Sensory assessment of intramuscular quadratus lumborum block at the L2 level in open inguinal hernia repair patients

Abstract

Background

The effectiveness of the quadratus lumborum block (QLB) for postoperative pain management depends on the injection pathway used. There is limited research on the block area produced by intramuscular injection of local anesthesia in the quadratus lumborum muscle. This study aimed to determine the cutaneous sensory blockade area produced by an intramuscular quadratus lumborum block (QLBi) at the L2 level.

Methods

Twenty patients aged 18–60 years with ASA grade I-II and a BMI of 18–30 kg/m² who were scheduled for open inguinal hernia repair with mesh underwent ultrasound-guided QLBi injection of 20 ml of 0.5% ropivacaine. The cutaneous sensory blockade area was measured by applying a cold stimulus 1 h after the block and then measured every hour after surgery until the sensation returned to normal. The duration of a blockade is defined as the time it takes for all affected areas to fully regain normal sensation following a blockade. Pain scores (numeric rating scale, NRS) were recorded at 2, 4, 8, 12, and 24 h after surgery. Adverse reactions to QLBi were recorded 24 h after surgery.

Results

All 20 patients had reduced or lost cold sensation areas. The greatest extent of cold sensation reduction occurred at T7 (10%), and the least amount of cold sensation reduction occurred at L3 (10%). The block level covered T8 (20%), T9 (30%), T10 (45%), T11 (90%), T12 (95%), L1 (100%), and L2 (15%). Eighteen patients experienced areas of sensory loss, with the highest range at T11 and the lowest at L2. The duration of the blockade was 8.9 ± 3.8 h, with a maximum of 24 h and a minimum of 5 h. One patient experienced quadriceps weakness after surgery.

Conclusion

Quadratus lumborum block of intramuscular pathway can produce effective cutaneous sensory blockade, which can be used for postoperative analgesia of indirect inguinal hernia operation, and may also be beneficial to analgesia of other lower abdominal operations. However, the best method needs further confirmation to determine specific anesthesia methods for various operations.

Chinese clinical trial registry

June 2, 2018; ChiCTR1800016457.

Introduction

Quadratus lumborum block (QLB) is widely used for postoperative analgesia, including cesarean section, hip replacement surgery, lower limb surgery, and pediatric inguinal hernia repair, among others [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. At present, there are four generally recognized ways of quadratus lumborum block [17,18,19,20]. In 2007, Blanco et al. [15] reported a technique for injecting local anesthetic between the posterior abdominal wall muscles and the quadratus lumborum muscle. Later, another technique for injecting local anesthetic between the erector spinae muscle and the quadratus lumborum muscle was discovered. The third technique involved injecting local anesthetic between the psoas major muscle and the quadratus lumborum muscle. The fourth technique involved intramuscular injection of local anesthetic into the quadratus lumborum muscle QLBi) [8]. These four techniques have different blocking ranges.

QLBi was first reported in 2016, with the injection site being within the quadratus lumborum muscle [8]. The procedure is simple, but its mechanism is not yet fully understood. In the spring of 2013, Dr. Jens Børglum from the University Hospital in Copenhagen (Denmark) published a new ultrasound-guided transmuscular QL blockade, describing the so-called “shamrock sign” (i.e., the transverse process of L4 and the 3 muscular structures consisting of the quadratus lumborum, psoas major, and erector spinae muscles), the sign of a shamrock for the detection of a local anesthetic injection point.

Watanabe and colleagues found that after injecting 15 ml of fluorescent agent into the quadratus lumborum muscle, the drug remained within the muscle. This suggests that an intramuscular injection of local anesthetic into the quadratus lumborum might block the nerves from passing through the muscle, producing an analgesic effect. In a volunteer study, after blocking within the quadratus lumborum muscle, an analgesic plane was observed from the anterior abdomen to the lateral upper thigh [16]. This indicates that the injection route within the quadratus lumborum can indeed block nerves to achieve an analgesic effect. However, no drug spread to the paravertebral space. Therefore, this blocking technique differs from the diffusion pathways of the other three QLB techniques [13].

To date, there have been very few studies on QLBi, and its analgesic effect is currently under debate [8, 18.] A recent study even suggested that QLBi may not be effective for postcesarean section analgesia [19]. Therefore, it is necessary to clarify the blocking range and effect of intramuscular injection into the quadratus lumborum muscle.

