Continuous sciatic popliteal nerve blocks are an effective method of pain management after foot surgery. Continuous infusions of short-acting anesthetic drugs have been a trend in clinical practice, increasing the flexibility of many anesthetic techniques.

However, in the case of regional anesthesia and acute post-operative analgesia, mostly long-acting agents are used. This practice has no clear reason, particularly when continuous perineural infusions are employed.

While the use of short-acting anesthetic drugs (shorter latencies, more titratable) is common in modern anesthesia (e.g., the use of remifentanil, propofol, and desflurane, to name a few), especially when administered as continuous infusions, the duration of the drug given in bolus form is not a significant factor in maintaining its effect. The intensity of this effect depends on the dose administered over time. In this regard, the use of an intermediate-duration local anesthetic like lidocaine, which is safe and whose efficacy in regional neuraxial and peripheral anesthesia is well recognized, may be an option that is at least not inferior to the current standard, which is to use long-acting local anesthetics in continuous infusion.

From a clinical utility perspective, using lidocaine, a local anesthetic that has a higher safety profile in terms of systemic toxicity (1) and is widely available while demonstrating a similar clinical effect [faster onset/earlier offset, more titratable (2)], at a fraction of the cost of the other drugs (3), appears clinically relevant.

We hypothesized that lidocaine solutions are as efficacious in providing postoperative analgesia as bupivacaine in continuous ambulatory sciatic popliteal nerve blocks. Therefore, we designed a non-inferiority trial to compare the quality of analgesia, motor function, and side effects between lidocaine and bupivacaine infusions in bilateral continuous popliteal nerve blocks for foot surgery.

We designed a prospective, double-blind, randomized, parallel-group, noninferiority study (ClinicalTrials.gov Identifier: NCT02121119, April, 2014). This study was approved by the Institutional Review Board of the School of Medicine, Pontificia Universidad Católica de Chile (IRB identifier: 13-289).

After written informed consent, subjects were enrolled at Hospital Clínico, Pontificia Universidad Católica de Chile, Santiago, Chile.

Seventy patients were enrolled. All received their assigned study intervention. In four cases, the catheter was dislodged and replaced on admission to the recovery room (3 in the lidocaine and 1 in the bupivacaine group). In 2 cases, the catheter was removed inadvertently at 24 h (bupivacaine group), and in 3 cases at 48 h (lidocaine group). Figure 1 shows the CONSORT diagram.

Both groups were similar with respect to patient characteristics and intraoperative data (Table 1).

The mean postoperative pain at 24 h of surgery was 2.06 (95% bCI 1.29, 2.83) and 1.82 (95% bCI 1.02, 2.62) in the lidocaine and bupivacaine group, respectively. The upper limit of the 95% bCI for the mean difference between lidocaine and bupivacaine was 0.82. Since 0.82 was below the pre-specified non-inferiority margin of 1.5, non-inferiority was declared (Figure 2).

No differences in the postoperative rescue analgesia use and satisfaction with care were found. No differences in postoperative NRS, sensory block and motor block were seen between groups (Figure 3).

The main finding of this study is that Lidocaine was non-inferior to Bupivacaine in providing postoperative analgesia through sciatic popliteal catheters in patients undergoing bilateral foot surgery.

Previous studies have reported the use of lidocaine in continuous perineural infusions, comparing it against long-acting local anesthetics (2, 3, 7). The existence of these prior studies attests to the rationale behind our approach, and all of them were conceived as superiority-designed studies, hypothesizing that using lidocaine infusions instead of long-acting local anesthetic choices could provide benefits in terms of faster onset time, quicker titration, or less toxicity. Unfortunately, the superiority design, statistically, given the sample sizes used, prevents ruling out whether the lack of difference is due to non-inferiority or a statistical power issue (type II error). Interestingly, from the clinical standpoint, none of those studies found any differences in analgesic effectiveness. Four studies were performed on truncal blocks and one on the upper extremity. All the studies performed on truncal blocks found no differences in analgesic effectiveness. Casati et al. found that lidocaine 1% had significantly more pain compared to ropivacaine 0.2% in the first 8 h, using a 0–100 mm pain scale (median 20 [range 0–60] vs. 0 [range 0–50]) but no differences were observed beyond this point. The use of rescue tramadol was also higher in the lidocaine group. Maybe the fact that we used a dual-guided (US and PNS) technique, ensuring a more precise location of the catheters, instead of electric peripheral nerve stimulation (PNS) alone as neuro-localization technique, could explain the different outcomes. Consequently, patients in our study had good pain control and clinically significant sensory block using 0.5% lidocaine instead of 1% lidocaine.

