Postoperative Analgesic Effects of Anterior Quadratus Lumborum Block vs Intravenous Analgesics Administered to Donors and Recipients in Renal Transplantation Surgery: A Prospective Cohort Study

Introduction

The prevalence and outcomes of organ transplantation have significantly improved due to the accessibility of new immunosuppressive drugs, advances in surgical techniques, improved postoperative care, and progress in anesthesia. Among these procedures, renal transplantation accounts for the largest share and remains the treatment of choice for patients with end-stage renal disease, offering improved survival and quality of life [1,2]. However, renal transplantation is associated with significant postoperative pain, which, if inadequately managed, can impair respiratory function, delay mobilization, prolong hospital stay, and reduce patient satisfaction. Effective postoperative analgesia in renal transplant patients is critical not only for patient comfort but also for optimal graft function. To achieve adequate analgesia, intrathecal, epidural, or intravenous opioid-based techniques have traditionally been employed. Despite their efficacy, opioids present considerable challenges, including nausea, vomiting, sedation, respiratory depression, ileus, and potential for immunosuppression [1–3]. With the introduction of ultrasound into anesthesia practice, fascial plane blocks, particularly truncal blocks, have emerged as viable alternatives to systemic analgesia. The quadratus lumborum block (QLB), first described by Blanco, has gained popularity as it can provide both somatic and visceral analgesia from T5 to L1 through the paravertebral spread of local anesthetic between the thoracolumbar and quadratus lumborum fascia [4,5]. Beyond its primary analgesic mechanism, Akerman et al proposed that QLB can facilitate the dispersion of local anesthetics toward the celiac ganglion, interacting with the sympathetic trunk via splanchnic nerves, thereby offering broader pain modulation [6].

Studies have demonstrated the effectiveness of QLB in various surgeries, including cesarean section, hip surgery, nephrectomy, and lower abdominal procedures [4,5,7]. Although laparoscopic approaches are often favored in nephrectomies, previous reports suggest that postoperative pain scores and opioid consumption remain comparable between open and laparoscopic methods [7].

In this context, the present study aims to evaluate the efficacy of the quadratus lumborum block in managing postoperative pain following renal transplantation. By assessing pain scores, opioid consumption, and potential complications, we sought to determine whether QLB can enhance recovery and serve as a safer alternative to conventional analgesic strategies.

Material and Methods

RESEARCH MODEL AND ETHICS APPROVAL:

Planned as a prospective cohort study, this research was implemented while adhering to the STROBE guidelines, after ethics consent was obtained (Ref. Date/No. 08.04.2023/484). Patient recruitment took place between October 2023 and May 2024 after registration at https://clinicaltrials.gov/study/NCT06011850 (Principal Investigator: Fatma Acil, MD; Registration Date: August 8, 2023). Before enrollment in the study, comprehensive written and verbal explanations were provided to all participants, and their informed consent was duly collected. Data gathering and recording were executed in the Gazi Yaşargil TRH operating room and organ transplant unit. The study was meticulously designed in strict compliance with the ethics guidelines outlined in the 2013 Declaration of Helsinki.

PARTICIPANTS:

A total of 94 adult patients (46 females and 48 males), aged 18–70 years, were included in the study. All patients were classified into American Society of Anesthesiologists (ASA) physical status categories I–III and underwent elective living-donor renal transplantation either as recipients or donors. The cohort consisted of 47 kidney recipients and 47 kidney donors. Among the recipients, 22 patients received anterior quadratus lumborum block (QLB), while 25 patients were administered intravenous paracetamol (IVA). In the donor group, 22 patients underwent QLB and 25 received IVA.

There were no missing data in this study. Data for all variables were prospectively collected in real time using standardized forms, and continuous monitoring ensured the completeness of the dataset for all 94 participants.

Baseline demographic and clinical characteristics, such as age, sex, ASA status, BMI, and known comorbidities (eg, hypertension, diabetes mellitus, or cardiovascular disease) were documented and compared between groups to ensure homogeneity and minimize potential confounding variables. No statistically significant differences were found between the QLB and IVA groups in terms of baseline characteristics (data not shown). Table 1 shows the demographic and clinical characteristics of the patients.

Exclusion criteria were: Refusal to participate, presence of abdominal fluid accumulation or cystic masses, diagnosed coagulopathy, body mass index (BMI) >35 kg/m², known allergies to local anesthetics, paracetamol, or tramadol, and history of preoperative chronic pain or long-term analgesic use.

