Analgesic efficacy of postoperative bilateral, ultrasound-guided, posterior transversus abdominis plane block for laparoscopic colorectal cancer surgery: a randomized, prospective, controlled study

Perioperative analgesia is essential for patients undergoing elective colorectal surgery in the enhanced recovery after surgery (ERAS) program. However, postoperative pain associated with colorectal surgery is considered neuropathic and requires a multimodal treatment approach to achieve effective pain control with fewer side effects [1, 2]. Transversus abdominis plane (TAP) block was suggested as a necessary part of the analgesia approach to control postoperative pain in several abdominal and gynecological surgical procedures [3]. The TAP technique includes injecting local anesthetics into a plane between the internal oblique (IO) and transversus abdominis (TA) muscles, which contain the thoracolumbar nerves originating from T6 to L1 spinal roots that supply the skin, muscles, parietal peritoneum, and sensation to the anterolateral abdominal wall [4, 5]. Performing an ultrasound-guided block enhanced the accuracy and efficacy of injecting local anesthetics into the TAP [6, 7].

The three primary approaches to TAP are subcostal, lateral, and posterior. The subcostal approach provides analgesia to the upper abdomen, whereas lateral and posterior approaches reduce the pain in the lower abdomen. Previous studies indicated that lateral TAP reduced the resting pain score within the first 6 h of laparoscopic colorectal surgery [8]. In contrast, posterior TAP provided 12 to 36 h of postoperative analgesia for total abdominal hysterectomy or cesarean delivery surgery [9, 10]. However, there is limited evidence suggesting that compared with systemic opioids or placebo, posterior TAP could reduce opioid consumption and pain scores after laparoscopic colorectal cancer surgery [2]. This study hypothesized that a postoperative bilateral, ultrasound-guided, posterior TAP could reduce the requirement for rescue analgesics within the first 24 h compared with placebo in patients undergoing laparoscopic colorectal cancer surgery.

One hundred twenty-six consecutive patients were assessed for eligibility between January 2018 and December 2019. Of these, 28 patients did not meet the inclusion criteria, and 6 patients refused to participate. The remaining 92 patients were randomized into Group TAP (n = 46) and Group Control (n = 46) to receive TAP intervention and a sham block, respectively. Laparoscopic surgeries were converted to open surgery in six patients of Group TAP and four patients in the Group Control. These ten patients were excluded from the outcome analysis. Eighty-two patients successfully underwent a postoperative bilateral, ultrasound-guided, posterior TAP block, which was determined by the bilateral appearance of a hypoechoic ellipsoid ultrasound image [12, 13]. Because no patient was lost to follow-up, 40 patients from Group TAP and 42 from Group Control were analyzed (Fig. 2). Both groups were similar in terms of sex, age, BMI, ASA, surgery duration, comorbidities, intraoperative analgesics, and extraction incision used (Table 1).

The (median [interquartile range]) cumulative consumption of rescue tramadol within 24 h was significantly lower in Group TAP (0 mg [0, 87.5]), compared with Group Control (100 mg [100, 200]), P < 0.001 (Table 2).

A longer time to first tramadol muscular injection request was observed in Group TAP than the Group Control (Fig. 3). The (median [interquartile range]) time to first request for tramadol was significantly more in Group TAP (1440 min [285, 1440]) compared with Group Control (50 min [30, 90]; P < 0.001) (Table 2).

Resting NRS scores were lower in Group TAP than in Group Control at 2 (1.3 ± 0.5 vs. 3.4 ± 1.1), 4 (1.5 ± 0.5 vs. 2.2 ± 0.4), 6 (1.7 ± 0.6 vs. 2.7 ± 0.6), 12 (1.7 ± 0.7 vs. 2.3 ± 0.6), and 24 h (1.7 ± 0.6 vs. 2.1 ± 0.4) after the surgery (all P < 0.001) but similar at 48 (2.1 ± 0.6 vs. 2.1 ± 0.5, P = 0.862) or 72 h (2.0 ± 0.7 vs. 2.1 ± 0.7, P = 0.648). In addition, movement NRS scores were lower in Group TAP than in Group Control at 2 (2.1 ± 0.4 vs. 4.1 ± 1.2), 4 (2.2 ± 0.5 vs. 3.1 ± 0.5), 6 (2.3 ± 0.6 vs. 3.5 ± 0.7), 12 (2.3 ± 0.5 vs. 2.9 ± 0.3), and 24 h (2.2 ± 0.4 vs. 2.7 ± 0.5) after the surgery (all P < 0.001) but similar at 48 h (3.1 ± 0.6 vs. 3.2 ± 0.7, P = 0.760) or 72 h (3.0 ± 0.5 vs. 3.0 ± 0.6, P = 0.992) (Figs. 4 and 5).