To explore the blocking range and effect of QLBi, we selected patients who were scheduled for open inguinal hernia repair and underwent ultrasound-guided L2-level quadratus lumborum intramuscular block before surgery. The main outcome was a cutaneous sensory blockade area after the block. The secondary outcome measures were the duration of the blockade.

Materials and methods

This study aimed to evaluate the efficacy of QLBi for postoperative pain management in patients who underwent open inguinal hernia repair with mesh. The study was registered on the Chinese Clinical Trial Registry (June 2, 2018; ChiCTR1800016457) and conducted from July 2018 (first patient enrolled: July 9, 2018) to June 2019 (last patient completed: June 27, 2019). This study was approved by the ethics committee of the First Affiliated Hospital of Wenzhou Medical University (clinical research ethics number 2018-033). Written informed consent was obtained from all patients included in the study.

Sample size calculation

Based on previous research, the standard deviation of the injection block range at the L2 level is 0.77 segments. In this study, the sample size was calculated using PASS software, with a confidence level of 95% and an expected standard error of 0.5 segments. The required sample size was determined to be 18. Considering a 10% dropout rate, the final sample size for this study was set at 20.

Study population

Twenty volunteers who were scheduled to undergo open inguinal hernia repair with mesh were selected for this study. The inclusion criteria were age 18–60 years, intact skin sensation in the abdomen, ASA I-II classification, and willingness to undergo open inguinal hernia repair with mesh. The exclusion criteria were body mass index (BMI) < 18 kg/m2 or > 30 kg/m2, language communication and comprehension disorders, history of local anesthesia allergy, spinal deformity, peripheral nerve disorders, and spinal cord dysfunction.

QLBi procedure

The volunteers fasted for 8 h and were prohibited from drinking water for 2 h before surgery. Routine monitoring of blood pressure, electrocardiogram, pulse oximetry, and forearm vein puncture was performed before the operation. A sedative and analgesic mixture of midazolam (1 mg/ml) and fentanyl (20 µg/ml) was intravenously administered at a dose of 1–2 ml to reduce discomfort caused by needle puncture. The volunteers were placed in the lateral position for the block, and the blockade was performed on the side facing upward. A marker was placed on the back to indicate the location of the L2 spinous process, and the area was disinfected and draped.

All volunteers received QLBi from an anesthesiologist with extensive experience in ultrasound-guided QLB. A sterile cover was placed over a low-frequency 3–6 MHz convex probe (SonoSite X-Porte, SonoSite Inc., Bothell, WA, USA), and the probe was positioned on the side of the blockade. The 12th rib was first identified with an ultrasound probe, and the L1, L2, L3, L4, and L5 spinous processes were identified by moving the probe downward. (Fig. 1A) The L2 transverse process and quadratus lumborum muscle were identified at the L2 level. The transverse process was located laterally, while the quadratus lumborum muscle was located dorsally, and the psoas major muscle was located ventrally. The needle was introduced in-plane, and a 0.7 mm*80 mm needle (Zhejiang Kangdelai Medical Equipment Co., Ltd., 0.7*80 TWLB) was inserted 1 cm from the probe. (Fig. 1B) After the needle reached the quadratus lumborum muscle, 1–2 ml of normal saline was injected to confirm the location, followed by an injection of 20 ml of 0.5% ropivacaine (batch no. LAYY. AstraZeneca, Cambridge, UK). The level of the block was evaluated by an ice test 1 h after injection (Fig. 1CD).

Fig. 1

Photograph and ultrasonographic images of the QLBi. (A) L2 level positioning; (B) Ultrasound probe positioning and puncture method; (C) Ultrasound image before puncture; (D) Ultrasound image after puncture. ESM: Erector Spinae Muscle; QLM: Quadratus Lumborum Muscle; TP: Transverse Process. Arrows indicate the trajectory direction of the needle tip

The medication used for QLBi in this study was prepared by an anesthesiologist who did not participate in the anesthesia procedure or postoperative assessment. After the area of the block was confirmed, general anesthesia was induced via a laryngeal mask. The anesthetic technique used was intravenous general anesthesia with oxygen supplied through a facemask. Anesthesia was induced with rocuronium (0.15 mg/kg), fentanyl (3–5 µg/kg), and propofol (1–2 mg/kg). A laryngeal mask was inserted when the corneal reflex disappeared, the jaw was relaxed, and mechanical ventilation was initiated. Propofol and remifentanil were administered via a pump during surgery to maintain anesthesia. The doses were adjusted based on changes in the volunteer’s blood pressure and heart rate. At the end of the operation, 50 mg of flurbiprofen was intravenously administered before the abdomen was closed.

