CORRESPONDENCE |
Perioperative analgesia for knee arthroplasty
E-mail: joerg.kuehne{at}ntlworld.comEditor—I welcome the study by Davies and colleagues1 comparing epidural infusion with combined single shot femoral and sciatic nerve block for perioperative analgesia after knee arthroplasty. The use of nerve blocks for this procedure is well established in other countries but appears to be used infrequently in the UK. The findings may not come as a surprise to the enthusiast and many of the results in this paper have been demonstrated before.
The Authors suggest the use of a continuous sciatic nerve block, in addition to a continuous femoral block, to improve the quality of analgesia instead of the single shot technique used in this study. Using continuous femoral nerve block, in my experience the addition of a single shot sciatic block with bupivacaine 0.25%, 20 ml is sufficient and thus avoids the problem of prolonged motor blockade and difficult catheter insertion.
McNamee's study2 demonstrates a reduction in morphine consumption when an obturator block is added; however, there was no statistically significant difference in the VAS pain scores. I add a separate obturator block postoperatively if the patient complains of severe pain on the medial aspect of the knee, which fails to respond to a top up of the femoral nerve catheter. Magnetic resonance imaging studies show that the spread of local anaesthetic after a femoral nerve block is not proximal but caudal, lateral and slightly medial.3 This usually reaches the anterior branch of the obturator nerve.
The postoperative nausea and vomiting (PONV) rate was similar between the two groups. The true incidence and possible difference between the two analgesic modalities may have been clouded by the choice of the general anaesthesia (GA) technique and subsequent use of morphine. Apfel and colleagues4 showed recently in a large randomized controlled trial with 5199 patients a reduction in the likelihood of PONV by about a quarter when comparing a standard inhalational with a total i.v. GA technique (41 vs 29%).
The Authors state that the maximum bupivacaine dose used was 3 mg kg–1, which is 50% above the maximum recommended dose. This dose has been shown in one study with 22 patients not to produce any clinical signs of local anaesthetic toxicity. Plasma levels were not measured.5 The large volumes of high dose local anaesthetic needed to provide surgical anaesthesia to the lower limb causes unease with some colleagues and may deter many from using this technique. This issue has been raised elsewhere and the safety of this and possibly even higher doses should be clearly demonstrated and data sheets amended.6
Lastly, Davies and colleagues close their discussion by rightly pointing out that alternative practices should not confer a disadvantage and ideally offer some additional benefit over the reference technique. Although well established, the reference technique (i.e. epidural analgesia) is not necessarily a logical choice to provide perioperative analgesia for total knee replacement (TKR).
Barnstaple, UK
E-mail: hgargi{at}aol.com
Editor—We read with interest the recent article by Davies and colleagues1 on perioperative analgesia for total knee replacement. We entirely agree with their findings that combined femoral and sciatic blocks are a practical alternative to epidural infusion for providing analgesia after TKR. Indeed in our practice, we only very seldom use epidural infusions and almost exclusively perform femoral and sciatic nerve blocks for TKR. However, one in four patients referred to our hospital with end-stage knee osteoarthritis undergo a unicompartmental knee replacement (UKR)7 rather than TKR.
Various techniques are used for pain relief after a UKR at our institute which can be broadly classified into four groups: femoral and sciatic nerve blocks, intra-articular infiltration, intra-articular infiltration with local anaesthetic top up the following day, and single shot spinal combined with intra-articular infiltration and top up. The femoral and sciatic nerve blocks are given in a standard fashion using 20 ml of 0.375% bupivacaine for each block. Intra-articular infiltration involves a mixture of ropivacaine 300 mg, adrenaline 500 µg and ketorolac 30 mg with normal saline added to make a volume of 100 ml. This is infiltrated into the soft tissues in the surgical field including the knee capsule as well as the skin incision. The local anaesthetic top up consists of bupivicaine 0.5%, 20 ml injected into the knee joint on the following morning through a 16G epidural catheter inserted into the knee joint at the time of operation. The spinal anaesthetic is given using 12.5–15 mg of heavy bupivacaine.