The incidence of nausea and vomiting was lower in Group TAP than in Group Control. No pruritus, sedation, and respiratory depression occurred in both groups (Table 3).

Table 4 shows patients’ postoperative satisfaction level on analgesia. Patients’ satisfaction was significantly higher in Group TAP on postoperative day 1 (P = 0.012) but similar on days 2 and 3, compared with Group Control.

The first time to get out of bed was significantly earlier in Group TAP than in Group Control (27.9 ± 7.8 vs. 33.9 ± 8.2 h, P = 0.001). Time to first passage of flatus was significantly earlier in Group TAP than in Group Control (32.4 ± 6.2 vs. 39.0 ± 8.7 h, P < 0.001) (Table 2). The mean length of hospital stay was significantly shorter in Group TAP than in Group Control (3.4 ± 0.5 vs. 3.9 ± 0.6 days, P < 0.001) (Table 2).

In this study, a postoperative bilateral, ultrasound-guided, posterior TAP using 0.5% ropivacaine (20 mL per side) reduced and delayed the requirement for rescue analgesics within the first 24 h. Besides, the resting and movement pain scores also decreased at 2, 4, 6, 12, and 24 h in Group TAP. Less related side effects, accelerated bowel function recovery, and shorter hospital stay were observed in Group TAP compared with Group Control.

Excessive perioperative opioid consumption increases the incidence of postoperative nausea and vomiting (PONV), sedation, pruritus, urinary retention, bowel dysfunction, and respiratory depression, and delays postoperative recovery [20‐22]. The resting and movement NRS scores in Group TAP were lower than those in Group Control at 2, 4, 6, 12, and 24 h after the surgery. Although the pain scores in Group TAP differentiate from Group Control slightly, early effective analgesia contributed to lower and delayed rescue analgesia requirement of tramadol muscular injection in Group TAP, resulting in tramadol spare-effect. In this study, the application of posterior TAP in Group TAP significantly reduced tramadol consumption and the incidence of PONV 24 h after the surgery compared with the Group Control. Thus, the reduction in PONV could be explained by the decrease in tramadol-related adverse effects. Early pain relief and fewer side effects allowed the patients to get up and ambulate. Moreover, it was associated with earlier mobilization, better bowel function recovery, shorter hospital stay, and better satisfaction [23]. However, the pain scores in the two groups were similar at 48 or 72 h and were consistently very low, this could be due to the analgesic effects of PCIA and the minimal invasive advantages of laparoscopic over open surgery for all participants [24]. However, half-day reduction of hospital stay was statistically significant (3.4 ± 0.5 vs. 3.9 ± 0.6 d, P < 0.001), the clinical significance was relatively limited.

