Comparative study between effect of pre- versus post-incisional transversus abdominis plane block on acute and chronic post-abdominal hysterectomy pain.

BACKGROUND: The prevalence of persistent chronic pain after abdominal hysterectomy is 5-32%. Our objectives were to determine the influence of transversus abdominis plane (TAP) block on the incidence of acute and chronic post-hysterectomy pain and to examine potential associations between time of block administration, either before surgical incision (preemptive) or after end of surgical procedure and its effect.
MATERIALS AND METHODS: Seventy-five patients undergoing elective total abdominal hysterectomy under general anesthesia were allocated randomly to receive TAP block either pre-incisional, or before emergence from anesthesia or sham block (just a needle puncture, control group). Pain was evaluated postoperatively at rest and movement by visual analogue scale. Peri-operative analgesic requirements, sedation, postoperative nausea and vomiting scores were recorded. Patients were questioned at three, and six months after surgery for type and severity of chronic pain.
RESULTS: Pain scores were significantly higher in Group II versus Group I (P<0.05), but both demonstrated significantly lower pain scores than control Group. Analgesic requirements decreased significantly in patients received TAP block (P<0.0001) with more significant decrease in the pre-incisional group. The incidence of chronic pain was significantly reduced in the pre-incisional group than others. The incidence of sedation was noted to be higher in the control group (61%) versus other groups (18% and 32% respectively), at time point 12 h postoperatively but was comparable between 12, 48 h (awake and alert). Incidence of postoperative nausea and vomiting (PONV) was reduced in patients who received TAP block (16% and 29%) in Group I and II respectively versus 66.5% in Group III. There were no complications attributed to the TAP block.
RESULTS: Pain scores were significantly higher in Group II versus Group I (P<0.05), but both demonstrated significantly lower pain scores than control Group. Analgesic requirements decreased significantly in patients received TAP block (P<0.0001) with more significant decrease in the pre-incisional group. The incidence of chronic pain was significantly reduced in the pre-incisional group than others. The incidence of sedation was noted to be higher in the control group (61%) versus other groups (18% and 32% respectively), at time point 12 h postoperatively but was comparable between 12, 48 h (awake and alert). Incidence of postoperative nausea and vomiting (PONV) was reduced in patients who received TAP block (16% and 29%) in Group I and II respectively versus 66.5% in Group III. There were no complications attributed to the TAP block.
CONCLUSIONS: TAP block seems to be an acceptable choice for postoperative analgesia; pre-incisional TAP block appeared to reduce the severity of acute pain, analgesic requirements with its undesirable side-effects and incidence of chronic pain in comparison with blockade before emergence from anesthesia.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Total abdominal hysterectomy (TAH) has been considered a major surgical procedure that results in substantial postoperative pain and discomfort.[1] The abdominal wall incision has been considered the main cause of such pain.[2] Introducing local anesthetics into the transversus abdominis plane via the triangle of Petit, could block the sensory nerves of the anterior abdominal wall before they pierce the musculature to innervate the abdomen.[3] The anatomical boundaries of this triangle consist of the latissimus dorsi posteriorly, the external oblique anteriorly, with the iliac crest forming the base of the triangle.[4]

Preemptive analgesia is defined as an antinociceptive treatment that blocks the setting up of altered central processing of afferent input which augments postoperative pain.[5] Many animal experimental studies stated the concept of preemptive analgesia.[6] However, regarding human studies, there were conflicting results, some studies had concluded that preemptive analgesia was effective.[78] Meanwhile others had concluded that it was effective only for certain analgesic drugs.[910] In contrary, some analyses have attributed no beneficial effect[11] whereas some have failed to reach a final conclusion regarding efficacy.[1213]

This study tries to answer the question whether TAP performed before surgical incision (preemptive) would provide better analgesia than TAP performed at the end of surgery, by comparing effects on post postoperative pain, total analgesic consumption and incidence of chronic pain after total abdominal hysterectomy.

MATERIALS AND METHODS

This study was approved by our institutional ethical committee and written informed consent was obtained from all patients enrolled in the study.

