Continuous Blocks Hasten Discharge For TKA Patients

Potential benefits ‘enormous,’ but questions about safety remain

Author Michael Vlessides in  Anesthesia News Sept 8, 2010

 Toronto—Patients who undergo total knee arthroplasty and receive a four-day continuous femoral nerve block for pain achieve hospital discharge criteria 15 hours faster than those who receive only an overnight infusion of local anesthetic, according to a recent study.

The results, although not quite as promising as findings from a single-center study that preceded the new trial, suggest that the prolonged ambulatory blocks can get knee replacement patients out of the hospital faster.

“Compared with an overnight continuous femoral nerve block, does a four-day ambulatory continuous femoral nerve block shorten the time to discharge readiness? The answer is yes,” said Brian M. Ilfeld, MD, MS, associate professor of anesthesiology at the University of California, San Diego, who led the research.

Compelling Numbers

More than 1 million knee and hip arthroplasties are performed every year in the United States, and that number is expected to grow to 4 million annually within the next 20 years (J Bone Joint Surg Am 2007;89:780-785). Providing perineural infusions at home—following a single night in the hospital—to patients who undergo total knee arthroscopy (TKA) may improve their quality of life, reduce their risk for infection and reduce their risk for morbidity resulting from errors by health care providers, Dr. Ilfeld said.

The potential financial savings are enormous, too, Dr. Ilfeld added. More than 315,000 TKAs are performed annually in the United States, at a cost of more than $25,000 each and more than $7 billion overall. Between 50% and 70% of those outlays involve hospitalization and ancillary services.

“While the percentage of TKA procedures that ambulatory perineural infusion could be applied to is unknown, this technique constitutes a potentially significant fiscal advantage,” Dr. Ilfeld said. “In addition, decreasing hospitalization duration allows for an increased census and therefore increased operating room capacity.”

In an earlier study (Anesthesiology 2008;108:703-713), Dr. Ilfeld’s group found that the four-day ambulatory continuous femoral nerve block decreased the time to attain discharge criteria by 46 hours (25 vs. 71 hours, on average, respectively). However, he said, that trial involved an “artificial research environment” of a stand-alone clinical research center with one-to-one patient–nurse staffing ratio.

“The question is: Can we generalize from this single study to all patients?” Dr. Ilfeld said. “So we chose to redo this study at four public and private hospitals, hoping to have the results more generalizable to the general population.”

Dr. Ilfeld and colleagues enrolled 77 patients into the trial, each of whom received the preoperative continuous femoral nerve block, which was kept in place until the following morning. Patients were then randomized to either continue with perineural ropivacaine (n=39) or switch to saline (n=38).

The primary end point was the time patients needed to attain the following discharge criteria: adequate analgesia, independence from IV opioids and the ability to walk at least 30 meters. Patients were discharged with their continuous block and a portable infusion pump as early as the third day after surgery. Their catheters were removed on the fourth postoperative day.

Patients who received 0.2% perineural ropivacaine for four days reached all three discharge criteria in a median of 47 hours, compared with 62 hours for those who received ropivacaine alone until the morning following surgery (P=0.028), the researchers said.

Dr. Ilfeld, who reported his group’s findings at the 2010 Spring meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 2), said patients undergoing the four-day infusion met the discharge criterion for pain relief in 20 hours (range, 0-38 hours), compared with 38 hours (range, 15-64 hours) for controls (P=0.009). Independence from IV opioids was attained in 21 hours (range, 0-37 hours) for the treatment group and 33 hours (range, 11-50 hours) for controls (P=0.061). The 30-meter ambulation benchmark was reached in 40 (range, 25-68 hours) and 45 hours (range, 25-66 hours), respectively (P=0.780), a difference that was not statistically significant.

Falling Short?

Although Dr. Ilfeld described the results as clinically significant, he also noted some important caveats. “Continuous femoral nerve blocks induce quadriceps weakness,” he said. “And there were four falls in three patients in the four-day block group.” No falls were recorded among patients receiving normal saline.

Dr. Ilfeld said his group will soon be publishing data showing that continuous peripheral nerve blocks of the lower extremities increase the risk for falling after knee and hip arthroplasty (Anesthesia & Analgesia, in press).

Perhaps as important as the trial’s clinical findings was the realization that scientific investigations do not always mimic real life. “If you want to [apply] those results to your own center, it’s probably better to use the multicenter study results,” Dr. Ilfeld said. However, he stressed, “I do not now suggest, nor have I ever suggested that ambulatory infusion be used outside carefully controlled and [institutional review board]-overseen clinical trials until more details are available.”

André P. Boezaart, MD, PhD, professor of anesthesiology at the University of Florida, in Gainesville, said the risks associated with continuous femoral nerve blocks are not from the infusion itself, but rather the effects of the medication.

The falls are “assumed to be from weak quadriceps muscles, which is not an unavoidable side effect of the procedure,” Dr. Boezaart said.

“We do not know the optimal dose to provide sensory analgesia without affecting motor nerves, but our anecdotal experience with a 0.1% ropivacaine infusion at 1 to 3 mL per hour has been satisfactory,” added Andrea T. Esch, MD, also of the University of Florida, in Gainesville. “Although infection historically has a higher risk of occurring at a femoral site than other locations, it is not a legitimate enough concern to pursue earlier discontinuation or avoidance of this technique.”

Dr. Ilfeld’s poster was recognized as one of the three best presented at the meeting