Postoperative Ultrasound Guided Continuous Femoral Nerve Blockade for Unilateral Total Knee Arthroplasty: A Comparison of 0.125% Bupivacaine and 0.2% Ropivacaine.

CONTEXT: Total knee arthroplasty (TKA) is associated with severe postoperative pain which increases morbidity and mortality. AIMS: The aim of the study was to compare the analgesic efficacy and motor blockade of continuous infusion of 0.125% bupivacaine and 0.2% ropivacaine in femoral nerve block following unilateral TKA and to assess the effectiveness of femoral nerve block. SETTINGS AND
DESIGN: One hundred and fifty patients undergoing unilateral total knee replacement surgery were included in this prospective observational comparative study. SUBJECTS AND METHODS: Patients are divided into two groups of 75 each. Femoral nerve catheter was placed at the end of surgery using ultrasound. Postoperative analgesia and motor blockade were compared for the next 24 h using visual analog scale (VAS) score, additional analgesic requirement, and Bromage scale. STATISTICAL ANALYSIS: Student's t-test and Chi-square test were applied.
RESULTS: There was no statistically significant difference in pain between the two groups though VAS score (during rest and movement) and opioid consumption were lower in bupivacaine group. Nearly 28.6% patients experienced pain and required additional analgesics. Seventy-two percent among them complained of pain in the popliteal region supplied by sciatic nerve. Eight patients excluded from the study also had pain in the popliteal fossa. There was a statistically significant difference in motor blockade between the two groups at 12, 18, and 24 h after starting infusion. Bupivacaine group had a higher percentage of type three blocks compared to ropivacaine group.
CONCLUSION: Continuous femoral nerve block (CFNB) with 0.125% bupivacaine infusion provided better analgesia with denser motor blockade compared to 0.2% ropivacaine infusion. CFNB alone is not sufficient to provide adequate analgesia following unilateral TKA.

INTRODUCTION

Pain is a distressing experience associated with actual or potential tissue damage with sensory, emotional, cognitive, and social components.[1] Total knee arthroplasty (TKA) is associated with severe postoperative pain leading to tachycardia, hypertension, increased O2 demand, and myocardial stress. Pain increases sympathetic activity, releases catabolic hormones, and reduces immunity.[2]

Various multimodal analgesic techniques are used for pain relief following TKA.[34] Recently, ultrasound-guided continuous femoral nerve block (CFNB) using local anesthetics has gained popularity as an effective method for treating postoperative pain following unilateral TKA.[5678] Local anesthetics produce motor blockade which delays early ambulation. Our study compared the analgesic effect and motor blockade of the local anesthetics 0.125% bupivacaine and 0.2% ropivacaine in CFNB following unilateral TKA.

SUBJECTS AND METHODS

This prospective observational comparative study was conducted at a tertiary care center over a period of 18 months from March 2015 to September 2016. After obtaining approval from the Institutional Ethics committee, 150 consenting patients in the age group of 18–80 years with physical status American Society of Anesthesiologists Classes I, II, and III were included in the study. We have observed the postoperative pain relief and motor blockade in unilateral TKA with CFNB by two different local anesthetic agents used in our institute.

Based on the results observed in earlier studies on the pain score compared between the two groups and with 95% confidence and 80% power, minimum sample size was calculated to be 75 in each group. A total of 150 patients satisfying the inclusion and exclusion criteria [Table 1] were randomly allocated into two groups (Group B - 0.125% bupivacaine and group R – 0.2% ropivacaine infusion).

Table 1

Inclusion and exclusion criteria

At the end of surgery, femoral nerve catheter was inserted using ultrasound guidance, and 20 ml bolus dose of either 0.5% bupivacaine (B group) or 0.5% ropivacaine (R group) was given. In the postoperative unit, patients received 6–8 ml/h infusion of the respective drugs. Hemodynamic parameters such as heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were recorded at 2 h intervals. Postoperative pain was assessed using visual analog scale (VAS). Pain score during rest and movement was recorded every 2 h for the next 24 h. Patients having a VAS score of more than three were given a bolus dose of 5 ml of the infusing drug. If pain persisted, 30 μg of intravenous fentanyl was given as rescue analgesic. In spite of three bolus doses of fentanyl if pain was not relieved, the block was considered as failed and the patient was treated with intravenous fentanyl infusion. Motor blockade was assessed every 6 h for the next 24 h using Bromage scale [Table 2].

Table 2

Bromage scale

Statistical analysis

The data were analyzed using IBM SPSS version 20 (IBM Corporation, Amonk, New York, USA). Student's t-test was applied to study the statistical significance of the difference in pain scores between the two groups. To test the statistical significance of association of various outcomes with the anesthetic drugs, Chi-square test was used. Demographic data were analyzed using Chi-square test.

RESULTS

This prospective observational comparative study was conducted on 150 patients who were randomly allotted into two groups, each having 75 patients (a total of 161 patients were included in the study, of which 11 ended up as failed block). Although there was a female predominance in both groups (B - 50/75 and R - 53/75), the sex distribution among the groups was well matched with a P = 0.597.

