Inguinal hernia repair is a commonly performed operation in day case surgical units. Postoperative pain after open hernia repair may be moderate to severe and is most intense on the day of surgery. It is associated with delayed return to normal daily activities and may also be related to persistent postsurgical pain, affecting between 0 and 43% of patients.1
In a recent systematic review, postoperative pain management was recommended to consist of a combination of paracetamol, a NSAID and a local anaesthetic technique.2 However, the well documented pain relief with ilioinguinal nerve block and wound infiltration is reported to have a limited duration of action of up to 6 to 8 h.3
Transversus abdominis plane (TAP) block is a regional anaesthetic technique which blocks neural afferents from the anterolateral abdominal wall.4 With the aid of ultrasound or anatomical landmark guidance, local anaesthetic is injected into the transversus abdominis fascial plane, where the nerves from T6 to L1 are located. The initial clinical trials assessing the analgesic effect of TAP blockade showed an effect for up to 24 h postoperatively.5–7 A TAP block with a possible prolonged analgesic effect may, therefore, represent an interesting analgesic option in this surgical population.
Our hypothesis was, therefore, that a TAP block as an adjunct to a basic analgesic regimen with paracetamol and ibuprofen would demonstrate an improved and prolonged analgesic effect after inguinal hernia repair compared with either placebo or a combination of ilioinguinal nerve block and wound infiltration.
The aim of this prospective, double-blind, randomised and placebo controlled study was, therefore, to investigate the effect of a TAP block on postoperative pain scores 0 to 24 h postoperatively while coughing (primary outcome) and pain scores at rest, opioid consumption and opioid side-effects (secondary outcomes) compared with a placebo group, and an active control group (ilioinguinal nerve block with wound infiltration), in patients undergoing inguinal hernia repair in a day case surgery unit.
The study was carried out at the Day Case Surgery Unit at Glostrup University Hospital, Copenhagen, Denmark. Approval was obtained from the Regional Ethics Committee, the Danish Medicine Agency and the Danish Data Protection Agency. The study was conducted in compliance with the Declaration of Helsinki and guidelines for Good Clinical Practice (GCP). The trial was registered at http://www.clinicaltrials.gov and monitored by The Copenhagen University Hospital GCP unit. Furthermore, the design and the description of the study are in accordance with the Consolidated Standards of Reporting Clinical Trials (CONSORT).8
The Regional Committee on Biomedical Research Ethics, Region Hovedstaden, Denmark (Chairperson Professor Mette Rasmussen) approved this study on 1 March 2010.
Adult patients (18 to 75 years) with American Society of Anesthesiologists’ (ASA) status 1–3 scheduled for primary inguinal hernia repair as day case patients were included in the study. Exclusion criteria were BMI below 18 or above 35 kg m−2, inability to understand Danish, relevant drug allergy, pregnancy, alcohol or drug abuse, daily opioid intake, consumption of pain medications within 24 h before surgery and infection at the injection site.
Patients received both written and oral information regarding the trial. Signed informed consent was obtained from all patients.
All patients received a standardised anaesthetic regimen. Anaesthesia was induced and maintained with remifentanil (0.6 mg ml−1) 0.4 ml kg−1 h−1 (fixed rate) and propofol (variable rate). The airway was managed with an I-gel supraglottic airway (Intersurgical Inc., Sankt Augustin, Germany). Ten minutes before the end of surgery, all patients received intravenous sufentanil 0.2 μg kg−1.
The patients all had inguinal hernia repair with a mesh using the Lichtenstein technique.9
A standardised postoperative analgesic regimen was used consisting of oral paracetamol 1 g every 6 h and ibuprofen 400 mg every 6 h, initiated 30 min before surgery. For the first 2 h in the postoperative care unit, intravenous morphine was given by a nurse on request by the patient. The initial morphine dose was 5 mg and subsequent doses were 2.5 mg with a minimum of 10 min between doses. From 2 to 24 h postoperatively, oral ketobemidone 2.5 mg was taken, based on the patient's own decision, with a prescribed minimum time interval of 1 h. For nausea scores of at least moderate intensity, ondansetron was given until discharge, with a first dose of 4 mg followed by 1 mg if needed. Prophylactic antiemetics were not administered.
