Postoperative pain after total hip arthroplasty (THA) can be difficult to control. It is severe in half of patients at rest and is often exacerbated on movement or by severe reflex spasms of the quadriceps muscle (1). Postoperative pain relief can be achieved by a variety of techniques, such as IV patient-controlled analgesia (PCA) (2,3), epidural analgesia (3,4), and lumbar plexus blockade (5–7). Recently, it has been shown that extended femoral nerve sheath block provides comparable pain relief but is associated with fewer side effects and technical problems than IV PCA or patient-controlled epidural analgesia (PCEA) (6). It is therefore the preferred analgesic technique after unilateral THA.
The continuous infusion of 0.125% bupivacaine at the rate of 10 mL/h is effective to maintain extended femoral nerve sheath block (6). However, this technique leads to the administration of large volumes of local anesthetic with a potential risk of toxicity caused by accumulation of the drug after a prolonged period of infusion (8). A dose-sparing infusion technique is thus desirable. For example, after hand trauma surgery, a PCA technique via an axillary brachial plexus catheter provides good postoperative analgesia and reduces local anesthetic consumption by 70%(9). This technique has not yet been evaluated with a femoral nerve sheath catheter. The aim of the present study was to assess its efficacy after unilateral THA.
After informed consent and with IRB approval, 45 ASA class I–III patients scheduled for elective unilateral THA under general anesthesia were included in this study. Patients were excluded if they had coagulation abnormality, were aged <18 or >80 yr, weighed <50 or >100 18 or 80 yr, weighed 50 or 100 kg, had a preexisting neurological deficit or diabetes, or were unable to understand pain scales or use a PCA device.
In all patients, a femoral nerve sheath block was performed before the induction of general anesthesia by using the landmarks of Winne et al. (10). The femoral artery was located below the inguinal ligament, and a 6-cm, 18-gauge, short-beveled, insulated needle through a plastic cannula (Alphaplex® set; Braun, Melsungen, Germany) was inserted just lateral to the artery. The femoral nerve was accurately located with a peripheral nerve stimulator (pulse duration, 40 μs; frequency, 1 Hz) (Anaestim MK III®; Meda, Antwerpen, Belgium). With a starting output of 100 nanocoulombs (nC) (2.5 mA), the needle was advanced with an angle of 30–45° to the skin until twitches of the quadriceps muscle (ascension of the patella) were elicited. Its position was then optimized and judged adequate when output lower than 40 nC (<1 mA) still elicited quadriceps contractions. By using a Seldinger technique, a 20-gauge catheter was then threaded 10–15 cm into the femoral nerve sheath. After a negative aspiration test for blood, 40 mL 0.25% bupivacaine with epinephrine 1:200,000 was injected through the catheter.
In all patients, general anesthesia was induced with 0.3 μg/kg sufentanil, 3–5 mg/kg thiopental, and 0.5 mg/kg atracurium. The trachea was intubated, and controlled ventilation was started. Anesthesia was maintained with a sufentanil infusion (0.005 μg · kg–1 · min–1 stopped approximately 45 min before the end of the procedure) and a mixture of nitrous oxide (66%) and isoflurane (0.5%–1%) in oxygen.
In all patients, ketorolac 30 mg IV was administered at the induction of general anesthesia and then three times daily during the first 48 h after surgery.
Thromboprophylaxis was given routinely with low-molecular-weight heparin, i.e., 7500 (<70 kg) or 10,000 (>70 kg) units nadroparin (Fraxiparine®; Sanofi-Winthrop, New York, NY) subcutaneously, and antiplatelet drug, i.e., 600 mg buflomédil (Loftyl®; Abbott, North Chicago, IL) PO, once daily, starting the evening of surgery.
In the recovery room, the correct position of the femoral nerve sheath catheter was confirmed by the presence of a sensory block (loss of cold sensation as assessed by using an ether-soaked swab) involving the distribution of the femoral nerve (anterior aspect of the thigh). Patients were then divided into three groups of 15 in a randomized fashion with a computer-generated list of random permutations. During the first 48 h after surgery, Group 1 received a continuous infusion of 0.125% bupivacaine with clonidine 1 μg/mL and sufentanil 0.1 μg/mL at the rate of 10 mL/h, Group 2 had PCA boluses only of 10 mL of the same solution with a lockout time of 60 min, and Group 3 had PCA boluses only of 5 mL of the same solution with a lockout time of 30 min. To blind the study, patients in Group 1 also had access to a PCA button, but it did not trigger any bolus administration.
