Ultrasound-guided Anterior Quadratus Lumborum Block for Postoperative Pain after Laparoscopic Pyeloplasty: A Randomized Controlled Trial.

BACKGROUND: Quadratus lumborum block (QLB) has provided adequate analgesia and lowered postoperative opioid requirement in comparison to controls for some urological surgeries. AIMS: The aim of this study was to assess the efficacy of postprocedure ultrasound-guided QLB in comparison to port-site infiltrations with local anesthetics (as control) in lowering postoperative pain after laparoscopic pyeloplasty. SETTINGS AND
DESIGN: This was a prospective, single-blinded, randomized controlled trial.
MATERIALS AND METHODS: Fifty-three adults undergoing laparoscopic pyeloplasty were randomly allocated to either anterior QLB group (n = 27) or port-site infiltration Group P (n = 26) with 20 mL of 0.5% ropivacaine. The primary outcomes were static and dynamic pain on the Visual Analog Scale (VAS) of 0-100 at the 30th min, 2nd, 6th, 12th, and 24th hour after surgery. The secondary outcomes were number of patients requiring rescue analgesics and having postoperative nausea or vomiting (PONV) in 24 hours after surgery. STATISTICAL ANALYSIS: Intergroup comparison of VAS was done with Student's t-test. Categorical data were analyzed using the Chi-square test.
RESULTS: The static VAS scores were found to be significantly lower in QLB group at the 2nd, 6th, and 12th hour, and the dynamic VAS was lower at all time points after the 30th min in the QLB group. The number of patients requiring rescue analgesics were significantly lower in the QLB group (13 as compared to 21 in Group P; P = 0.015). The incidence of PONV was comparable. No other side effects were seen.
CONCLUSION: Ultrasound-guided anterior QLB is more effective in comparison to traditional technique of port-site local anesthetic infiltration for providing analgesia after laparoscopic pyeloplasty. Copyright:

INTRODUCTION

The advent of ultrasound has made it possible for an anesthesiologist to target nerves lying in different fascial planes. The arena of abdominal truncal blocks for analgesia has thus expanded well in the past decade.

Quadratus lumborum block (QLB) is an abdominal truncal block which was first described by Blanco et al. in 2007[1] as a variant of transversus abdominis (TA) plane block, and since then, several variations of QLB have been advocated and are increasingly been used for analgesia in abdominal surgeries.[2] The anterior QLB involves deposition of local anesthetics (LAs) in the fascial plane between quadratus lumborum (QL) and psoas major (PM) muscles. It is known to reduce both somatic and visceral pain with duration of analgesia lasting to at least 24 hours.[23] The reported dermatomal coverage is variable in studies, but consensus in contemporary literature is on lower thoracic and upper lumbar involvement.[234]

Laparoscopic pyeloplasty is a urological surgery for patients suffering from ureteropelvic junction obstruction. It is associated with postoperative pain at operation site, pain due to residual intraperitoneal carbon dioxide, and visceral pain at renal pelvis. The institutional practice is to administer intravenous (i.v.) fentanyl and paracetamol along with port and drain site infiltration with LAs. However, despite these measures, patients are seen to suffer from pain localized to the lumbar area of the operative side. Previous studies have shown that patients receiving QLB had improved analgesia in comparison to controls after urological surgeries such as percutaneous nephrolithotomy (PCNL) and laparoscopic nephrectomy (LN).[456] However, the plight of adults undergoing laparoscopic pyeloplasty has remained unaddressed so far. Hence, we decided to compare the efficacy of QLB with the usual practice of infiltration of LA at incision sites in these subsets of patients. Since the block provides both visceral and somatic analgesia from T7 to L1 dermatomes,[7] we hypothesized that patients receiving ultrasound-guided (USG) QLB after surgery will have reduced pain scores compared to those who receiving port-site infiltration.

