A Comparison of Analgesic Effect between Preoperative and Postoperative Transversus Abdominis Plane (TAP) Blocks for Different Durations of Laparoscopic Gynecological Surgery

Aim. -is study aims to compare the postoperative analgesia between preoperative and postoperative ultrasound-guided transversus abdominis plane (TAP) blocks for different durations of laparoscopic gynecological surgery. Methods. A total of 120 patients, ASA I-III, 18–65 years of age, were divided randomly into 2 groups: preoperative TAP group (pre-TAP group) and postoperative TAP group (post-TAP group). Patients in the pre-TAP group (n� 60) and post-TAP group (n� 60) received bilateral TAP blocks of 0.375% ropivacaine, 40mL, preoperatively and postoperatively, respectively. Duration of surgery, postoperative pain score, consumption of analgesics, and postoperative nausea and vomiting (PONV) during the first 24 h postoperatively were recorded. Results. For all the patients in the two groups, similar analgesia was obtained with no statistical difference.-e same results were found in duration of surgery <180min. Meanwhile, patients undergoing surgery >180min in the post-TAP group obtained lower postoperative pain score, lower analgesics consumption, and higher satisfaction score than those in the pre-TAP group. Conclusion. Postoperative TAP block could offer better postoperative analgesia than preoperative TAP block for patients undergoing surgery >180min. No difference was found in analgesia effect between preoperative TAP block and postoperative TAP block for patients undergoing surgery <180min.

PCEA plays a direct role in the near operative region and possesses a more immediate analgesic mechanism; thus, it could offer fast, clear, and accurate analgesic effect and reduce the use of opioids. PCEA seems to be an ideal method for postoperative pain control; it could be demonstrated to have a good postoperative analgesic effect in many common operations such as abdominal and gynecological surgeries [3,4]. PCIA acts on the whole body through intravenous analgesics with relatively longer and more rapid analgesic effect with the PCA device. It has the advantages of simple operation and a wide range of drug uses, including the narcotic analgesics and nonsteroidal anti-inflammatory drugs. PCIA is applicable to pain, postoperative pain, wound pain, after-burn pain, and inflammatory pain [5,6].
However, the side effects of PCEA and PCIA are also notable [4,7]. PCEA might cause low blood pressure, pruritus, paresthesia, nausea, and vomiting, and PCIA could cause itching and respiratory depression due to the inevitable use of opioids [4,7,8]. At the same time, with the development of laparoscopic minimally invasive surgery, the surgical incision is reduced, and the postoperative pain is not as strong as open surgery [2,[9][10][11].
In view of the shortcomings of PCEA and PCIA, nerve block has the advantages of less trauma, less impact on systemic circulation, no inhibition of the respiratory center, and relief of nausea and vomiting [2,9,12,13]. Transversus abdominis plane (TAP) block is a regional technique for analgesia of the anterolateral abdominal wall [14] and may offer good analgesia on abdominal surgery, especially gynecologic surgery [15][16][17][18]. TAP block seems to be an interesting alternative in patients with, for example, severe obesity, where epidural or spinal anesthesia/analgesia is technically difficult and/or poses a risk [19][20][21].
Previous studies showed that it was inconsistent to determine the optimal time on TAP for patients undergoing surgeries. Some investigators recommended that TAP be performed before surgery [17,20,22], some preferred postoperative performance [15,16,23,24], and others found that there was no difference between the two time points.
Till now, there have been no report to show the analgesic effect of TAP on patients undergoing surgeries of different duration. We aimed to compare analgesia between preoperative and postoperative TAP blocks for different duration of laparoscopic gynecological surgery.

Materials and Methods
is prospective, randomized, single-blind clinical trial was approved by the ethics committee of the Second Hospital of Dalian Medical University and clinical trials registration number is ChiCTR1900027881.

