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The value of continuous blockade of the lumbar plexus as an adjunct to acetylsalicyclic acid for pain relief after surgery for femoral neck fractures

Spansberg, N. L. M.; Anker-Møller, E.; Dahl, J. B.; Schultz, P.; Christensen, E. F.

European Journal of Anaesthesiology: July 1996 - Volume 13 - Issue 4 - p 410-412
Original Papers

In a randomized, double-blind investigation the analgesic effect of continuous blockade of the lumbar plexus as an adjunct to acetylsalicyclic acid by suppository after surgery for femoral neck fractures under spinal anaesthesia was examined in 20 patients. Before surgery, a catheter was inserted into the femoral nerve sheath. The patients were allocated randomly to receive bupivacaine or saline by bolus and then continuous infusion, started immediately after the operation. No statistically significant differences in additional morphine requirements, visual analogue pain scores or adverse effects were observed between the two treatment groups. It is concluded that continuous blockade of the lumbar plexus as an adjunct to rectal acetylsalicyclic acid offers no major additional pain relief after surgery for femoral neck fractures under spinal anaesthesia.

Department of Anaesthesiology, Aarhus Amtssygehus, University Hospital of Aarhus, DK-8000 Århus C, Denmark

Accepted August 1994

Correspondence: E. Anker-Møller, Dyrehavevej 27, DK-8000 Århus C, Denmark.

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Post-operative morbidity after surgery for femoral neck fracture in the elderly includes pulmonary dysfunction and mental confusion, which may be made worse by pain and opioids. Continuous blockade of the lumbar plexus may be better than conventional opioid-based methods of post-operative pain relief, with their inevitable systemic side effects [1-3]. Nonsteroidal anti-inflammatory drugs certainly reduce pain and the need for opioids after major orthopaedic surgery [4-6].

This study was designed to evaluate the analgesic effect of continuous blockade of the lumbar plexus as an adjunct to rectal acetylsalicylic acid after surgery for femoral neck fracture under spinal anaesthesia.

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Patients and methods

Twenty patients with femoral neck fractures were included in the study. Informed consent was obtained from all patients, and the study was approved by the local Ethics Committee and the Danish National Health Service.

Premedication consisted of diazepam 0.25 mg kg−1 orally 1 h before surgery. Before the operation a catheter was placed in the fascial sheat of the femoral nerve. The femoral artery was identified just below the inguinal ligament and a 14 s.w.g. intravenous (i.v.) infusion cannula (Viggo, Sweden) was inserted just lateral to the artery. The femoral nerve was identified with a nerve stimulator (Biometer, Denmark) and a catheter (Portex, epidural, 16 s.w.g.) was inserted and advanced 8-15 cm cranially. All patients underwent spinal anaesthesia with 3.5 mL bupivacaine 0.5%. During operation the patients received oxygen 3 L min−1. Immediately post-operatively, the patients were randomly allocated (Medstat computer program, ASTRA, Denmark) to receive either bupivacaine (bolus: 0.4 mL kg−1 bupivacaine 0.5%; continuous infusion: 0.14 mL kg−1 h−1 bupivacine 0.25%) or saline in identical volumes via the lumbar plexus catheter. Infusions of bupivacaine or saline were maintained for 16 h postoperatively. Patients, recovery staff and observers were blind to the solution used.

All patients received 1.5 g acetylsalicylic acid by suppository every 6 h beginning immediately after operation, which is routine in this department. Patients received 2.5 mg morphine i.v. on demand for the first 2 h after operation, and 0.125 mg kg−1 morphine intramuscularly (i.m.) on demand for the next 14 h. This was administered by recovery ward nursing staff, experienced in the treatment of post-operative pain.

The demand for morphine in the first 16 h after the operation was recorded. Pain severity was expressed by the patient on a visual analogue scale (0-100 mm: 0 mm, no pain; 100 mm, worst pain imaginable) at 0, 2, 4, 6, 8, 12 and 16 h after surgery. Cutaneous sensation to pin prick in the areas innervated by the femoral and obturator nerves and the lateral cutaneous nerve of thigh was sought. Nausea and vomiting, haematomas at the site of the femoral catheter, and the need for catherization of the urinary bladder were recorded.

Data are described by median and range. The Mann-Whitney U-test and Friedmann's two-way analysis of variance were used for statistical calculations. The level of significance was P<0.05.

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The two groups of patients were comparable (Table 1).

Table 1

Table 1

The median use of morphine in the first 16 h was 12.5 mg (range 0-29 mg) in patients receiving saline (P=0.24). No significant differences in visual analogue pain scores were observed between the groups (Fig. 1).

Fig. 1

Fig. 1

Nine of the 10 patients receiving bupivacaine, were analgesic to pin prick in the distribution of all three nerves. The other patient was analgesic only in the distribution of the lateral femoral cutaneous nerve of thigh. No patient treated with saline was analgesic.

Two patients in each group experienced nausea and vomiting. One patient in each group developed urinary retention requiring catheterization. There were no haematomas at the site of the femoral catheters.

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A combination of different analgesics or methods of pain relief may be better than single-drug regimens. The additive effects of combining neural blockade by cryoanalgesia with non-steroidal anti-inflammatory drugs (NSAID) have been shown [7]. Spinal anaesthesia using a long-acting local anaesthetic provides more prolonged post-operative pain relief than general anaesthesia, and fixed NSAID regimens are effective for post-operative analgesia after major orthopaedic surgery, reducing opioid requirements by up to 60% [4-6].

There is a worry that peri-operative NSAIDs may increase the risk of bleeding [8]. In this study, signs of impaired coagulation were not sought, but NSAID (acetylsalicylic acid) was given after surgery.

Blockade of the lumbar plexus, in uncontrolled studies, was claimed to be effective after surgery on the femoral neck [1-3]. In a recent randomized study, lumbar plexus blockade combined with subcostal nerve block reduced the opioid requirement following surgery for femoral neck fracture under general anaesthesia [9]. In other controlled studies, continuous blockade of the lumbar plexus reduced pain and opioid requirements after knee arthroplasty [10] and open knee surgery [11]. However, we saw no advantages of continuous lumbar plexus blockade, either in opioid requirements or pain scores, nor in the frequency of adverse effects.

The power of our study was low since only 20 patients were included (Type 1 error: 5%, Type 2 error: 10%), but we were interested only in a large (>50%) reduction in morphine consumption and pain intensity because the use of resources (application of a catheter, use of infusion pump) and the invasive nature of the method have to be balanced against any possible advantages.

In conclusion, the addition of continuous blockade of the lumbar plexus to post-operative rectal acetylsalicylic acid provides no important additional pain relief after surgical correction of a fractured neck of femur under spinal anaesthesia.

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© 1996 European Academy of Anaesthesiology