European Journal of Cardiovascular Medicine

Peripheral nerve blocks, when optimally employed, offer an advantageous alternative to conventional techniques during surgeries. ¹

These blocks minimize interference with vital physiological functions, reduce stress responses, and avoid polypharmacy, fostering an alert and cooperative patient. ¹Originating from Dr. Carl Koller's use of cocaine in 1884, regional anesthesia has evolved with the development of newer agents, particularly aminoamide compounds, revolutionizing modern surgery demands. ²

Long-acting anesthetics facilitate extended surgeries in orthopedic, vascular, and plastic procedures.

Specific nerve blocks, like combined femoral and sciatic nerve blocks, offer advantages over spinal and epidural anesthesia without autonomic blockade.

While bupivacaine has been widely used, concerns about cardiotoxicity led to the synthesis of ropivacaine, a newer aminoamide local anesthetic.³

Ropivacaine is anticipated to provide comparable analgesia with less motor blockade and cardiotoxicity than bupivacaine, addressing safety concerns raised in previous research.³

Aims and Objectives

Aim: Evaluating the efficacy and safety of 0.5% Bupivacaine versus 0.5% Ropivacaine in combined femoral and sciatic nerve block (posterior approach).

Objectives:

• To compare duration of postoperative analgesia and motor blockade of 0.5% bupivacaine and 0.5% ropivacaine.
• To compare the onset of sensory and motor blockade of 0.5% bupivacaine and 0.5% ropivacaine.
• To assess intraoperative hemodynamic changes. 

Study Design: Hospital based Cross-sectional study.

Study Setting: Dept of Anaesthesiology, Fakhruddin Ali Ahmed Medical College and Hospital, Barpeta.

Study Sample Size: 30 for each group (Total 60).

Statistical Analysis: For comparing 2 groups, Student’s t-test was utilized.

Inclusion Criteria

• American Society of Anesthesiologists (ASA) Grade I and II physical status, scheduled for elective lower limb below knee orthopedic surgeries under combined femoral and sciatic nerve block.
• Age group of between 18 and 50 years irrespective of gender.

Exclusion Criteria

• Patients' refusal for peripheral neve block.
• ASA Grades III, IV, or V.
• History of allergy or hypersensitivity to any of the study drug, local or systemic infection, and marked pelvic deformities.
• Patients with Cardio-vascular System (CVS), renal or hepatic dysfunction, neuromuscular disorders, severe metabolic disorders, and with marked coagulopathies.
• Uncooperative patients.
• Pregnant or lactating mothers.
• Inadequate block (need for conversion into general anesthesia).

After obtaining Institutional Ethics committee approval, and written consent from the patients, they were randomly allocated into 2 groups with 30 patients in each group after matching the patient’s age, sex and ASA grading:

Group A: Patients who received Bupivacaine 0.5% (3mg/kg).

Group B: Patients who received Ropivacaine 0.5% (3mg/kg).

Vitals were monitored every 5 minutes for 1^st 30 minutes and every 15 minutes thereafter.

Sensory assessment was done by response to pinprickusingModified Hollmen’s scale⁴- assessed by pinprick with a 23G hypodermic needle every minute for the first 30 minutes, then every 30 minutes thereafter. The onset of sensory block was defined as thetime between drug administration and absence of the pinprick sensation (Hollmen's ≥3).

Motor assessment included Modified Bromage Scale⁵ ranging from no paralysis to complete loss of ankle dorsiflexion. The duration of motor block was defined as the time from injection to complete return of muscle power.

Duration of analgesia was the interval between the time of giving block to the first dose of rescue analgesic required.

Post-operative pain was assessed using the Visual Analogue Scale (VAS) at specific intervals.

Fig: Hollmen scale and Modified Hollmen scale for sensory block.

RESULTS AND DISCUSSIONS:

Table-1: Distribution of patients as per onset of sensory blockade between Study group

[N= Number of Cases, % = Percentage, *statistically significant]

Figure-1: Graphical presentation of distribution of patients as per onset of sensory blockade between Study group

Table-2: Distribution of Mean and standard deviation of onset time of sensory block between study groups

For the femoral nerve block, both groups showed similar patterns of onset, with the majority of patients experiencing sensory blockade between 12.5-15 minutes (83.3% in Group A and 90% in Group B). There was lack of statistical significance (p=0.331) in the onset times between the two groups.

However, for the sciatic nerve block, present study revealed a statistically significant difference (p=0.010) in the distribution of onset times between the two groups. Group B (Ropivacaine) showed a tendency towards earlier onset, with 63.3% of patients experiencing blockade between 15-17.5 minutes, compared to only 30% in Group A (Bupivacaine).

Despite these distributional differences, the mean onset times for both femoral (13.52 ± 0.80 vs 13.85 ± 0.73 minutes) and sciatic (17.18 ± 0.91 vs 17.32 ± 0.79 minutes) blocks were not statistically significant between the groups.

The observed differences in onset times between femoral and sciatic nerve blocks could be attributed to several factors. Anatomical differences, such as the more superficial location of the femoral nerve compared to the sciatic nerve, may lead to more consistent onset times for femoral blocks regardless of the local anesthetic used. Variations in nerve fiber composition between the two nerves could affect how quickly different local anesthetics take effect. Local tissue characteristics surrounding each nerve, such as fat content and vascularity, might influence drug absorption and distribution. Technique variability could play a role, with femoral blocks potentially being more standardized while sciatic blocks may be more operator-dependent. Although, both drugs were used at 0.5% concentration, their relative potencies at this concentration might differ for sciatic versus femoral nerve blocks.

