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Analgesia: Research Report

The Transversus Abdominis Plane Block Provides Effective Postoperative Analgesia in Patients Undergoing Total Abdominal Hysterectomy

Carney, John, MB*†; McDonnell, John G., MB, FCARCSI*†‡; Ochana, Alan, MB; Bhinder, Raj, MB; Laffey, John G., MD, MA, BSc, FCARCSI*†‡

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doi: 10.1213/ane.0b013e3181871313
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Total abdominal hysterectomy (TAH) is a commonly performed major surgical procedure that results in substantial postoperative pain and discomfort.1–3 These patients require a multimodal postoperative pain treatment regimen that provides high quality analgesia with minimal side effects. Opioids, such as morphine, delivered using a patient-controlled analgesia (PCA) device, remain the mainstay of postoperative analgesic regimens for patients post-TAH. However, the use of opioids can result in significant adverse effects, including sedation, nausea, and vomiting.1–3 Alternative approaches, which reduce the requirement for strong opioids postoperatively, are required.

An important component of the pain experienced by patients after abdominal surgery derives from the abdominal wall incision. The abdominal wall sensory afferents course through the transversus abdominis (neurofascial) plane superficial to the transversus abdominis muscle.4 Our group has described a novel approach to block these sensory nerves before they leave this plane, via the bilateral lumbar triangles of Petit, which we have termed a transversus abdominis plane (TAP) block5,6 (Figure 1). We have recently demonstrated the efficacy of the TAP block in providing postoperative analgesia in patients undergoing colonic resection surgery involving a midline abdominal wall incision6 and patients undergoing cesarean delivery.7 In addition, the TAP block has been reported to provide effective analgesia in a series of patients undergoing radical prostatectomy.8 This study was designed to test the hypothesis that the TAP block, as part of a multimodal analgesic regimen, would provide effective analgesia in the first 48 h after TAH, in comparison to a placebo block.

Figure 1.
Figure 1.:
Line drawing of a transverse section through the abdominal wall at the level of the lumbar triangle of Petit (TOP). The floor of the triangle is composed, from superficial to deep, of the fascial extensions of external oblique, internal oblique, and transversus abdominis, respectively, and the peritoneum. The needle is inserted through the triangle, using the loss-of-resistance technique. The needle is shown in the transversus abdominis plane, and the fascial layers have separated as a result of the injection of local anesthetic. LS = lumbar spine; LD = latissimus dorsi; pm = psoas major; QL = quadratus lumborum; MM = multifidus muscle; IL = longissimus iliocostalis; TA = transversus abdominis; IO = internal oblique; EO = external oblique; ST = subcutaneous tissue.

METHODS

After obtaining approval by the Hospital Ethics Committee and written informed patient consent, we studied 50 ASA physical status I-III patients scheduled for TAH in a randomized, double-blind, controlled, clinical trial. Patients were excluded if there was a history of relevant drug allergy, or they were receiving medical therapies considered to result in tolerance to opioids.

Patients were randomly allocated to undergo TAP block (TAP, n = 24) with 1.5 mg/kg ropivacaine 0.75% (to a maximal dose of 150 mg) per side or TAP block with saline 0.9% (CON, n = 26). The allocation sequence was generated by a random number table, and group allocation was concealed in sealed, opaque envelopes, which were not opened until patient consent had been obtained. The patients, their anesthesiologists, and staff providing postoperative care were blinded to group assignment. All patients received a standardized general anesthetic with standard monitoring. Anesthesia was induced with IV fentanyl (1–1.5 μg/kg to a maximum of 100 μg) and propofol (2–3 mg/kg). All patients also received IV morphine 0.15 mg/kg, rectal diclofenac 100 mg, and rectal acetaminophen 1 g immediately before surgical incision. Prophylactic antiemetics were not administered.

The TAP block was performed bilaterally before surgical incision by one of three investigators, (JC, JMcD, RB), using the double loss-of-resistance technique, as previously described (Figure 1).5–7 After placement of the needle in the transversus abdominis fascial plane, and careful aspiration to exclude vascular puncture, a test dose of 1 mL was injected to determine resistance to flow, and confirm needle tip placement within the fascial plane. After this, 1.5 mg/kg of 0.75% ropivacaine (to a maximum dose of 150 mg or 20 mLs each side) was injected through the needle in 37.5 mg increments, while observing closely for signs of toxicity. The TAP block was then performed on the opposite side using an identical technique.