Patient Population.
We assumed that the difference in consumption of postoperative analgesics between groups was 20%; thus, at least 58 patients should be recruited in each group. For convenience, we planned to recruit 60 patients in each group. e inclusion criteria were planned as follows: (1) ASA I-III (2) 18-65 years of age (1) Patients with history of chronic pain therapy during the past half year (2) Addiction (including opioids and benzodiazepines) (3) Allergy to prescription medications (4) Psychological disorders (5) Pregnancy (6) Any contraindication to TAP block (7) Refusal of consent 2.2. Procedure. After signing the written consent, all the patients were allocated into 2 groups randomly, pre-TAP group and post-TAP group. Heart rate (HR), blood pressure (BP), saturation of oxygen (SpO 2 ), and bispectral index (BIS) were monitored and data collected every 5 minutes. All the patients received standard general anesthesia. Induction of general anesthesia was induced using 0.03 mg/kg Midazolam (Jiangsu Nhwa Pharmaceutical Co., Ltd., Xuzhou, China), 0.3 μg/kg Sufentanil (Yichang Humanwell Pharmaceutical Co., Ltd., Yichang, China), 0.3 mg/kg Etomidate (Jiangsu Nhwa Pharmaceutical Co., Ltd., Xuzhou, China), and 0.3 mg/kg Cisatracurium (Jiangsu Hengrui Medicine Co., Ltd., Jiangsu, China). Following intubation, maintenance of general anesthesia was total intravenous anesthesia including propofol (4-12 mg/kg/h), remifentanil, and dexmedetomidine. e dosage was determined by the anesthesiologist according to keeping BIS at the scope 50 ± 5, systolic blood pressure (SBP) was controlled within 20% of the base value, and the mean arterial blood pressure (MBP) was not lower than 65 mmHg. Cisatracurium was added at 0.05 mg/kg according to the requirements of surgeons. Crystals and colloidal liquid solutions are used for volume displacement, and all aspects of anesthesia management are performed by the anesthesiologist in accordance with current clinical practice. e tidal volume was set at 6-8 ml/kg, respiratory rate was set at 12 breaths/min, and end-expiratory partial pressure of carbon dioxide (CO 2 ) was maintained at 35-45 mmHg. Dizocine (10 mg) and Ramosetron 0.3 mg were given intravenously 30 minutes before the end of surgery. If HR was lower than 45 bpm or higher than 120 bpm, we intravenously injected atropine 0.5-1 mg and esmolol 0.5 mg/kg, respectively; if BP was lower than 80% of basic value or SBP was higher than 160 mmHg, we administered norepinephrine 8-12 ug/min and nicardipine 2-10 ug/kg/min, respectively.
After induction of anesthesia, patients in the pre-TAP group received USG bilateral TAP block with 0.375% ropivacaine (Beijing Taide Pharmaceutical Co., Ltd., Beijing, China), 20 mL each side, before incision and patients in the post-TAP group were given same medications after the end of surgery and before extubation. After extubation, patients were transferred to postanesthesia care unit (PACU). When patients reached the criteria of leaving PACU, they could be transferred to ward. At ward, patients would be asked for the pain score, which was visual analogue scale (VAS) at 0, 2, 6, 12, and 24 h postoperatively. Flurbiprofen axetil (Jiangsu Hengrui Medicine Co., Ltd., Jiangsu, China), 50 mg intravenously, used as postoperative analgesic should be given if VAS was more than or equal 4.

Outcome Measures.
Vital signs including HR, RR, BP, SpO 2 , and BIS value were recorded every five minutes from entrance to operating room to leaving the PACU. Consumption of opioids during surgery, consumption of postoperative analgesics, times of rescue, which means times of postoperative analgesics demanding, duration of surgery, pain score at 0, 2, 6, 12, and 24 h postoperatively, mean duration of first analgesic demanding after surgery, postoperative nausea and vomiting (PONV), and satisfaction scores of patients and surgeons were also recorded.
VAS of 0 indicated no pain. VAS of 10 meant an ultimate pain. e VAS of patients was measured by a researcher who did not know this study. Degree of PONV was measured with a categorical scoring system (none � 0; mild � 1; moderate � 2; severe � 3). Satisfaction score ranges from 0 to 10, and 0 means totally unsatisfactory, while 10 means totally satisfactory. Duration of surgery was regrouped to three subgroups: subgroup S, in which duration of surgery was <90 mins; subgroup M, in which duration of surgery was 90-180 mins; and subgroup L, in which duration of surgery was >180 mins. Only the patients were blinded to the group assignment.

