Quadratus lumborum block for postoperative analgesia after full abdominoplasty: a randomized controlled trial

1 Introduction

Abdominoplasty is a common postbariatric procedure that reduces physical as well as psychological complaints from excess skin. It involves loosening subcutaneous tissue on the entire anterior abdominal wall to remove excess tissue, and to facilitate reconstructive surgery on the anterior fascial sheets and may cause significant postoperative pain. The current gold standard of pain treatment are multimodal analgesic regimens consisting of various combinations of paracetamol, non-steroidal anti-inflammatory drugs, opioids, local infiltration and regional analgesia. Compared to previous abdominal plane blocks, the quadratus lumborum block (QLB) may potentially spread to the paravertebral space, extending the analgesia above the level of the umbilicus which is theoretically ideal for a full abdominoplasty [1], [2], [3], [4], [5]. However, QLB effectiveness in this setting is unknown. Therefore, the aim of study was to investigate whether a QLB provides an additional benefit to a multimodal analgesia regimen in postbariatric patients treated with standard full abdominoplasty. The primary objective was to compare the opioid consumption between a QLB using ropivacaine with that of placebo. Secondary objectives were to observe patient reported acute and chronic pain, satisfaction, side effects, and other practical aspects of the intervention in relation to the postoperative period.

2 Methods

Triple blinded, randomized, controlled trial (RCT) on 50 adult postbariatric patients (age 18–64) treated with full standard abdominoplasty. The study was performed at Baerum Hospital, a district general hospital in Norway. The study was performed according to the Declaration of Helsinki and approved by the Norwegian Medicines Agency and the South East Regional Ethics Committee, Norway. Prior to inclusion, the study was registered with EudraCT (No 2016-002538-58), clinicaltrials.gov (NCT02949778), and written informed consent was obtained from all subjects. At Baerum Hospital, postbariatric abdominoplasty is performed on medical indication only (i.e. physical disturbances such as intertrigo, odor, pain, difficulties with clothing, or a very abnormal physical appearance). Contraindications to the procedure are body mass index above 28, smoking, and American Society of Anesthesiologists Physical Status Classification (ASA) 3–4 [6]. The patient must have a stable body weight for at least 6 months to be considered for surgery. For the study, participants were excluded in cases of weight <60 kg, a history of anaphylactic shock, cardiovascular disease other than hypertension and/or hyperlipidemia, known allergy to ropivacaine or morphine, psychiatric comorbidity, a history of chronic pain or regular use of opioid pain medication or neuroleptic drugs, coagulation disorders or treatment with platelet inhibitors, pregnancy or breast-feeding, or any medical contraindication to the study intervention according to the attending anesthetist or surgeon.

Concealed computerized block randomization with 1:1 allocation ratio was performed by the hospital pharmacy using an algorithm programmed in R and the package blockrand [7]. On the day of inclusion, The Amsterdam preoperative anxiety and information scale was performed to assess anxiety and information desire [8].

Algometry was performed with a pressure algometer (Somedic AB, Solltuna, Sweden) with one square centimeter pressure surface pressed into the nail bed, increasing the pressure by 20 kPa per second. The patients were instructed to click as soon as pressure was experienced as pain and a second time when pain was no longer tolerable. Patients were prior to surgery given 1.5 g paracetamol orally with additional 0.5 g if total body weight was above 65 kg. Both groups received a bilateral QLB, using 2×20 mL of ropivacaine 3.75 mg/mL in the ropivacaine group (R), and sterile saline 9 mg/mL in the placebo group (P). The study drugs were visually identical. The block was administered immediately before induction of anesthesia according to a study by Murouchi et al. [5]. In brief, with the patient in a supine slightly lateral position, the probe was placed from the posterolateral side slightly cephalad to the iliac crest, and the needle inserted medial to the probe and advanced in a posterior direction until the tip was placed at the posterior border of the quadratus lumborum muscle (using a L4-12t linear or C1-5 curved probe (LOGIQ e R7, GE Vingmed Ultrasound, Horten, Norway), and SonoPlex Stim 80 or 100 mm needle (PAJUNK GmbH, Geisingen, Germany), both depending on patient anatomy). Needle trajectory, tip, and drug dissemination along the posterior border of the quadratus lumborum muscle were confirmed during ultrasound guidance. To reduce QLB variation, QLB was performed by study personnel proficient in ultrasound-guided blocks and the QLB in particular (TB, TY, and KL). All three employ the same technique and frequently use the block as part of normal clinical practice.

