Pain relief after thoracotomy
London, UK
* E-mail: i.mcgovern{at}rbht.nhs.uk
Editor—We read with interest the editorial regarding alternatives to epidural analgesia after thoracotomy1 and congratulate the authors on their account of the pathophysiology of pain after thoracotomy. However, we are concerned that their advocacy of intrathecal morphine as an adjunct to paravertebral analgesia in place of thoracic epidural analgesia may be over-enthusiastic.
It is widely believed that intrathecal morphine will provide analgesia for up to 24 h before additional administration of opioid is required.2 After a single intrathecal dose of opioid, the subsequent means of delivering opioid would be via an i.v. patient-controlled analgesia (PCA) system. Even when combined with a paravertebral infusion of local anaesthetic solution, supplementary systemic opioids will be required after 24 h. There is potential for significant respiratory depression during the overlapping of the residual intrathecal opioid and the subsequent i.v. opioid. On a more practical note, the presence of a concurrent paravertebral local anaesthetic infusion necessitates the use of a second infusion device with cost and risk management implications. An epidural catheter with a single infusion of a combination of local anaesthetic and opiate can safely be left in situ for up to 72 h and avoids the need for a second infusion device.
We recognize that in a large case series of patients undergoing mainly non-thoracic surgical interventions, the serious adverse effects of intrathecal opioid administration, with a dose range of 0.2–0.8 mg, are relatively low (3%).3 Our experience would suggest that in the rather elderly and often respiratory-impaired thoracic surgical patient population the incidence is somewhat greater. In our randomized-controlled study looking at the role of intrathecal morphine as an adjunct to i.v. PCA after thoracoscopic talc pleurodesis surgery, we found that a single lumber intrathecal injection of preservative-free morphine (5 µg kg–1, range 0.25–0.5 mg) resulted in a 10% incidence of respiratory depression requiring treatment with naloxone.4
In discussing the side-effects of thoracic epidural analgesia when compared with paravertebral administration of local anaesthesia, we would suggest that the hypotension often associated with thoracic epidural analgesia and, perhaps to a lesser extent, paravertebral blockade5 is largely due to an unmasking of underlying hypovolaemia and can usually be alleviated with appropriate and judicious fluid replacement. We note that the studies that demonstrated a greater hypotensive effect with epidural block used a bupivicaine 0.25% infusion regime. Our practice is to combine levo-bupivicaine 0.125% with fentanyl 4 µg ml–1 in our thoracic epidural infusions. Hypotension requiring vasoconstrictor therapy is rarely a problem.
We have been unable to find a randomized controlled trial comparing thoracic epidural analgesia with the combination of intrathecal opioids and paravertebral analgesia in thoracotomy patients. The review of Davies and colleagues5 concedes that ‘negative studies are less likely to be submitted or accepted for publication and considerable variation can exist between studies in terms of different interventions and different clinical circumstances’. This potential for publication bias should not be ignored when authors commend a potentially useful but untested alternative analgesic technique without the support of randomized-controlled trials.
We applaud the debate Drs Ng and Swanevelder will no doubt stimulate, but feel that any technique for providing pain relief after thoracotomy will have to be compared with the gold standard of a thoracic epidural infusion delivering a combination of local anaesthetic solution and opioid, and must be effective for at least 24 h after operation.
Wolverhampton and Leicester, UK
* E-mail: Alexander.Ng{at}rwh-tr.nhs.uk
Editor—Thank you for the opportunity to respond to this letter. We appreciate the comments as acute and chronic pain after thoracotomy is a problem and thus requires healthy debate.6 7
The first point to which McGovern and colleagues refer is the postoperative administration of i.v. morphine by PCA. We would like to stress that morphine by PCA was neither mentioned nor implied in our Editorial.1 We suggested that a bimodal technique comprising low-dose intrathecal morphine and a paravertebral infusion of local anaesthetic would be effective for analgesia after thoracotomy. In this situation, morphine by PCA would not be required.