Outcome measures

Cutaneous sensory blockade area [20]

After the blockade, various lines on the abdomen were marked: the midline in the front and back, the vertical line passing through the anterior superior iliac spine, the axillary posterior line, the horizontal line through the navel, the rib line, the iliac crest line, the greater trochanter of the femur, and the ischial tuberosity.

One hour after the blockade, ice was applied at a rate of 2 cm/s to determine the distribution of sensory loss on the trunk skin from the midline in the front to the midline in the back. The ice was moved and marked when the volunteer’s skin sensation changed from 2 to 1 or from 1 to 0 (according to the skin temperature blockage, there were three levels: level 2 represented normal sensation, level 1 represented cold sensation reduction, and level 0 represented cold sensation loss). The cold sensation-reduced area was connected with a solid blue line. The cold sensation loss area is connected with a solid red line.

The distribution area of sensory reduction or loss on the trunk skin was covered with a colorless transparent square film, and the trunk skin sensory blockade image and the marked lines were transferred to the transparent film. The pixel size of the scanned image (fixed pixels) was set, a scanner (Bizhub Press c7000) was used to convert the prepared transparent film into a digital image, which was saved in JPG format on a computer.

Duration of blockade

The cold sensation was tested every hour after the surgery. The testing method was the same as before, and testing continued until the sensation was the same as that on the contralateral side. The duration of the blockade is defined as the time when the cold sensation returns to normal.

Analgesic Effect and Adverse Reactions.

Visits were made to the volunteers at 2, 4, 8, 12, and 24 h after surgery. The time when the patient first felt pain and the use of analgesics within 24 h were recorded. The NRS score of the volunteer was recorded at each time point after the surgery. A score of 0 indicates no pain, and a score of 10 indicates extreme pain. Adverse reactions, including hypotension, nausea and vomiting, and decreased muscle strength in the lower limbs, were recorded. Hypotension was defined as a decrease in systolic blood pressure of more than 30% from before surgery.

Statistical analysis

SPSS 22.0 software was used for statistical analysis. Height, weight, age, and action time are expressed as the mean ± standard deviation, and other data are expressed as the median and interquartile range. GraphPad Prism 8 was used to create the figures.

Results

There were 20 volunteers for open inguinal hernia repair, including 7 males and 13 females, with an average age of 47 ± 9 years, weight of 62.5 ± 7.3 kg, and height of 162.8 ± 7.9 cm. The operation time was 51.0 ± 7.5 min.There were 5 patients with left-sided QLB and 15 patients with right-sided QLB. Lumbar plexus block was successful in all patients, and one hour after injection, the cold test was used to assess the area of decreased or lost sensation.

Cutaneous sensory blockade area

All 20 patients had decreased cold sensation (Fig. 2). The cold sensation reduced area was between T7 (10%) and L3 (10%). The blocking plane covered T8 (20%), T9 (30%), T10 (45%), T11 (90%), T12 (95%), L1 (100%), and L2 (15%).

Fig. 2

Frequency of dermatomes blocked at 60 min after completion of block

Eighteen volunteers had an area of lost cold sensation, with the highest range at T11 and the lowest at L2. There was no area of lost sensation between T7 and T10 (Fig. 3, 2).

Fig. 3

Areas of reduced cold sensation and cold sensation loss in 20 volunteers after 60 min of blockade. Each volunteer had four small pictures showing the front, side, and back of the trunk, as well as a schematic diagram of the blockade area. The blue line area represents cold sensation reduced area, and the red line area represents cold sensation loss area

Duration of blockade

The average duration of the block was 8.9 ± 3.8 hours, with the longest being 24 hours and the shortest being 5 hours (Fig. 4).

Fig. 4

Regression of duration of the blockade after QLBi

Analgesic effects and adverse reactions

All patients had an NRS score of no more than 3 after surgery and did not use other analgesics. Only one volunteer with a blocking plane to the L3 level experienced weakness in the lower limbs during a bathroom visit one hour after surgery, which was considered to be a decrease in quadriceps strength, and normal muscle strength was restored after 6 h. There were no other adverse reactions.

