Abstract

Regional anesthesia offers benefits such as improved pain control and reduced opioid use, but controversies remain regarding techniques and outcomes. This review examines key debates in the field, including the necessity of circumferential spread of local anesthetics, the impact of regional anesthesia on diagnosing compartment syndrome, the choice of diluent, and the safety of performing peripheral nerve blocks (PNBs) in awake versus anesthetized patients. To explore these topics, we conducted a literature search to synthesize relevant studies and expert perspectives, offering a comprehensive analysis of current evidence. While circumferential spread may enhance block onset, studies show that it does not consistently improve success. The potential for regional anesthesia to mask compartment syndrome is not definitively supported, as ischemic pain often breaks through analgesia. Dextrose diluents accelerate sensory block onset compared to saline, though effects vary with different anesthetics. In awake versus anesthetized PNBs, sedation and general anesthesia provide safety and comfort, especially for non-cooperative patients, with no clear superiority. Overall, regional anesthesia techniques should be tailored to individual patient needs, and further research is necessary to refine best practices.

Keywords

local anesthetic, peripheral nerve block, regional anesthesia

---

Introduction

Regional anesthesia has become an essential component of modern anesthetic practice, offering benefits such as superior postoperative pain control, reduced opioid consumption, and improved patient satisfaction. ¹ Ultrasound guidance now serves as the standard for peripheral nerve blocks (PNBs), enhancing both precision and safety. It has also enabled the development of techniques that were previously infeasible with landmark-based approaches. Debates persist regarding optimal methods of anesthetic delivery and local anesthetic regimens, highlighting variability in clinical practice across institutions and providers. This paper explores key areas of contention, examining the literature to provide a summary of current evidence and identify potential directions for future research in regional anesthesia.

Methods

We conducted a narrative review to explore four key controversies in regional anesthesia: (1) the necessity of circumferential spread of local anesthetic, (2) the impact of regional anesthesia on the diagnosis of acute compartment syndrome (ACS), (3) the effect of dextrose versus saline as a diluent, and (4) the safety of performing PNBs in awake versus anesthetized patients.

A literature search with an English language restriction was performed in Ovid MEDLINE (from inception to January 31, 2025) and Google Scholar for each of the four topics. Search terms included combinations of “regional anesthesia,” “local anesthetic,” “nerve block,” “circumferential,” “compartment syndrome,” “dextrose,” “saline,” “sedative,” and related synonyms. The full search strategy is outlined in Appendix 1.

For each topic, we included studies that directly addressed the clinical question and included adult or pediatric surgical populations. For circumferential spread, we selected trials and observational studies that used ultrasound to compare spread patterns and reported outcomes such as block onset or success rates. Studies on compartment syndrome were included if they discussed the diagnostic impact of regional anesthesia in orthopedic trauma, including case reports and reviews. For the diluent comparison, only studies that evaluated the clinical effects of dextrose versus saline on block characteristics in human subjects were selected, prioritizing randomized controlled trials. Lastly, studies comparing awake, sedated, or anesthetized patients during PNB placement were included if they reported outcomes related to safety, efficacy, or patient comfort. Across all topics, preference was given to randomized trials, large observational cohorts, and systematic reviews involving adult or pediatric surgical populations. We excluded abstracts, editorials, animal studies, and non-English articles. Selected studies were grouped by theme and summarized narratively. Key findings are synthesized and presented in Appendix 2 as summary tables.

Discussion

Is the Circumferential Spread of Local Anesthetic Necessary?

Ultrasound-guided injection of local anesthetic has enabled visualization and precise targeting of nerve structures. A common practice is achieving a circumferential spread of the anesthetic around the nerve, but the necessity of this technique remains debated. While some studies associate circumferential coverage with improved block quality, others report comparable efficacy with just partial spread.

