In all, 281 studies were identified after searching for relevant articles; five articles[13-17] with data for 274 patients were eligible for this analysis. Figure 1 shows the process of study selection.
Summary characteristics of the included studies
The characteristics of the included studies are shown in table 1. These five studies were all published from 2013 to 2019 and met both the inclusion and exclusion criteria. Three of them were studies on GI surgery[14-16], one was on posterior spinal surgery[17], and one was on laparoscopic gynaecological surgery and only involved female patients[13]. Regarding the time of SGB, it was performed before the induction of general anaesthesia in three studies[14-16]; in two studies, SGB was performed after the induction of anaesthesia and before the beginning of surgery[13, 17]. The left SG was blocked in one study[14], and the right SG was blocked in three studies[13, 15, 17]; one study did not mention whether SGB was conducted on the left or right[16]. Regarding local anaesthetics, 0.5% ropivacaine was used in one study[14], while 1% lidocaine was used in the others[13, 15-17], and the volume of local anaesthetics injected into the SG varied among these five studies. Furthermore, three studies performed a sham procedure in the control group with 0.9% NS (normal saline) in the same volume of local anaesthetics[13, 14, 17], while in the other two studies, no operations were performed on the SG in the control group[15, 16].
Quality of the included studies
The quality of the studies was assessed according to the Cochrane Collaboration’s tool for assessing risk of bias. Figures 2 and 3 show detailed information about this assessment. All studies had complete outcome data and reported all anticipated outcomes. Four studies reported how the random sequence was generated[13-15, 17], while one only stated that patients were randomly allocated into two groups but did not mention how randomization
Quality of the included studies
The quality of the studies was assessed according to the Cochrane Collaboration’s tool for assessing risk of bias. Figures 2 and 3 show detailed information about this assessment. All studies had complete outcome data and reported all anticipated outcomes. Four studies reported how the random sequence was generated[13-15, 17], while one only stated that patients were randomly allocated into two groups but did not mention how randomization was performed[16]. Two included studies did not perform any sham procedures, so the allocation concealment and blinding of participants and personnel could not be assessed,
Table 1 Characteristics of the included studies.
Study ID
|
Type of operation
|
Age (years)
|
Sex
M/F
|
Time of SGB (before or after induction of general anaesthesia)
|
Treatment of the SGB group (sample size; drugs; volume)
|
Treatment of the control group (sample size; drugs; volume)
|
Time to resuming peristaltic sound
|
Flatus time
|
Time to postoperative eating
|
Incidence and degree of abdominal bloating
|
Injury related to SGB
|
Chunying Z [13]
|
Laparoscopic gynaecological surgery
|
43.57±9.06
|
0/41
|
After
|
Right SGB; 21; 1% Lidocaine; 2ml
|
Right SGB; 20; 0.9% NS; 2ml
|
SGB group: 22±20.298 Control group: 30.3±20.145
|
SGB group: 15.4±4.4; Control group: 20.7±5.1
|
-
|
SGB group: 1.286±6.698; Control group: 2±5.071
|
No
|
Lihua C
[14]
|
GI surgery
|
57.69±9.47
|
41/14
|
Before
|
Left SGB; 18; 0.5% Ropivacaine; 7ml
|
Left SGB; 37; 0.9% NS; 7ml
|
SGB group: 46±31; Control group: 73±36
|
SGB group: 66±34; Control group: 95±45
|
-
|
-
|
No
|
Renbo S
[16]
|
GI surgery
|
62.07±15.86
|
43/35
|
Before
|
SGB; 39; 1% Lidocaine; 8-10ml
|
-
|
-
|
SGB group: 27.58±6.72; Control group: 54.64±8.91
|
SGB group: 32.46±6.29; Control group: 86.37±9.54
|
-
|
No
|
Peng K
[17]
|
Posterior spinal surgery
|
43.60±9.05
|
21/19
|
After
|
Right SGB; 20; 1% Lidocaine; 6ml
|
Right SGB; 20; 0.9% NS; 6ml
|
SGB group: 16.2±24.901; Control group: 32.1±24.787
|
SGB group: 12±4.4; Control group: 14.7±4.6
|
-
|
SGB group: 1.1±5.9221; Control group: 1.8±3.196
|
No
|
Yuxin S
[15]
|
GI surgery
|
57.45±8.12
|
48/12
|
Before
|
Right SGB; 39; 1% Lidocaine; 8-10ml
|
-
|
-
|
SGB group: 72.15±17.05; Control group: 85.8±20.53
|
SGB group: 179.8±41.74; Control group: 229.35±83.63
|
-
|
No
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Data are described as the mean ± SD. Items that could not be extracted from the original articles are described as “-”. SGB, stellate ganglion block; GI, gastrointestinal; NS, normal saline; h, hours.
leading to a high risk of selection and performance bias[15, 16]. Furthermore, no studies described blinding of outcome assessments. All studies had no other bias.