MATERIALS AND METHODS

The study was conducted in accordance with the revised Helsinki Declaration. It is a single-blinded randomized controlled trial, conducted after obtaining Institutional ethics committee approval (IEC 2107-132-IP-99; dated August 17, 2017) and registering the trial in ctri.nic.in (CTRI/2017/10/010281; dated October 31, 2017). The participants were enrolled in consensus with CONSORT checklist. Sixty patients aged 18–60 years of American Society of Anesthesiologists (ASA) Physical Status I and II scheduled to undergo laparoscopic pyeloplasty were evaluated to be included in the trial. Exclusion criteria were refusal to participate in the study, known allergy to LA, coagulopathy or thrombocytopenia, body mass index (BMI) above 35 kg.m−2, and infection at site of injection. After obtaining written informed consent, patients included were randomized by computer-generated table to receive either USG anterior QLB (Group QLB) with 20 mL of 0.5% ropivacaine or port-site infiltration (Group P) with the same amount of drug after completion of surgery. The group allocation was concealed in an envelope which was opened in operation theater before surgery. QLB was performed by the same anesthesiologist for all the patients, who was well versed in the technique. The patients were blind to group allocation.

During preanesthetic checkup, the night before the surgery, all patients were acquainted with Visual Analog Scale (VAS) (a 0–100 VAS, where 0 was no pain at all and 100 was maximum possible pain) for postoperative pain assessment. In the operation theater, monitors were attached and injection midazolam 0.03 mg.kg−1 and 2 μg.kg−1 fentanyl were given intravenously. General anesthesia was administered with titrated doses of i.v. propofol (1–2 mg.kg−1) and vecuronium (0.1 mg.kg−1). Trachea was intubated. Anesthesia was maintained with sevoflurane (1%–2%) in oxygen and air mixture. 0.5 μg.kg−1 fentanyl and vecuronium i.v. were given as and when required. All patients received 1 g paracetamol i.v. before incision. Surgery was performed in lateral kidney position with the help of three laparoscopic port incisions. A perinephric drain was placed after completion of surgery. Patients in Group QLB received anterior QLB with 20 mL of 0.5% ropivacaine.

Performance of ultrasound-guided quadratus lumborum block

The lateral position of patients was maintained after completion of surgery. Maintaining aseptic precautions, a curved ultrasound probe (2–6 MHz Edge II, Fujifilm Sonosite, Inc., Bothell, WA 98021, USA) was placed transversely at the iliac crest on posterior axillary line. The three abdominal muscles external oblique, internal oblique, and TA were visualized and were traced posteriorly where IO and TA merged to form thoracolumbar fascia (TLF). Here, the QL muscle was visualized and traced posteriorly till transverse process of L4, where PM muscle was seen to lie anterior to QL muscle. A 20G (100 mm) nerve block needle (Quincke Sono Plex Pajunk, Germany) was introduced in plane from the posterior margin of transducer and directed anteromedially toward the plane between PM and QL muscles. Once the needle tip crosses through the QL muscle, the plane between QL and PM muscle is identified with hydrodissection. 20 mL of 0.5% ropivacaine was deposited between QL and PM muscles. The anterior TLF was seen to split as the spread of drug was visualized anteriorly. No local infiltration of drug was done in this group of patients.

Patients in Group P were infiltrated with 20 mL of 0.5% ropivacaine subcutaneously distributed at port and drain sites by the operating surgeon.

After completion of procedure, the patients were turned supine, neuromuscular blockade adequately reversed, and trachea extubated once they started following commands. The patients were shifted to recovery units thereafter. All patients received 1 g i.v. paracetamol 8 hourly for the first 24 hours. 100 mg i.v. tramadol (infusion in 100 mL normal saline over 10 min) was used as a rescue analgesic given by paramedical staff on demand of patients. A lockout interval of 6 hours was determined between two doses of tramadol.

Outcome assessment

The primary outcomes were static and dynamic pain, assessed by VAS of 0–100 at 30th min, 2nd, 6th, 12th, and 24th hour after extubation of trachea. The dynamic VAS was the pain, the patient pointed on VAS on flexion of lower limbs. The secondary outcomes were number of patients requiring rescue analgesics at the same time points, presence of any postoperative nausea or vomiting (PONV), or other complications in the first 24 hours after surgery. These outcomes were assessed by an anesthesiologist blinded to group allocation and not involved in data processing.