Blinding and randomisation
The study was randomised, double-blinded and placebo-controlled. The patients were assigned randomly to one of three groups. In group TAP, a unilateral TAP block was performed with ultrasound guidance using 25 ml of 0.75% ropivacaine; a placebo ilioinguinal nerve block and placebo infiltration were also employed. In group infiltration, ilioinguinal nerve block was performed with 10 ml of 0.375% ropivacaine, the wound was infiltrated with 40 ml of 0.375% ropivacaine and a placebo TAP block was performed. In group placebo, placebo TAP block, placebo ilioinguinal block and placebo infiltration were undertaken.
Study medication was prepared by the hospital pharmacy and placed in identical boxes containing either 25 ml of isotonic saline or 25 ml of 0.75% ropivacaine, with two boxes for each patient marked infiltration/ilioinguinal nerve block or TAP block. The boxes were sealed and marked with the name of the project, the investigators’ names and consecutive numbers according to a computer generated block randomisation list prepared by the hospital pharmacy (block size = 9). The boxes were opened and the study medication was drawn into neutral syringes by a nurse who was not part of the study or involved in the patient's care. The study medication for the ilioinguinal nerve block and infiltration was diluted with 25 ml of saline, which resulted in a total of 50 ml of study solution. The patients, the anaesthesiologists and staff providing postoperative care were blinded to group assignments. The investigators (PLP, PS) performed all assessments.
TAP block was performed unilaterally before surgical incision by one of two investigators (PLP, PS). An ultrasound probe (Venue 40; GE Healthcare, Chalfont St. Giles, UK) was placed transversely in the midaxillary line between the iliac crest and the costal margin at the level of the umbilicus. The external oblique, internal oblique and transversus abdominis muscles and their fascias were visualised. A Pajunk 22 gauge, 80 mm needle (Medizintechnik, Geisingen, Germany) was introduced anteriorly and in the plane of the ultrasound probe, and on entering the TAP, 2 ml of 0.9% saline was injected to verify the correct position of the needle. Following negative aspiration, 25 ml of the study solution was injected and the injectate was seen spreading in the TAP as a dark oval shape.
The surgeon performed a blind ilioinguinal nerve block before incision using 10 ml of study solution. In addition, 40 ml of study solution was injected in a standardised stepwise manner intravenously and subcutaneously, subfascially and in the deeper layers during the operation, as described in a previous study.10
The primary outcome measure of the study was visual analogue scale (VAS) pain scores while coughing, estimated as area under the curve (AUC24 h) based on pain scores at 0, 2, 4, 6, 8, 19 and 24 h postoperatively.
The secondary outcome measures of the study were VAS pain scores at rest (AUC24 h) based on pain scores at 0, 2, 4, 6, 8, 19 and 24 h postoperatively, morphine consumption 0 to 2 h postoperatively, ketobemidone consumption 2 to 24 h postoperatively, levels of nausea and sedation based on measurements at 0, 2, 4, 6, 8, 19 and 24 h postoperatively, number of vomiting episodes and number of patients vomiting during the first 24 h.
Before operation, all patients were instructed in the use of an ungraded 100 mm VAS with 0 equal to no pain and 100 equal to worst pain imaginable.
Patients were interviewed at 0, 2, 4, 6, 8, 19 and 24 h after operation by the investigators either in person or by telephone after discharge. The investigators recorded the patients’ assessments of VAS pain scores at rest and while coughing, opioid consumption and the patients’ assessments of side-effects at each interview.
Doses of on request intravenous morphine (mg) in the first 2 h and oral ketobemidone (mg) taken by the patients 2 to 24 h postoperatively were recorded.
Severity of nausea and sedation were assessed by the patients on a four-point scale (none, mild, moderate or severe). The number of productive vomits (above 10 ml) in the postoperative periods 0 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 19 and 19 to 24 h was reported by the patients. Finally, the number of patients who received ondansetron was recorded.
We were not able to find a study of inguinal hernia repair, which used VAS pain scores calculated as AUC. Therefore, we based our sample size calculation on the highest postoperative VAS score from a questionnaire conducted at our day case surgical unit. The anticipated VAS score at 6 h postoperatively was 40 (SD 20) mm. We considered a 50% reduction in VAS pain scores between the TAP group and the placebo group to be of clinical relevance. With a type 1 error of 0.05 and a type 2 error of 0.10, a sample size calculation determined that 66 patients were needed in the study. To allow for dropouts and exclusions, we aimed to recruit an additional 24 patients to the study, thus aiming for a total of 90 patients.