Postoperative flatus time
Figure 4 shows a comparison of the postoperative flatus time between the SGB and control groups. All included studies reported this outcome, but with great heterogeneity (P<0.00001, I2=98%). Our analysis showed an overall effect size (mean difference, MD) of -15.07 h (95% CI: -27.58, 2.56), with a Z value of 2.36 (P=0.02<0.05). However, as shown in Figure 5, when we deleted a study[16], the heterogeneity was reduced greatly (P=0.02<0.05, I2=71%), and the overall effect size (MD) became -6.77 h (95% CI: -11.67, 1.88), with a Z value of 2.71 (P=0.007<0.05). We think that this phenomenon was caused by the low quality of that study, as shown in Figures 1 and 3; this study did not describe how the random sequence was generated, the SG did not receive any treatment in the control group, and the side on which SGB was performed in the SGB group was not reported. Furthermore, the population in this study was the oldest among those of all five studies, and the surgery was performed to treat GI tumours. However, despite the heterogeneity, whether that study was included did not influence the effect of SGB on the postoperative flatus time.
Three of the included studies were on GI surgery[14-16], and in all of these studies, SGB was performed before the induction of general anaesthesia, so we performed an additional analysis of this group of studies, as shown in Figure 6. The overall effect size (MD) was -23.92 h (95% CI: -36.49, 11.35), with a Z value of 3.73 (P=0.0002<0.05), indicating that SGB before anaesthesia significantly shortened the time to flatus after GI surgery.
Overall, our analysis suggests that SGB can shorten the postoperative flatus time in patients undergoing different surgeries with general anaesthesia, with a mean time reduction of more than 6 h. This reduction was even more obvious in GI surgery, with a mean reduction of approximately an entire day.
Time to resumption of peristaltic sounds
Three of the included studies reported the time to resumption of peristaltic sounds after surgery; these studies were on GI, laparoscopic gynaecological and posterior spinal surgery, respectively[13, 14, 17]. However, the data were in the form of the number of patients whose bowl sounds recovered within a period of time after the operation, such as before 12 h, 24 h, 36 h, 48 h, and 72 h postoperatively. For convenience, we converted these data, as follows: the average time of the time points was used as the time to resumption of peristaltic sounds of patients in this period; thus, this outcome was also analysed as continuous. Figure 7 shows a comparison of the postoperative peristaltic sound resumption time between the SGB and control groups. As presented in Figure 7, the overall effect size (MD) was -14.67 h (95% CI: -23.21, -6.12), with a Z value of 3.36 (P=0.0008<0.05). Furthermore, the heterogeneity was low (P=0.25>0.05, I2=28%), indicating the combined analysis of these three studies is reasonable. This outcome shows that SGB can promote GI movement after different surgeries with general anaesthesia.
Time to postoperative eating
Two of the included studies reported time of postoperative eating, with high similarity, as follows[15, 16]. First, both studies were on GI surgery. Second, SGB was performed before the induction of general anaesthesia in both studies. Third, local anaesthetics consisted of 8-10 ml of 1% lidocaine in both studies. Last, neither study had a sham group, and no treatment was applied in the control group. Figure 8 shows the data for this outcome. There was no heterogeneity between these 2 studies (P=0.80>0.05, I2=0%). The overall effect size (MD) was -53.86 h (95% CI: -57.43, -50.29), with a Z value of 29.60 (P<0.00001). This result suggests that in GI surgery under general anaesthesia, performing SGB before the induction of anaesthesia can significantly shorten the time to postoperative eating by more than 2 days.
Time to postoperative eating
Two of the included studies reported time of postoperative eating, with high similarity, as follows[15, 16]. First, both studies were on GI surgery. Second, SGB was performed before the induction of general anaesthesia in both studies. Third, local anaesthetics consisted of 8-10 ml of 1% lidocaine in both studies. Last, neither study had a sham group, and no treatment was applied in the control group. Figure 8 shows the data for this outcome. There was no heterogeneity between these 2 studies (P=0.80>0.05, I2=0%). The overall effect size (MD) was -53.86 h (95% CI: -57.43, -50.29), with a Z value of 29.60 (P<0.00001). This result suggests that in GI surgery under general anaesthesia, performing SGB before the induction of anaesthesia can significantly shorten the time to postoperative eating by more than 2 days.
Incidence and degree of postoperative abdominal bloating
Two studies included data on the incidence and degree of postoperative abdominal bloating[13, 17]. One study was on laparoscopic gynaecological surgery[13], and the other was on GI surgery[17]. Both articles described this index by degree (mild, moderate and severe), as ranked data. To facilitate data analysis, we converted different abdominal bloating degrees to scores from 1-4, with no abdominal bloating defined as 1, mild abdominal bloating as 2, moderate abdominal bloating as 3, and severe abdominal bloating as 4, so that this variable could be analysed as continuous. As shown in Figure 9, after analysis, no heterogeneity was found (P=0.98>0.05, I2=0%), and the overall effect size (MD) was -0.68 (95% CI: -2.96,1.61), with a Z value of 0.58 (P=0.56>0.05). However, as shown in Figure 10, if we analysed this outcome as dichotomous (whether abdominal bloating occurred), the overall effect size (odds ratio, OR) was 0.18 (95% CI: 0.06, 0.51), with a Z value of 3.22 (P =0.001<0.05). These results indicate that SGB reduced the incidence of postoperative abdominal bloating, but there was no significance between the SGB and control groups regarding the degree of abdominal bloating, suggesting that SGB might have no effect on the degree of postoperative abdominal bloating.
