Major knee surgery is in most cases associated with moderate or severe post-operative pain. Although intrathecal morphine has been shown to be effective against pain after hip prosthesis surgery [2,3] it has been insufficient after major knee surgery . Side effects such as nausea, vomiting, urinary retention and pruritis also limit the usefulness of this technique. Continuous blockade of the lumbar plexus for pain after knee prosthesis surgery has given promising results . The purpose of this randomized prospective study was to compare intrathecal morphine and continuous femoral 3-in-1 [5,6] block for pain after major knee surgery.
The study was approved by the Ethics Committee of the hospital and informed consent was obtained from each patient. Forty patients (ASA Grade I-III) undergoing major knee surgery (total knee replacement or open ligament surgery were studied).
Premedication was with oral diazepam 10-20 mg 1 h before arrival in the operating theatre. All patients received spinal anaesthesia with isobaric 0.5% bupivacaine 20 mg. The subarachnoid puncture was performed in the midline of L3-4 interspace using a 27-gauge spinal needle. In a random order, 20 patients received a single dose of preservative free morphine 0.3 mg mixed with bupivacaine (morphine group). In the remaining 20 patients, who had similar spinal anaesthesia without morphine, a femoral 3-in-1 block was performed post-operatively (femoral group). The femoral plexus was identified using a nerve stimulator (Dualstim®, Life-Tech, USA). A cannula (Contiplex®, B. Braun-Melsungen, Germany) was introduced into the femoral sheath. A catheter was then inserted through the cannula 10 cm into the femoral sheath. Initially, 0.5% bupivacaine 2 mg kg−1 was injected through the catheter for a 3-in-1 block. An infusion of bupivacaine 0.25% at a rate of 0.1 mL kg−1 h−1 was started and continued until the next morning. The femoral block was considered adequate if analgesia was still found by pin prick on the first post-operative morning.
Oxycodone 0.1-0.14 mg kg−1, intramuscular (i.m.) was given as a rescue analgesic to all patients according to age on request. Droperidol 1.25 mg i.m. was given in case of persistent nausea and vomiting. On the ward the patients were allowed to drink and eat light meals.
Pain was assessed using a verbal rating scale at 3-h intervals: 0 = no pain, 1 = mild pain, 2 = moderate pain, and 3 = severe pain. Post-operative side effects (nausea, vomiting, itching, sedation and urinary difficulties) and request for additional analgesic were noted by the authors or by trained nurses during the patients' stay in the operating theatre and in the recovery room, and also on the ward by trained nurses for 24 h after induction of the spinal anaesthesia. The investigators interviewed all patients on the first post-operative morning.
The results are expressed as mean ± SD. Data were analysed with repeated measurements Anova with Bonferroni correction, Kruskal-Wallis test, χ2-test or Fisher's exact test where appropriate. A P-value less than 0.05 was considered significant.
The groups were comparable with respect to demographic or anaesthesiological data (Table 1). In both groups there were 17 knee prosthesis operations and three major ligament operations. Three patients in the morphine group and one patient in the femoral group did not request any additional oxycodone. In the morphine group on average 2.8 ± 2.1 (range 0-7) additional doses of oxycodone were needed during the study period. This figure was 3.2 ± 1.5 (0-5) doses in the femoral group. Five or more doses of additional opioid were requested by three patients in the morphine group and by five patients in the femoral group in 24 h. The mean pain scores tended to be lower in the morphine group. The difference between the groups was statistically significant at the 9 and 12 h recording points (P<0.01 and <0.05, respectively) (Fig. 1). The mean pain scores in the femoral group were also statistically different from the base-line at the same recording points (P<0.01 and <0.05, respectively).
One femoral block was inadequate despite successful identification of the femoral nerve with a nerve stimulator. After insufficient pain relief the inadequacy of the block was verified also by pin prick. Another patient's femoral catheter was dislodged about 8 h after the insertion. Results from these two patients were excluded.