Pain at rest and on movement (visual analog scale [VAS] ranging from 0 = no pain to 100 = worst pain imaginable) and sensory block (loss of temperature sensation assessed by using an ether-soaked swab) in the cutaneous distribution of the lateral femoral cutaneous (LFC) (lateral aspect of the thigh), femoral (anterior aspect of the thigh), and obturator (inner aspect of the knee) nerves were assessed 4, 24, and 48 h after the operation. A postoperative pain score (PPS) (0 = no pain; 1 = moderate pain only when moving; 2 = moderate pain at rest, severe pain when moving; 3 = constant severe pain) was also recorded by the nurses every 2 h during the first 12 h after surgery and then every 4 h. Supplemental postoperative analgesia was standardized. If PPS was ≥1, patients received 2 g of IV propacetamol, a derivative of paracetamol (Prodafalgan®; Upsamedica, Brussels, Belgium), followed by 10–20 mg of IM piritramide, a synthetic μ-agonist opioid (Dipidolor®; Janssen Pharmaceutica, Beerse, Belgium) if PPS remained unchanged after 30 min. Supplemental analgesia, bupivacaine consumption, side effects, and satisfaction score (with a VAS ranging from 0 = not satisfied to 100 = entirely satisfied) at the end of the study period were recorded. All data were collected by an anesthesiologist not involved in the administration of anesthesia or in patient care in the recovery room.
The patients were seen at the surgeon’s clinic 6 wk and 3 mo after the procedure. They were then asked about any adverse effects or complications.
On the basis of a previous study (11), we hypothesized that we could observe at least a 30% reduction in the consumption of bupivacaine between Groups 1 and 2. A power analysis (mean consumption of 500 [Group 1] and 350 [Group 2] mg of bupivacaine with a standard deviation of 80 mg) estimated that 10 patients would be needed in each group to provide a 95% chance of detecting such reduction at the 0.01 level of significance.
Statistical analysis was performed with the GB-Stat, version 6.5 (Dynamic Microsystems, Inc., Silver Spring, MD) computer package. Parametric data (age, weight, height, pain scores, supplemental analgesia, bupivacaine consumption, and satisfaction score) were compared by using one-way analysis of variance. Post hoc comparisons were performed with Dunnett two-tailed t-test by using Group 1 as the reference control group. PCA demands were analyzed with a Kruskal-Wallis test followed by Wilcoxon’s rank sum test for multiple comparisons. Discrete variables (sex ratio, sensory block, and side effects) were compared by using χ2(2) and Yates correction when appropriate. P < 0.05 was considered significant. Results are expressed as mean ± sd.
Population data are presented in Table 1. No statistically significant difference was noted among the groups. In the recovery room, complete loss of temperature sense in the distribution of the femoral nerve was observed in all patients.
The VAS scores at rest and on movement, nurse PPSs, supplemental analgesia, bupivacaine consumption, and satisfaction scores are presented in Table 2. Pain scores at rest were comparable in the three groups. When compared with Group 1, VAS on movement at 48 h was significantly lower in Group 3 (P < 0.01). Supplemental analgesia was not significantly different among the three groups. When compared with Group 1, bupivacaine consumption was significantly less in Groups 2 and 3 (P < 0.01). No difference was noted between these groups. At 48 h, satisfaction scores were significantly higher in Group 3 when compared with both other groups.
The use of PCA was significantly less frequent (23 ± 27, 54 ± 34, and 84 ± 109 demands per 48 h in groups 1, 2, and 3, respectively [overall P = 0.01]) in Group 1 than in both other groups (P < 0.05).
Sensory block in the cutaneous distribution of the LFC, femoral, and obturator nerves is presented in Table 3. No significant difference was noted among the groups. In the three groups, LFC and femoral nerve blocks were well maintained during the entire study period. Obturator nerve block was more evanescent, particularly in Group 2.
Except for nausea, vomiting, or both (3, 3, and 5 patients in groups 1, 2, and 3, respectively), no side effects or technical problems were noted in the three groups. No complication related to the analgesic technique was observed at 6 wk and 3 mo after the procedure in all patients.
Postoperative pain relief after THA can be achieved by a number of techniques. Because it provides a steady state of analgesia at rest, IV PCA with morphine produces better pain relief than conventional IM opioid therapy (2). However, it does not provide efficient analgesia on movement and is ineffective to prevent or relieve reflex spasms of the quadriceps muscle, which are frequent after hip surgery (12). Different studies have shown that, after hip surgery, epidural or intrathecal morphine gives superior pain relief compared with conventional IM opioids or IV PCA with morphine. However, the benefit in consistency and quality of pain control is offset by side effects, such as nausea, vomiting, pruritus, urinary retention, and a significant risk of respiratory depression (3,13). Epidural local anesthetics, with or without small doses of opioid, provide as efficient analgesia at rest as IV PCA with morphine but better analgesia on movement (4). However, local anesthetics induce some bilateral motor blockade, which makes the patient more nurse dependent, and sympathetic blockade, which requires hemodynamic monitoring.