After completion of the surgical procedure, patients were transferred to the postanesthesia care unit (PACU). A standardized postoperative analgesic regimen, consisting of regular rectal acetaminophen 1 g every 6 h and rectal diclofenac 100 mg every 16 h, combined with IV PCA morphine (bolus dose 1 mg, lock out 6 min, 4 h maximum dose 40 mg), was commenced on admission to the PACU in both groups. The presence and severity of pain was assessed by an investigator blinded to group allocation using a visual analog scale (VAS) and a categorical scoring system. All patients were asked to score their pain at rest and on movement (knee flexion). Nausea was measured using a categorical scoring system (none = 0; mild = 1; moderate = 2; severe = 3). Sedation scores were assigned by the investigator using a sedation scale (awake and alert = 0; quietly awake = 1; asleep but easily roused = 2; deep sleep = 3). The patient was deemed to have been nauseated or sedated if they had a nausea or sedation score >0 at any postoperative time point. Rescue antiemetics were offered to any patient who complained of nausea or vomiting. These assessments were performed in the PACU and at 2, 4, 6, 12, 24, 36, and 48 h after admission to the PACU.

The primary outcome measure in this study was 48 h morphine consumption. Secondary outcome measures included time to first request for morphine, VAS scores, and side effects associated with morphine consumption. For the purposes of sample size calculation, we assumed that a clinically important reduction in 48-h morphine consumption would be a 25% absolute reduction. Based on initial pilot studies, we projected a mean 48-h morphine requirement of 45 mg with a standard deviation of 10 mg in the control group. We calculated that 21 patients would be required per group for an experimental design incorporating 2 equal sized groups, with α = 0.05 and β = 0.2. To minimize any effect of data loss, we elected to recruit 50 patients into the study.

Statistical analyses were performed using a standard statistical program (Sigmastat 3.5, Systat Software, San Jose, CA). Demographic data were analyzed using Student’s t or Fisher’s exact tests as appropriate. The data were tested for normality using the Kolmogorov-Smirnov normality test. Repeated measurements (pain scores, nausea scores) were analyzed by repeated measures analysis of variance where normally distributed, with further paired comparisons at each time interval performed using the t-test. For non-normally distributed data, between group comparisons at each time point were made using Wilcoxon’s ranked sum test. Categorical data were analyzed using the χ2 analysis or Fisher’s exact test. The time to first request for morphine was analyzed using the log rank test. Normally distributed data are presented as mean ± sd (sd), non-normally distributed data are presented as median (interquartile range), and categorical data are presented as raw data and frequencies. The α level for all analyses was set as P < 0.05, and the Bonferroni correction for multiple comparisons was used where appropriate.

RESULTS

Fifty-three patients were entered into the study. Three patients, two from the control group and one from the treatment group were excluded after enrollment due to postoperative analgesic protocol violations. Of the remaining 50 patients, 24 were randomized to undergo TAP blockade with ropivacaine, and 26 were randomized to undergo TAP blockade with normal saline.

Groups were comparable in terms of age, weight and height, and history of abdominal surgery (Table 1). In all patients, the triangle of Petit was located easily on palpation, the transversus abdominis neuro-fascial plane was localized after one to two attempts, and the block performed without complication.

Table 1
Table 1:
Baseline Patient Characteristics

Patients undergoing TAP block had reduced 48-h morphine requirements (Figure 2), and a longer time to first PCA morphine request (Figure 3) compared to the placebo block group. The median (interquartile range) time to first request for morphine was significantly longer in patients who received a TAP block (Table 2). The TAP block with ropivacaine reduced cumulative postoperative morphine consumption compared to placebo block at all time points (Figure 2). Morphine consumption at 12 h intervals was also significantly lower at 12, 36, and 48 h in the patients that underwent TAP blockade (Table 2). Postoperative VAS pain scores at rest and on movement were reduced after TAP block at most, but not at all time points assessed (Figure 4 and Table 3). Categorical pain scores were lower in patients who received the TAP block, at 6, 36, and 48 h postoperatively, but not at the other time points (data not shown).

Figure 2.
Figure 2.:
Mean postoperative cumulative morphine consumption in each group in the first 48 postoperative hours. *Indicates significantly (P < 0.05, t-test post ANOVA) higher visual analog scale score compared to the TAP block group.
Figure 3.
Figure 3.:
A Kaplan-Meier graph of the proportion of patients in each group over time that did not require supplemental morphine (P < 0.002, Log Rank test).
Table 2
Table 2:
Postoperative Analgesic Requirement
Figure 4.
Figure 4.:
Mean postoperative visual analog scale (VAS) pain scores on movement in each group over the first 48 postoperative hours. *Indicates significantly (P < 0.05, t-test post analysis of variance) higher VAS score compared to the TAP block group.
Table 3
Table 3:
Postoperative Pain Scores

There was no significant difference in the incidence or severity of nausea between groups at any time point (Table 4). The TAP block significantly reduced the incidence of sedation, from 63% in the control group to 37% in the TAP group (Table 4). Postoperative sedation scores were reduced in patients who received the TAP block at 1 and 24 h postoperatively, but not at the other time points (Table 4).