Postoperative analgesia is an essential part of perioperative anesthetic management and the enhanced recovery program. After the surgery, acute pain significantly contributes to the increased hospital stay and patient dissatisfaction [25]. Pain derived from the abdominal wall incision was the primary component experienced by the patients after abdominal surgery [12]. Recently, TAP has been recommended as an essential component of multimodal analgesia techniques because it provides effective analgesia for abdominal surgical procedures, including colorectal surgery [26, 27]. It blocks the T6–L1 spinal nerves’ neural branches dominating the anterolateral abdominal wall [11]. After the anterior rami of these nerves exit their respective vertebral foramina, they enter the anterior abdomen muscles and reach the neurofascial plane between the internal oblique and transversus abdominis muscles. The sensory nerve branch first sends out a lateral cutaneous branch in the mid-axillary line and continues to move within the plane to supply the anterior skin [12]. The posterior TAP is located between the costal margin and the iliac crest. In the present study, the needle was inserted at the mid-axillary line. A large volume of a local anesthetic was deposited in the transverse abdominal plane by the mid-axillary line puncture that blocked the lateral cutaneous branches, thereby completely blocking the anterior abdominal wall [12]. Similar research on cadavers and volunteers demonstrated that posterior TAP provided analgesia effect from the anterior–lateral abdominal area to the post-axillary line [28, 29]. In addition, different approaches of TAP substantially influenced the spread pattern of local anesthetics within the plane. It has been reported that local anesthetics mostly spread into the layer between the internal oblique and external oblique muscles in the subcostal and lateral TAP approaches without extending into the paravertebral space, resulting in somatic pain relief in the anterior abdominal wall. However, in posterior TAP, local anesthetic may partly enter the paravertebral space covering T4 to L1 in a retrograde fashion and potentially blocking a few degrees along with the thoracolumbar sympathetic system, resulting in a more comprehensive somatic pain relief in the abdominal wall [30‐32]. Because the sympathetic nervous system mediates pain after the surgery, the posterior TAP could achieve a prolonged analgesic effect. Besides, the postoperative TAP may prolong the analgesic effect by delaying the metabolism process compared with preoperative TAP [33]. Finally, the posterior TAP injection probably causes deposition of the local anesthetic in the aponeurosis, which acts as “warehouse effect” that plausibly intensifies and prolongs the effect of posterior TAP [34, 35]. Taking all these into account, we considered that a single shot of posterior and postoperative TAP with 0.5% ropivacaine relieved the pain efficiently during 24 h follow-up although the duration of ropivacaine only lasted 4–8 h in pharmacokinetic, our results were similar to previous studies [12, 36].

A previous study indicated that a preoperative bilateral, ultrasound-guided, lateral TAP block using 2 mg/kg levobupivacaine (40 mL) equally split between the sides (up to a total maximum dose of 150 mg) decreased the pain scores only at 2, 4, and 6 h [33]. However, we observed that the postoperative bilateral, ultrasound-guided, posterior TAP produced 24 h analgesia in laparoscopic colorectal surgery, indicating that the posterior TAP prolonged postoperative analgesia. Thus, it is not surprising that the posterior TAP block in our study provided a reliable, satisfied, and durable analgesia effect for laparoscopic cancer surgery. Moreover, both preoperative and postoperative timings are suitable for performing TAP. However, we selected the postoperative TAP over preoperative TAP, owing to its advantages, such as avoiding local anesthetic distribution within the muscle layers caused by the long head-down position and delaying the local anesthetic metabolization [33].

TAP block is a superficial technique, where the target depth is usually between 1 and 3 cm, with a small but finite risk of complications [37]. The ultrasound-guided TAP block is a relatively safe intervention without adverse outcomes [12, 38, 39]. The semi-lateral position ensures abdominal organs to be considerably away from the needle trajectory, making posterior TAP safe. Therefore, ultrasound-guided posterior TAP block is considered a safe technique for postoperative analgesia.

Our study had several limitations. First, our study did not measure the plasma concentrations of ropivacaine. Ropivacaine for TAP block could result in systemic toxicity, indicating it is essential to monitor the local anesthetic concentration. However, any symptoms of local anesthetic systemic toxicity, such as seizures, cardiovascular collapse, metallic taste, and tinnitus, did not occur in our study, whether immediately after the block or in the follow-up period. Second, the sensory block effect of posterior TAP was not assessed because the patient was still under general anesthesia. However, we confirmed that the needle passed through different muscle layers until its tip entered the layer between the internal oblique and transverse muscles. A hypoechoic ellipsoid with well-defined margins was indicative of successful injection under the ultrasound-guided TAP block, similar to previous studies [12, 13]. Third, although TAP block was a considerable analgesic regimen for laparoscopic colorectal cancer surgery, it was not more beneficial in patients who underwent different abdominal surgeries, especially those who received multimodal analgesia, which contained epidural analgesia, continuous lidocaine infusion, wound local infiltration, or quadratus lumborum block [40‐42].

This prospective, randomized, double-blinded trial showed that postoperative bilateral, ultrasound-guided, posterior TAP block using 20 mL of 0.5% ropivacaine per side decreased the cumulative consumption of rescue tramadol within 24 h after the surgery. The pain scores also decreased significantly at rest and movement at 2, 4, 6, 12, and 24 h for patients undergoing laparoscopic colorectal cancer surgery. A delayed and lower requirement of tramadol muscular injection accelerated the bowel function recovery, and shorter hospital stay was observed compared with placebo without an increase in adverse events.