Statistical analysis

SPSS Statistics for Windows, version 20.0 (IBM Corp., Armonk, New York, USA), was used for data analysis. All quantitative variables were estimated using mean and standard deviations. Normality of data was tested, and a variable was considered normally distributed when Z score of skewness was within ± 3.29. For normally distributed data, means were compared using Student's t-test. VAS scores were found to be normally distributed, so Independent Student's t-test was used for intergroup comparison. Qualitative or categorical variables were compared using the Chi-square test. All statistical tests were two-sided and performed at a significance level of α = 0.05.

Sample size

A pilot study was conducted to calculate the effect size. The pilot study was conducted in 20 patients, and dynamic VAS pain score on flexion of legs at 2 hours after extubation was recorded. The scores were found to be 60 ± 20 in GroupP and 40 ± 15 in Group QLB (effect size, 1.13). Hence, using this effect size with minimum two-sided 95% confidence interval and 90% power of the study, the estimated sample size in each group came out to be 18. Finally, 25 patients were included in each of the two study groups. The sample size was estimated using software Power analysis and sample size version 16 (PASS-16, NCSS, LLC, USA).

RESULTS

Sixty patients were assessed to be included in the study. Four refused to participate, one had skin infection at site of injection, one was obese with BMI 40 kg.m−2, and one was known allergic to LAs. Fifty-three remaining patients were randomized and included in the two groups. In two patients, the surgical plan was changed to nephrectomy, and in one, the surgery was converted to open pyeloplasty. Finally, 50 patients were analyzed at the end of study [Figure 1].

Figure 1

Consort diagram

There was no difference in the demographic data (age, gender, BMI, and ASA status), intraoperative fentanyl given, and duration of surgery in the two groups [Table 1]. The VAS scores of static pain at the 30th min after extubation were higher in the QLB group compared to the control group although not statistically significant (P = 0.729) [Table 2]. Apart from the 24th hour, static pain scores were reduced significantly in the QLB group at other time points (P < 0.05) [Table 2]. The dynamic VAS scores were similar in both the groups at the 30th min, following which the scores were significantly lower in the QLB group at all remaining time points [Table 3].

Table 1

Demographic data, intraoperative fentanyl requirement, and duration of surgery

	Group QLB (n=25)	Group P (n=25)	P
Age (years)*	27.44±8.06	28.08±7.26	0.769
Gender (male/female)†	11/14	9/16	0.564
BMI (kg.m−2)*	21.99±5.46	22.14±4.61	0.916
ASA status (I/II)†	25/ 0	23/2	0.149
Intraoperative fentanyl (μg)*	146.0±17.13	147.50±17.04	0.757
Duration of surgery (min)*	145.55±18.34	150.81±15.72	0.281

Values are presented as mean±SD or number of patients. *Independent Student’s t-test, †Chi-square test/Fischer’s exact test. P<0.05 is statistically significant. QLB=Quadratus lumborum block, BMI=Body mass index, ASA=American Society of Anesthesiologists Physical Status, SD=Standard deviation

Table 2

Comparison of static Visual Analog Scale between groups

Time points after Surgery	Group QLB (n=25)	Group P (n=25)	Mean Difference (95% CI)	P
30th min	36.80±17.25	34.40±29.87	2.40 (−11.56-16.36)	0.729
2nd h	29.20±17.05	43.40±19.18	−14.20 (−24.52-−3.87)	0.008
6th h	27.80 ± 13.85	37.20±12.99	−9.40 (−17.03,−1.76)	0.017
12th h	26.80±14.05	35.60±15.29	−8.80 (−17.15-−0.44)	0.039
24th h	24.80±10.05	28.80±12.01	−4 (−10.29-2.29)	0.208

P<0.05 is statistically significant. Independent Student’s t-test done for intergroup comparison. Values presented as mean±SD. VAS=Visual Analog Scale; QLB=Quadratus lumborum block; CI=Confidence interval, SD=Standard deviation