Discussion

This study revealed that among 20 patients, 2 had decreased sensation to cold but no obvious disappearance areas. The greatest range of decreased sensation to cold was at T7, and the lowest was at L3. The blocking planes of 18 volunteers (90% of the participants) covered T11, T12, and L1. Eighteen volunteers had areas of decreased sensation to warmth, with the highest range at T11 and the lowest at L2. The average duration of the block was 8.9 ± 3.8 h. Murouchi et al. [8] reported that the peak time of ropivacaine use in QLB was 30–60 min. Therefore, we chose to begin testing the areas of dermatomal disappearance one hour after the block.

According to the sensory loss plane tested in this study, intramuscular injection of the quadratus lumborum muscle can be widely used for perioperative analgesia in various lower abdominal surgeries, including postcesarean section analgesia, intestinal surgery analgesia, hip replacement surgery analgesia, and inguinal hernia repair analgesia. We did not find an obvious blocking pattern in the sensory disappearance area tested in this study, possibly because some of the local anesthetic drugs do not effectively diffuse in the muscle after entering the quadratus lumborum muscle. To date, no studies have measured the level of blockade after intramuscular injection. Therefore, our experiments provide a basis for the application of this method.

We used a concentration of 0.5% ropivacaine, which is higher than the concentrations used in most previous studies and may be one of the reasons for the differences in our results [15]. In addition, we chose the L2 level as the block site, which is 1–2 segments higher than the number of block sites used in other studies. Other studies [6, 20] have suggested that the duration of analgesia can exceed 24 h, while the sensory block regression time we tested was generally less than 24 h. We believe that this may be due to differences in testing methods. In addition, autonomous nerve blockades can reduce visceral pain and have a long duration of blockade. However, we were unable to determine the duration of autonomous nerve blockade by testing the sensory area of the skin, which may also be one of the reasons for the differences in our results compared to those of other studies.

In our study, one volunteer exhibited sensory loss that extended to the anterior abdominal area, which slightly deviates from the findings of Watanabe et al. [16] The specific reason remains unclear, but we speculate that the drug might have slowly diffused to the anterior side of the quadratus lumborum muscle (possibly penetrating the fascia of the anterior side of the muscle during the puncture process) and then spread to the paravertebral space. However, the likelihood of such diffusion is presumed to be very low.

In our study, one volunteer experienced a decrease in quadriceps muscle strength that affected their ability to walk, which differs from the findings of previous studies, such as that of Ueshima et al. [17], which reported no decrease in muscle strength. According to our results, the farthest sensory block reached the L2 level in three volunteers and the L3 level in two volunteers, indicating that muscle weakness may still have occurred.

This study revealed that local anesthesia injected into the muscle can produce a certain degree of sensory blockade, but the mechanism underlying this blockade is not yet fully understood. Our explanation is that the local anesthetic drug injected into the lumbar muscles may spread through the fascia to the peripheral nerves and even the epidural area. However, it cannot be ruled out that some local anesthetic drugs may still remain in the muscle, making the diffusion of the drug within the muscle unstable.

We observed that apart from one patient with a vanished sensation extending toward the side of the spine, no vanished sensation areas were detected in two patients. In the remaining 17 patients, the vanished sensation areas were primarily located between the anterior superior iliac spine and the posterior axillary line, specifically in the anterior-lateral and posterior-lateral regions of the abdomen. These areas were predominantly affected at the T11-L2 level. This finding supports Tamura’s conclusion that the analgesic effect of QLBi is consistent from the anterior-lateral abdomen to the posterior-lateral abdomen and from the outer abdomen at the T8 level to the upper outer thigh [21].

There are several limitations to our study. First, the sample size was small, and we did not address the issue of surgical time; therefore, more experimental data may be needed to confirm our results. Second, our study did not include a control group, so we cannot draw conclusive conclusions on the effectiveness of nerve block for this type of surgery. Finally, we were unable to evaluate whether QLBi is suitable for children or elderly patients. As the obesity rate among humans continues to increase, evaluating the effectiveness of QLBi in obese patients will become an important topic for future research.

Conclusions

QLBi can produce effective sensory reduction or disappearance planes and can be used for postoperative analgesia in various surgeries in the lower abdomen. The operation is simple, but the effect of QLBi varies among individuals and requires further study. There is a risk of lower limb muscle weakness, and patients undergoing day surgery should be closely monitored.