Adding a Low-concentration Sciatic Nerve Block to Total Knee Arthroplasty in Patients Susceptible to the Adverse Effects of Nonsteroidal Anti-inflammatory Drugs (NSAIDs)

A Randomized Controlled Trial

Busara Sirivanasandha; Kulwadee Sutthivaiyakit; Thippatai Kerdchan; Suppachai Poolsuppasit; Suwimon Tangwiwat; Pathom Halilamien


BMC Anesthesiol. 2021;21(282) 

In This Article


Study Design and Population

Prior to commencement, this single-center, prospective, double-blinded, randomized controlled trial was approved by the Siriraj Institutional Review Board (COA no. Si123/2018) and registered at, NCT03486548, Registered 3 April 2018, The investigation was conducted on patients aged 50–85 years; had American Society of Anesthesiologists physical statuses of I–III; and were scheduled to undergo elective, unilateral, primary TKA at Siriraj Hospital May 2018–December 2019. The inclusion criteria were patients susceptible to the adverse effects of NSAIDs: history of chronic kidney disease (estimated glomerular filtration rate < 50 ml/min/1.73 m2), coronary artery disease, cerebrovascular disease, gastric ulcer, or an allergy to NSAIDs other than ketorolac. The exclusion criteria were a bodyweight of < 45 kg; allergy to bupivacaine, ketorolac, or dexamethasone; uncontrolled diabetes; contraindication to regional anesthesia; cognitive impairment; preexisting neuropathy; a neurological deficit in the lower extremities; and preexisting pain requiring the chronic use of oral morphine (20 mg/day or equivalent). Patients who declined to participate were also excluded.

Randomization and Blinding

The patients (n = 50) were randomized into an intervention group and a control group in blocks of four. This was achieved by using the sealed-envelope technique and computer-generated randomization lists sourced from an internet-based application ( In the intervention group (n = 25), the patients received an SNB with an infusion of 0.125% bupivacaine (20 ml) and dexamethasone (5 mg). As to the control group (n = 25), the patients received only a subcutaneous injection of 1% xylocaine (1 ml) in the popliteal area without an SNB. The patients and assessors were blinded to the treatment allocations.

Anesthetic Protocol

After being briefed on the research objectives and the experimental methods, each eligible patient signed a consent document on their respective day of admission. Two hours before surgery, each patient was given an oral premedication of paracetamol (1000 mg). Following standard anesthetic monitoring (pulse oximetry, non-invasive blood pressure monitoring, and electrocardiogram), the patients were sedated using intravenous fentanyl (25–50 mcg) and midazolam (0.5–1 mg) before being administered oxygen through a nasal cannula (3 L/min).

For both groups, an anesthesiologist specializing in regional anesthesia performed an ultrasound-guided ACB in the popliteal area, using 15 ml of 0.33% bupivacaine. All patients were then placed in the lateral decubitus position. Both the control- and intervention-group patients were administered a subcutaneous local infiltration of 1% xylocaine (1 ml). However, the intervention-group patients subsequently also received an ultrasound-guided SNB (the popliteal approach); for that procedure, a mix of 0.125% bupivacaine (20 ml) and dexamethasone (5 mg) was used.

In the operating room, the patients received 2.0 ml of spinal anesthesia with isobaric bupivacaine and an intravenous propofol infusion (25 to 50 mcg/kg/min) to achieve a mild to moderate sedation. At the end of the operation, all patients received PIA with 0.25% bupivacaine (40 ml) and ketorolac (30 mg). During the first three postoperative days, the standard oral postoperative regimen was followed for all patients: paracetamol (1000 mg every 6 h), gabapentin (300 mg before bedtime), and intravenous morphine for pain, as needed (1 mg/hour).

Outcomes and Measurement

The primary outcome was the effects of using a combination of a low concentration of popliteal-SNB and dexamethasone as an adjunctive technique for TKA in patients susceptible to the adverse effects of NSAIDs on their pain scores during the first 24 postoperative hours. Postoperatively, the pain scores and motor function were determined by only one assessor, who was blinded to the group allocations. At 6, 12, 18, and 24 h after surgery, we assessed the postoperative pain scores at the anterior and posterior aspects of the knee while at rest and with motion (45 degrees of knee flexion). At the same times, the function of the tibialis anterior muscle was assessed and graded into 3 categories: 0 (normal); 1 (dorsiflexion, but less powerful than the untreated side); and 2 = no strength to flex the ankle. Pain scores during physiotherapy were also recorded.

Sample Size

Drawing upon data relating to adductor canal blocks and multimodal periarticular analgesia from work by Gwam et al.,[7] a prospective power analysis revealed that 50 patients provided a 90% chance (power) to detect a reduction in visual-analog-scale score of 1.94 out of 10 during the first 24 h after surgery. The value of 1.94 represented a reduction from a moderate level of pain (scores 4–6) to a mild level (scores 1–3), e.g., from 4.94 in the control group to 3.00 in the SNB group. The type I error was 0.05 by an F-test; the standard deviation was not greater than 1.86 of the means; and a correction of the values for non-normal distribution was assumed.

Statistical Analysis

All data were analyzed using IBM SPSS Statistics for Windows (version 24.0; IBM Corp., Armonk, NY, USA). The data were tested for normal distribution using histograms. Continuous data were presented as means and standard deviations (SD) or as medians and interquartile ranges (IQR), whereas categorical data were reported as numbers and percentages. A comparative analysis of the data of the 2 groups used the chi-squared test for group data, the unpaired t-test for continuous data with normal distribution, and the Mann–Whitney U test for continuous data with an abnormal distribution.