Regional anesthesia techniques, particularly with the development and incorporation of ultrasonography technology into anesthesia practice, have become popular and widely used by anesthesiologists over the past few decades, both as effective anesthesia techniques and as essential components of multimodal analgesia [1–3].

Approximately 20 million open or laparoscopic inguinal hernia repairs are performed annually, making it one of the most common operations conducted in general surgery [4]. Effective pain management is crucial for both types of surgeries, though patients undergoing open inguinal hernia repair (OIHR) often experience nociceptive pain initially and can potentially develop moderate to severe long-term chronic pain due to factors such as nerve damage. Some studies report an incidence of chronic pain up to 20% within 1–5 years of OIHR performed using a Liechtenstein incision [5]. While some publications suggest that incorporating regional anesthesia techniques into conventional analgesic approaches can mitigate chronic postoperative pain, evidence supporting this claim remains limited [5,6].

Opioids, non-steroidal anti-inflammatory drugs, and other analgesics are conventionally recommended to manage postoperative pain post-OIHR. However, procedure-specific pain management (PROSPECT) guidelines recommend a multimodal analgesic approach for postoperative pain management, including regional nerve techniques such as infiltrative analgesia, ilioinguinal/iliohypogastric (II-IH) nerve block, and transversus abdominis plane block [7,8].

In OIHR surgery, the subcostal nerve (T12), ilioinguinal nerve (L1), iliohypogastric nerve (T12-L1), and sometimes the genitofemoral nerve (L1-L2) provide sensory innervation to the incision area [9–11]. According to the literature, II-IH and transversus abdominis plane (TAP) blocks are used most frequently to treat postoperative pain following OIHR surgery [12]. To provide a wider sensory block to the inguinal region, some clinicians have chosen to apply blocks more proximal than the TAP and II-IH blocks. While the transversalis fascia plane block (TFPB) inhibits both the lateral cutaneous branches of the IH and subcostal nerves, it also inhibits sensory transmission to the T12-L1 dermatomes. This technique, originally only used for analgesia in iliac crest harvesting, has since been applied in a variety of surgeries including inguinal hernia repair, cesarean section, and varicocelectomy [13–15]. Numerous studies have also been conducted on the quadratus lumborum block and erector spinae plane block (ESPB), among others, which have become increasingly popular for adult and pediatric lower abdominal surgery [16–18].

The ultrasound-guided TFPB is a regional anesthesia technique defined by Hebbard that targets the T12-L1 dermatomes [19]. Similar to the techniques mentioned above, the TFPB has been used for inguinal region and lower abdominal surgeries owing to the target region of the block, and has been the subject of various clinical studies [20,21]. Although both the TFPB and ESPB have been found to reduce postoperative analgesic consumption in OIHR, no study has compared analgesic consumption between these two techniques in inguinal hernia repair surgery.

We hypothesized that these two techniques, which provide sensory block in similar anatomical regions, would show comparable reduction in analgesic requirements. This randomized controlled trial aimed to compare the effects of ESPB and TFPB on the analgesic requirement in the first 24 h after unilateral OIHR surgery. A secondary aim was to compare the pain scores between the two techniques within the same timeframe.

Eighty-four patients agreed to participate in the study, four of which were excluded: two for inadequate/failed spinal block and two for PCA device failure. Therefore, 40 patients per group were included in the study. The CONSORT flow diagram for this study is shown in Fig. 1.

Males comprised the majority of patients in both groups (TFPB group: 38/40 and ESPB group: 35/40). The ASA classification; average age, height, weight, and BMI of the patients; and surgical times were similar between the groups, as shown in Table 1 (P > 0.05).

When the mean 24-h tramadol requirements of the groups were compared, the TFPB group was found to have a lower tramadol requirement than the ESPB group, with a statistically significant difference (88 ± 75.2 vs. 131 ± 93.7 mg, MD: −43, 95% CI [−80.82, −5.18], P = 0.027).

As shown in Table 2 and Fig. 2, the cumulative amount of tramadol consumed in the TFPB group was significantly lower than that consumed in the ESPB group at all time points, with the exception of the first hour. In addition, when we used time intervals rather than time points of cumulative tramadol and repeated the comparisons, the use of tramadol for hours 1–3 was statistically significantly lower in the TFPB group than in the ESPB group (10.5 ± 20.24 vs. 24.5 ± 31.86 mg, MD: −14, 95% CI [25.88, −2.12], P = 0.018). No significant differences in the amount of tramadol required was found between hours 3–6, 6–9, 9–12, 12–18, or 18–24 (P > 0.05). Fig. 2 shows a comparison of tramadol consumption between the groups at different time intervals. Meperidine was not required for any patient in either group.