Table 3

Comparison dynamic Visual Analog Scale between groups

Time points after surgery	Group QLB (n=25)	Group P (n=25)	Mean difference (95% CI)	P
30th min	51.60±21.73	54.00±32.66	−2.40 (−18.23-13.43)	0.761
2nd h	36.80±16.25	62.00±21.55	−25.20 (−36.05-−14.34)	0.000
6th h	31.60±13.12	52.80±13.07	−21.20 (−28.65-−13.74)	0.000
12th h	33.20±13.76	50.00±16.33	−16.80 (−25.38-−8.21)	0.000
24th h	30.00±12.91	40.00±12.91	−10.0 (−17.34-−2.65)	0.000

Values presented as mean±SD. Independent sample t-test done for intergroup comparison. P<0.05 is statistically significant. VAS: Visual Analog Scale; QLB: Quadratus lumborum block; CI: Confidence interval, SD=Standard deviation

The need for rescue medication was lower in Group QLB (13 [52%]) as compared to that in Group P(21 [84%]) (P = 0.015) [Table 4]. Figure 2 shows the distribution of requirement of rescue analgesics over 24 hours. 12/13 patients required analgesics by the 30th min and 1/13 by the 2nd hour in Group QLB. In Group P, 11/21 patients required analgesics by the 30th min and 8/21 by the 2nd hour (P = 0.009). One patient was in need of analgesic from the 2nd to 6th hour and one from the 6th to 12th hour in Group P. No patients required analgesics after the 2nd hour in Group QLB.

Table 4

Requirement of rescue medication in first 24 hours postoperatively

Pain medication required	Group QLB (n=25), n (%)	Group P (n=25), n (%)	P
Yes	13 (52)	21 (84)	0.015
No	12 (48)	4 (16)
Total	25	25

Chi-square test performed. P<0.05 is statistically significant. Values presented as number of patients. QLB=Quadratus lumborum block

Figure 2

Distribution of rescue analgesic requirement in patients

The incidence of PONV was similar in both the groups. Ten (40%) patients suffered in Group QLB and 15 (60%) in Group P. None of the patients had any episode of hypotension, hematoma, or infection at site of injection, and none showed symptoms of LA toxicity. No incidence of weakness of limbs was observed, and there was no evidence suggestive of liver, kidney, or bowel injury in either group.

DISCUSSION

Although patients undergoing laparoscopic pyeloplasty have lesser total narcotic requirement and shorter hospital stay than open procedure,[8] yet early postoperative pain cannot be ignored. Epidural catheters and paravertebral blocks (PVBs) have been used for other urological surgeries in adults such as PCNL and LN.[6910] Each of the above procedures has its own set of complications such as hypotension, urinary retention, PONV, inadvertent motor blockade with epidural analgesia, and risk of vascular puncture, hematoma, pneumothorax, and nerve injuries with PVB.[11] QLB has been compared with continuous epidural analgesia in patients undergoing LN. It was found to have equal analgesic efficacy for a period of 24 hours with higher blood pressures and shorter urinary catheterization time.[6] QLB was observed to have analgesic efficacy similar to PVB after radical cystectomy, but the study was underpowered to comment on side effects of each procedure.[12]

The anterior QLB is known to provide coverage from T7 to L1 dermatomes[7] adequate to cover somatic pain of three ports, one drain and visceral pain at renal pelvis after laparoscopic pyeloplasty. Till date, not many complications of QLB are known.[2] Hence, we chose USG-QLB as part of our multimodal analgesia. The present study observed that anterior QLB significantly reduced both static and dynamic pain from the 2nd to 12th hour postlaparoscopic pyeloplasty. The static pain was similar in both the groups at the 24th hour, but the patients receiving QLB maintained lower dynamic pain scores even at this time point.

The volume of drug used in our study (20 mL) was similar to that used by Okmen and Okmen[4] in their RCT on patients undergoing PCNL. They observed a lower VAS score and a lower consumption of opioids in patients receiving QLB and intravenous patient-controlled analgesia (PCA) with morphine in comparison to those receiving i.v. PCA alone. Our study observed a similar VAS score in both the groups at the 30th min after surgery much like that seen by Ökmen. The reduction in VAS scores in Group QLB was seen from the 2nd to 24th hour thereafter, again in consensus with Ökmen's study. The reason behind this observation may lie in proposed mechanism of action of the block.

