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Anesth Analg 2004;99:1539-1543 © 2004 International Anesthesia Research Society doi: 10.1213/01.ANE.0000136470.51029.52
Denise J. Wedel Section Editor |
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Abstract |
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Postoperative pain after total knee arthroplasty (TKA) is severe, and achieving adequate analgesia remains a clinical challenge. We tested the hypothesis that, in patients having unilateral TKA under intrathecal (IT) anesthesia, the addition of a femoral nerve block would provide superior analgesia when compared with IT morphine and demonstrate fewer adverse side effects. In a single-blinded and controlled trial, 41 ASA I–III patients undergoing unilateral TKA were randomized into 2 groups. Both groups received 15 mg of IT hyperbaric bupivacaine for the surgical anesthetic. Group ITM received 250 µg of IT morphine and group FNB received an ultrasound-assisted femoral nerve block with 40 mL of 0.5% ropivacaine, 5 µg/mL of epinephrine, and 75 µg of clonidine. At 1, 2, 4, 6, 12, and 24 h postoperatively, we measured visual analog scales for pain, cumulative IV morphine consumption, hemodynamics, and side effects. There were no statistically significant differences in morphine consumption, pain at rest, or pain with movement. However, group FNB had fewer perioperative side effects including nausea, vomiting, and pruritus (P < 0.05 for each event). This corresponded to a decrease in patient satisfaction in group ITM, in which 20% of the patients rated their experience as "unsatisfactory" (P < 0.05). We conclude that, in comparison with IT morphine, a single injection femoral nerve block provides equivalent analgesia but with a significant reduction in side effects for patients having TKA under bupivacaine intrathecal anesthesia.
IMPLICATIONS: In this prospective, randomized, and single-blinded trial we identify a side effect-sparing postoperative analgesic approach for total knee replacement surgery. A single injection femoral nerve block provides equivalent analgesia with a reduction in side effects when compared with intrathecal morphine.
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Introduction |
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Achieving adequate analgesia after total knee arthroplasty (TKA) can be a challenging task. Most patients rate their pain as severe (1). Several approaches have been proposed and include patient-controlled IV analgesia (PCA), nerve blocks, and neuraxial techniques (2–4). Immediate anticoagulation may limit the options for epidural analgesia, arguably the most effect technique (5).
We have demonstrated that intrathecal (IT) morphine with and without the addition of clonidine can improve postoperative analgesia after knee replacement surgery (6). However, the patients experienced a frequent incidence of side effects, including nausea, vomiting, pruritus, and hypotension.
Given these drawbacks of IT morphine, this prospective and randomized clinical study was intended to identify an approach that provides postoperative pain relief comparable to IT morphine but with fewer side effects. We hypothesized that, in patients undergoing TKA with IT bupivacaine, the addition of a femoral nerve block would provide superior analgesia when compared to IT morphine and demonstrate fewer adverse effects. Finally, we speculated that if patients experienced fewer side effects, they would then rate their anesthetic experience more favorably.
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Methods |
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This prospective and randomized clinical study was reviewed and approved by the Dartmouth College Committee for Protection of Human Subjects. After giving written informed consent, 41 ASA physical status I–III patients undergoing single TKA were enrolled in the clinical study. Patients were excluded if they were <18 yr of age, pregnant, or had a history of the following: chronic obstructive lung disease, allergy to a study drug, chronic pain syndrome unrelated to their knee pathology, chronic opioid use, or contraindications to IT or regional analgesia. Once enrolled, patients were removed from the study if they experienced a failed femoral nerve block or IT anesthetic. For each patient, we recorded gender, age, weight, height, presence of a preexisting diagnosis of hypertension, and the ASA physical status classification.
