Since the first description of the ultrasound-guided transversus abdominis plane (TAP) block in 2007,1 conflicting results have been reported regarding its analgesic efficacy.2–7 Several systematic reviews have attempted to clarify the magnitude of analgesic effect of this block. Interpretation of their results is limited, however, by the absence of quantitative meta-analysis8,9 or the inclusion of a restricted number of trials ranging from 4 to 12, with a maximum of 641 participants.10–18
More importantly, these reviews did not discriminate between the trials that used anatomic landmark approaches based on the Triangle of Petit and those performed with the aid of ultrasonography.8–18 Potential significant differences between the 2 block techniques may expose these analyses to important bias, because trials that used anatomic landmark techniques have reported consistently positive results.19–23 Despite these early positive findings, needle placement after a landmark-based technique has been shown to result in injection within the correct intermuscular plane in fewer than 25% of attempts, when systematically verified by ultrasonography.24
Ultrasonography-guided techniques may provide the advantage of being effective and safe through direct needle visualization; however, many recently published trials that use ultrasonography have reported conflicting analgesic results.2–7 This meta-analysis evaluated the analgesic efficacy of the ultrasonography-guided TAP block exclusively for abdominal surgery in adult patients.
Literature Search and Inclusion Criteria
The authors applied the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement.25 The electronic databases MEDLINE (until June 2013), the Cochrane Central Register of Controlled Clinical Trials (until June 2013), Excerpta Medica database (EMBASE; until June 2013), and the database of the Cumulative Index to Nursing and Allied Health Literature (CINAHL; until June 2013) were searched with the following terms: Echo-guided OR Echography OR Ultrasound OR Ultrasound guided. These search results were associated with Transversus abdominis plane block OR Transversus abdominis OR Transverse abdominis plane OR TAP block OR TAP. The findings were further restricted by associating with Nerve block OR Regional nerve block OR Peripheral nerve block OR Analgesia OR Local anesthesia OR Local anaesthesia OR Regional anesthesia OR Regional anaesthesia. The following keywords also were searched: Echo*, Ultrasound*, Transvers*, TAP*, Analg*, Anesth*, Anaesth*. Finally, bibliographies of retrieved articles were scrutinized for any relevant trials not yet identified in the primary search. Search results were limited to English, German, Spanish, or French.
This meta-analysis addresses male or female adults who underwent any abdominal surgical procedures.
Intervention and Comparator
Only randomized trials that compared single-shot injection, unilateral or bilateral ultrasound-guided TAP block with a control group or placebo and combined with general or spinal anesthesia were included in this meta-analysis. Trials that investigated TAP blocks performed after an anatomic landmark-guided approach,19–23 compared an ultrasonography-guided technique with an anatomic landmark technique,26 compared a continuous infusion with IV fentanyl patient-controlled analgesia,27 or compared TAP block with surgical incision infiltration,6,28,29 and against a bolus of IV morphine30 or with analgesic adjuncts were excluded.31
The specific outcomes sought from each article were derived from the American Society of Regional Anesthesia Pain Medicine’s Acute Postoperative Pain Database initiative.32 The primary acute pain–related outcome was cumulative IV morphine consumption at 6 hours postoperatively. Secondary acute pain–related outcomes were pain scores at rest and on movement at 6 hours postoperatively, cumulative IV morphine consumption at 24 hours postoperatively, pain scores at rest and on movement measured at 24 hours postoperatively, time to first analgesic request, incidences of postoperative nausea or vomiting, pruritus within the first 24 hours postoperatively, sedation score at 24 hours postoperatively, and participant satisfaction. Additional relevant outcomes evaluated were time to discharge and rates of block-related complications, including seizure, arrhythmia, intraperitoneal puncture, infection, hematoma, or other.
Extracted trial characteristics included type of surgery; type of surgical anesthesia; type and dose of intrathecal opioid, if any; type, concentration, and volume of local anesthetic used; approach of ultrasonography-guided TAP block; and type of postoperative analgesia. Ultrasonography-guided TAP blocks were divided into the subcostal approach (probe positioning and needle insertion below the rib cage), lateral approach (probe positioning in the mid-axillary line between the costal margin and the iliac crest; needle insertion in a lateral to medial direction), posterior approach (probe positioning in the mid-axillary line between the costal margin and the iliac crest; needle insertion in an anterior to posterior direction), or not specified.
Rating of the Studies
The quality of the research methodology of each randomized trial was assessed following the Cochrane Collaboration’s Risk of Bias Tool for randomized controlled trials.33 Two authors separately screened, reviewed, and rated the items for each trial by using this method and extracted data for the analyses. Disagreements with scoring or extracted data were addressed after discussion with the senior author (E.A.).