Statistical
Analysis. GraphPad Prism version 5 (GraphPad Software, Inc.) was used for data analysis. Demographic data was analyzed by chi-square test and t-test. Haemodynamic data, pain score and consumption of analgesics and opioids, were analyzed by repeated-measures analysis of variance and post hoc pairwise comparison for different stages of anesthesia. P < 0.05 was considered to have a statistically significant difference.

Subject Characteristics.
We totally recruited 132 patients. 3 patients were deleted because they refused to cooperate postoperatively, 7 patients were excluded because they were changed from laparoscopic surgeries to open ones during the surgeries, and 2 patients were deleted because of being diagnosed as retroperitoneal tumor during surgeries and they received abdominal surgery instead of gynecological surgery. us, finally we recruited 60 patients in each group.
ere was no significant difference in gender, height, weight, ASA status, and duration of surgery between the two groups (Table 1). ere was also no significant difference in cases, height, weight, and ASA status among the three subgroups (Table 2).

Clinical Results.
No difference was found in vital signs between pre-TAP group and post-TAP group; and no severe accident happened.
ere was no significant difference in postoperative pain score between pre-TAP group and post-TAP group ( Figure 1).
In subgroup L, VAS in the pre-TAP group was higher than that in the post-TAP group at 0, 2, and 6 hours postoperatively (2.0 ± 1.3 versus 0.5 ± 0.7, 2.5 ± 1.3 versus 1.0 ± 0.8, and 3.1 ± 1.5 versus 1.6 ± 1.3, respectively) with significant difference, P < 0.01 (Figure 2). No statistical difference in postoperative pain score was found in subgroup S and subgroup M between the pre-TAP group and post-TAP group. Data in Table 3 show that, for all the patients recruited, there was no difference in duration of first rescue, times of rescue, and satisfaction scores of patients and surgeons between the pre-TAP group and post-TAP group. Consumption of opioids (remifentanil) in the pre-TAP group was significantly lower than that in the post-TAP group (269.7 ± 86.4 versus 324.6 ± 136.4, P � 0.03). Degree of PONV in the pre-TAP group was lower than that in the post-TAP group (0.5 ± 0.8 versus 0.8 ± 0.9, P � 0.03).
In the three subgroups, consumption of opioids and degree of PONV in the pre-TAP group were lower than those in the post-TAP group with statistical difference. For subgroup S and subgroup M, no statistical difference was found in duration of first rescue, times of rescue, and satisfaction scores of patients and surgeons between pre-TAP and post-TAP groups. Meanwhile, in subgroup L, duration of first rescue in the pre-TAP group was lower than that in the post-TAP group (3.4 ± 2.8 h versus 11.0 ± 1.8 h, P � 0.01). Times of rescue in the pre-TAP group was 1.0 ± 0.5, which was significantly lower than that in the post-TAP group (0.5 ± 0.5) with P � 0.03. Patients in the pre-TAP group gave higher satisfaction score compared to their counterparts in the post-TAP group (7.4 ± 0.9 versus 8.8 ± 1.0), and the difference was significant (P � 0.04) (see Table 4).