A second intravenous (iv) cannula was placed during general anesthesia and connected to an electronic pump for patient-controlled analgesia (PCA). The pump was programmed with no continuous infusion, and a bolus of 1 mg morphine with a 5-min lockout time. All patients were given iv dexamethasone 8 mg. General anesthesia was induced with an iv bolus of 100 μg fentanyl, and target controlled infusions of propofol and remifentanil, before placing a laryngeal mask. Additional fentanyl and desflurane was given as needed during the anesthesia at the discretion of the nurse anesthetist or anesthetist.

To reduce surgical variation, a single surgeon (JF) performed or assisted according to his instructions all abdominoplasties. In brief, the abdominoplasty began with local infiltration anesthesia along the planned incision lines. Second, 3–400 mL of liposuction solution (lidocaine 0.4 mg/mL and adrenaline 1 μg/mL in Ringer-acetate) was administered in the anterior abdominal surface, followed by en bloc removal of the skin and subcutaneous tissue from the umbilicus to the pubic area. Third, the skin above the umbilicus was undermined in the midline towards the xiphoid process to expose the anterior muscle fascia from the xiphoid process to the pubis. After plicating this fascia, 20 mL bupivacaine 2.5 mg/mL with adrenaline was administered in the rectus sheet along the suture line. Finally, the umbilicus was pulled through a new opening, the skin adapted, and a single 18 French vacuum drain placed through a separate lateral opening.

Postoperative pain was treated with oral paracetamol 1 g quater in die, and PCA with iv morphine as needed for at least 24 h, which was replaced by oral oxycodone at the time of hospital discharge. If patients presented with strong postoperative pain where the PCA protocol was deemed inadequate for rapid pain control, rescue therapy with additional iv opioids were allowed.

Patient characteristics, duration of surgery and analgesics used during the hospital stay were obtained from medical records. To assess baseline pain tolerance, an algometer was used prior to injection of the block. Pain was assessed on the numerical rating scale (NRS) from 0 to 10 at rest and when coughing. Here, 0 was no pain and 10 the worst pain imaginable. If patients reported NRS between two numbers, the mean of these numbers were used (i.e. 5–6 was analyzed as 5.5). The area under the curve (AUC) of NRS from hour 0 to 48 was calculated using the linear trapezoid rule. The time until discharge from the post-anesthetic care unit (PACU) was recorded, representing time until adequately awake and with satisfactory pain control. The time elapsed until mobilization to the sitting position and walking was recorded. Pain, side effects, and opioid use were noted at observation points, which were on arrival and hourly afterwards in the PACU, and 12, 24, and 48 h after surgery. Beginning at the time of PACU admission, all opioids administered were converted to iv morphine equivalent units according to standard tables [9]. At the time of hospital discharge, a tablet of slow-release oxycodone was administered prior to disconnecting the morphine PCA pump. This opioid was counted in the period from 24 to 48 h. Remifentanil and fentanyl administered peroperatively could influence postoperative opioid requirements, but were not included in the analysis because administration is not necessarily due to pain perceived by the patient. Postoperative nausea and vomiting (PONV) was defined as nausea and/or vomiting at any point during the first 48 postoperative hours [10]. All patient-reported side effects were recorded. Patient satisfaction was measured on a five-point scale (very dissatisfied, dissatisfied, neither satisfied or dissatisfied, satisfied, or very satisfied). Patients were also followed up at three and 6 months to assess chronic pain defined as persisting and subjectively problematic on a yes/no scale. The primary endpoint was postoperative opioid consumption the first 24 h.

