic needle is inserted along the posterior border of the sternocleidomastoid muscle, landmark was identi ed as the midline between the mastoid process and clavicular head of the sternocleidomastoid muscle, and three injections of 5 mL of local anesthetic were done behind the posterior border of the sternocleidomastoid muscle subcutaneously, perpendicularly, cephalad, and caudad in a fan fashion. As a standard of care, patients were given 10 mg dexamethasone during induction to prevent surgery related to postoperative nausea and vomiting. Afterwards, standard anesthesia management with endotracheal intubation and monitoring were maintained.
At PACU, patients were asked to report their pain based on the 11-point NRS score as soon as the patient starts to fully respond to verbal command. e NRS score and other variables were documented at 3rd hour, 6th hour, 12th hour, and 24th hour at wards after the end of surgery. A time in minutes from the end of surgery to the rst analgesia request was documented together with total analgesia consumed in the rst 24 hours. In addition, the incidence of postoperative nausea and vomiting was also documented when it was reported within 24 hours.
Statistical analysis was done using the SPSS version 20 software. e Shapiro-Wilk test was used to test for distributions of data, while homogeneity of variance was assessed using Levene's test for equality of variance. Comparison of numerical variables between study groups was done using the unpaired Student's t-test and Mann-Whitney test. e frequency and percentage were used to describe categorical variables, and the statistical di erence between groups was tested using the chi-square test. A p value < 0.05 with a power of 80% was considered statistically signi cant.

Demographic and Perioperative Characteristics.
A total of 66 patients (33 on each group) were involved in the study.
ere was no statistical di erence between two groups in age with a p value of 0.429. e majority of study participants were female owing to the higher incidence of thyroid disease in females, but there is no statistical di erence between two groups. e demographic status and peri-induction data were comparable between two groups with a p value greater than 0.05 as shown in Table 1.

Postoperative Recovery Room Vital Sign.
e baseline vital signs (PR, SBP, DBP, MAP, and SPo2) taken in the recovery room before any medication was given were comparable between two groups with the exception of the heart rate ( Table 2).

Comparison of Total Intraoperative Analgesia Consumption between Groups.
Tramadol and diclofenac were used as intraoperative supplementation based on secondary data obtained from the anesthesia chart. e median and interquartile range between groups are shown in Table 3.

Comparison of Postoperative Numeric Pain Rating
Scale.
e median NRS score was lowest in the block group at recovery room, 3rd, 6th, 12th, and 24th hour. Using the Mann-Whitney test, a signi cant statistical di erence was observed at all time between block and control groups (p < 0.05) (Figure 1).

Comparison of Time to First Analgesia Request and Total Analgesia Consumption.
ere was a statistically signi cant di erence in regard to median time to rst analgesia request in minutes between the two groups as well as total tramadol consumption within 24 hours but no di erence in total diclofenac consumption within 24 hours (Table 4).

Incidence of Nausea and Vomiting.
e incidence of nausea and vomiting over 24 hours is 69.7%. e proportion of patients with nausea and vomiting is lower (63.63%) in the block group (BSCPB) compared to the control group which is 75.7% with a p value of 0.42 (Figure 2).