Discussion
is was the first study to compare postoperative analgesia effect between pre-TAP and post-TAP blocks for different duration of surgeries.
Previous studies showed that it was inconsistent to determine the optimal time on TAP for patients undergoing surgeries. Some investigators recommended that TAP be performed before surgery [17,20,22]. Mansouri et al. found that bilateral intrapleural block performed before cardiac surgery could get better analgesia than postoperative manipulation due to preemptive analgesia [25]. Niraj et al. obtained same results in patients undergoing open appendicectomy [26]. Some researchers concluded that the analgesic effect of TAP block performed postoperatively was prior to emergence from anesthesia [15,16,23,24]. Mcdonnell et al. found that the sensory block produced by lidocaine 0.5% receded over 4 to 6 hours, which was supported by magnetic resonance imaging studies that showed a gradual reduction in contrast in the transversus abdominis plane over time. French et al. reported that general anesthesia with postoperative supplementary bilateral ultrasound-guided TAP blocks was chosen to reduce the requirements for postoperative opioids and the risk of postoperative respiratory depression [27,28]. Meanwhile other clinicians like Fibla et al. found that blocking time did not seem to affect postoperative pain scores [29].
In our study, for all the patients in pre-TAP and post-TAP groups, no difference was found in postoperative pain score, which was similar to the results of previous studies [29,30]. In subgroups, no difference was found in subgroup S and subgroup M between pre-TAP and post-TAP group. Meanwhile, in subgroup L, postoperative scores in pre-TAP groups were significantly lower than those in post-TAP group at 0, 2, and 6 hours postoperatively, and the duration    In group L, VAS in the pre-TAP group was higher than that in the post-TAP group at 0, 2, and 6 hours postoperatively. * * P < 0.01. explains why no difference was found in subgroup S and subgroup M between pre-TAP and post-TAP groups. e durations of surgery in subgroup S and subgroup M were <2 hours, which indicates that the analgesic effect of bilateral TAP of 0.375% ropivacaine had not begun to fade yet. But this block duration was shorter than that in Stoving et al.'s study, approximately 10 hours with large variation [31]. Although the concentration was the same in these two studies, difference of block duration might be due to the different pharmaceutical factory. From the above results, we might conclude that it was necessary to decide the time of TAP block according to the duration of surgery.
In our study, the consumption of opioids and dosage of remifentanil in pre-TAP group were significantly lower than those in post-TAP group (269.7 ± 86.4 versus 324.6 ± 136.4 ug/kg.min, P � 0.03). e same results happened in all the subgroups. In subgroup S, subgroup M, and subgroup L, patients in pre-TAP group consumed less remifentanil compared to their counterparts in post-TAP group with statistical difference. is result showed that pre-TAP block could offer better analgesia than postoperative manipulation due to preemptive analgesia, which leads to the lower intraoperative consumption of opioids. is result was also consistent with studies from Mansouri [25] and Niraj et al. [26]. However, in subgroup L, patients in pre-TAP group consumed less postoperative analgesics compared to their counterparts in post-TAP group. is difference might be due to the fact that the block duration of bilateral TAP of 0.375% ropivacaine was 4-8 hours after manipulation. e lower pain score and lower consumption of rescue could be the reason why in subgroup L patients in post-TAP group got higher satisfaction score compared to their counterparts in post-TAP group. e degree of PONV in pre-TAP group was lower than that in post-TAP group, and the same results happened in all the subgroups. is might be due to the lower consumption of opioids in pre-TAP group. is result was consistent with Shin et al.'s study [30].

Conclusion
It was necessary to decide the time of TAP block according to the duration of surgery. For patients undergoing laparoscopic gynecological surgery, preoperative TAP block was recommended for duration of surgery <180 min for lower consumption of intraoperative opioids, while postoperative TAP block was better than preoperative manipulation for duration of surgery >180 min, which might obtain lower postoperative pain score, less postoperative analgesics, and higher satisfaction score. Further research is warranted to investigate whether the TAP block technique can be improved by optimizing dose and technique-related factors.

Data Availability
All the underlying data supporting the results of this study can be found in IRB of the Second Hospital of Dalian Medical University.

Disclosure
Meiyu Wei and Ming Liu are the co-first authors.

Conflicts of Interest
e authors declare that there are no conflicts of interest.

Authors' Contributions
Meiyu Wei and Ming Liu contributed equally to this work.