PICO STRATEGY:

Participants/population(s): Male and female kidney recipients and donors aged 18–70 years who were enrolled in the kidney transplant program.

Intervention(s): Received anterior quadratus lumborum plane block as part of standard anesthesia care.

Comparator(s)/Control: Received intravenous paracetamol without any regional block.

Outcome(s): Postoperative pain (NRS), total tramadol consumption, and secondary recovery outcomes.

PRIMARY OUTCOMES:

The primary outcomes of the study were:

SECONDARY OUTCOMES:

The secondary outcomes were:

SAMPLING TECHNIC AND BLINDING:

During the study period, patients scheduled for elective living-donor kidney transplantation were prospectively enrolled in the study. A total of 94 patients who met the inclusion criteria were included consecutively as they presented for surgery, ensuring a natural representation of the transplant population. Group allocation (QLB or IVA) was determined based on routine clinical practice and anesthesiologist preference and availability, without researcher intervention. As such, no randomization was performed. This approach reflects real-life clinical decision-making processes and is consistent with the design of an observational cohort study.

To reduce detection bias, postoperative assessments were conducted by anesthesiologists who were not involved in the intraoperative care and who were blinded to the type of analgesic technique used. These outcome assessors conducted evaluations in the recovery room and the transplant ward based on predefined criteria, without knowledge of group assignments.

No crossover between groups occurred, and all enrolled participants were followed prospectively from the intraoperative period through to hospital discharge.

PREOPERATIVE PERIOD:

After the patients underwent a preoperative evaluation in the organ transplant unit, they were thoroughly briefed on the analgesic block technique to be applied.

INTRAOPERATIVE PERIOD:

All patients were admitted to our hospital’s operating room for standard general anesthesia. Five-lead electrocardiography, peripheral oxygen saturation, and invasive arterial monitoring were performed according to ASA standards. Two venous accesses were established 30 minutes before surgery using a 20-G cannula in the antecubital region. Upon receiving midazolam premedication, anesthesia was induced with fentanyl (2 μg/kg) and propofol (2–3 mg/kg), while tracheal intubation was performed with the aid of rocuronium (0.6 mg/kg). Once adequate muscle relaxation was achieved, patients were intubated using a suitably sized endotracheal tube. General anesthesia was maintained using sevoflurane at a concentration of 2–2.5% in a 50/50 oxygen-air mixture. If the mean blood pressure increased by 20% or more during surgery, additional analgesia was provided with 0.5–1 μg/kg i.v. fentanyl, and this was recorded. At the end of surgery, the inhalation agent was turned off, and 8 mg of ondansetron was administered. Muscle-relaxant effects were antagonized, and patients were extubated once they had regained adequate muscle strength.

ANTERIOR-TYPE QUADRATUS LUMBORUM BLOCK (ANT. QLB): Once general anesthesia was induced, patients in the supine position were repositioned into a lateral tilt toward the side of the renal implantation. The areas to be treated were sterilized with a 0.5% chlorhexidine solution. A convex ultrasound (USG) probe (Samsung HM70 EVO, Cheonho-daero, Gangdong-gu, Seoul, S. Korea) was covered with a sterile sheath. The probe was slowly advanced cranially until the 3-layered abdominal muscles were clearly visualized. The USG probe was directed posteriorly, and when the quadratus lumborum (QL) muscle was clearly visualized, the probe was fixed in place (Figure 1A). The quadratus lumborum (QL) muscle, psoas major muscle, and the transverse processes of the vertebrae were visualized. A 20-G, 100-mm injection needle for nerve blocks (Stumplex® Ultra 360®, Braun, Germany) was guided under ultrasound visualization into the interfascial space between the quadratus lumborum (QL) muscle and the psoas major muscle. A total of 20 mL of a 1: 1 mixture of 0.25% bupivacaine and saline (max. 2 mg/kg) was injected bilaterally in kidney donors, whereas kidney recipients received a single injection on the side of the incision (Figure 1B). The local anesthetic drug distribution was monitored.

INTRAVENOUS ANALGESIC ADMINISTRATION:

In this group of kidney recipients and donors, 1000 mg of intravenous paracetamol was administered 1 minute after the induction of general anesthesia and approximately 10 minutes before the surgical incision. No regional block was applied to patients in this group.