Previous studies on the TAP block have shown a reduction in morphine consumption of approximately 40% [2], [3]. Employing the current practice of using local infiltration analgesia along the rectus musculature in both groups, we assumed a more moderate but still marginally clinically relevant difference of 25%, using 19 mg in the P group as reported by Sforza et al. and estimating 14 mg in the R group [3], [11]. Using a 50% increased standard deviation of 6.0 in both groups, alpha 0.05, and beta 0.8, we estimated a sample size of 23 [12]. To allow for dropouts, we decided to include 25 patients in each group for a total of 50 patients.

Data are presented as mean or number of observations with 95% confidence intervals (CI) for the mean, median, or difference as appropriate. Where quantile–quantile plots indicated a normal distribution, treatment group comparisons were done with Student’s t-test. Comparisons for non-normally distributed data were performed using the Mann-Whitney U-test. Time to first rescue analgesia, PACU discharge, and mobilization were compared between the groups with log-rank tests. Opioid use the first 24 h was log-transformed before Student’s t-test was performed. A linear mixed model was fitted to the repeated measurements of morphine equivalent units and NRS. The model contained fixed effects for treatment, time, and treatment × time interaction, and a random intercept. Time was modeled as piecewise linear with separate time effects from PACU to 12 h, from 12 h to 24 h, and from 24 h to 48 h. The Fisher mid-P test (Fisher-Irwin) was used for 2×2 tables with few events. The Wilcoxon-Mann-Whitney test was used for sum of side effects and satisfaction at 48 h (ordered 2×4 tables) [13]. The blinding was upheld for patients, personnel, and throughout primary statistical analysis, after which the allocation sequence was obtained from the pharmacy upon the study monitors request. After unblinding, to account for the possible interaction between opioid use and pain, a Silverman integrated assessment of pain and opioid requirements was performed [14]. Two-sided p-values less than 0.05 were considered statistically significant. The statistical calculations were performed using R version 3.4.3 with the package survival, Stata 14 (StataCorp LLC, College Station, TX, USA), and Matlab R2014a (Mathworks, Inc.) [7].

3 Results

Seventy nine patients were evaluated for participation from November 2016 through June 2017. Fifty patients were included, randomized and received the allocated treatment (Fig. 1).

Fig. 1:

CONSORT style flowchart of patient recruitment and analysis of primary endpoint. ASA=American Society of Anesthesiologists physical status classification system.

Patient characteristics were similar in both groups (Table 1). Opioid use was similar in both groups at all measurement points (Fig. 2). The primary endpoint, morphine equivalent units administered the first 24 postoperative hours, was mean (SD) 26 (25) in R patients and 33 (33) mg in controls (p=0.44). Secondary outcomes were similar between groups (Table 2, Fig. 3). All patients had discontinued all scheduled pain medication within 6 months of surgery. Sum of ranks in a Silverman integrated assessment of pain and opioid use were similar in both groups (p=0.41, Supplementary material 1) [14].

Fig. 2:

Morphine equivalent units administered in different time periods. h=hours; PACU=post-anesthetic care unit.

Fig. 3:

Numerical rating scale (NRS) reported at rest and during coughing. h=hours; PACU=post-anesthetic care unit.

Regarding administration of the QLB, a suboptimal view (n=8) was the most common problem when administering the block, followed by loose tissue complicating needle placement (n=2), less than 3 mL missing the target injection site (n=2, one of which was due to a partial disconnection between the needle and line to syringe), paresthesia (n=1, duration in the order of seconds) and difficulty confirming correct spread despite what appeared to be optimal needle tip placement and an optimal view (n=1). Subtracting the paresthesia this translates to technical difficulties in 26% of subjects. In sum, successful block placement as assessed by ultrasound failed in 2 out of 100 blocks. No blood was aspirated on the needle in any of the administrations. In one patient, morphine was replaced with oxycodone in the PCA pump due to localized urticaria at the point of morphine injection.