In anterior QLB, the LA is deposited in the anterior layer of TLF. The drug then seeps cephalad to thoracic paravertebral space, through the arcuate ligament of diaphragm, and blocks the thoracic somatic nerves.[13] Since the block was performed after completion of surgery, the seepage of drug and blockade of somatic nerves may not have been achieved by the 30th min time point. By the 2nd hour after surgery, the blockade of all somatic and visceral fibers in paravertebral space[13] and TLF[2] may have been completed to provide significantly better pain scores then and thereafter. The VAS scores were not assessed between the 30th min and the 2nd hour, so the exact time of establishment of action of QLB cannot be determined in the present study.

The mean difference in static VAS scores [Table 2] of both the groups in our study was far less as compared to that seen in Ökmen and Ökmen.[4] This may be because unlike Ökmen's study, comparison in ours was with a parallel group receiving LA infiltrations. The mean difference in dynamic VAS in both the groups was more appreciable and similar to the Ökmen's study.

The mean static and dynamic VAS scores, however, were higher in our study as compared to Ökmen's study, may be because of different nature of surgery, use of tenoxicam 20 min postoperatively, and PCA pumps with morphine in their patients. While, we avoided NSAIDs completely and no PCA pumps were used in our study. In our study, the pain scores obtained in Group QLB were more in line with that observed by Elsharkawy et al.[14] in their case series of 22 adults undergoing urological surgeries.

The static VAS scores were significantly less in patients receiving QLB from the 2nd to 12th hour time points. The dynamic VAS, however, remained significantly less in Group QLB throughout after the 30th min. This observation was consistent with that seen by Blanco et al.[1] in patients undergoing cesarean section.

In another RCT on anterior QLB, Zhu et al.[5] found that the block provided effective analgesia, reduced opioid consumption, and allowed early recovery in patients undergoing laparoscopic nephrectomies. However, pain scores in terms of VAS or Numeric Rating Scale were not mentioned in their study. The number of patients requiring rescue analgesics in our study was 13 (52%) in Group QLB and 21 (84%) in Group P. The numbers were higher in both the groups in comparison to that shown by Zhu et al. In their study, 6/29 (20.7%) patients in the QLB group and 18/29 (62.1%) patients in controls required a rescue analgesic in 24 hours postoperatively. The difference was probably because Zhu et al. had used IV PCA with sufentanil in both cases and controls, reducing the requirement of additional analgesics.

Our results show that rescue medication was required in 12 out of 13 patients in Group QLB by the 30th min while only one required it by 2 hour. Such skewing of data was not present in Group P. The possible explanation of such skewing could be that the peak effect of QLB is achieved after some lapse of time from injection, leaving the patients in need of systemic analgesics in the interim period. This explanation is also seconded by the observation seen by Ökmen and Ökmen[4] where like our study the block was performed postoperatively and consumption of morphine was found to be similar in both cases and controls initially. The cumulative morphine consumption reduced only 2 hours later, may be pointing to delayed onset of action of block.

Complications may arise after administration of QLB. Weakness in lower limbs, due to blockade of femoral nerve,[515] has been observed after single-shot injection with a drug volume as low as 20 mL. The volume of drug administered may put the patient at a theoretical risk of hypotension and LA systemic toxicity.[7] Although, no such side effects were observed in our study.

To the best of our knowledge, it is the first RCT comparing the effect of anterior QLB to more traditional method of LA infiltration at wound site in adult laparoscopic pyeloplasty. We have tried to elicit the differential effect of QLB on dynamic and static pain, which we feel has not been explored sufficiently in contemporary literature. Our study had certain limitations. The time of onset of anterior QLB, its duration, and number of dermatomal segments affected were not assessed. The amount of opioids used as rescue analgesics was not seen, and the study ended 24 hours postoperatively. After analyzing the results of the present study, we suggest that the analgesic efficiency of the block would be more profound if it is performed preoperatively, allowing time to reach its full potential by postoperative period. However, future research is required in this direction to validate the statement.

CONCLUSION

Anterior QLB provides better analgesia than mere port-site LA infiltration in patients undergoing laparoscopic pyeloplasty.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.