POSTOPERATIVE PERIOD:

In the postoperative period, sedation-agitation and pain assessments were performed after extubation. Patients were routinely administered 1000 mg of intravenous paracetamol every 8 hours. If the pain severity (NRS) was 4 or above, 100 mg of tramadol was given and documented. If pain persisted, 50 μg of fentanyl was administered intravenously as additional rescue analgesia, and this was also recorded.

DETERMINATION OF SAMPLE SIZE:

The sample size calculation was performed using G*Power version 3.1.9.4 (Kiel University, Germany) [10]. A one-tailed t-test for independent means was selected, as the study aimed to detect a directional difference in postoperative pain scores between groups. The following parameters were used: effect size (Cohen’s d): 0.80, power (1−β): 0.80, alpha error (one-tailed): 0.05, Group allocation ratio (N2/N1): 1. These parameters were based on data from a previous study that reported 14th-hour Numeric Rating Scale (NRS) scores of 3.1±0.45 in the QLB group and 3.6±0.75 in the control group [11] (Table 2). Using this effect size and assuming equal group sizes, the minimum total sample size required to detect a statistically significant difference was calculated as 42 participants (21 per group). To improve the reliability and generalizability of results, a larger sample of 94 patients was ultimately enrolled.

STATISTICAL METHODS:

Statistical analyses were performed using SPSS version 16.0 for Windows (SPSS, Inc., Chicago, IL, USA). The Kolmogorov-Smirnov test was used to evaluate whether continuous variables followed a normal distribution. Normally distributed continuous variables were summarized as mean±standard deviation (SD) and analyzed using the independent samples Student’s t-test. This parametric test was selected because it compares means between 2 groups when the assumptions of normality and homogeneity of variance are met. Non-normally distributed continuous variables were presented as median with interquartile range (IQR) and compared using the Mann-Whitney U test, a non-parametric alternative appropriate when normal distribution cannot be assumed. Categorical variables were expressed as frequencies and percentages and analyzed using the Chi-square (χ²) test, which is suitable for detecting associations or differences in proportions between independent groups.

All analyses were two-tailed, and a p-value <0.05 was considered statistically significant. The choice of statistical tests was based on the scale of measurement, distribution characteristics, and study objectives, ensuring methodological appropriateness.

Because the 2 main groups in our study (recipients and donors) were independent, no correction for multiple comparisons (eg, Bonferroni) was deemed necessary. Similarly, the subgroups within each main group (QLB and IVA) were also independent; therefore, additional correction methods were not applied in their comparisons.

Results

There were no statistically significant differences between the QLB and IVA groups in either the donor or recipient cohorts regarding demographic or intraoperative characteristics.

In the donor group, the mean age was 45.59±12.08 years in the QLB group and 43.88±11.13 years in the IVA group (P=0.61). The BMI values were comparable (QLB: 43.88±11.13 kg/m2 vs IVA: 23.43±1.74 kg/m2; P=0.17). The mean surgery duration was 2.0±0.00 hours in the QLB group and 2.04±0.2 hours in the IVA group (P=0.34), while anesthesia duration was 2.5±0.49 hours and 2.8±0.40 hours, respectively (P=0.07). The length of hospital stay was 3.2±0.53 days in the QLB group and 2.80±0.40 days in the IVA group (P=0.73).

Sex distribution was similar (QLB: 13 females [59.1%], 9 males [40.9%]; IVA: 14 females [56%], 11 males [44%]; P=0.83). The proportion of smokers was also not significantly different (QLB: 9 [40.9%] smokers; IVA: 16 [64%] smokers; P=0.11).

In the recipient group, the mean age was 37.37±14.05 years in the QLB group and 39.60±13.59 years in the IVA group (P=0.56). The BMI was slightly higher in the QLB group (27.32±4.59 kg/m2) than in the IVA group (25.48±3.61 kg/m2), though not statistically significant (P=0.13). Surgery durations (QLB: 2.89±0.37 h; IVA: 2.86±0.36 h; P=0.81) and anesthesia durations (QLB: 3.55±0.51 h; IVA: 3.52±0.51 h; P=0.86) were similar. Hospital stay length was 11.14±4.36 days in the QLB group and 12.24±6.05 days in the IVA group (P=0.54).

Sex distribution in recipients was balanced across groups (QLB: 9 females [40.9%], 13 males [59.1%]; IVA: 9 females [36%], 16 males [64%]; P=0.73). Smoking status did not differ significantly (QLB: 7 [31.8%] smokers; IVA: 9 [36%] smokers; P=0.76).