4 Discussion

The QLB did not reduce postoperative opioid requirements, pain, PONV, time to first analgesia, time to mobilization, time in PACU, other side effects, or chronic pain, when administered as part of a multimodal pain regimen to postbariatric patients undergoing standard full abdominoplasty. The observed effect appeared smaller and SD larger than assumed in the sample size estimation. To our knowledge, this is the first controlled trial of the effect of a QLB for significant supraumbilical pain, one of few randomized studies on a QLB, and the only study employing triple blinding to avoid patient, observer and analytical bias.

The lack of effect contrasts most previous studies, where an opioid sparing effect, lower serum concentrations, and superior effect compared to TAP has been described [5], [15], [16], [17]. However, these studies involved pain of subumbilical origin, and local infiltration anesthesia was not used. Until recently, studies on the QLB were few and of low quality, consequently with a high risk of bias [18]. The duration of effect of the QLB was more than 24 h in an open study with historical controls [5]. A recent double-blind randomized controlled trial reported reduced need for ketobemidone in the first 24 h after cesarean section, but the mean difference appeared to remain constant after roughly 12 h in a figure [15]. In the secondary endpoints, pain at rest and when coughing, the inter-group difference disappeared within the first 12 h [15]. A reduced need for opioids was also reported only in the first 12 h in another double blind RCT after cesarean section [17]. The exact duration of effect of the QLB on opioid use may vary, but appears to be equal to or less than 12 h in these double-blind RCTs. Using triple blinding in this study, no statistically significant differences were found.

The integrated assessment suggests the lack of additional effect is not due to interaction between pain and opioid use. The study was designed to detect a difference of 25% or more, and SD was larger than expected. We can therefore not exclude the possibility QLB leads to a reduction of less than 25%. Assuming a difference was missed, based on previous QLB literature and duration of local infiltration anesthesia, it was likely between PACU and 12 h. Here, a non-statistically significant reduction of approximately 20% or less in favor of QLB in terms of opioid consumption and pain was observed. However, international consensus is to consider 20% a minimal change of little clinical importance [11]. NSAIDS were not part of the multimodal regimen at our hospital at the time of study planning. However, NSAIDS would likely have diminished the observed minimal difference even further. Considering the additional labor and patient discomfort associated with the QLB, a clear benefit must be present to justify adding it to a multimodal pain regimen. Having reached the sample size with no statistically significant differences, and with estimates pointing towards no or a minimal difference, it is unlikely that a clear benefit was missed.

Firstly, a limitation of this study is that patients with chronic pain or with regular use of opioids were excluded to avoid introducing bias because they may require large amounts of opioids with little clinical effect. However, these represented only 8% of all patients screened for inclusion. Secondly, the supraumbilical effect of a QLB depends on local anesthetic spread to the paravertebral space (PVS), but is not well described in clinical use, and varies with small studies on cadavers, volunteers and technique [4], [19], [20], [21], [22]. The affected dermatomes were not tested in this study due to blinding and the use of local infiltration anesthesia. A preoperative evaluation by a blinded observer would require a delay for onset of block prior to evaluation, which would shorten postoperative duration of effect and observed effectiveness. Therefore, the study results are limited by an unknown block success rate, and the prevalence of spread to the PVS in postbariatric patients remains unknown. Third, although using oxycodone instead of morphine could have allowed more precise titration and evaluation, both inter-individual variation and relative inter-group differences would likely be similar [23]. Finally, the aim of study was to investigate QLB effectiveness as part of a multimodal analgesic regimen, and not QLB efficacy alone. Thus, the inter-group difference is, compared to QLB efficacy when used alone, mitigated by the multimodal analgesic regimen as it would be in normal clinical practice. Therefore, the study should not discourage QLB use for abdominoplasty in cases where a multimodal analgesic regimen is impossible or inadequate.

The consistency of paravertebral spread, dermatome levels, and the efficacy of the various quadratus lumborum blocks for supraumbilical pain needs further investigation.

5 Conclusions

The QLB did not provide significant additional benefit in terms of reduced opioid requirements, postoperative pain, PONV, other side effects, or chronic pain, when administered as part of a multimodal pain regimen to postbariatric patients undergoing standard full abdominoplasty. A minimal difference of little clinical importance the first 12 postoperative hours may have been missed.