Ambulatory continuous femoral nerve blocks decrease time to discharge readiness after tricompartment total knee arthroplasty: a randomized, triple-masked, placebo-controlled study

Abstract

Background: The authors tested the hypotheses that, compared with an overnight continuous femoral nerve block (cFNB), a 4-day ambulatory cFNB increases ambulation distance and decreases the time until three specific readiness-for-discharge criteria are met after tricompartment total knee arthroplasty.

Methods: Preoperatively, all patients received a cFNB (n = 50) and perineural ropivacaine 0.2% from surgery until the following morning, at which time they were randomly assigned to either continue perineural ropivacaine or switch to perineural normal saline. Primary endpoints included (1) time to attain three discharge criteria (adequate analgesia, independence from intravenous analgesics, and ambulation of at least 30 m) and (2) ambulatory distance in 6 min the afternoon after surgery. Patients were discharged with their cFNB and a portable infusion pump, and catheters were removed on postoperative day 4.

Results: Patients given 4 days of perineural ropivacaine attained all three discharge criteria in a median (25th-75th percentiles) of 25 (21-47) h, compared with 71 (46-89) h for those of the control group (estimated ratio, 0.47; 95% confidence interval, 0.32-0.67; P <0.001). Patients assigned to receive ropivacaine ambulated a median of 32 (17-47) m the afternoon after surgery, compared with 26 (13-35) m for those receiving normal saline (estimated ratio, 1.21; 95% confidence interval, 0.71-1.85; P = 0.42).

Conclusions: Compared with an overnight cFNB, a 4-day ambulatory cFNB decreases the time to reach three important discharge criteria by an estimated 53% after tricompartment total knee arthroplasty. However, the extended infusion did not increase ambulation distance the afternoon after surgery. (ClinicalTrials.gov No. NCT00135889.).

Fig. 1

Study design overview. POD = postoperative day.

Fig. 2

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) after tricompartment total knee arthroplasty. Data presented are Kaplan-Meier estimates of the cumulative percentages of patients meeting all three discharge criteria at each time point and subsequent time points. Data are for patients randomly assigned to the ropivacaine group (perineural ropivacaine from surgery through postoperative day 4) or the placebo group (perineural ropivacaine from surgery through 06:00 postoperative day 1 followed by perineural normal saline through postoperative day 4).

Fig. 3

Effects of femoral perineural ropivacaine infusion on ambulation and passive knee flexion after tricompartment total knee arthroplasty. Kaplan-Meier estimates include the cumulative percentages of patients ambulating at least 30 m at each time point and subsequent time points. Other data are expressed as median (horizontal bar) with 25th–75th (box) and 10th–90th (whiskers) percentiles for patients randomly assigned to the ropivacaine group (perineural ropivacaine from surgery through postoperative day 4) or the placebo group (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 endpoints. P values are provided where statistical comparisons were applied.

Fig. 4

Effects of femoral perineural ropivacaine infusion on postoperative pain after tricompartment total knee arthroplasty. Pain severity is 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 25th–75th (box) and 10th–90th (whiskers) percentiles for patients randomly assigned to the ropivacaine group (perineural ropivacaine from surgery through postoperative day 4) or the placebo group (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 endpoints. For this reason, no statistical comparisons were applied to the data of this figure. PACU = postanesthesia care unit.

Fig. 5

Effects of femoral perineural ropivacaine infusion on intravenous morphine consumption after tricompartment total knee arthroplasty. Kaplan-Meier estimates include the cumulative percentages of morphine-free patients at each time point and subsequent time points. Other data are expressed as median (horizontal bar) with 25th–75th (box) and 10th–90th (whiskers) percentiles for patients randomly assigned to the ropivacaine group (perineural ropivacaine from surgery through postoperative day 4) or the placebo group (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 endpoints. P values are presented where statistical comparisons were applied.