To the best of our knowledge, this is the first study evaluating the effectiveness of lidocaine, comparing it against long-acting local anesthetics such as bupivacaine, assuming a non-inferiority approach. A non-inferiority design assuming a margin that is clinically acceptable allows us to demonstrate that lidocaine is not significantly less effective than bupivacaine but is safer and more affordable than bupivacaine.

There are clinical and practical implications to the results of the study. The findings of non-inferior analgesia using lidocaine offer a cost-effective and cost-efficient alternative to long-acting local anesthetics, such as bupivacaine or ropivacaine.

One advantage of using lidocaine for continuous peripheral nerve blocks could be lower toxicity as compared to other agents (1).

Previous studies using lidocaine in epidural analgesia ⁵ have reported adequate pain relief, without any effect on lower extremity motor function when 1% lidocaine is used. In the setting of open shoulder surgery, Casati et al. (7) reported that patients receiving 1% lidocaine infusion through an interscalene catheter had higher pain scores and required rescue analgesic medications more frequently than patients receiving 0.2% ropivacaine infusions. Maybe the fact that we used a dual-guided (US and PNS) technique, ensuring a more precise location of the catheters, instead of electric peripheral nerve stimulation (PNS) alone as neuro-localization technique, could explain the different outcomes. As a consequence, patients in our study had good pain control and clinically significant sensory block using 0.5% lidocaine instead of 1% lidocaine.

A pilot study conducted by Ghisi et al. (3) reported adequate pain control after abdominal surgeries when 0.25% lidocaine was used in paravertebral blocks. This study emphasizes a cost-containment effect of using lidocaine for continuous infusions when it is compared with ropivacaine infusions (60% reduction in costs). This consideration is an important driver in terms of the adoption of any continuous regional analgesic technique.

Additionally, a critical shortage of both bupivacaine and ropivacaine had occurred in United States and Canada due to an apparent increase in drug demand and back orders from the suppliers. The Society of Obstetric Anesthesia and Perinatology (SOAP) raised a clinical practice advisory and safety alert, providing suggestions to all anesthesia providers who work in labor and delivery (8). This shortage also affects other regional anesthesia/analgesia areas, including continuous peripheral nerve blocks. In this context, lidocaine can be a reliable option to perineural infusions using more traditional drugs such as ropivacaine or levobupivacaine. Furthermore, demonstrating a similar clinical effect at a fraction of the cost of the other drugs, appears clinically relevant. This is particularly true in middle and low-income countries, where healthcare-associated costs are a significant concern and directly influence the type of care patients receive.

Our study has several limitations: Patients in both groups received a combination of regional analgesia and systemic oral analgesics: Acetaminophen and celecoxib. The analgesic effect of this combination arguably can affect our capacity to assess the effectiveness of our intervention. In modern Anesthesiology however, it is nearly impossible not to employ a multimodal analgesic approach in the perioperative period. There is an extensive body of literature and practical guidelines supporting this practice. While we are aware that the use of a non-steroidal anti-inflammatory (NSAID) drug such as celecoxib on a scheduled basis should influence reported pain scales (and the same can be said about the use of acetaminophen), our study aimed to establish comparisons between the two solutions of local anesthetics in the context of a pragmatic analgesic scheme. This would allow us to understand our findings with regular clinical practice (external validity of our results). On the other hand, if we consider that the subjects were randomly assigned to the groups, it is possible to assume that, since all characteristics were similar, there are no differences between the groups in their pain scales attributable to the assigned local anesthetic solution, and that the intensity of the reported pain would be what a patient would report under actual clinical conditions.

This is a single center randomized controlled trial and further investigations are needed to systematically assess lidocaine efficacy in this setting. Additionally, in terms of safety, the absence of any significant complications should be considered with caution, due to the limited number of subjects participating in the study.

In conclusion, our results show that lidocaine 0.5% and bupivacaine 0.1% provided similar postoperative analgesia through a sciatic popliteal catheter in patients undergoing bilateral foot surgery. This represents an option with lower costs and potentially, less risk of systemic toxicity complications in the ambulatory setting.