Patients were randomized into one of two treatment groups on the day of surgery using a computer-generated assignment. Randomization was blocked into groups of six to minimize any time effect. Premedication consisted of 1–2 mg of IV midazolam at the discretion of the anesthesia team. Both groups received 15 mg of IT hyperbaric bupivacaine as the surgical anesthetic. The intrathecal blocks were performed with the patient in the sitting or lateral position using the L3-4 or L4-5 interspace. The first group received 250 µg of IT preservative-free morphine mixed with the 15 mg of hyperbaric bupivacaine (ITM group). The second group received a single injection femoral nerve block before the IT injection. (FNB group). The femoral artery and nerve were visualized using a high resolution ultrasound device (Sonosite, C11 probe, 11-mm broadband curved array transducer with a frequency of 4–7 MHz, Bothell, WA). These structures were marked on the skin. A 22-gauge B-bevel shaped needle was advanced under stimulation (Stimuplex, B Braun, Bethlehem, PA). The end-point used for injection was an ipsilateral quadriceps contraction at <0.5 mA. At this point, 40 mL of 0.5% ropivacaine with 75 µg of clonidine and 5 µg/mL of epinephrine were injected slowly after negative aspiration. Needle advancement and the injection of local anesthetic were not visualized with ultrasound. A sensory level to cold temperature in the femoral nerve distribution was established before performance of the IT blockade. Each patient, regardless of group assignment, had a dry sterile dressing placed on his or her groin.
Intraoperatively, patients received any medications thought necessary by the anesthesia team. Intraoperative data that were collected included the estimated blood loss and the duration of surgery, defined as the time elapsed from skin incision to bandage application. In the postanesthesia care unit (PACU), all patients were provided with PCA with morphine set at a demand dose of 1 mg with a lockout interval of 6 min. Subsequent adjustments in the PCA settings were not constrained by the study protocol. While in the PACU, patients could receive supplemental IV morphine to achieve satisfactory analgesia as defined by the individual patient. Nursing staff were instructed to use a visual analog scale (VAS) score of 3 or less to define an end-point for administering morphine. All patients were given ketorolac on a scheduled basis. Patients <55-yr-old were given 30 mg IV every 6 h, and patients older than 55 yr were given 15 mg IV every 6 h. For dosing of antiemetic medications, patients followed a standard institutional clinical pathway for TKA. This consisted of first-line treatment with ondansetron and second-line treatment consisting of either dexamethasone or promethazine. Time 0 was arbitrarily defined as arrival in the PACU. Research nurses collected data at 1, 2, 4, 6, 12, and 24 h postoperatively. Data included minimum interval systolic blood pressure and oxygen saturation. Morphine consumption and any ancillary medications were also recorded. In addition, patients were asked on a numeric scale if they experienced nausea, vomiting, or itching. The scale was 1 = none, 2 = mild, 3 = moderate, 4 = severe. At each data point, the patients were asked to fill out a VAS for pain, where 0 = no pain and 10 = worst possible pain. VAS scores were obtained at rest and with movement. In addition, at each measuring interval, a sensory examination to cold temperature was performed to assess the presence or absence of a femoral nerve block. One week after discharge, patients were contacted to assess their satisfaction with their anesthetic experience on a four-point categorical scale (1 = unsatisfactory, 2 = satisfactory, 3 = very good, 4 = outstanding.)
Our primary outcome was the amount of IV morphine used in the first 24 h. Using a standard deviation of 22 mg of morphine estimated from a previous study at our institution with 250 µg of IT morphine, 20 patients per group would give us approximately 82% power to detect a difference of 20 mg of IV morphine use (6). Univariate analysis was accomplished using unadjusted Pearson 
2 for categorical variables and Student’s t-test for continuous variables. Ninety-five percent confidence intervals of differences are reported for continuous variables, whereas relative risks are reported for binary variables. Logistic regression, ordinal regression, and standard regression techniques were used as appropriate based on the response to explore predictors of satisfaction, morphine use, and morbidities such as nausea. A P value of 
0.05 was used to indicate statistical significance.