The mean age in Group B was 65.39 ± 7.39 years whereas it was 62.39 ± 6.99 in Group R. The mean weight in Group B was 67.63 ± 10.49 and, in Group R, it was 65.95 ± 7.83. There was no statistical difference in age and weight.

Postoperative hemodynamic parameters did not show any statistical significance between the groups. However, the values of HR, SBP, and MBP were lower in bupivacaine group than in ropivacaine group. DBP did not show any difference.

Pain experienced during rest and movement was assessed using VAS score. Bupivacaine group had lower VAS scores both during rest and movement compared to ropivacaine group though the difference was not statistically significant [Figures 1 and 2]. Additional analgesic requirement (opioid consumption) was higher in ropivacaine group than in bupivacaine group [Figure 3].

Figure 1

Visual analog scale score at rest

Figure 2

Visual analog scale score during movement

Figure 3

Comparison of extra analgesic requirements

In this study, 43 patients complained of pain (VAS score >3) and required additional analgesics. Out of this, 31 patients (72%) had pain in the popliteal region (B group - 16/18 and R group - 15/25).

Eleven patients were excluded from the study due to failed block. In three patients, the failure was due to catheter displacement. Remaining eight patients were excluded because their pain was not relieved with three additional doses of rescue analgesics. All these patients complained of pain in the popliteal region.

Motor block was assessed using Bromage scale [Table 3 and Figure 4]. Immediately after starting the infusion (at 0 h), 26.7% in Group B and 24% in Group R had a complete motor block, 57.3% in Group B and 62.7% in group R had almost complete block, and 16% in Group B and 13.3% in Group R had a partial block. At 6th h, 41.3% in Group B and 56% in group R had a partial block and 58.7% in Group B and 44% in Group R had almost complete block. The difference between the groups was statistically insignificant at zero and 6th h (P = 0.072). There was a statistically significant difference in motor block between the two groups at 12th h (P = 0.022), 18th h (P = 0.022), and 24th h (P = 0.009).

Table 3

Motor block in bromage scale

Figure 4

Comparison of motor block

DISCUSSION

Adequate postoperative analgesia without motor blockade for early mobilization is the goal of every surgeon in TKA surgeries. Pain and motor block delays early ambulation and may increase the incidence of venous thromboembolism.[910] Uncontrolled pain may deprive the patient of good sleep and may lead to chronic pain and psychological problems.[11] Ineffective postoperative pain management may result in delayed discharge and increase the cost of treatment.[12]

Various multimodal analgesic techniques such as nonsteroidal anti-inflammatory drugs, intravenous opioids, continuous epidural infusion,[13] patient controlled analgesia,[6] and patient-controlled regional analgesic are employed for postoperative pain relief in TKA. CFNB has fewer side effects such as pruritus, hypotension, nausea, and vomiting. We have compared the analgesic efficacy and motor blockade of 0.125% bupivacaine and 0.2% ropivacaine in CFNB.

In our study, gender comparison did not show any statistical difference between the groups, but the number of females who underwent TKA was higher than males (103 females/47 male 68.8%). This is because females are more severely affected by osteoarthritis compared to males.[14] There was no significant difference in hemodynamic variables between the groups, but HR, SBP, and MAP were lower in Group B than Group R. This may be due to better pain relief in patients receiving bupivacaine.

Analgesic efficacy of the drugs did not show any statistically significant difference between the groups though VAS scores during rest and movement were lower in bupivacaine group than ropivacaine group. Additional analgesic requirement (opioid consumption) was less in B group (18/75) than R group (25/75). Similar finding with better analgesic effect of 0.125% bupivacaine over 0.2% ropivacaine was noted in the study by Heid et al.[15]

In our study, 43 (28.6%) patients complained of pain (VAS > 3) and required additional analgesics. Thirty-one patients out of this 43 (72%) had pain in the popliteal fossa. Popliteal fossa is innervated by sciatic nerve. Femoral nerve block alone may not be able to provide adequate analgesia in the popliteal region. This corroborates with the findings of Grape et al.[16] They studied the postoperative analgesic efficacy of sciatic nerve block when combined with femoral nerve block following TKA. In their study, they concluded that combined femoral and sciatic nerve block provides better postoperative analgesia within the first 12 postoperative hours compared with femoral nerve block alone for patients undergoing TKA.

Bromage scale was used to assess the intensity of motor block. There was no significant difference in motor block in both groups at 0 h and 6th h because of either the residual spinal effect or due to the bolus administration of the local anesthetics. From 12th h onward, statistically significant denser motor blockade was seen in the bupivacaine group compared to ropivacaine group. Alain et al.[17] compared the postoperative analgesia and motor blockade in continuous interscalene block with 0.2% ropivacaine and 0.125% bupivacaine after major open shoulder surgery. They found better preservation of power of the hand in the ropivacaine group. With lesser motor blockade, ropivacaine infusion may help in early ambulation of patients following unilateral TKA.

CONCLUSION

CFNB with 0.125% bupivacaine infusion provided better analgesia and denser motor blockade than 0.2% ropivacaine infusion. CFNB alone is not sufficient to provide adequate analgesia following unilateral TKA. CFNB with ropivacaine may be useful for early ambulation of patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.