Table 4
Table 4:
Postoperative Sedation and Nausea Scores

DISCUSSION

This randomized, double-blind, controlled trial demonstrates that TAP block provides effective analgesia, when used as part of a multimodal analgesic regimen, in patients undergoing TAH. The TAP block reduced postoperative morphine consumption, improved pain scores at rest and on movement, and increased the time to first requirement for supplemental analgesia. The TAP block also reduced sedation in these patients, but did not impact on the incidence of postoperative nausea and vomiting (PONV).

The current regimen for the provision of postoperative analgesia after TAH at our institution consists of PCA morphine (or meperidine), in combination with regular nonsteroidal analgesics and acetaminophen. Patients generally require PCA morphine for up to 48 h, after which they are converted to oral analgesic drugs. Although PCA morphine provides satisfactory analgesia in patients after TAH, it is associated with adverse effects, such as sedation,1 nausea, and vomiting.2,3 Adjunctive strategies, which reduce the requirement for postoperative opioids, would be of considerable a benefit to patients recovering from TAH.

A multimodal approach to postoperative analgesia after TAH is required, because of the need to block nociceptive transmission from both the abdominal wall incision and from pelvic and abdominal visceral sites. One promising approach is to block nociceptive transmission from the surgical incision. However, strategies to block the incisional component of the pain have met with relatively limited success. In a qualitative systematic review, Moiniche et al. found little evidence to support the use of instillation of local anesthetics into the wound incision.9 In contrast, the combination of intraperitoneal and incisional bupivacaine did provide some analgesia in this patient group.9 However, more effective strategies are required for patients undergoing TAH.

The TAP block has been demonstrated to provide excellent analgesia to the skin and musculature of the anterior abdominal wall in patients undergoing colonic resection surgery involving a midline abdominal wall incision,6 patients undergoing cesarean delivery,7 and patients undergoing radical prostatectomy.8 In this study, we demonstrate for the first time the effectiveness of the TAP block in reducing postoperative pain and reducing morphine consumption after TAH via a transverse lower abdominal incision. The finding that the TAP block reduced morphine requirements for each 12 hourly interval up to 48 h is of importance in that it demonstrates that a single-shot TAP technique can produce effective analgesia for up to 48 h. The reasons for the prolonged duration of analgesic effect after TAP blockade are not entirely elucidated. However, this may relate to the fact that the TAP is relatively poorly vascularized, and therefore drug clearance may be slowed.

Somewhat surprisingly, given the reduction in postoperative opioid requirements, the TAP block did not reduce the incidence or severity of PONV. This may have been because the amount of morphine consumed in the TAP block group was sufficient to induce PONV. In calculating the incidence of PONV, any score of above zero at any time point was taken as indicating that the patient had PONV. However, at each time point, individual nausea scores were low and confined to a small number of patients, as evidenced by median nausea scores of zero at each time point in each group. Therefore, our method of detecting nausea may have been overly sensitive. In contrast, the TAP block did reduce the incidence and severity of sedation. A reduction inpatient sedation, combined with the reduction in postoperative pain severity with the TAP block, may improve compliance with postoperative care including movement and mobilization, breathing exercises, and communication.

There are a number of limitations to this study. First, the blocks in this study were performed by three different anesthesiologists and, while the block technique was the same, there is always some degree of technique variability. Further studies are required to determine the success rate of the block when performed by less experienced practitioners. Second, the dose of the local anesthetic ropivacaine (3 mg/kg) used in this study, while it may be considered high, is still within the recommended safe dose range for this drug.10 Third, there are difficulties blinding these studies as there is an appreciable loss of sensation or paraesthesia associated with the TAP block. Although patients and the investigator conducting the postoperative assessments were blinded to group allocation, true blinding may not have been possible. Investigators were instructed not to determine the level of sensory blockade in order to reduce the risk of unblinding of group allocation. Fourth, the study size was not adequate to assess block safety. For example, performance of this block could produce inadvertent peritoneal puncture if the technique described is not followed. However, we have performed this block in several hundred patients, and we have not encountered complications relating to peritoneal puncture. The performance of this block under ultrasound guidance, which is increasingly used by our group and others,11 facilitates identification of the needle tip in the TAP and may result in reduced risk, particularly in obese patients.

We conclude that the TAP block holds considerable promise as part of a multimodal analgesic regimen after TAH. The TAP block was easy to perform, and provided reliable and effective analgesia in this study, and no complications due to the TAP block were detected.

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© 2008 International Anesthesia Research Society