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Results |
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Forty-one patients were enrolled in the study. One patient was removed from the study after a failed femoral nerve block. This patient, secondary to anxiety, moved throughout the attempted femoral nerve block. Because of safety reasons, the operator chose to abort the procedure after 15 mL of local anesthetic was injected. This patient failed to achieve a sensory level in the femoral nerve distribution.
The patients were similar in terms of the demographics (Table 1). Intraoperative data revealed no significant differences in sedative, analgesic, antipruritic, pain, or antiemetic medications given between groups. Only one patient received an antiemetic or antipruritic medication in the operating room. This patient was in the ITM group.
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Table 2 reveals the cumulative IV morphine consumption and VAS scores at the different time intervals. There were no statistical differences between the groups during any of the time intervals. Ketorolac use was similar between groups as it was administered on a regular basis to both groups. The ITM group received 75 ± 6 mg and the FNB group received 72 ± 7 mg of IV ketorolac (P > 0.05).
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Table 3 lists the various side effects in each of the treatment groups. The incidences of nausea, vomiting, and pruritus were significantly more frequent in the ITM group. The use of antiemetic and antipruritic medication was also more frequent in the ITM group. Although not statistically significant, there was a trend towards a more frequent incidence of desaturation events, higher sedation scores, and hypotension in the ITM group. The effect of IT morphine on nausea and vomiting was not changed in any significant way when adjusted for age, sex, and total morphine dose.
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In the follow-up satisfaction survey, 20% of the patients in the ITM group rated their anesthetic experience as "unsatisfactory" as compared with none in the FNB group (P = 0.035) (Table 4). For the four patients who were unsatisfied, all were in the IT morphine group, all were women, and all had severe vomiting at least once. Neither age, maximum pain at rest, maximum pain with movement, total morphine used, nor maximum morphine used were associated with an unsatisfactory rating. All four patients who rated their anesthetic experience as unsatisfactory cited either nausea or vomiting as the reason.
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The sensory block in the femoral nerve distribution resolved in 1 patient between 4–6 h, 3 patients between 6–12 h, and 15 patients between 12–24 h. One patient still had an intact femoral block at 24 h; this sensory block resolved by 28 h.
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Discussion |
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The main finding in this study is that a ropivacaine-clonidine femoral nerve block provides equal analgesia with a reduction in side effects compared with 250 µg of IT morphine for patients having TKA under bupivacaine IT anesthesia (Tables 2 and 3 ). We hypothesize that the improvement in patient satisfaction in the FNB group was attributable to this reduction in side effects.
IT morphine provides effective postoperative pain control for major orthopedic procedures (6,7). The addition of morphine to an IT anesthetic is an attractive therapeutic option because of its simplicity, as its use does not expose the patient to an additional procedure. The major drawback to IT morphine is the frequent incidence of drug-related side effects. These include sedation, nausea, vomiting, pruritus, urinary retention, and delayed respiratory depression. Because side effects are dose related, the doses necessary for postoperative analgesia in TKA result in a side effect incidence ranging from 50% to 100% (6–8). Our data confirm these findings.
Femoral nerve blocks, both continuous and single injection techniques, are effective strategies for providing postoperative analgesia after TKA (2–4). In addition, femoral nerve blocks have been found to facilitate physical therapy and early ambulation, and reduce the length of hospitalization (4,5). There is only one study that has compared femoral nerve block to IT morphine. Tarkkila et al. (9) found superior analgesia with 300 µg of IT morphine when compared with a continuous femoral nerve block. They also found, with the exception of pruritus, a similar incidence of side effects. In contrast, our results reveal that though both groups achieved equal analgesia, the FNB group had significant reduction in opioid-induced side effects and, therefore, had more satisfied patients.