Some inconsistencies in findings may stem from methodological differences, patient variability, and the inherent challenge of consistently achieving circumferential spread. Marhofer et al. ² studied median nerve blocks in 21 volunteers, aiming for either circumferential or non-circumferential spread. Despite the controlled conditions, the intended spread pattern was only achieved in 67% of the circumferential group and 33% of the non-circumferential group. Regardless of spread type, success rates were similar (90%), though sensory block onset was faster with circumferential spread (median 15 vs. 20 minutes). These findings suggest that circumferential spread may not be necessary for median nerve block success. Similarly, Szűcs et al. ³ examined femoral nerve blocks in 52 patients positioned for spinal anesthesia. Local anesthetic was deposited above, below, or circumferentially around the femoral nerve. Block failure rates were similar in the circumferential (17.6%) and above-nerve groups (20%) but significantly higher in the below-nerve group (46.7%). The authors concluded that circumferential spread offers no advantage over above-nerve deposition.

Conversely, some studies support circumferential spread. Brull et al. ⁴ investigated popliteal sciatic nerve blocks in 64 foot and ankle surgery patients, comparing circumferential versus single-location injections. Sensory block success was higher in the circumferential group (94%) than in the single-location group (69%), suggesting circumferential injection enhances efficacy. Dieguez-Garcia et al. ⁵ studied median and ulnar nerve blocks in 124 carpal tunnel surgery patients. While complete sensory block rates were similar at 15 and 30 minutes, circumferential injection resulted in significantly faster onset at 5 minutes—2.4 times more frequent for the median nerve and 3.0 times more frequent for the ulnar nerve. However, this required a large local anesthetic volume (6 mL), limiting applicability in typical PNBs.

Overall, circumferential spread does not consistently offer clinical advantages over non-circumferential spread for achieving sensory block, particularly for smaller nerves. Studies demonstrate that differences in sensory block success are generally observed only within the first 15 minutes, suggesting that circumferential spread may be warranted in urgent procedures requiring a rapid onset of anesthesia. Beyond this early period, sensory block success appears to equalize between circumferential and non-circumferential techniques by 30 minutes. For the sciatic nerve, single-point injection may fail to capture one of the common peroneal or tibial nerves, and multipoint injections are preferable. Clinicians should carefully balance these factors with the potential drawbacks of circumferential injection—such as increased needle passes and prolonged procedure time, which could ultimately offset its occasionally observed advantage of faster sensory block onset—in order to optimize their approach based on the specific clinical context and procedural priorities.

Regional Anesthesia and ACS

PNBs are widely used in orthopedic surgeries to provide effective pain control while reducing the need for systemic opioids. ⁶ However, concerns persist about their potential to obscure symptoms of ACS, a limb-threatening condition requiring prompt intervention. ⁷ The primary issue is that regional anesthesia may obscure ischemic pain, the key symptom of ACS, leading to delayed recognition and treatment. ⁷ This concern stems from anecdotal reports of ACS being missed due to local nerve blocks in the area, ⁸ yet no consensus exists on the safety of PNBs in limbs at risk of ACS.

Despite these concerns, current literature does not definitively establish a significant risk of PNBs delaying ACS diagnosis. Tran et al. ⁹ conducted a systematic review analyzing six single-patient case reports on PNBs following long bone fractures. Two reports noted delayed ACS diagnosis, while four found no such delay. In these four cases, pain remained the primary presenting symptom despite regional anesthesia, suggesting that ischemic pain may be intense enough to break through PNB-induced analgesia. ⁹ Additionally, in one of the two cases of delayed treatment, the authors noted that the patient could have been stratified pre-operatively as being high risk for ACS, which could have informed the sensory blockade used. ⁹ However, given the rare combination of PNB and ACS, the available literature is limited, and no definitive conclusions could be drawn regarding the safety of PNBs in orthopedic trauma.

Another systematic review assessed 34 studies (28 case reports and 6 research articles) on the effects of regional anesthesia and patient-controlled analgesia (PCA) on ACS diagnosis in orthopedic extremity procedures. ¹⁰ Of these, 55.9% suggested regional anesthesia or PCA masked symptoms, 26.5% found no masking effect, and 17.6% were inconclusive. However, among case reports published after 2009, 75% reported no increased risk of delayed ACS diagnosis with regional anesthesia. This shift may be attributed to ultrasound-guided nerve blocks, which enhance precision and reduce anesthetic volume. ¹⁰ Two identified prospective studies—both with small sample sizes—found no ACS cases but advised that PNBs be used cautiously. The authors emphasized vigilance for atypical ACS presentations, particularly in high-risk patients.