Seventy-five patients, American Society of Anesthesiology patient classification status I-II undergoing elective TAH were allocated randomly to one of three groups. Group I received standard general anesthesia with TAP block performed after induction of anesthesia. Group II received standard general anesthesia with TAP block performed before emergence from anesthesia. Group III received standard general anesthesia and a sham block was considered for the control group where the needle was inserted and nothing was injected. Through using prospective, randomized (sealed envelopes), double-blind design, both patients and postoperative assessors were blinded to the establishment of TAP block.

Anesthesia was standardized in all patients. After preoxygenation for 3–4 min anesthesia was induced with propofol 2 mg/kg and fentanyl 1.5 μg/kg. Trachea intubation was facilitated with rocuronium 0.6 mg/kg. Anesthesia was maintained with 1% isoflurane, 70% nitrous oxide in oxygen, and incremental rocuronium doses were repeated to maintain neuromuscular block.

Respiratory rate and tidal volume parameters were adjusted to maintain end-tidal carbon dioxide level at 35–45 mm Hg. Signs of light anesthesia (e.g., increases in arterial pressure, tearing, or sweating) were managed with additional boluses of 1 μg/kg fentanyl, and its requirement was recorded for each patient. At the end of surgery, neuromuscular block was reversed with neostigmine 2.5 mg and atropine 1 mg.

TAP block had been performed after induction of anesthesia in Group II and before emergence from anesthesia in Group II. After application of skin antiseptic solution, the site was drapped, then the iliac crest was palpated from anterior to posterior till the latissimus dorsi muscle. The triangle of Petit is located anterior to the latissimus dorsi muscle. The base of the triangle is composed of the following layers, fascial extensions of external oblique, internal oblique, and transversus abdominis, respectively, and the peritoneum.

Using a blunt regional anesthesia needle (22G, B. Braun, Germany), the skin was pierced just cephalic to the iliac crest over the triangle of Petit. The needle was introduced at a right angle to the skin in a coronal plane until resistance was encountered. This resistance indicated that the needle tip had reached the external oblique muscle. Slowly, advancement of the needle resulted in a "pop" sensation as the needle reached the plane between the external and internal oblique fascial layers. Further careful advancement of the needle was done till a second pop was encountered which indicated entry into the transversus abdominis fascial plane. After aspiration to exclude vascular puncture, 20 mL of 0.375% bupivacaine solution was injected. Then, TAP block was performed on the adjacent side using an identical technique.[1415] Twenty minutes elapsed between block and surgical incision in Group I in whom block was performed before surgical incision.

Balanced salt solution was used for fluid therapy. Monitors for patients included pulse oximetry, electrocardiography, end-tidal carbon dioxide and noninvasive arterial blood pressure.

Patients were transferred to the postoperative care unit after tracheal extubation. Duration of TAP block using 20 ml of 0.375% levobupivacaine has been shown up to 24 h.[15] Successful block was confirmed by loss of cold sensation in the distribution of T7-L1 dermatomes on the side of the block.[16] Checking levels of block in the recovery unit was done by a blinded data collector.

When patients suffered from pain in the recovery room, they received a titrated dose of morphine (2 mg bolus at 5-min intervals) until the visual analogue score was ≤30. Intravenous morphine in a dose of 20–50 mcg/ kg was given as necessary to relieve severe pain which was rated by using visual analog scale greater than 30 for the first 48 h after surgery.

Analgesia was assessed at both rest and movement (sitting from lying down position) at 2, 4, 8, 12, 24, 48 h after surgery by an observer blinded to treatment groups using a 100-mm VAS. Total amount of morphine consumption was recorded.

Complications of TAP were recorded which may include failure of the block, intramuscular hematoma and abscess, visceral puncture or perforation. Undesirable effects from opioid use as postoperative nausea and vomiting (PONV), sedation and respiratory depression were also monitored and recorded. These assessments were performed at 2, 4, 8, 12, 24, and 48 h after end of surgical procedure.

PONV was measured using a categorical scoring system (none=0; mild=1; moderate=2; severe=3). Detection of nausea occurred when nausea score was >0 at any time point postoperatively.