We conducted a prospective audit to assess the efficacy of these methods in achieving adequate pain control in the first 48 h after Oxford UKR using a minimally invasive surgical technique. Eighty-nine consecutive patients who underwent cemented medial Oxford UKR were included in the audit. Patients were allocated to one of the four groups: Group I, GA plus femoral and sciatic block (n=25); Group II, GA plus local infiltration (n=25); Group III, GA plus local infiltration plus top-up on next morning (n=22); and Group IV, spinal anaesthetic plus local infiltration plus top-up next morning (n=17). All patients were prescribed morphine as rescue analgesia and received regular acetaminophen and ibuprofen. Pain scores were collected every 6 h for the first 24 h using a visual analogue scale (VAS, 0–10) and morphine requirements were also noted. Patients in Groups I and IV had significantly less pain (P<0.05) than those in Groups II and III, in the first 6 h after surgery. In general, the pain was less severe in these Groups (I and IV) throughout the first day, however, it did not reach statistical significance. Patients in Groups III and IV (groups with top-up of local anaesthetic next morning) had less pain during the second day and night, however, this did not reach statistical significance.
These findings have important implications in decision-making regarding patient mobilization and early discharge after a UKR and warrant further investigation.
Oxford, UK
E-mail: anthony.davies{at}phnt.swest.nhs.uk
Editor—Thank you for the opportunity to respond to Dr Kühne's comments. The authors would agree that a continuous femoral block is more likely to have a positive effect on overall analgesia than a supplementary continuous sciatic technique. The latter, is technically challenging and there is considerable debate over the importance of the sciatic component to post-knee arthroplasty analgesia. The authors do not undertake separate obturator blocks and would welcome evidence-based research to clearly define its potential role in suboptimal femoral/sciatic blocks.
The choice of GA will obviously affect the incidence of PONV and it is now clearly established that a total intravenous anaesthesia (TIVA) technique can lower PONV rate. The GA was standardized in this study to minimize any differential effect between groups. The other comparative studies quoted in the article also show little difference in incidence of PONV between epidural and nerve block analgesic techniques.
Dr Kühne refers to Misra and colleagues5 study of bupivacaine doses. This study did in fact look at serum levels as well as clinical signs of local anaesthetic toxicity. The plasma levels found were reassuring for those who routinely use 3 mg kg–1 in the anterior femoral and sciatic compartment. The authors would, however, suggest that this study should be repeated with levobupivacaine in view of the increasing clinical use of this single isomer local anaesthetic.
Dr Kühne raises issues with epidural analgesia being the reference technique. Femoral and sciatic blocks may well supersede this central neuraxial technique for knee arthroplasty analgesia. Indeed, this study has already been instrumental in facilitating a shift in clinical practice locally.
The letter from Varanese and colleagues strongly supports the use of combined femoral and sciatic nerve blocks for TKRs. They highlight the results of their recent prospective audit of four potential analgesic techniques for UKRs. We would agree that this area warrants further research in view of the increasing use of this surgical technique.
Plymouth, UK
References
1 Davies AF, Segar EP, Murdoch J, Wright DE, Wilson IH. Epidural infusion or combined femoral and sciatic nerve blocks as perioperative analgesia for knee arthroplasty. Br J Anaesth 2004; 93: 368–74
2 McNamee DA, Parks L, Milligan KR. Post-operative analgesia following total knee replacement: an evaluation of the addition of an obturator nerve block to combined femoral and sciatic nerve block. Acta Anaesthesiol Scand 2002; 46: 95–9[CrossRef][Web of Science][Medline]
3 Marhofer P, Nasel C, Sitzwohl C, Kapral S. Magnetic resonance imaging of the distribution of local anesthetic during the three-in-one block. Anesth Analg 2000; 90: 119–24
4 Apfel CC, Korttila K, Abdalla M, Kerger H, IMPACT Investigators. A factorial trial of six interventions for the prevention of postoperative nausea and vomiting. N Engl J Med 2004; 350: 2441–51
5 Misra U, Pridie AK, McClymont C. Plasma concentrations of bupivacaine following combined sciatic and femoral 3-in-1 nerve blocks in open knee surgery. Br J Anaesth 1991; 66: 310–13
6 Kühne J. Loco-regional anaesthesia for a total knee arthroplasty in a high-risk cardiac patient. Acta Anaesthesiol Scand 2004; 48: 135–6[CrossRef][Web of Science][Medline]
7 Price AJ, Webb J, Topf H, Dodd CAF, Goodfellow JW, Murray DW. Rapid recovery after Oxford unicompartmental arthroplasty through a short incision. J Arthroplasty 2001; 16: 970–6[CrossRef][Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||