In the study in which intrathecal morphine 0.25–0.50 mg and i.v. morphine by PCA were given to patients who had thoracoscopic talc pleurodesis, we were unable to obtain further details of the study. However, naloxone appeared to be necessary in 10% of patients. This problem can occur after administration of opioids by any route, and epidural opioids are also associated with concentration-dependent respiratory depression.8 In addition, we find it surprising that intrathecal morphine was used for management of pain after talc pleurodesis. We suggest that intrathecal morphine should be reserved for video-assisted thoracoscopic procedures that are associated with more tissue damage and nociception, for example decortication and lobectomy. Patients are often taking oral analgesics, which seem to be sufficient to bridge the ‘analgesic gap’ when the effects of intrathecal morphine have dissipated.9
In the third point, they note that epidural analgesia is associated with hypotension which may be managed adequately by fluid administration, without the use of vasoconstrictors. Although this may be applicable for general surgical patients, it may be less so for patients who are at risk of lung injury, after thoracotomy.10 Indeed, patients with limited lung function, particularly those who have had a pneumonectomy, should be given fluids sparingly, and thus we suggest that paravertebral blockade may allow more judicious administration of fluids than epidural analgesia.
The fourth point is concerned with publication bias and intervention studies on pain relief after thoracotomy. From a recent meta-analysis of randomized controlled clinical trials comparing epidural analgesia with paravertebral block, there seems to be reasonable statistical evidence that paravertebral analgesia alone is more optimal for analgesia than a thoracic epidural.5 This inference has arisen, not because paravertebral block is better for pain relief than epidural analgesia, but because it is associated with a significantly lower occurrence of several adverse outcomes, for example hypotension, urinary retention, block failure, and nausea. Such limiting effects may impede recovery and rehabilitation in the postoperative period.11 To provide analgesia before insertion of a paravertebral catheter at the end of surgery, we suggested that low-dose intrathecal morphine would be useful as part of a bimodal analgesic plan.
In conclusion, thoracic epidurals are effective for analgesia after thoracotomy and will be the preferred choice of many anaesthetists. However, we have presented evidence to show that this method may not be the most optimal. We hope that we have rekindled the search for the Holy Grail of pain relief after thoracotomy.
References
1 Ng A, Swanevelder J. Pain relief after thoracotomy: is epidural analgesia the optimal technique? Br J Anaesth (2007) 98:159–62.
2 Neustein SM, Cohen E. Intrathecal morphine during thoracotomy, Part II: effect on postoperative meperidine requirements and pulmonary function tests. J Cardiothorac Vasc Anesth (1993) 7:157–9.[CrossRef][Medline]
3 Gwirtz KH, Young JV, Byers RS, et al. The safety and efficacy of intrathecal opioid analgesia for acute postoperative pain: seven years' experience with 5969 surgical patients at Indiana University Hospital. Anesth Analg (1999) 88:599–604.
4 Walker C, Cox F, Wilton P, et al. Intrathecal (IT) morphine as an adjunct to intravenous (i.v.) patient-controlled analgesia (PCA) in thoracoscopic talc pleurodesis surgery. 13th World Congress of Anaesthesiologists, 2004: Paris, France.
5 Davies RG, Myles PS, Graham JM. A comparison of the analgesic efficacy and side-effects of paravertebral vs epidural blockade for thoracotomy—a systematic review and meta-analysis of randomized trials. Br J Anaesth (2006) 96:418–26.
6 Ochroch EA, Gottschalk A, Augostides J, et al. Long-term pain and activity during recovery from major thoracotomy using thoracic epidural analgesia. Anesthesiology (2002) 97:1234–44.[CrossRef][Web of Science][Medline]
7 Senturk M, Ozcan PE, Talu GK, et al. The effects of three different analgesia techniques on long term postthoracotomy pain. Anesth Analg (2002) 94:11–5.
8 Tan CNH, Guha A, Scawn NDA, Pennefather SH, Russell GN. Optimal concentration of epidural fentanyl in bupivacaine 0.1% after thoracotomy. Br J Anaesth (2004) 92:670–4.
9 Ng A, Hall F, Atkinson A, Kong KL, Hahn A. Bridging the analgesic gap. Acute Pain (2000) 3:172–80.
10 Baudouin SV. Lung injury after thoracotomy. Br J Anaesth (2003) 91:132–42.
11 Bonnet F, Marret E. Influence of anaesthetic and analgesic techniques on outcome after surgery. Br J Anaesth (2005) 95:52–8.
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