Authors: Machi AT, et al
Discharge Readiness After Tricompartment Knee Arthroplasty: Adductor Canal Versus Femoral Continuous Nerve Blocks—A Dual-Center, Randomized Trial
This prospective randomized trial studied patients undergoing primary, unilateral knee arthroplasty to determine whether using a catheter to deliver a continuous adductor canal block reduced the interval until a patient is deemed ready for discharge, compared with using a continuous femoral nerve block.
The investigators assumed from other studies that the average time to discharge readiness would be expected to be approximately 39 hours, or just short of 2 days.
The study was conducted at two academic institutions in San Diego, California. Before the surgery, 30 mL of lidocaine 2% were delivered via a perineural catheter placed under ultrasonographic guidance; then, a ropivacaine 0.2% infusion at 6 mL/h was initiated, which was stopped the morning of the third postoperative day. For the surgery itself, 70% of the patients received a general anesthetic and the remainder a spinal anesthetic.
The primary outcome was the time to attainment of all of the following:
- Adequate analgesia, defined as pain severity of 4 or less on a numeric rating scale of 0-10;
- Independence from intravenous opioids for at least 12 hours;
- Ability to independently stand up and sit down; and
- Unassisted ambulation of at least 30 meters (evaluated using the 6-minute walk test).
Patients had physical therapy twice a day, beginning as early as the afternoon of surgery if they reached the orthopedic wards by 2 PM on the day of surgery.
The study found that patients with an adductor canal catheter (n = 39) reached all four criteria in a median of 55 hours (interquartile range, 42-63 hours), which did not differ meaningfully from the 61 hours (interquartile range, 49-69 hours) among those with a femoral catheter (n = 41) (P = .12).
Although the overall time to discharge was not statistically different, 72% of patients with an adductor canal catheter were able to independently ambulate 30 meters and also independently stand and then sit on postoperative day 1, compared with 27% of patients with a femoral catheter (P < .001).
The femoral catheter group reported average pain during physical therapy sessions of 2 out of 10 on a numeric rating scale, compared with 4 out of 10 in the adductor canal catheter group (P = .02).
Improving methods for pain relief and rapid recovery after knee replacement surgery is important for several reasons: The procedure is one of the most commonly done surgeries in the country, it is known to be one of the more painful surgeries, and analgesia will facilitate early rehabilitation and hospital discharge.
Before the advent of nerve blocks, epidural catheters were one option used for analgesia for knee replacement surgery. However, the presence of a neuroaxial catheter complicated the anticoagulation management intended to reduce the risk for deep venous thrombosis.
Femoral nerve blocks became more popular in part because they simplified the timing and dosing of anticoagulation; the local anesthetic injections were not in and around the spinal canal, but rather in the inguinal area and targeted the specific nerve associated with most of the pain associated with the surgery.
More recently, there has been concern that the quadriceps weakness associated with anesthetizing the femoral nerve with local anesthetics may increase the risk for the patient falling. As a result, alternatives have been explored—including delivering local anesthetic to the femoral nerve more distally, such as in the adductor canal in the middle third of the thigh, which contains sensory nerves and only one motor nerve. This thereby results in less quadriceps weakness compared with a single-injection femoral nerve block.
It is important to point out that these nerve block techniques are done as one element of a multimodal approach to analgesia in these patients. This might include adding nonsteroidal anti-inflammatory drugs, acetaminophen, and opioids, all of which all the patients in this study received.
This study found that a continuous adductor canal block did improve time until they were able to independently ambulate 30 meters and independently stand, walk 3 meters, return, and then sit down. Despite this positive effect, the time to overall discharge readiness compared with a continuous femoral nerve block did not change. This was because time to independence from intravenous opioids for at least 12 hours and time to reach adequate analgesia did not differ. The patients still needed opioids to manage pain, even if they could ambulate earlier with the adductor block.
One always has to think about whether enough patients were studied to detect a difference in discharge readiness. The sample size calculation by the authors had 90% power to detect a 10-hour difference in time to discharge readiness.
The four endpoints were measured three times a day (at 8 AM, 4 PM, and midnight). Another question to ask is whether would the results have been different had the measurements been made more frequently, such as every 4 hours.
A couple of other observations: More of the femoral catheter patients had their basal infusion rate decreased by postoperative day 3, and more adductor canal catheter patients had their basal infusion rate increased. Perhaps, had the basal infusion rate for the adductor canal block been set higher from the get-go, a reduction in time to discharge would have been found.
Of course, one always wonders whether other changes in the infusion rate, drug used, and bolus amount could also affect the efficacy of each of the nerve block techniques. In addition, both groups received intraoperative joint infiltration of ropivacaine, ketorolac, epinephrine, and tranexamic acid, which is another confounder to generalizing the findings from this study to other facilities and practitioners who might inject other substances in the joint.
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