Statistical analyses were performed using SPSS 19 (SPSS, Chicago, IL). Data are presented as median and interquartile range (IQR) or mean and SD, as appropriate. The Kolmogorov–Smirnov test was used to test for normality. VAS pain scores at rest and while coughing were calculated as AUC (AUC24 h). These data followed a normal distribution and were compared with one-way analysis of variance (ANOVA). Morphine and ketobemidone consumption did not follow a normal distribution and were compared using the Kruskal–Wallis test. If the Kruskal–Wallis test was significant, a group-wise comparison among the three groups was performed using the Mann–Whitney test. Bonferroni's correction was used for multiple comparisons. Categorical data (number of patients vomiting and number of patients requiring ondansetron) were analysed using the χ 2 test. For comparing side effects (nausea and sedation), numerical values were assigned to the scores from each patient; none, 0; slight, 1; moderate, 2 and severe, 3. A P value less than 0.05 was considered statistically significant. The investigators did all statistical analyses.
One hundred and twenty-seven patients were approached for participation in the study from June 2010 to November 2011. Ninety patients were recruited and randomly assigned to their treatment group. However, four patients were later excluded, resulting in 86 patients in the final analyses (Fig. 1).
All TAP blocks were performed as described in the methods section and without any complications. Three patients in group infiltration had partial paralysis of the thigh musculature and were discharged with crutches. Patients’ characteristics and perioperative data are shown in Table 1, with no major differences among groups.
VAS pain scores calculated as AUC24 h both while coughing (primary outcome) and at rest demonstrated no significant differences among the three study groups. VAS pain scores in groups infiltration, TAP and placebo were 19 (SD 12), 22 (11) and 15 (9) mm, respectively, at rest (P = 1.00) and 37 (19), 41(15) and 37 (14) mm while coughing (P = 1.00).
To test the sensitivity of our study, an additional analysis was conducted for the first 6 h postoperatively. VAS pain scores (AUC6 h) were significantly lower in group infiltration than in group TAP: 10 (SD 9) versus 25 (13) mm, P < 0.001 [mean difference 15 mm, 95% confidence intervals (CIs) 8 to 22 mm] at rest and 17 (14) versus 40 (14) mm, P < 0.001 (mean difference 23 mm, 95% CI 13 to 33 mm) while coughing. VAS pain scores expressed as AUC6 h were also lower in group infiltration than in group placebo: 10 (9) versus 20 (11) mm, P = 0.003 (mean difference 10 mm, 95% CI 3 to 17 mm) at rest and 17 (14) versus 38 (17) mm, P < 0.001 (mean difference 21 mm, 95% CI 10 to 31 mm) while coughing.
VAS pain scores at rest and while coughing at each time point are shown in Figs 2 and 3.
Median (IQR) morphine consumption in the first 2 h postoperatively was lower in group infiltration than in group placebo: 0 mg (0 to 0 mg) versus 5 mg (0 to 5 mg; P < 0.003). There were no significant differences in morphine consumption between group TAP [0 mg (0 to 1.25 mg)] and the other two groups.
Ketobemidone consumption between 2 and 24 h postoperatively was low and there were no statistically significant differences among groups: group TAP 2.5 mg (0 to 5 mg), group infiltration 0 mg (0 to 5 mg), group placebo 0 mg (0 to 5 mg).
The incidence of side effects was generally low and there were no significant differences among groups (Table 2).
In this study, we have demonstrated that patients undergoing day case open inguinal hernia repair, receiving a basic analgesic regimen of paracetamol and ibuprofen, did not benefit from the additional use of TAP block or local infiltration and ilioinguinal nerve block. When additional comparisons were performed on pain scores at rest and while coughing for the first 6 h, which is the expected maximum analgesic efficacy time period for local anaesthetic infiltration, a significant analgesic effect was demonstrated in the infiltration/ilioinguinal nerve block group compared with TAP block and placebo. This finding demonstrates that our study had sufficient assay sensitivity to detect additional analgesic effects even in the presence of the basic analgesic regimen. Consequently, we are able to reject with confidence the hypothesis that TAP block has any major analgesic effect after inguinal hernia repair.