The incidence of itching was 40% in the morphine group. None of the patients in the femoral group suffered from itching (P<0.01). The incidence of other side effects were similar in the two groups (Table 1). All patients in both groups were satisfied with their pain therapy at the interview on the first post-operative morning.
In this study, major knee surgery resulted in moderate or severe pain and a request for additional opioid by 90% of the patients despite prophylactic pain therapy. Both intrathecal morphine and continuous femoral 3-in-1 block alone were insufficient for post-operative analgesia in these patients. The effect of morphine for post-operative pain tended to be more constant than that of femoral block. In the morphine group, the mean pain scores remained below 1 (mild pain) until mobilization on the following morning. In the femoral group, the mean pain scores varied between 1 and 2 (mild to severe pain) at the 9 h and 12 h recording points.
A visual analogue scale (VAS) is often used in similar studies. However, in clinical practice we have found the use of VAS to be difficult in older patients. Therefore we used a verbal rating scale(VRS) in the present study. According to Tigerstedt and Tammisto , a VAS does not seem to offer any advantages over a VRS when assessing analgesic efficacy in the immediate post-operative period.
Adding morphine to intrathecal bupivacaine before the spinal block is a simple and reliable means of pain relief. After subarachnoid block, morphine reaches the central nervous system within 60 min . The dose of morphine (0.3 mg) was chosen to compare with that used in previous studies in major joint surgery [3,9]. The clinical benefit of a higher dose of morphine may have been questionable because of the risks of respiratory depression, urinary retention, sedation and itching. We also did not have a femoral block with placebo in the morphine group. The potential complications induced by the placebo block were considered unethical.
In previous studies, better pain relief has been achieved with the femoral block after major knee surgery [5,6,10]. In the series by Edwards et al. six of the 19 patients (32%) who had total knee replacement under general anaesthesia followed with continuous femoral block with 0.125% bupivacaine, did not need supplemental analgesics post-operatively. In the study by Dahl et al., 40% of the patients with a continuous femoral block for open knee-joint surgery, did not need any additional analgesics.
In the present study, only one patient of the 18 (6%) with adequate continuous femoral block, was pain-free. We can offer no explanation for this difference. Probably our patients had more severe surgical trauma, or less rigorous criteria for 'patient request' were used. However, in all of these quoted studies some patients requested several doses of analgesics despite successful femoral block.
The patients in the femoral group often specified that the pain was coming from the distal part of the extremity, indicating that the sciatic nerve may have been involved with the pain sensation. Therefore, one cannot expect any clinical benefit from a higher dose of bupivacaine. Combined sciatic and femoral 3-in-1 nerve blocks have been successfully used by Misra and colleagues . They used bupivacaine in a dose of 3 mg kg−1 which exceeds the recommended dose. Despite that, they found neither clinical signs of toxicity nor plasma concentrations of bupivacaine greater than 2 mg ml−1. However, if the sciatic nerve is blocked with simultaneous femoral block, the simplicity of the method is lost and the risk of toxic reactions increases. Probably a real multimodal regime including optimal combination therapy with local anaesthetics and analgesics would enhance the analgesic power for severe pain after major knee surgery without increasing the risk of side effects.
Intrathecal morphine has been shown to significantly increase the incidence of post-operative side effects (nausea, vomiting, urinary retention and itching) [9,13]. In the present study the incidence of side effects was not different between the groups. Itching was associated only with intrathecal morphine. A 40% incidence of itching in the morphine group is comparable with earlier studies . Schultz et al. achieved similar pain relief after open knee surgery with continuous lumbar plexus block and epidural morphine 4 mg. In their study, the incidence of side effects after epidural morphine was higher than in our patients following intrathecal morphine. This difference may be due to the different doses and routes of administration. After lumbar plexus block the incidence of side effects reported by them was smaller than in the present study. The high incidence of side effects in the present study may be related to prosthesis surgery.
In conclusion, intrathecal morphine tended to be more effective than femoral 3-in-1 block for pain after major knee surgery. However, additional i.m. opioid was needed for adequate pain relief in both groups. Despite patient satisfaction more effective pain treatment still needs to be sought.
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