There are several possible explanations for the analgesic difference seen between the present study and that of Tarkkila et al. (9). First, Tarkkila et al. (9) used a larger dose of IT morphine. The analgesic efficacy of intrathecal morphine is dose related (8). Second, we added clonidine to the femoral block, which has been shown to improve the analgesia of peripheral nerve blocks (10). Finally, the enhancement in analgesic efficacy after the femoral nerve blockade may have also been the result of using an ultrasound to identify the pertinent anatomy. It has been demonstrated that ultrasound guidance improves the sensory analgesia after femoral three-in-one nerve blocks (11). An additional difference between the studies is that our patients received IV morphine postoperatively, as opposed to IM oxycodone in the previous study, which could have contributed to a different side effect and analgesic profile.
In the present study, a single injection femoral nerve block was used for its simplicity and efficiency. All patients were assessed for cold sensory levels on the anterior thigh to confirm the nerve block. We acknowledge that a continuous nerve block may provide even better pain control, extending past the 24-h study period. The downsides to a continuous infusion are the infection risk of an indwelling catheter (12) and a prolonged motor block that could impair early mobilization. In addition, placing a continuous catheter can be technically more difficult and time consuming as compared with a single injection procedure.
To get complete postoperative analgesia, one would have to perform a true femoral 3-in-1 block or lumbar plexus block coupled to a sciatic nerve block. Although the need for the addition of the sciatic nerve block is controversial (4), we believe that it explains the reason for the morphine consumption in the FNB group. There are sacral plexus osteotomes and dermatomes involved in the operative dissection in TKA. Previous studies examining the role of a femoral nerve block in TKA all demonstrate an opioid requirement postoperatively, supporting the notion that the sciatic nerve is important (2,4,5,9). It should be noted that we did not assess whether or not we obtained successful lateral femoral cutaneous or obturator blocks. Therefore, some of the postoperative pain could have been from these nerve distributions.
The reason there was no difference between the ITM and FNB groups with respect to VAS scores and morphine consumption is unclear. The duration of the femoral nerve block was quite variable, with 20% having no sensory level by 12 hours. It is possible that the analgesic affect of IT morphine varies to a similar extent. This notion is supported by Bailey et al. (8), who found the maximal analgesic effect of IT morphine in volunteers occurred between hours 4 and 7 using variable doses. This analgesic effect then declined after 7 hours towards baseline at 10–15 hours.
There are two major criticisms of our study design. First, we did not measure secondary outcome variables such as success of physical therapy, time to discharge, and cost analysis. Second, we collected data only for the first 24 h postoperatively. This decision was based on our institution’s predefined clinical pathway. In this clinical pathway, patients must be weight-bearing with recovery of quadriceps strength on postoperative day 1. To achieve this goal, the treatments in the two groups consisted of analgesic approaches that would not produce motor weakness for the first physical therapy session. Given the resolution of IT and peripheral nerve analgesia by postoperative day 1, we did not expect any significant differences beyond 24 hours. Although this study does not address differences in the aforementioned secondary outcome variables, we do demonstrate increased patient satisfaction and fewer side effects with a femoral nerve block.
It should be noted that there is currently no universally agreed-upon technique for measuring pain (13). In our study, we chose to measure morphine consumption as an objective assessment of pain and use VAS scores as a subjective means of measuring pain intensity. We hoped that, whereas morphine use was an average over time, the VAS scores would be more sensitive in capturing differences in pain during periods of intense stimulation. The VAS scoring system has been validated in several studies (14,15). The obvious downside to using morphine consumption as a marker of pain is that patients may use morphine for other reasons besides pain.
This study supports the notion that a single shot femoral nerve block provides side effect sparing analgesia (Table 3). The 30% incidence of moderate to severe nausea in the FNB group was most likely attributable to the supplemental IV opioid use. Although speculative, this morphine use was most likely needed to provide analgesia in the sciatic nerve distribution. Therefore, two future research projects could be performed. The first would couple the femoral nerve block with small doses of IT morphine and clonidine. The hypothesis of this future study would be that the dose of these IT drugs will simultaneously provide analgesia for the sciatic nerve distribution and maintain an acceptable level of side effects. The other study would emulate a combined femoral and sciatic nerve block in comparison with IT analgesia.