Regarding comorbidities in recipients, hypertension and diabetes mellitus were common but similarly distributed between groups. COPD and CHF were rare and showed no meaningful differences (Table 1).

Postoperative total tramadol consumption during the first 24 hours was significantly lower in the QLB group compared to the IVA group for both donors and recipients. Among the donors, the mean tramadol consumption was 93.2±24.1 mg in the QLB group versus 161.4±28.3 mg in the IVA group (P<0.001). For recipients, the corresponding values were 98.6±21.3 mg for the QLB group and 172.7±26.9 mg for the IVA group (P<0.001). Similarly, intraoperative fentanyl consumption was significantly reduced in patients who received QLB. Donors in the QLB group required 50±15 μg compared to 84±18 μg in the IVA group (P=0.014), while recipients required 56±13 μg versus 91±21 μg in the QLB and IVA groups, respectively (P=0.026) (Table 3).

Pain levels, as measured by the Numeric Rating Scale (NRS) at the 1st, 2nd, 6th, 12th, and 24th postoperative hours, were significantly lower in the QLB group at all time points for both donors and recipients (P<0.001) (Table 4 and Figures 2, 3). In addition, the time to first rescue analgesic administration was significantly longer in patients who received QLB compared to those in the IVA group, and in both subgroups (P<0.001) (Table 3).

There were statistically significant differences between the QLB and IVA groups in terms of sedation-agitation levels and patient satisfaction in both donor and recipient populations. According to the RSAS scores, patients in the QLB group were more frequently rated as “Calm and cooperative” compared to the IVA group (36.2% vs 10.6% in donors and 23.4% vs 0% in recipients, P<0.001). Conversely, higher levels of agitation, including “Agitated,” “Very agitated,” and “Dangerous agitation,” were more common in the IVA group (Table 5).

Patient satisfaction was also significantly higher in the QLB group. The proportion of patients reporting being “Very satisfied” or “Satisfied” was greater in the QLB group for both donors and recipients, while neutral or negative responses were more frequent in the IVA group (P<0.001) (Table 5).

Regarding postoperative nausea and vomiting (PONV), there were no statistically significant differences between the groups. Among donors, the incidence of PONV was 18.2% in the QLB group and 22.4% in the IVA group (P=0.72). Among recipients, the rates were 20.0% for QLB and 28.0% for IVA (P=0.12) (Table 6). These results suggest that both analgesic strategies were similarly well tolerated in terms of gastrointestinal adverse effects.

Discussion

LIMITATIONS:

Despite these favorable outcomes, several limitations of the study should be acknowledged. First, the observational design without randomization or double-blinding may have introduced selection and observer bias. Although the interventions were standardized and outcome assessors were blinded, the absence of random allocation limits the ability to draw causal inferences. Additionally, while the sample size was adequate for analyzing primary outcomes, it may have been insufficient to detect subtle differences in secondary outcomes. Technical factors such as operator skill, anatomical variations, and the spread of local anesthetic, although potentially impactful, were not objectively assessed.

Future randomized controlled trials are warranted to determine the optimal timing, technique, and dosing strategy for QLB, and to compare its efficacy with other regional anesthesia techniques.

Conclusions

Use of anterior quadratus lumborum block (QLB) in kidney transplant recipients and donors was associated with significantly lower postoperative pain scores and opioid consumption compared to intravenous analgesia. Furthermore, patients who received anterior QLB reported higher satisfaction levels in the early postoperative period. These findings suggest that anterior QLB can be an effective component of multimodal analgesia in renal transplantation.

What sets this study apart is its inclusion of both kidney donors and recipients within the same cohort, providing a dual perspective on the efficacy of anterior QLB across different but related surgical populations. To the best of our knowledge, this is among the first studies to simultaneously evaluate anterior QLB in these 2 patient groups, thereby offering novel insights into its broader applicability.

Given the observed reductions in opioid use and improvements in patient satisfaction, the integration of anterior QLB into perioperative care protocols may support enhanced recovery strategies and reduce opioid-related adverse effects. These outcomes are particularly relevant in the context of renal transplantation, where optimizing pain control is critical for patient comfort, graft protection, and early mobilization.

However, the generalizability of our results is limited by the study’s single-center design and non-randomized methodology. Further randomized controlled trials are warranted to validate our findings, explore the comparative efficacy of different QLB techniques (eg, anterior vs posterior), and assess the potential benefits of catheter-based or adjuvant-enhanced local anesthetic approaches. Such research could help optimize perioperative pain management protocols in kidney transplant patients.