After unilateral THA, single-dose femoral nerve block (0.5% bupivacaine 40 mL) provided better postoperative analgesia than IV PCA with morphine, but only during the first eight hours after surgery (5). Therefore, different authors have advocated the use of extended femoral nerve sheath block after such surgery (14). In a recent, large-scale (more than 1300 patients), prospective study, we demonstrated that such block is as efficient as IV PCA with morphine or PCEA. Because it induces fewer technical problems and side effects, it is presently the preferred technique (6). This study confirms the analgesic efficiency of extended femoral nerve sheath block after unilateral THA.
A continuous infusion of 0.125% bupivacaine at the rate of 0.14 mL · kg–1 · h–1 is optimal to maintain extended femoral nerve sheath block (15) : neither the extent of anesthesia nor the quality of analgesia is improved by increasing the infusion rate (16). However, this technique leads to the administration of large volumes of local anesthetic with a potential risk of toxicity caused by accumulation of the drug after prolonged periods of infusion (8). In this study, the use of PCA boluses alone provided efficient pain relief and a significant reduction (64% to 73%) in the local anesthetic consumption. Moreover, as expressed by the patients, this technique allowed rapid reinforcement of the block before a hip physiotherapy session. Of the two techniques tested, PCA boluses of five milliliters with a lockout time of 30 minutes were associated with the smallest local anesthetic consumption and the greatest patient satisfaction. It is therefore the recommended extended femoral nerve sheath block technique; however, this technique requires some time to teach the patient. The patient has to learn which pain will be relieved by the catheter (from the anesthetized area) and thus requires a PCA button push, and which pain will not be relieved by the catheter (outside the anesthetized area) and thus requires a nurse call for supplemental parenteral analgesia.
In our study, the extent of anesthesia during extended femoral nerve sheath block varied with time. Although the LFC and femoral nerve blocks were well maintained in the three groups, obturator nerve block was more evanescent, particularly at 48 hours after surgery. Similar results have been obtained by Barthelet et al. (17).
The choice of lockout intervals in our PCA groups was based on experience with PCEA. During PCEA, lockout intervals of at least 15 to 30 minutes are recommended to minimize the possibility of the patient self-administering a bolus dose before the previous dose has had time to exert its analgesic effect (18). Moreover, studies on labor pain relief have shown that the quality of analgesia is unaffected by the duration of the lockout interval as long as effective hourly doses of local anesthetic are administered (19). When considering our previous study during knee surgery (11) and the present one, we can speculate that it would be the same when using a PCA technique for continuous peripheral nerve block. However, further studies are required to confirm this statement.
In accordance with the concept of “balanced analgesia” advocated by Kehlet (20), IV ketorolac was systematically administered to all patients, and clonidine and sufentanil were included in our continuous infusion. When added to the local anesthetic solution, clonidine prolongs the duration of both anesthesia and analgesia after a single-shot brachial plexus block (21). Unpublished data support the same effects during continuous peripheral nerve block. This observation must be confirmed by a large randomized study.
In a recent metaanalysis, Picard et al. (22) concluded that there is no evidence for a clinically significant positive effect of opioids during peripheral nerve blocks. That is why, after the completion of the present study, we no longer add sufentanil to the local anesthetic solution used to maintain extended femoral nerve sheath block. No significant change in the efficiency of the technique was observed.
In this study, there were no complications attributable to the use of PCA techniques. However, the small number of patients does not permit us to make definitive conclusions about its relative safety.
In conclusion, this prospective, randomized, double-blinded study confirmed that, when associated with IV ketorolac, extended femoral nerve sheath block provides efficient pain relief after unilateral THA. It demonstrated that, compared with a continuous infusion, PCA techniques reduce the local anesthetic consumption without compromise in patient satisfaction or VAS scores. Of the two PCA techniques tested, PCA boluses of five milliliters of 0.125% bupivacaine with clonidine 1 μg/mL and sufentanil 0.1 μg/mL with a lockout time of 30 minutes were associated with the smallest local anesthetic consumption and the highest degree of patient satisfaction. It is therefore the recommended technique.
The authors are grateful to F. Veyckemans, MD, and L.J. Van Obbergh, MD, PhD, for their valuable criticism of the manuscript and their comments.
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