Means, SD, SEMs, 95% confidence interval (CI), number of events, and total number of participants were extracted from the text, tables, or graphs from each source study. The authors of the trials that failed to report the sample size or results as a mean and SD or SEM or 95% CI were contacted twice by e-mail to request the missing data or raw data. If no reply was received, median and interquartile range were used for means and SD approximation as follows: the mean was estimated as equivalent to the median and the SD was approximated to be the interquartile range divided by 1.35.34 When the trials included >2 groups, data from the group with the highest local anesthetic concentration were recorded, along with data from the control group. All opioids were converted into equianalgesic doses of IV morphine for analysis (10 mg IV morphine = 30 mg oral morphine = 1.5 mg IV hydromorphone = 7.5 mg oral hydromorphone = 75 mg IV pethidine = 20 mg oral oxycodone = 100 mg IV tramadol).35,36 Pain scores and satisfaction scores reported as Visual, Verbal, or Numeric Rating Scales were converted to a standardized 0 to 100 analog scale for quantitative evaluations. Finally, we rated the quality of evidence for each outcome following the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) Working Group system.37
Meta-analyses were performed with the assistance of Review Manager software (RevMan version 5.2; The Nordic Cochrane Centre, The Cochrane Collaboration 2012, Copenhagen, Denmark). This software estimates the weighted mean differences for continuous data and risk ratio for categorical data between TAP block and control groups, with an overall estimate of the pooled effect. Data were analyzed with a random effects model, because most were heterogeneous, and are presented as the mean difference or relative risk with 95% CI, except sedation score at 24 hours postoperatively where standardized mean difference was used because of inconsistency in the measurement scales. Our primary outcome (cumulative IV morphine consumption at 6 hours postoperatively) was analyzed in subgroups according to the type of surgery (abdominal laparoscopy, abdominal laparotomy, cesarean delivery), the type of surgical anesthesia (general anesthesia, spinal anesthesia with intrathecal long-acting opioid and spinal anesthesia without intrathecal long-acting opioid), the timing of injection (before or after the surgery), the ultrasonography-guided block approach adopted (subcostal, lateral, posterior, not specified), and the presence of postoperative multimodal analgesia (defined as a combination of opioids with acetaminophen and/or nonsteroidal anti-inflammatory drugs versus analgesia based on the opioids only). We conducted a meta-analysis when 2 or more trials reported similar outcomes. I2 was used to evaluate heterogeneity with predetermined thresholds for low (25%–49%), moderate (50%–74%), and high (>75%) levels.38 Publication bias was evaluated for our primary outcome by drawing a funnel plot of SEM difference (y-axis) as a function of the mean difference (x-axis) and confirmed with Duval and Tweedie trim and fill test,39 performed using Comprehensive Meta-analysis version 2 software (Biostat, Englewood, NJ). A meta-regression analysis was performed to assess the impact of total bilaterally injected local anesthetic dose (milligrams of bupivacaine equivalent) on the primary outcome, according to the type of surgery. Doses of ropivacaine were converted to equipotent doses of bupivacaine (1 mg bupivacaine = 1.4 mg ropivacaine).40,41 This latter analysis was performed with JMP 9 statistical package (SAS Institute, Cary, NC). A 2-sided P value <0.05 was considered significant.
Ninety trials were identified from the literature search strategy, 31 of which met the inclusion criteria, representing a total of 1611 participants (Fig. 1). Table 1 presents the trial characteristics. According to our assessment following the Cochrane Collaboration Risk of Bias tool (Fig. 2), the majority of trials had a low risk of bias. The trials were conducted on participants who underwent abdominal laparotomy (45%),3,42–54 abdominal laparoscopy (32%),2,4,7,55–61 and cesarean delivery (23%).62–68 Attempts were made to contact 22 authors,3,42–49,51,53–55,57,60–65,67,68 and 11 authors provided the additional data requested.3,45,48,53,54,57,61,63–65,68 In 4 trials, data were approximated from median and range.43,44,55,56
Ultrasound-guided TAP block was combined with general anesthesia in 25 trials (80%),2–4,7,42–61,68 with spinal anesthesia and intrathecal long-acting opioid in 3 trials (10%),64–66 or with spinal anesthesia and intrathecal short-acting opioid in 3 trials (10%).62,63,67 The volume of local anesthetic used per side varied between 12 mL47 and 30 mL7 with a total dose of bupivacaine equivalent ranging from 60 mg47 to 214 mg.52 Three trials combined the local anesthetic with epinephrine,7,48,57 whereas 1 trial administered a mixture of an equal volume of 1% lidocaine and 0.25%bupivacaine.43 Ultrasound-guided TAP block was performed before the surgery in 18 trials (58%).2–4,7,42,43,46–48,50,51,53–56,58,59,61 The approach was subcostal in 2 trials (6%),7,61 lateral in 18 trials (58%),3,42–45,47–50,52,58,59,62–66,68 posterior in 8 trials (26%),2,4,46,51,55,56,60,67 and was not specified in 3 trials (10%).53,57,61 With the exception of 3 trials,53,54,61 where it was not specified, the authors performed a single injection.