Sedation scores were rated using a sedation scale (awake and alert=0; quietly awake=1; asleep but easily roused=2; deep sleep=3). Sedation was defined as a sedation score >0 at any postoperative time point.

Respiratory depression was defined as respiratory rate <8 breaths per min and / or PaCO2 >45 mmHg.

Patients were invited to pain evaluation three, six months later. In addition, they were requested to answer a short questionnaire. The evaluation included the following reports [Table 1].

Table 1

Chronic pain questionnaire

The primary outcome measures included VAS scores at rest and movement, postoperative opioid consumption in the first 48 h and any complications with TAP. The secondary outcome measures included PONV, sedation, respiratory depression and chronic postoperative pain at three, and six months after surgery.

Statistical analysis

Pre-study power analysis determined that a sample size of 20 patients was required in each group in order to detect a 25% reduction in opioid consumption in the first 48 h postoperatively at the 0.05% level of significance, with a power of 0.8, assuming a mean morphine consumption of 80 mg with a standard deviation of 20 mg in the control group. However, we decided to recruit 25 patients in each group to avoid bias resulting from failure of technique which would not be detected accurately because the patients were anesthetized.

Data were presented in the form of mean±SD or number and percentage as appropriate. Data were analyzed with Fisher's exact test, unpaired t-test and Mann-Whitney test, as appropriate; P<0.05 was considered to be statistically significant.

RESULTS

This study was completed on 68 patients. Two patients in Group I and one patient in Group II were excluded from the study because of failure of TAP block. One patient in Group II and three patients in the control group refused to attend for assessment. The characteristics of these patients are shown in Table 2. Statistical analysis revealed no significant differences between groups regarding demographic data, and duration of the operative procedure.

Table 2

Demographic and operative data in the study groups

There was significant decrease in fentanyl requirement in the operating room in the pre-incisional TAP block group than the others (81±9, 170±5, 166±6, mean±SD), (P<0.0001).

There was significant decrease in analgesic requirement in the recovery room in the pre-incisional TAP block group, intravenous morphine was 4.7±0.5, 7.3±0.6, 11.2±1.6 (mean±SD) in Group I, Group II and Group III respectively (P<0.0001). The total morphine consumption in the ward in the first 48 h was significantly reduced in the pre-incisional TAP block group (mean±SD), (21±4, 33±5, 66±5) in the three groups respectively (P<0.0001). However, patients who received TAP showed a significant decrease in analgesic requirements than the control ones (P<0.0001).

Time to first analgesic requirement in the ward (mean±SD) was 135±18, 120±16, 102±14 minutes and it was significantly prolonged in patients who received TAP block (P<0.0001 between Group I and III, P=0.0002 between Group III and II), with more increase of time to first analgesic requirement in the pre-incisional TAP block group, P=0.0046, between Group I and II.

The data on postoperative pain at rest are shown in Figure 1. Postoperative pain scores at rest in 2, 4, 8, 12, 24, 48 h were statistically significantly higher in the post-surgical TAP block group than those in the pre-incisional TAP block group (P<0.05). Both groups demonstrated significantly lower pain scores than the control group at all time points assessed.

Figure 1

The data on postoperative pain at rest, values are mean±SD

The data on postoperative pain at movement are shown in Figure 2. There were statistically significant decreases in VAS in the pre-incisional TAP block group in comparison with those who received post-surgical TAP block at 4, 8, 12, 24, 48 h postoperatively (P<0.05). However, patients who received TAP showed significant decrease in postoperative pain scores than control ones at all time points assessed.

Figure 2

The data on postoperative pain at movement, values are mean±SD

The failure rate of the technique was 6% with no other potential complications recorded.

Incidence of sedation (sedation score > 0) was noted to be higher in the control group (61%) in comparison to the other groups (18% and 32% for group I and group II, respectively) in the early postoperative period (12 h postoperatively) as correlated to decrease in opioid use. However, between 12, 48 h postoperatively all patients in the three groups had score 0 (awake and alert). There were statistically significant differences between the post-surgical and pre-incisional TAP block groups in the early postoperative period as correlated to decrease in opioid use but not at the other time points assessed.

