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LETTER TO THE EDITOR

Do Continuous Femoral Nerve Blocks Affect the Hospital Length of Stay and Functional Outcome?

Department of Anesthesiology; Virginia Mason Medical Center; Seattle, WA; francis.salinas{at}comcast.net

In Response:

We appreciate Drs. Chelly and Ben-David's interest (1) in the design and interpretation of our study (2). Although Dr. Chelly et al.'s study (3) demonstrated that continuous femoral nerve block after total knee arthroplasty (TKA) resulted in improved analgesia and a 20% reduction in hospital length of stay compared to opioid-based analgesia after, any conclusions from this study must be interpreted within the limitations of a prospective, nonrandomized, cohort study.

Drs. Chelly and Ben-David stated that we "... questioned the value of continuous femoral blocks because there was no benefit in length of stay or the degree of flexion of the knee at 6 and 12 wk." We stated that the lack of benefit of improved analgesia from continuous femoral nerve block compared to single-injection femoral nerve block suggests that the quality of postoperative analgesia after TKA may have minimal impact on functional recovery and hospital length of stay. However, our last sentence states "Continuous femoral nerve block after TKA provides the anesthesiologists the opportunity to play a central role in optimizing postoperative analgesia, because provision of continuous femoral nerve block addresses one of primary concerns of patients (postoperative pain) more effectively than single femoral nerve block."

Regarding the specific criticisms of our study design:

1. We disagree that the discharge criteria were subjective. The discharge criteria established by our orthopedic surgeons and physical therapy department focus on functional criteria that allow safe, independent ambulation.
   
2. The study design called for both groups to receive a primary anesthetic block (ropivacaine 112.5 mg) in the postanesthesia care unit, followed by the start of the secondary analgesic block (ropivacaine 20 mg/h) 6 h later. We expected both groups to have complete motor block on the afternoon of the day of surgery. Both groups had a physical therapy session the same day of surgery, consisting of passive knee range of motion, transfer from the bed, and ambulation in the room with a wheeled walker. We did not intend to measure any difference in the degree of analgesia on the day of surgery as both groups would have had the benefit of the primary anesthetic block. One of our goals was to demonstrate the added benefit of the secondary analgesic block beginning on the day after surgery when the effects of the primary anesthetic block resolved. Dr. Chelly and Ben-David's reference (4) regarding the benefits of an "aggressive program" as a key element of accelerated functional recovery was based on patients randomized to begin inpatient rehabilitation either on postoperative day (POD) 3 versus POD 7 after TKA. This study (4) cannot be compared to our study or to previous studies (5,6) comparing continuous femoral nerve block to systemic opioid-based analgesia after TKA. Additionally, there are no data to support the contention that the frequency of physical therapy sessions per day improves early recovery. In fact, a recent, prospective, randomized trial (7) comparing once versus twice daily sessions of physical therapy after TKA failed to demonstrate an improvement in either hospital length of stay or range of motion at discharge.
   
3. While we acknowledge that patient-derived outcome scales (such as the SF-36) have become increasingly important to both physicians and clinical researchers for measuring improvement in function after surgery, all patients in both groups of our study were seen in follow-up at 12 wk by the primary orthopedic surgeon and were felt to be functionally independent. The results of our study confirm previous studies (5,6) of continuous femoral nerve block versus opioid-based analgesia demonstrating no difference in long-term functional outcome, as measured by knee range of motion.
   
4. Both groups in our study participated in either clinic-based or home-based rehabilitation programs. Although our study may be criticized for not controlling the type of outpatient physical therapy program, there appears to be no difference in functional outcome between clinic-based or home-based rehabilitation programs after TKA (8,9).
   

As Dr. Chelly and Ben-David point out, early functional recovery depends on multiple factors including the surgical technique and postoperative pain management. The goal of our study was to evaluate whether a single variable (improved analgesia provided by a continuous femoral nerve block for 48 h) would enhance functional recovery (as defined in our institution-specific clinical pathway) after conventional TKA to the point of decreasing hospital length of stay by 25%. Our participating surgeons did not perform minimally invasive surgery. At the time of our study, we were not routinely sending patients home after TKA with ambulatory continuous femoral nerve block. Although Ilfeld et al.'s data, with TKA as an overnight stay procedure using continuous femoral nerve block, are promising (10), it was only a feasibility study and requires validation by future, prospective, randomized, controlled trials.

In summary, our study was designed to assess the affect of a single variable on the short-term and long-term outcome of inpatient continuous femoral nerve block after TKA. We believe our study design and conclusions are valid. Improvements in surgical technique (minimally invasive TKA), continuous ambulatory peripheral analgesia, as well as a comprehensive and multidisciplinary approach involving the orthopedic surgeon, anesthesiologist, and rehabilitation protocols, may accelerate short-term recovery after TKA.

REFERENCES

1. Chelly JE, Ben-David B. Do continuous femoral nerve blocks affect the hospital length of stay and functional outcome? Anesth Analg 2007;104:996–7.[Free Full Text]
2. Salinas FV, Liu SS, Mulroy MF. The effect of single-injection femoral nerve block versus continuous femoral nerve block after total knee arthroplasty on hospital length of stay and long-term functional recovery within an established clinical pathway. Anesth Analg 2006;102:1234–9.[Abstract/Free Full Text]
3. Chelly JE, Greger J, Gebhard R, et al. Continuous femoral blocks improve recovery and outcome of patients undergoing total knee arthroplasty. J Arthroplasty 2001;16:436–46.[Web of Science][Medline]
4. Munin MC, Rudy TE, Glynn NW, et al. Early inpatient rehabilitation after elective hip and knee arthroplasty. JAMA 1998;279:847–52.[Abstract/Free Full Text]
5. Capdevila X, Barthelet Y, Biboulet P, et al. Effects of Perioperative analgesic technique on the surgical outcome and duration of rehabilitation after major knee surgery. Anesthesiology 1999;91:8–15.[Web of Science][Medline]
6. Singelyn FJ, Deyaert M, Joris D, et al. Effects of intravenous patient-controlled analgesia with morphine, continuous epidural analgesia, and continuous three-in-one block on postoperative pain and knee rehabilitation after total knee arthroplasty. Anesth Analg 1998;87:88–92.[Abstract/Free Full Text]
7. Lenssen AF, Crijns YH, Waltje EM, et al. Efficiency of immediate postoperative inpatient physical therapy following total knee arthroplasty: an RCT. BMC Musculoskeletal Disord 2006;7:71.
8. Kramer JF, Speechley M, Bourne R, et al. Comparison of clinic-and home-based rehabilitation programs after total knee arthroplasty. Clin Orthop Relat Res 2003; 410:225–34.
9. Rajan Ra, Pack Y, Jackson H, et al. No need for outpatient physiotherapy following total knee arthroplasty. A randomized trial of 120 patients. Acta Orthop Scand 2004; 75:71–3.[Web of Science][Medline]
10. Ilfeld BM, Gearen PF, Enneking FK, et al. Total knee arthroplasty as an overnight stay procedure using continuous femoral nerve blocks at home: a prospective feasibility study. Anesth Analg 2006; 102:87–90.[Abstract/Free Full Text]

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