Cumulative IV morphine consumption was reduced by an average of 6 mg in favor of the ultrasound-guided TAP block group (95% CI, −7 to −4 mg; I2 = 94%; P < 0.00001) at 6 hours postoperatively. This difference persisted whether the surgery was an abdominal laparotomy (I2 = 84%; P < 0.00001), an abdominal laparoscopy (I2 = 78%; P = 0.0004), or cesarean delivery (I2 = 98%; P = 0.04), without difference between subgroups (I2 = 0%; P = 0.55; Fig. 3). There was no association between the total dose of local anesthetic injected and the reduction in morphine consumption at 6 hours postoperatively (r2 = 0.12; P = 0.17). Regarding the type of surgical anesthesia, ultrasound-guided TAP block reduced cumulative IV morphine consumption when combined with general anesthesia (I2 = 90%; P < 0.00001) or spinal anesthesia without long-acting opioid (I2 = 69%; P < 0.0001), but not when combined with spinal anesthesia including intrathecal long-acting opioid (I2 value not applicable; P = 0.05; Fig. 4). The magnitude of the reduction in morphine consumption at 6 hours postoperatively was not influenced by the timing of injection (I2 = 0%; P = 0.72; Fig. 5), the block approach adopted (I2 = 0%; P = 0.72; Fig. 6), or the presence of postoperative multimodal analgesia (I2 = 73%; P = 0.05; Fig. 7).
With regard to the funnel plot for our primary outcome, the Duval and Tweedie trim and fill test revealed the point estimate for the combined studies to be −1.2 (95% CI, −1.6 to −0.8), suggesting a risk of publication bias in favor of ultrasound-guided TAP block. Heterogeneity was assessed with I2 values of 94%. The quality of evidence for our primary outcomes is moderate, according to the GRADE working system.
Table 2 presents secondary acute pain–related outcomes and opioid-related side effects. The reduction in IV morphine consumption at 24 hours postoperatively and mean pain scores at rest and on movement at 6 hours postoperatively reached statistical significance, although the clinical impact of these reductions is questionable. There were no significant differences in the other secondary outcomes, such as postoperative nausea or vomiting (I2 = 1%; P = 0.59) and pruritus (I2 = 12%; P = 0.58).
One study reported a shorter time to discharge in the ultrasound-guided TAP block group.56 Finally, 19 studies,2,4,7,42,46,49,50,52,53,55,56,59,60,62,63,65–68 including 1028 participants, sought to report observed complications. One participant in the ultrasonography-guided TAP block group sustained an anaphylactoid reaction,63 and 1 bruise63 was reported in each group.
This meta-analysis and systematic review of the literature is the first to evaluate the postoperative analgesic efficacy of specifically ultrasonography-guided TAP block. On the basis of 31 randomized controlled trials and 1611 participants, our results show that ultrasonography -guided TAP block marginally reduces opioid consumption at 6 hours postoperatively after abdominal laparotomy, abdominal laparoscopy, and cesarean delivery, without serious complications, and independent of the timing of the procedure, the adopted block approach, or the presence of postoperative multimodal analgesia. This reduction in opioid consumption is not present in patients receiving spinal anesthesia, including long-acting opioids. A volume of 12 mL of local anesthetic per side with a total dose of bupivacaine equivalent of 60 mg was adequate to produce this effect with no further improvement reported after greater doses. Although pain scores at rest and on movement at 6 hours postoperatively and opioid consumption at 24 hours postoperatively are also statistically reduced, the clinical impact is questionable. Despite the high number of randomized controlled trials included, we report the quality of evidence for both our primary and secondary outcomes as moderate. This is because of the evidence of publication bias for the primary outcome and the inconsistency in absolute effects observed for all outcomes.
The ultrasonography-guided TAP block’s lack of efficacy when combined with intrathecal long-acting opioid should be interpreted with caution, because only 165 of the 364–66 studies examining this regimen reported the primary outcome of our meta-analysis. A previous meta-analysis focused on cesarean delivery also concluded an absence of benefit when the TAP block was combined with intrathecal long-acting opioid.15 However, this conclusion was again drawn from the results of 2 studies,65,69 1 of which used an anatomic landmark-guided technique.69 Additional trials comparing TAP block with intrathecal long-acting opioid are required to corroborate this finding.