The risk of masking ACS may also depend on PNB administration protocols. A retrospective review examined PNB use in patients with long bone fractures at a level I trauma center over 10 years. ¹¹ Despite concerns about delayed ACS diagnosis, the institution followed a structured protocol involving avoidance of dense blockade, continuous rather than single-injection analgesia, frequent monitoring, and staff education on ACS symptoms. Among 26,537 patients, 20% required surgery, and 91.5% of them received regional anesthesia. The ACS incidence was 0.1% (27 patients), with 6 experiencing long-term neurological deficits.

Current evidence does not conclusively indicate that PNBs significantly increase the risk of delayed ACS diagnosis. While concerns remain, studies suggest ischemic pain may still be perceived, allowing for timely recognition in many cases. To mitigate potential risks, a multidisciplinary, protocolized approach is recommended—incorporating risk stratification, avoiding dense blockade, using continuous techniques with diluted local anesthetics, frequent monitoring, and provider education. These strategies may help balance effective pain management with patient safety. Nonetheless, practitioners should exercise caution given the paucity of evidence in this area.

Dextrose or Saline as Diluent for Local Anesthetics in Nerve Blocks

Local anesthetics work by blocking sodium ion channels, leading to a reversible blockade of nerve conduction. It is believed that high sodium concentrations in neural tissue may interfere with local anesthetic binding, potentially reducing analgesic efficacy (Lim et al. ¹² in 2016). This raises the question of whether diluting anesthetics with saline (which contains sodium) affects blockade compared to sodium-free diluents like dextrose.

The onset time of nerve blocks is a crucial factor in clinical practice. Lim et al. ¹² compared the onset of complete analgesia and motor blockade in 55 patients receiving a supraclavicular block with 0.75% ropivacaine diluted in either normal saline or 5% dextrose. The dextrose group had a faster analgesic onset (37.6 ± 12.9 min vs. 45.2 ± 13.9 min, P = 0.05). Likewise, Dhir et al. ¹³ found that in 550 patients receiving an axillary block with 0.5% ropivacaine, the dextrose group had a shorter sensory block onset (18.3 ± 6.1 min vs. 22.5 ± 6.4 min, P < 0.001), though no significant difference in clinical nerve deficits was observed. These studies suggest that dextrose accelerates nerve block onset. However, neither of these studies reported on block duration. Similar results were reported by Faiz et al. ¹⁴ who investigated the onset of sensory and motor blocks for upper limb surgeries when diluting 0.5% bupivacaine with either dextrose or normal saline. The dextrose group experienced a faster sensory block onset (19.8 ± 9.3 min vs. 26.6 ± 14.0 min), while motor block onset and hemodynamic parameters remained unchanged. The authors suggested that dextrose may accelerate sensory block onset but acknowledged that variations in nerve size, which could influence block onset and duration, were not accounted for in their analysis.

Mosaffa et al. ¹⁵ reported different findings in a randomized trial of 60 patients receiving lidocaine with epinephrine for supraclavicular blocks, diluted with either dextrose or saline. They found no significant differences in sensory or motor block onset or in the number of patients achieving complete blockade, suggesting that for fast-acting anesthetics like lidocaine, the choice of diluent may not influence block characteristics.

Taken together, the evidence suggests that diluting local anesthetics with dextrose led to a modestly faster onset when compared to saline. These differences may reflect the variation in the pharmacodynamic interactions between specific anesthetics and diluents. While dextrose does appear to reduce the time to sensory block in certain scenarios, the lack of consistent differences in motor block onset, hemodynamic parameters, and required anesthetic volumes underscores the complexity of these interactions.

PNB in Awake vs. Anesthetized Patients

The choice of whether to perform PNBs in awake, sedated, or anesthetized patients remains controversial. Awake patients can provide feedback on pain or paresthesia, helping prevent intraneural injection and nerve damage. Conversely, general anesthesia eliminates patient discomfort and movement, making it particularly useful in pediatric populations without significantly increasing complication rates. However, there is no consensus on the safest or most effective approach.