Compared to patients in the ESPB group, a significantly higher rate of patients in the TFPB group required no additional analgesia (7.5% vs. 25%, P = 0.033). The time to first analgesia requirement was longer in the TFPB group than in the ESPB group, although the difference was not significant (264.8 ± 140.1 vs. 209.2 ± 110.6 min, MD: 55.6, 95% CI [−0.59, 111.79], P = 0.053) (Table 1). Fig. 3 shows a Kaplan-Meier graph of the time to first analgesic requirement according to group. The median values along with the (Q1, Q3) were as follows: 317.5 min (Q1, Q3; 152.5, 1227.5) for the TFPB group and 180 min (Q1, Q3; 120, 330) for the ESPB group. The log-rank test revealed a noteworthy distinction between the two groups, favoring the TFPB group in terms of both time to first analgesic requirement and analgesic consumption (P = 0.006).

At rest, the NRS scores were similar between the groups at all time points except at hour 3, as shown in Table 3. Dynamic NRS scores were similar across all time points and between groups. Only one patient in the ESPB group experienced quadriceps weakness for up to 9 h after surgery; the other patients experienced no motor weakness at or after 6 h.

In our study, patients in the TFPB group who underwent unilateral OIHR surgery under spinal anesthesia required significantly less tramadol for postoperative analgesia than those in the ESPB group. The NRS scores were comparable across most timeframes. Since the scheduled analgesia was adequate in the TFPB group, the proportion of patients who did not request an additional PCA rescue dose in the first 24 h was 25%, whereas it was 7% in the ESPB group. This difference was statistically significant.

As mentioned, available studies for both techniques included in this study are limited. In OIHR, the TFPB has only been used in a few studies. Lopez-Gonzalez et al. [22] conducted a retrospective observational study in which 30 ml of 0.25% levobupivacaine was administered through the TFPB and anterior TAP block at the conclusion of unilateral OIHR surgery performed under general anesthesia and found comparable postoperative analgesic outcomes for both techniques. Fouad et al. [15] compared the postoperative analgesic effects of the TFPB and anterior quadratus lumborum block and found both to be effective and comparable in inguinal hernia surgery. One controlled study examined the postoperative analgesic effect of a preemptive TFPB in patients undergoing OIHR and concluded that it reduces both postoperative analgesic requirements and pain intensity following pediatric inguinal herniorrhaphy [23].

The ESPB, introduced by Forero in 2016 [24], involves administering LA in the interfacial plane between the transverse process of the vertebrae and the erector spinae muscle group with the goal of blocking both the dorsal and ventral rami. The ESPB can be adapted to various spinal levels, potentially producing paravertebral block-like effects [24,25], and has been used for postoperative pain management as part of multimodal analgesia for nearly all types of operations (except for distal extremities and cephalic operations) with positive results [25,26].

Previous studies have shown the efficacy of ESPB after OIHR surgery in both adult and pediatric patients [27,28]. El-Emam and El Motlb [27] administered ESPB to children at a volume of 0.5 ml/kg from the L1 transverse process and found a lower rescue analgesic requirement, lower FLACC scores, and a longer time to first analgesic request compared to the II-IH block in OIHR. Sakae et al. [28] performed ESPB at T8 level with 20 ml ropivacaine (0.5%) LA, determined that it did not reduce the rescue analgesic requirement, and reported that it was ineffective for OIHR. Given the volume and concentration of ESPB used in that study [28], we did not expect it to be effective for OIHR.

In our study, we observed that TFPB outperformed ESPB in terms of the postoperative analgesic requirement in patients undergoing OIHR under spinal anesthesia, whereas the effects on pain scores and first analgesic requirement were comparable. Despite differences in the clinical study methodology, tramadol requirements in both groups were comparable or lower than those in regional anesthesia studies in the same patient group [29,30]. The TFPB group required 33% less tramadol than the ESPB group; however, this difference may not be clinically significant. To date, no minimum clinically important difference (MCID) studies have been conducted for OIHR, and no data have been provided regarding the threshold at which change in opioid requirements or NRS scores would be significant. As a result, we could not make any definitive statements regarding the clinical significance of this statistical difference between the groups. However, asserting the clinical significance of this difference, which is equivalent to an oral morphine dose of approximately 13 mg, may not be reasonable given the currently available literature (generally, a reduction ≥ 30 mg or > 40% is considered significant). For a stronger claim, the MCID for OIHR surgery should be calculated along with the concept-specific MCID, which is already recommended for similar types of surgeries [31,32].