Previous meta-analyses concluded that the TAP block provides effective postoperative analgesia but relied on 5 or fewer trials,12,15,16 7 to 9 trials,10,11,13,14 and 1018 and 12 trials.17 The 2 larger meta-analyses demonstrated a reduction of IV morphine consumption of 9.117 and 5.7 mg18 within the first 24 hours postoperatively, which is equivalent to our finding. Therefore, previous conclusions regarding the positive efficacy of the intervention should be considered in context with the marginal clinical benefit likely from this magnitude of opioid reduction in the postoperative period and the evidence of substantial publication bias for our primary outcome.
Another important finding of our study is the absence of major complications when anesthesiologists adopt an ultrasonography-guided technique. Recently, McDermott et al.24 studied 36 patients who had a bilateral TAP block performed following a classical anatomic landmark-based technique. After placement of the needle by the anesthetist, the needle tip position was verified with ultrasound. This investigation was terminated early because of an unacceptably high 18% needle penetration of the peritoneal cavity. In addition, the needle tip was located subcutaneously or IM in 58% of the cases. The authors concluded that <25% of the injections were within the correct intermuscular plane. Case reports also have described the blind, “double-pop” technique leading to the liver,70 small bowel,71 or colonic puncture.72 Neither cardiac nor neurologic complications were identified by our meta-analysis, despite 2 recent publications that found increased and potentially toxic plasma concentrations of local anesthetics after bilateral TAP block with a similar range of doses.73,74 In view of our findings, the ultrasonography-guided TAP block is associated with a high safety profile.
We were unable to determine any association between the total dose of bupivacaine and the magnitude of reduction in morphine consumption at 6 hours postoperatively, regardless of the type of surgery. Our finding is in contrast to a recent meta-analysis of TAP block for laparoscopic procedures, which identified a relationship between the total dose of local anesthetic and the reduction of morphine consumption and pain scores at 24 hours postoperatively.18 This discrepancy may stem from the difference in time from block to outcome. Local anesthetic effect may be more profound at 6 hours regardless of the total mass injected, whereas the residual effect at 24 hours may be more closely correlated to the dose of local anesthetic administered.
The results of our meta-analysis have several limitations. Although we attempted to explain the observed heterogeneity by grouping results according to the type of surgery, the type of anesthesia, the timing of the procedure, the adopted approach, and the presence of postoperative multimodal analgesia, heterogeneity remained high. None of the included studies specifically sought to assess the sensory blockade after the ultrasound-guided TAP block. Thus, the success rate of the technique is unknown and may therefore have affected our analysis. This concern notwithstanding, given that the included trials followed an intention-to-treat protocol, we believe that our results realistically reflect routine daily practice. Finally, we were unable to conduct a meta-analysis on time to discharge, because only 1 trial sought to capture this outcome. Consequently, the impact of the ultrasonography-guided TAP block on functional outcomes during postoperative recovery remains undetermined.
In conclusion, ultrasonography-guided TAP block provides marginal postoperative analgesic efficacy after abdominal laparotomy or laparoscopy and cesarean delivery. However, it does not provide additional analgesic effect in patients who also received spinal anesthesia containing a long-acting opioid. The minimal analgesic efficacy is independent of the timing of injection, the block approach adopted, or the presence of postoperative multimodal analgesia. A volume of 12 mL of local anesthetic used per side with a total dose of bupivacaine equivalent of 60 mg is sufficient. The degree of heterogeneity of the results suggests that these findings should be interpreted with caution.
Name: Moira Baeriswyl, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Moira Baeriswyl has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.
Conflicts of Interest: Moira Baeriswyl declares no conflicts of interest.
Name: Kyle R. Kirkham, MD.
Contribution: This author helped design the study, conduct the study, and write the manuscript.
Attestation: Kyle R. Kirkham has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.
Conflicts of Interest: Kyle R. Kirkham reported no conflicts of interest.
Name: Christian Kern, MD.
Contribution: This author helped design the study, conduct the study, and write the manuscript.
Attestation: Christian Kern has seen the original study data and approved the final manuscript.
Conflicts of Interest: Christian Kern declares no conflicts of interest.
Name: Eric Albrecht, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Eric Albrecht has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.
Conflicts of Interest: Eric Albrecht has received grants from the Swiss Academy for Anesthesia Research (SACAR), Lausanne, Switzerland (no grant numbers attributed).
This manuscript was handled by: Terese T. Horlocker, MD
The authors thank Mrs. Isabelle von Kaenel, Head Librarian, Centre Hospitalier Universitaire Vaudois, University of Lausanne, Lausanne, Switzerland, for the assistance in the literature search.
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