Table-3: Distribution of patients as per duration of sensory block between study groups

Figure-2: Graphical presentation of distribution of patients as per duration of sensory block between study groups

Table-4: Distribution of Mean and standard deviation of duration of sensory block between study groups

Present study revealed a striking difference in the duration of sensory blockade between the two groups. The majority of patients in Group A (Bupivacaine) experienced longer block durations, with 76.7% between 870-900 minutes and 16.7% exceeding 900 minutes. In contrast, Group B (Ropivacaine) showed shorter durations, with 73.3% of patients experiencing block duration less than 840 minutes.

This significant difference (p<0.001) in block duration is reflected in the mean durations: 890.07 (± 11.36) minutes for Group A versus 834.50 (±10.20) minutes for Group B.

The longer duration of sensory block with bupivacaine could be attributed to its pharmacological properties. As noted by Shafiei et al., 2023⁽⁶⁾, bupivacaine has high protein binding and lipid solubility, which contribute to its prolonged duration of action. This extended duration could be advantageous in procedures requiring longer post-operative analgesia but might delay mobility in cases where early movement is desired.

Table-5: Distribution of patients as per onset of motor block between study groups

Figure-3: Graphical presentation of distribution of patients as per onset of motor block between study groups

Table-6: Distribution of Mean and standard deviation of onset time of motor block between study groups

Regarding the onset of motor block, bupivacaine demonstrated a notably faster action compared to ropivacaine. In the bupivacaine group, 90% of patients experienced motor block onset within 20-22 minutes, while only 36.7% of the ropivacaine group achieved motor block in this timeframe. The mean onset times (21.43 ± 0.77 minutes for bupivacaine vs 22.60 ± 0.69 minutes for ropivacaine) further underscores this difference, which was found to be statistically significant (p<0.001).

Table-7: Distribution of patients as per duration of motor block between study groups

Figure-4: Graphical presentation of distribution of patients as per duration of motor block between groups

Table-8: Distribution of Mean and standard deviation of duration of motor block between study groups

The duration of motor block showed even more pronounced differences between the two groups. Bupivacaine consistently provided longer-lasting motor blockade (225-255 minutes) compared to ropivacaine (180-210 minutes). The mean durations (242.67 ± 6.39 minutes for bupivacaine vs 192.83 ± 4.86 minutes for ropivacaine) were significantly different (p<0.001), indicating that bupivacaine offers approximately an hour of additional motor block duration.

The faster onset and longer duration of motor block with bupivacaine compared to ropivacaine can be primarily explained by their different lipid solubilities and protein binding characteristics⁽⁶⁾. Bupivacaine has higher lipid solubility than ropivacaine, allowing it to penetrate nerve membranes more rapidly and extensively, leading to a quicker onset of action⁽⁷⁾. Additionally, bupivacaine's higher protein binding affinity (95% vs. 94% for ropivacaine) contributes to its longer duration of effect, as it remains at the site of action for an extended period⁽⁶⁾. Ropivacaine's slightly lower pKa (8.1 compared to bupivacaine's 8.2) might also play a role, affecting the proportion of the drug in its active, ionized form at physiological pH^(7,8). Furthermore, bupivacaine's greater potency in blocking sodium channels, particularly those responsible for motor function, could explain its more pronounced and prolonged motor blockade⁽⁶⁾. These pharmacological differences collectively result in bupivacaine's faster onset and longer-lasting motor block compared to ropivacaine in combined femoral and sciatic nerve blocks.

Table-9: Distribution of Mean and Standard deviation of VAS Score at different time frames in each study groups

Table-10: Comparison of mean and standard deviation of rescue analgesia time between study groups

Present findings regarding postoperative pain, as measured by Visual Analog Scale (VAS) scores, provide valuable insights into the analgesic efficacy of bupivacaine (Group A) and ropivacaine (Group B) in combined femoral and sciatic nerve blocks. The observed pattern of pain progression aligns with the expected pharmacodynamics of these long-acting local anesthetics. Both groups experienced complete pain relief (VAS score 0) for the first 8 hours postoperatively, indicating effective initial analgesia. The gradual increase in pain scores thereafter reflects the wearing off of the anesthetic effect over time.

The findings on time to first rescue analgesia provide further insight into the analgesic efficacy of bupivacaine and ropivacaine in combined femoral and sciatic nerve blocks. The slight difference in mean time (14.08 ± 1.95 hours for bupivacaine vs 13.49 ± 1.71 hours for ropivacaine) was not statistically significant, indicating comparable analgesic duration for both drugs.

The hemodynamic changes observed in present study comparing bupivacaine (Group A) and ropivacaine (Group B) in combined femoral and sciatic nerve blocks provide valuable insights into the cardiovascular effects of these local anesthetics. Our findings indicate generally similar hemodynamic profiles between the two groups, with some statistically insignificant differences at some time points.

The study findings indicate that ropivacaine demonstrated a significantly shorter duration of motor blockade in femoral and sciatic nerve blocks, suggesting potential advantages in specific clinical scenarios such as early post-op mobilization and better safety profile.

Hemodynamics and complications showed no significant differences between the two local anesthetics.

Overall, both ropivacaine and the comparator are deemed effective and safe for the procedure, with ropivacaine potentially holding benefits in specific clinical contexts.

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