The incidence of PONV was reduced in patients who received TAP block (16% and 29%) in Group I and II respectively versus 66.5% in Group III. However, the decrease in PONV scores in the pre-incisional TAP group was significant in comparison to the post-surgical one. Respiratory depression was not recorded in any patient.

Regarding chronic pain [Table 3], the incidence of pain decreased significantly in Group I in comparison to Group II and Group III (P=0.035, 0.029 respectively) at three and six months postoperatively.

Table 3

Chronic pain characteristics in each group of patients at three and six months postoperatively

More patients in the control (17.4%) and Group II (13.6%) were using analgesics in the form of non-steroidal anti-inflammatory drugs for pain control at three and six months postoperatively compared to none in Group I.

DISCUSSION

The clinical evidence of an important effect of TAP block after open hysterectomy is still sparse. Although the actual study seems to show a difference between pre- and post-surgical blockade, a placebo group had been included in the study in order to validate that this blockade is effective.

This is a small prospective randomized trial on 75 patients. The authors reported statistically significant decrease in pain scores, analgesic requirements, PONV, sedation, and incidence of chronic pain in the group with the pre-incisional TAP block compared with post-surgical one. However, patients who received TAP showed significant decrease in analgesic requirement, pain scores, PONV and sedation than the control ones. The technique was potentially safe, the failure rate was 6% and no complication was recorded.

TAP block holds considerable promise for postoperative analgesia in abdominal surgery with both transverse and midline incisions.[17]

Many articles and case studies have demonstrated the analgesic effect of TAP block when it had been performed at the end of surgery, before emergence from anesthesia.[1418]

Others have reported the analgesic effect of TAP block when it had been performed after anesthetic induction, before surgical incision.[19]

Dierking et al.,[20] found no significant difference in morphine requirement and pain scores between the groups when did inguinal field block before surgical incision or before emergence from anesthesia in herniorrhaphy.

Incidence of PONV was reduced by more than half (66.5% versus 16% and 29%) in the TAP block group. However, the decrease in PONV scores in the pre-incisional TAP group was significant in comparison to the post-surgical group.

Sedation scores were also significantly reduced in the patients who underwent TAP blockade, in the first 12 h postoperatively. However, decrease in sedation scores in the pre-incisional TAP group was significant in comparison to the post-surgical group, which was attributed to decrease in use of opioids.

The analgesic role of TAP block when used as part of a multimodal regimen is a matter of controversy. Joseph et al.,[21] concluded that the TAP block, when used as part of a multimodal regimen inclusive of intrathecal morphine, did not improve the quality of post-Cesarean delivery analgesia. On the contrary, Belavy et al.[22] concluded that TAP block reduced morphine requirements after Cesarean delivery when used as a component of a multimodal analgesic regimen.

Chronic pain is reported by 5–32% of women after hysterectomy.[23] In this study it was about 8% in the pre-incisional TAP group versus 35% in the other two groups. By inhibiting the altered central sensory processing, preemptive analgesia is thought to diminish the incidence of hyperalgesia and allodynia after surgery.[7]

There are many limitations of this study, the blocks in this study were performed in anesthetized patients using blind technique because of the lack of availability of a suitable intraoperative sonar probe in many of the hospitals in developing countries. It is therefore impossible to assume that all blocks were working perfectly. This point may have biased the validity of the results but confirming successful block by loss of cold sensation in the distribution of T7-L1 dermatomes detected three cases of failure of the procedures which were excluded from the study. There are difficulties in adequately blinding studies because TAP block produces loss of sensation of the abdominal wall. The other problem was that it was important to assess morphine consumption in a sequential way (0-12 h, 12-24 h, 24-30 h, 30-48 h) which was not done in this study.

CONCLUSIONS

TAP block was an acceptable choice for postoperative analgesia. The author showed that a pre-incisional TAP block reduced acute pain, analgesic requirements and incidence of chronic pain when compared to a block performed before emergence from anesthesia.