With the continuously increasing incidence of disease with surgical indications, the number of patients who need general anaesthesia is also increasing. As mentioned in the introduction, both surgical manipulation and analgesia, including surgical methods and sites, anaesthesia methods and analgesic drugs, blood perfusion, inflammation and neuroendocrine changes, can lead to postoperative GI dysfunction. Normally, after GI surgery, gastric motility recovers in 24-48 h, small intestinal motility in 12-24 h, and colonic motility in 3-5 days[18]. The inhibition of GI function can bring about GI dysfunction and discomfort, causing nausea, vomiting, abdominal bloating, and delayed flatus and defecation; more seriously, it could lead to systematic inflammation and even multiple organ dysfunction syndrome[19]. Such outcomes prolong the hospitalization duration and increase the cost of care, the postoperative mortality rate, and burden on both the hospital and patient.
There have been many studies aiming to explore methods to facilitate postoperative GI recovery, including the following: 1) multimodal analgesia to reduce the use of opioids, e.g., other analgesic methods and non-steroidal anti-inflammatory drugs (NSAIDs)[20, 21]. 2) laparoscopic surgery[22]; 3) goal-directed fluid therapy[22]; 4) early enteral nutrition[23]; 5) gum chewing[24]; 6) opioid receptor antagonist[25]; 7) traditional Chinese medicine[26]. All of these methods play a limited role.
We know that the digestive system is mainly governed by the autonomic nervous system. As a major stressor, surgery under general anaesthesia leads to functional changes in this system, causing stimulation of the sympathetic system, inhibition of the parasympathetic system and the release of catecholamine. Based on this thesis, sympathetic blockade might play an important role in the recovery of GI function. The blockage of cervical sympathetic nerves has a long history; this approach promotes the establishment of homeostasis via regulation of the neuro-endocrine-immune system[27], and the SG, which provides sympathetic input to the ipsilateral upper extremity, chest, face, and head, is the most commonly blockaded cervical ganglion, with wide applications[7, 8]. SGB can be applied blindly or with imaging guidance (computed tomography, ultrasound) [6, 28]. A series of local anaesthetics, such as lidocaine, bupivacaine and ropivacaine, can be chosen for reversible blockade, and neurolytic agents, such as alcohol, can be used for permanent blockade. Manifestations including Horner’s syndrome, an increase in skin temperature, loss of the galvanic skin response and an increase in blood flow in the innervated areas all indicate success of the block. With the popularization of ultrasound, performing SGB under ultrasound guidance, which provides direct visualization of soft tissue structures around the sympathetic chain, appears to offer increased safety and efficacy[6].
To determine whether SGB plays a role in postoperative GI function, we performed this meta-analysis. Although the included studies had different patients undergoing different surgeries, the results still suggest that SGB can promote postoperative GI recovery in patients undergoing surgery with general anaesthesia. As shown in Figures 4-6, SGB caused a mean reduction of 15 h in the time to flatus after different surgeries; after excluding a study causing heterogeneity, the mean reduction was still greater than 6 h. further analysis of only GI surgery showed a mean reduction of approximately an entire day. Data regarding the recovery of peristaltic sounds are shown in Figure 7; the results suggest that in different surgeries, SGB can promote the recovery of regular bowl sounds earlier than the control group by 14.67 h on average. Regarding nutrients, early enteral nutrition facilitates postoperative recovery, and as indicated in Figure 8, the use of SGB in GI surgery can shorten the total parenteral nutrition time by more than 50 h. Finally, as shown in Figures 9 and 10, SGB can prevent the occurrence of postoperative abdominal bloating; however, once abdominal bloating occurs, SGB does not affect the degree. All studies included reported no complications related to SGB. SGB can be performed in different kinds of surgeries in both men and women on either the right or left and with different local anaesthetics at different volumes. Among the included studies, SGB was performed after and before the induction of anaesthesia in two and three studies, respectively. In our opinion, performing SGB before induction can provide visible evidence of block success, such as Horner’s syndrome but prevents blinding of the patients and doctors, while performing SGB after induction can allow blinding but increases the difficulty of judging block efficacy. However, if the operator is skilled or can perform SGB under ultrasound guidance, performing SGB after induction is a good choice theoretically.
However, there are still some limitations to our study. First, only 5 studies were included in our analysis, limiting the subgroup analysis and yielding an inadequate sample size. These five studies were on 3 different surgeries, with only 1 or 3 studies for each kind of surgery, and thus lacked repeatability. Second, all included clinical trials were carried out in People’s Republic of China, restricting the generalizability of our conclusions. Moreover, SGB is an invasive treatment, and block success needs to be verified by some manifestations, making blinding impossible; thus, the quality of the included studies was not very high.
As a result, further clinical trials of high quality are needed to confirm these results and apply SGB in other surgeries and other countries.