Discussion
e main nding of the study was the lower pain scores in the block group with a median (IQR) pain score of 3 (2-4) compared to 5 (3)(4)(5)(6) in the control group with a p value of 0.002 at the immediate recovery room. e median NRS score at 3rd postoperative time is lower for the block group 2 (1-3) compared to 4 (3)(4)(5) in the control group (p < 0.0001). e median postoperative pain score was also lower at 6th, 12th, and 24th postoperative time with a statistically signi cant di erence of <0.0001, 0.004, and <0.0001, respectively. e result of this study is in line with the study done in France showing the lower pain score in the block group compared to the control group. is randomized controlled trial demonstrates that the median (IQR) pain score in the treatment group is 3 (0-10) and 5 (0-8) in the control with placebo group, respectively, p � 0.01 [12]. e likely explanation for the similarity between two studies is the performance of the block, which was done after induction of anesthesia in both studies. ough the latter one       patients who require additional morphine in the recovery room is 69%, where 39.1% of them were from the placebo group and 29.9% were from the bupivacaine group with a p value of 0.006. ough the same assessment tool NRS was used, adherence of patients to NRS between two populations may be attributed to the proportion di erence observed [14]. e total postoperative tramadol consumption in the study was lower in the block group. e median (IQR) tramadol was 0 (0-50) mg in the block group compared to 100 (25-150) mg in the control group with p � 0.001. Such a nding is comparable with the Turkey study which shows that median tramadol consumption was lower in the treatment group compared to the control group, 0 (0-50) versus 40 (0-180) mg, respectively, p < 0.05 [15]. ough di erent drugs were used, a study done in France reveals that total postoperative morphine consumption in the bupivacaine group is lower than that of the control group with median (range) 6 mg (2-39) compared to 12 mg (2-39). e use of BSCPB before surgery also decreased the total tramadol consumption within the rst 24-hour period 0 mg (0-50 mg) versus 100 mg (50-150 mg) with a p value of 0.001. ough our study used tramadol. By using the opioid conversion factor suggested in studies, a 100 mg of tramadol could deliver equal analgesic potency as 10 mg of morphine. Hence a comparable result [14,16].
We also observed that the median (IQR) of total diclofenac consumption within 24 hours was not statistically signi cant between block and control groups (75 mg (0-75 mg) versus 75 mg (0-75 mg), resp. (p � 0.775)). We couldnt verify our ndings because most studies only use opioids for postoperative pain management in both treatment and control groups. us, lack of the standard postoperative pain management protocol in the study hospital was among the possible factors for the similarity of diclofenac consumption between groups.
With regard to the time to rst analgesia request, the nding showed a signi cant di erence between the groups. e median (IQR) minute is 360 (190-720) versus 180 (65-360) between block and control groups, respectively (p � 0.006). e result is comparable with a study done in Taiwan with a median time of 410.1 9 (15-1050) minutes in the treatment group with levobupivacaine and 360.8  minutes in the treatment group with bupivacaine 0.5% longer than the placebo group with NS 82.1  minutes. e median time in minutes required for analgesia request was higher in bupivacaine and levobupivacaine groups compared to saline having a signi cant p value of 0.0004 [17]. e overall incidence of nausea and vomiting within 24 hours was found to be 69.7%. is proportion is higher in the control group with an incidence of 75.7% compared to 63.63% in the treatment group. ough there is a proportion di erence, there is no statistical di erence between two groups (p � 0.422). e ndings are higher compared to Andrieu et al. study where the incidence of PONV is 36% [13]. e likely explanation for this incongruity would be that Andrieu et al. used premedication with hydroxyzine and used propofol as a standard induction agent which is known for its prophylaxis for nausea and vomiting. e main limitations of this study are as follows: lack of randomization and control over the confounding factor even though most variables are comparable between groups; variability in the performance of the BSCPB since di erent anesthetists were involved; lack of the standard pain management protocol in the study hospital; and use of secondary data for preoperative and intraoperative variables. e main strength could be the homogeneity between the two groups.
As a summary, the result of our study demonstrates that bilateral super cial cervical plexus block (BSCPB) performed after induction of anesthesia with 0.25% bupivacaine is an e ective and useful technique for postoperative analgesia for thyroid surgery patients. We recommend that BSCPB be considered as a primary analgesic method for such patients.

ASA:
American Society of Anesthesiologist BSCPB: Bilateral super cial cervical plexus block IASP: International Association for the Study of Pain IM: Intramuscular IV: Intravenous GA: General anesthesia MAP: Mean arterial pressure NRS: Numeric rating scale NS: Not statistically signi cant NSAIDs: Nonsteroidal anti-in ammatory drugs PACU: Postanesthesia care unit PONV: Postoperative nausea and vomiting PR: Pulse rate PCA: Patient-controlled analgesia SBP: Systolic blood pressure SCM: Sternocleidomastoid muscle SCPB: Super cial cervical plexus block SD: Standard deviation SPO2: Saturation VAS: Visual Analogue Scale WHO: World Heath Organization.

Conflicts of Interest
e authors declare that they have no con icts of interest.