A multicenter, randomized, triple-masked, placebo-controlled trial of the effect of ambulatory continuous femoral nerve blocks on discharge-readiness following total knee arthroplasty in patients on general orthopaedic wards

Abstract

A continuous femoral nerve block (cFNB) involves the percutaneous insertion of a catheter adjacent to the femoral nerve, followed by a local anesthetic infusion, improving analgesia following total knee arthroplasty (TKA). Portable infusion pumps allow infusion continuation following hospital discharge, raising the possibility of decreasing hospitalization duration. We therefore used a multicenter, randomized, triple-masked, placebo-controlled study design to test the primary hypothesis that a 4-day ambulatory cFNB decreases the time until each of three predefined readiness-for-discharge criteria (adequate analgesia, independence from intravenous opioids, and ambulation 30m) are met following TKA compared with an overnight inpatient-only cFNB. Preoperatively, all patients received a cFNB with perineural ropivacaine 0.2% from surgery until the following morning, at which time they were randomized to either continue perineural ropivacaine (n=39) or switch to normal saline (n=38). Patients were discharged with their cFNB and portable infusion pump as early as postoperative day 3. Patients who were given 4 days of perineural ropivacaine attained all three criteria in a median (25th-75th percentiles) of 47 (29-69)h, compared with 62 (45-79)h for those of the control group (Estimated ratio=0.80, 95% confidence interval: 0.66-1.00; p=0.028). Compared with controls, patients randomized to ropivacaine met the discharge criterion for analgesia in 20 (0-38) versus 38 (15-64)h (p=0.009), and intravenous opioid independence in 21 (0-37) versus 33 (11-50)h (p=0.061). We conclude that a 4-day ambulatory cFNB decreases the time to reach three important discharge criteria by an estimated 20% following TKA compared with an overnight cFNB, primarily by improving analgesia.

Figure 1

Effect of femoral perineural ropivacaine infusion on the time to reach three important discharge criteria (adequate analgesia, independence from intravenous opioids, and the ability to ambulate at least 30 m) following total knee arthroplasty. Data presented are Kaplan-Meier estimates of the cumulative percentages of subjects meeting all three discharge criteria at each time point and subsequent time points. Data are for subjects randomly assigned to group Ropivacaine (perineural ropivacaine from surgery through postoperative day 4) or group Placebo (perineural ropivacaine from surgery through 06:00 postoperative day 1 followed by perineural normal saline through postoperative day 4). Subjects given four days of perineural ropivacaine attained all 3 discharge criteria in a median (25^th–75^th percentiles) of 47 (29–69) hours, compared with 62 (45–79) hours for those of the control group (Estimated ratio=0.80, 95% confidence interval: 0.66–1.00; p=0.028).

Figure 2

Effects of femoral perineural ropivacaine infusion on postoperative pain following total knee arthroplasty. Pain severity indicated using a Numeric Rating Scale of 0–10, with 0 equal to no pain and 10 being the worst imaginable pain. Data are expressed as median (horizontal bar) with 25^th–75^th (box) and 10^th–90^th (whiskers) percentiles for subjects randomly assigned to group Ropivacaine (perineural ropivacaine from surgery through postoperative day 4) or group Placebo (perineural ropivacaine from surgery through 06:00 postoperative day 1 followed by perineural normal saline through postoperative day 4). Because each comparison dilutes all other P-values, we restricted our analysis to 11 comparisons among secondary end points. P-values are provided where statistical comparisons were applied. Kaplan-Meier estimates include the cumulative percentages of subjects with the discharge criterion of a median Numeric Rating Scale < 4 in the 8-hour period and subsequent time points. Subjects given four days of perineural ropivacaine attained this analgesia discharge criterion in a median (25^th–75^th percentiles) of 20 (0–38) hours, compared with 38 (15–64) hours for those of the control group (Estimated ratio=0.52, 95% confidence interval: 0.28–0.84; p=0.009). “Eve”: Evening; and “Nit”: Night.

Figure 3

Effects of femoral perineural ropivacaine infusion on intravenous morphine consumption following total knee arthroplasty. Data are expressed as median (horizontal bar) with 25^th–75^th (box) and 10^th–90^th (whiskers) percentiles for subjects randomly assigned to group Ropivacaine (perineural ropivacaine from surgery through postoperative day 4) or group Placebo (perineural ropivacaine from surgery through 06:00 postoperative day 1 followed by perineural normal saline through postoperative day 4). Because each comparison dilutes all other P-values, we restricted our analysis to 11 comparisons among secondary end points. P-values are presented where statistical comparisons were applied. Kaplan-Meier estimates include the cumulative percentages of subjects with the discharge criterion of independence from intravenous opioids during the 8-hour period and subsequent time points. Subjects given four days of perineural ropivacaine attained this discharge criterion of independence from intravenous opioids during an 8-hour period in a median (25^th–75^th percentiles) of 21 (0–37) hours, compared with 33 (11–50) hours for those of the control group (Estimated ratio=0.69, 95% confidence interval: 0.42–1.01; p=0.061). “Eve”: Evening; and “Nit”: Night.

Figure 4

Effects of femoral perineural ropivacaine infusion on ambulation following total knee arthroplasty. Data are expressed as median (horizontal bar) with 25^th–75^th (box) and 10^th–90^th (whiskers) percentiles for subjects randomly assigned to group Ropivacaine (perineural ropivacaine from surgery through postoperative day postoperative day 4) or group Placebo (perineural ropivacaine from surgery through 06:00 postoperative day 1 followed by perineural normal saline through postoperative day 4). Kaplan-Meier estimates include the cumulative percentages of subjects ambulating the discharge criterion of at least 30 m at each time point and subsequent time points. Subjects given four days of perineural ropivacaine attained this discharge criterion in a median (25^th–75^th percentiles) of 40 (25–68) hours, compared with 45 (25–66) hours for those of the control group (Estimated ratio=1.00, 95% confidence interval: 0.75–1.26; p=0.778). “Eve”: Evening.

Figure 5

Effects of femoral perineural ropivacaine infusion on passive knee flexion and extension following total knee arthroplasty. Data are expressed as median (horizontal bar) with 25^th–75^th (box) and 10^th–90^th (whiskers) percentiles for subjects randomly assigned to group Ropivacaine (perineural ropivacaine from surgery through postoperative day postoperative day 4) or group Placebo (perineural ropivacaine from surgery through 06:00 postoperative day 1 followed by perineural normal saline through postoperative day 4). Because each comparison dilutes all other P-values, we restricted our analysis to 11 comparisons among secondary end points. Therefore, statistics were not applied to the data of this figure. “Eve”: Evening.