A previous randomised controlled study compared the analgesic efficacy of TAP block with blind ilioinguinal block after inguinal hernia repair in adults.11 In contrast to our study, the authors reported a beneficial effect of TAP block on VAS pain scores at rest 4, 12 and 24 h postoperatively. However, that study had several limitations which may challenge the outcome: there was no placebo group, pain scores were generally low, VAS pain scores during mobilisation or coughing were not assessed and the actual differences in pain scores were small (between 4 to 10 mm on a 100 mm scale). Finally, morphine consumption was significantly lower in the TAP block group for the first 48 h postoperatively, but the actual reduction in morphine consumption was low (3 to 4 mg) and probably of limited clinical relevance.
We expected to demonstrate a long-lasting effect of TAP block because the initial TAP block studies demonstrated an analgesic effect for 24 h.5–7 These studies were all from the same group of investigators, who used the blind TAP block technique via the Triangle of Petit.12 Recently, it has been suggested that this technique might lead to a paravertebral spread of local anaesthetic,13 which may explain the longer duration and greater analgesic efficacy of the initial as compared to later studies.4,4,14–17 In ultrasound-guided techniques for performing TAP block, the local anaesthetic is injected and spread more anteriorly in the transversus abdominis fascial space and may, therefore, have a more narrow sensory block and shorter duration.18,19 However, a recent study investigated the actual spread of local anaesthetic after a blind TAP block with ultrasound and questioned the accuracy of the needle placement with this technique because it found correct placement and local anaesthetic spread in only 24% of patients.4,20 The question of a possible superiority of one TAP block method compared to another, therefore, remains unanswered.
Our research group has previously investigated the efficacy of a TAP block in another procedure commonly performed as day case surgery, laparoscopic cholecystectomy.21 Although our primary endpoint in that study [pain score (AUC24 h) while coughing] was significantly in favour of TAP block, the actual difference of 8 mm on a 0 to 100 mm scale compared to the placebo block was rather small. In that study, in the study of Aveline et al. 11 and in the present study, all patients received a basic analgesic regimen with paracetamol and NSAID. Furthermore, another study comparing TAP block with local anaesthetic infiltration of the trocar insertion sites in laparoscopic cholecystectomy did not find any difference in favour of TAP block in pain scores at rest 4 or 24 h postoperatively.22 Consequently, it may be questioned whether a TAP block is justified in relatively minor abdominal procedures, especially if the patients receive a basic multimodal analgesic regimen with paracetamol and NSAID.
There are a number of limitations of the present study. First, despite performance of the TAP block with real time ultrasound, we do not know whether all TAP blocks produced a sensory blockade because we did not make sensory assessments, so as not to unblind the study. Even if a third and independent person had tested the sensory levels of the TAP block, this would have unblinded the patients and, therefore, could have influenced the result of the study. Furthermore, the spread of the sensory blockade does not necessarily reflect the analgesic effectiveness of TAP block. This is more truly reflected in differences in pain scores or opioid consumption.
Second, we have no assessment points from 8 to 19 h postoperatively and we, therefore, have limited information on any differences between groups during this period.
Third, we used the ultrasound-guided posterior approach at the umbilical level to perform the TAP block, which may produce a variable involvement of L1. Tran et al. 23 found involvement of L1 in 93% of cases in a cadaveric study with injection of 20 ml of aniline dye, whereas Lee et al. 18 found involvement of L1 in only 50% of TAP blocks after injection of 20 ml of ropivacaine 0.5%.
Fourth, the ilioinguinal block was performed blindly and the success rate of this block in the present study is also unknown.
We did not encounter any complications with the TAP block, but complications are rare and our study is underpowered to detect complications.
In conclusion, our study showed no postoperative analgesic effect of unilateral TAP block for inguinal hernia repair compared to either placebo or ilioinguinal nerve block with wound infiltration when administered together with a basic analgesic regimen with paracetamol and ibuprofen. Our results confirm previous findings that a combination of an ilioinguinal nerve block and wound infiltration improves analgesia for the first 6 h postoperatively after inguinal hernia repair compared with placebo.
Assistance with the study: none declared.
Financial support and sponsorship: this work was supported by the Department of Anaesthesiology, Copenhagen University Hospital, Denmark.
Conflicts of interest: none declared.
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© 2013 European Society of Anaesthesiology
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