In conclusion, we compared postoperative analgesia and side effects between IT morphine and a single injection femoral nerve block in patients having a unilateral TKA under IT anesthesia. Patients experienced equal postoperative analgesia, whereas the FNB group sustained fewer side effects, including nausea, vomiting, and itching. Patients receiving IT morphine were overall less satisfied, presumably attributable to IT opioid-induced adverse effects. Both techniques are insufficient to provide complete postoperative analgesia.
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Acknowledgments |
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Supported, in part, by a Quality Research Grant sponsored by Dartmouth Medical School.
The authors are grateful for the excellent help during the study by our research nurse Janice Gregory, RN.
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References |
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- Bonica J. Postoperative pain. In: Bonica J, ed. The management of pain, 2nd ed. Philadelphia: Lea & Febiger, 1990: 461–80.
- Singelyn F, Deyaert M, Pebdeville E, Gouverneur J. Effects of intravenous patient-controlled analgesia with morphine, continuous epidural analgesia, and continuous three-in-one block on postoperative pain and knee rehabilitation after unilateral total knee arthroplasty. Anesth Analg 1998; 87: 88–92.
[Abstract/Free Full Text] - Horlocker T, Hebl J, Kinney M, Cabanela M. Opioid-free analgesia following total knee arthroplasty: a multimodal approach using continuous lumbar plexus (psoas compartment) block, acetaminophen, and ketorolac. Reg Anesth Pain Med 2002; 27: 105–8.[Web of Science][Medline]
- Allen HW, Liu SS, Ware PD, et al. Peripheral nerve blocks improve analgesia after total knee replacement surgery. Anesth Analg 1998; 87: 93–7.
[Abstract/Free Full Text] - Capdevila X, Barthelet Y, Bivoulet 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]
- Sites B, Beach M, Biggs R, et al. Intrathecal clonidine added to a bupivacaine-morphine spinal anesthetic improves postoperative analgesia for total knee arthroplasty. Anesth Analg 2003; 96: 1083–8.
[Abstract/Free Full Text] - Grace D, Bunting H, Milligan KR, Fee JPH. Postoperative analgesia after co-administration of clonidine and morphine by the intrathecal route in patients undergoing hip replacement. Anesth Analg 1995; 80: 86–91.[Abstract]
- Bailey P, Rhondeau S, Schafer P, et al. Dose response pharmacology of intrathecal morphine in human volunteers. Anesthesiology 1993; 79: 49–59.[Web of Science][Medline]
- Tarkkila P, Tuominen M, Huhtala J, Lindgren L. Comparison of intrathecal morphine and continuous femoral 3-in-1 block for pain after major knee surgery under spinal anesthesia. Eur J Anaesthesiol 1998; 15: 6–9.[Medline]
- Casati A, Magistris L, Fanelli G, et al. Small-dose clonidine prolongs postoperative analgesia after sciatic-femoral nerve block with 75% ropivacaine for foot surgery. Anesth Analg 2000; 91: 388–92.
[Abstract/Free Full Text] - Marhofer P, Schrogendorfer K, Koinig H, et al. Ultrasound guidance improves sensory block and onset time of three-in-one blocks. Anesth Analg 1997; 85: 854–7.[Abstract]
- Cuvillon P, Ripart J, Lalourcey L, et al. The continuous femoral nerve catheter for postoperative analgesia: bacterial colonization, infectious rate and adverse effects. Anesth Analg 2001; 93: 1045–9.
[Abstract/Free Full Text] - Turk D, Melzack R. The measurement of pain and the assessment of people experiencing pain. In: Turk D, Melzack R, eds. Handbook of pain assessment, 2nd ed. New York: The Guilford Press, 2001: 9.
- Jensen MP, Karoly P, Braver S. The measurement of clinical pain intensity: a comparison of six methods. Pain 1986; 27: 117–26.[Web of Science][Medline]
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