As mentioned, ESPB is a popular, easy, and safe technique that is frequently used for both acute and chronic pain, and successful applications for perioperative analgesia have been reported for both open and laparoscopic inguinal hernia surgeries. The possible mechanism of action is explained as the transition of LA to the paravertebral area when applied to the posterior of the transverse process. However, clinical, cadaveric, and radiological studies have shown that for many interfacial plane blocks, this same distribution is not always observed [33,34]. Although the ESPB sometimes results in limited sensory block in the paraspinal region, it also sometimes works as a multilevel paravertebral block [35,36]. Conversely, the TFPB application point is very close to the nerve tissue and is a more target-specific block. The differences in tramadol requirements between the groups may have resulted from these anatomical differences. When we reanalyzed tramadol consumption using time intervals instead of cumulative tramadol consumption, we determined that the statistical difference was found in the 1–3 h interval and the main difference in the subsequent measurements was due to the difference at this interval. Although the LA is applied directly adjacent to the nerve in TFPB, it is applied far from these neuronal structures in ESPB and reaches the target via leakage from the fascial planes. This may also help explain the difference determined clinically earlier.

Performance-oriented characteristics, such as ease of sonoanatomical visualization and identification, necessity of positioning, and block onset time, are also important, as well as whether the technique used in regional anesthesia is effective as an analgesic. In our study, we placed all patients undergoing ESPB in the lateral decubitus position, which increased the time required to perform the block. However, we were able to perform this technique in the supine position in 37 of the 40 patients who received the TFPB. This not only saves practitioner time but also eliminates the need for an additional healthcare professional to maintain the patient under spinal anesthesia in the lateral position. The block performance time for the TFPB was significantly shorter and the effort required was lower. However, this was not documented in detail as it was not one of our outcomes.

Ten patients in the TFPB group and three patients in the ESPB group did not require any tramadol from their PCA devices, with a statistically significant difference.

Quadriceps weakness was a secondary outcome of our study. We found quadriceps weakness in one patient in the ESPB group when the groups were assessed at 6 h after the block, which persisted until 9 h postoperatively. At 6 h postoperatively, no quadriceps weakness was found in the TFPB group. Transient quadriceps weakness has been reported anecdotally in the literature after the administration of a TFPB or ESPB at or below the T11 level, though it usually resolves within 24 h [37,38]. As with all regional anesthesia techniques, complications such as intravascular injection, systemic anesthetic toxicity, and injury to adjacent tissues can be observed. Practitioners must be aware of this complication and potential side effects of LA spread.

This study also had some limitations. The first limitation was that neither cutaneous blockage mapping nor dermatomal sensory analysis were conducted after regional anesthesia. We chose not to perform these measurements because the patients included in the study underwent surgery under spinal anesthesia and because doing so might have been confusing in the event of prolonged spinal anesthesia. A recent Delphi consensus advised that block characteristics such as sensory testing of the block and block duration should be noted and reported [39]. Compared with peripheral nerve block studies, determining the duration of facial plane blocks is significantly more difficult. Instead, we assessed the time to first analgesic request, which was ≥ 3.5 h for both block groups. The Delphi consensus study also suggests recording and reporting patient satisfaction. Although we conducted patient satisfaction surveys, such as the QoR-15, and almost all our patients provided positive feedback, the fact that this was not documented is a significant limitation. As our work was planned prior to the release of this Delphi consensus, we were unable to follow these and similar recommendations, but we recommend that those who work on regional anesthesia in the future consider the consensus recommendations.

Although the lack of a control group can be considered a limitation, our research was defined and conducted as a comparative study, as previous controlled/observational studies have demonstrated the effectiveness of both blocks. In studies investigating the postoperative analgesic efficacy of facial plane blocks, patients may undergo surgery under general or spinal anesthesia [40]. In our clinic, spinal anesthesia is often preferred as the main method of administration in patients with OIHR. Considering our clinical practice, we believe that it would be more appropriate to add a facial block after spinal anesthesia, rather than administering spinal anesthesia alone. Another limitation is that we did not evaluate and note the duration of spinal anesthesia in some timeframes. Unfortunately, this concern is common in similar studies investigating the effectiveness of interfacial plane blocks performed at the end of surgeries performed under spinal anesthesia. Features such as the type and volume of LA in the spinal anesthesia, and the duration of surgery were kept similar, and all blocks were performed at the end of surgery, thus minimizing the effects of spinal anesthesia duration on pain and analgesic consumption. A non-inferiority/superiority or equivalence trial may have been more appropriate. However, because of the absence of an established gold standard for both the ESPB and TFPB techniques and the lack of prior comparative studies, this particular methodology was not employed.

In the absence of spinal morphine, our study revealed that patients who underwent unilateral OIHR under spinal anesthesia experienced a lower cumulative analgesic requirement during the 24-h postoperative period when ultrasound-guided TFPB was added as part of the multimodal analgesia than when ESPB was added.