Kubulus et al. ¹⁶ conducted a retrospective study of 21,338 PNB cases, comparing outcomes among patients who received sedation, general anesthesia, or remained awake. Serious complications, including local anesthetic toxicity and pneumothorax, were rare across all groups. Sedation was associated with fewer multiple skin punctures, premature terminations, block failures, and postoperative paresthesia but increased the likelihood of bloody taps. General anesthesia similarly reduced postoperative paresthesia but was linked to more multiple skin punctures and bloody taps compared to awake patients. The study concluded that sedation may enhance both safety and procedural success in PNB placements. Additionally, Taenzer et al. ¹⁷ examined regional anesthesia safety in pediatric patients under general anesthesia versus awake or sedated conditions. Postoperative neurologic symptoms were significantly lower in the general anesthesia group (0.93 per 1,000 vs. 6.82 per 1,000), as was local anesthetic systemic toxicity (0.08 per 1,000 vs. 0.34 per 1,000). No group required an extended hospital stay.

In contrast, Ben-David et al. ¹⁸ retrospectively reviewed 336 axillary nerve block cases, where sedated patients were all adults, and most under general anesthesia were pediatric. The nerve injury rate was higher in general anesthesia patients (7.5%) than in sedated adults (2.6%), though the authors acknowledged demographic differences limited conclusions.

Ultimately, the choice between awake, sedated, or general anesthesia should be based on patient characteristics and procedural needs. Sedation improves patient comfort and potentially compliance, while general anesthesia is useful for non-cooperative patients and is generally considered safe. Mild sedation should be the default option for cooperative patients. When rendering PNB under general anesthesia, one must weigh the benefit of PNB versus the potential and theoretically elevated risk of nerve injury.

Conclusion

This review highlights the ongoing controversies in regional anesthesia, demonstrating that while various techniques and approaches offer potential benefits, none have shown universally superior outcomes across all patient populations and clinical settings. Studies on topics such as circumferential spread, the impact of regional anesthesia on compartment syndrome, and block placement techniques have yielded mixed results, reflecting the complexity of these issues. As such, decisions regarding PNB techniques should be guided by individual patient factors, institutional protocols, and the clinical expertise of providers. Rather than adhering to rigid guidelines, anesthesiologists should adopt a flexible, patient-centered approach that balances efficacy, safety, and practicality within their specific practice environment. Further research, particularly large-scale prospective studies, is needed to provide more definitive guidance on these debated topics.

References

---

Appendix

Appendix 1: Literature Search Strategy

Topic 1: Is the circumferential spread of local anesthetic necessary?

1. Anesthesia, conduction/ or regional anesth*.mp.

2. Anesthetics, local/ or local anesth*.mp.

3. Nerve block/ or nerve block.mp.

4. Circumferential

5. 1 or 2 or 3

6. 4 and 5

Topic 2: Regional anesthesia and compartment syndrome

1. Anesthesia, conduction/ or regional anesth*.mp.

2. Anesthetics, local/ or local anesth*.mp.

3. Nerve block/ or nerve block.mp.

4. Compartment syndrome.mp. or compartment syndromes/

5. 1 or 2 or 3

6. 4 and 5

Topic 3: Dextrose or saline as diluent for local anesthetics in nerve blocks

1. Anesthesia, conduction/ or regional anesth*.mp.

2. Anesthetics, local/ or local anesth*.mp.

3. Nerve block/ or nerve block.mp.

4. Dextrose.mp.

5. Saline.mp

6. 1 or 2 or 3

7. 4 and 5

8. 6 and 7

Topic 4: Peripheral nerve block in awake vs. anesthetized patients

1. Anesthetics, local/ or local anesth*.mp.

2. Nerve block/ or nerve block.mp.

3. Postoperative complications/

4. (wakefulness or awake or sedated or asleep).mp

5. 1 or 2

6. 3 and 4 and 5

Appendix 2: Summary Tables of Included Studies