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© 2002 International Anesthesia Research Society
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Abstract |
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Despite receiving thoracic epidural analgesia, severe ipsilateral shoulder pain is common in patients after thoracotomy. We recruited 44 patients into a double-blinded randomized placebo-controlled study to investigate whether suprascapular nerve block would treat postthoracotomy shoulder pain effectively. All patients received a standard anesthetic with a midthoracic epidural. Thirty patients who experienced shoulder pain within 2 h of surgery were randomly assigned to receive a suprascapular nerve block with either 10 mL of 0.5% bupivacaine or 10 mL of 0.9% saline. Shoulder pain was assessed before nerve blockade, at 30 min, and then hourly for 6 h after the block using a visual analog scale (VAS) and a 5-point verbal ranking score (VRS). The incidence of shoulder pain before nerve block was 78%. There was no significant decrease in either VAS or VRS in the Bupivacaine group. These results suggest that this pain is unlikely to originate in the shoulder and lead us to question the role of a somatic afferent in referred visceral pain. We conclude that suprascapular nerve block does not treat ipsilateral shoulder pain after thoracotomy in patients with an effective thoracic epidural.
IMPLICATIONS: This randomized, double-blinded, placebo-controlled trial showed that suprascapular nerve block does not treat the severe ipsilateral shoulder pain that patients experience after thoracotomy. This has implications for established theories of referred pain and indicates that this pain is unlikely to originate in the shoulder.
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Introduction |
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A constant severe ache occurs in the ipsilateral shoulder of 75% of patients after thoracotomy (1), marring the otherwise excellent analgesia produced by thoracic epidural. This difficult problem has been reported in case series (1,2) and a randomized controlled study (3) and can persist for up to 20 h (2).
Effective analgesia for postthoracotomy shoulder pain has been achieved by infiltrating local anesthetics around the phrenic nerve (3), demonstrating the role of referred pain via the phrenic nerve. Interscalene brachial plexus block has also been successful in the abolition of ipsilateral shoulder pain after thoracotomy (2), possibly as a result of concurrent phrenic nerve blockade. A potential problem with interscalene brachial plexus and phrenic nerve blocks is diaphragmatic dysfunction and the associated risk of respiratory depression (3,4).
The suprascapular nerve has a similar origin to the phrenic nerve and provides the sensory innervation to the shoulder joint. Blockade of this nerve is safe and minimally invasive and has been effective in the management of frozen shoulder (5), cancer pain (6), and postoperative pain after shoulder surgery (7). However, its role in treating ipsilateral postthoracotomy shoulder pain has not been assessed.
We postulated two theories for the role of the suprascapular nerve in postthoracotomy shoulder pain. First, this nerve could transmit pain originating from excessive strain of the shoulder joint capsule and ligaments that may occur when positioning the patient in the lateral thoracotomy position (8,9); or, second, in keeping with Mackenzie’s convergence facilitation theory (10), the suprascapular nerve could represent the somatic afferent component of referred pain emanating from the diaphragm via the phrenic nerve. On the basis of these two hypotheses, we aimed to investigate whether a suprascapular nerve block would provide effective analgesia in patients with ipsilateral shoulder pain after thoracotomy occurring despite effective thoracic epidural analgesia.
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Methods |
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The study protocol was approved by the local research ethics committee and written informed consent was obtained from each patient. Forty-four patients, who were listed for thoracotomy with thoracic epidural as postoperative analgesia, were recruited into this double-blinded, randomized, placebo-controlled trial. Patients were excluded if they had any contraindication to thoracic epidural analgesia, preexisting shoulder pain, were aged over 80 yr, or had an ASA physical status of more than III. Those who were unable to understand the visual analog scale (VAS) scoring system despite preoperative coaching were also excluded.
Patients were premedicated with oral diazepam 5 or 10 mg according to the anesthesiologist’s preference. Anesthesia was induced with propofol 2–3 mg/kg and fentanyl 1 µg/kg. Tracheal intubation with a double-lumen tube (Mallinckrodt® Broncho-CathTM, Athlone, Ireland) was facilitated with atracurium 0.6 mg/kg and the patients’ lungs were ventilated with 1%–2% isoflurane in an oxygen/air mixture.
A thoracic epidural was sited between T4 and T8 before the commencement of surgery. After a test dose of 3 mL of 0.5% bupivacaine with adrenaline (1:200,000), a bolus of 0.1 mL/kg of epidural solution (0.1% bupivacaine and fentanyl 5 µg/mL) was administered before the commencement of surgery. The epidural solution was then infused at 0.1 mL · kg-1 · h-1 intraoperatively. All patients were placed in the lateral position. Care was taken to avoid excessive strain on the shoulder joint by ensuring that there was <90 degrees flexion of the upper arm. A standard surgical technique with respect to rib retraction and chest tube placement was used in all patients.
In the postoperative period, the levels of dermatomal block achieved with thoracic epidural were assessed by pinprick and temperature. Additional boluses of the epidural solution (0.1% bupivacaine and fentanyl 5 µg mL-1) were provided to achieve adequate analgesia with dermatomal block between T2/3 and L1/2. All patients who complained to the recovery nurse within 2 h of extubation of ipsilateral shoulder pain were assessed to differentiate shoulder pain from pain arising in the upper part of the wound. Patients who experienced ipsilateral shoulder pain were randomly assigned to one of the two groups according to instructions contained in preshuffled, sealed opaque envelopes. Patients in the study group received suprascapular nerve block with 10 mL of 0.5% bupivacaine (Group B), whereas patients in the control group received 10 mL of 0.9% saline (Group S). An independent anesthesiologist performed the suprascapular nerve blocks, so that both the investigators assessing the pain and the patient were blinded to the treatment.
The technique of suprascapular nerve block involved introducing the needle 1 cm above the midpoint of the scapular spine as described by Dangoisse et al. (11). The suprascapular nerve was located with the aid of a nerve stimulator (Stimuplex® HNS, B. Braun, Melsungen, Germany) looking for twitching in the supraspinatus muscle, giving rise to slight abduction and external rotation of the arm at 0.5 mA. A short beveled, 6-cm 23-g insulated needle (pole needle) was used to administer the trial solution.
Shoulder pain was assessed before nerve blockade (baseline) and at 30 min, 1, 2, 3, 4, and 6 h after the nerve block. The severity of pain was measured using a 10-cm VAS, where 0 represented no pain and 10 represented the worst pain imaginable, and a 5-point verbal ranking score (VRS) as follows: 0 = no pain, 1 = mild pain, 2 = moderate pain, 3 = severe pain, and 4 = unbearable pain. The volume of epidural solution used intraoperatively and during the 6-h study period was recorded for each patient.
Power calculations had revealed that 30 patients were required to detect a clinically significant 20% difference in VAS with power of 0.8 and significance of 0.05. As a result of the frequent prevalence of nonnormality, continuous data are presented as median with 5th and 95th centiles. The possibility that differences between outcomes was a consequence of chance was sought using repeated-measures analysis of variance of ranks (Freedman’s analysis) for VAS and VRS using preblock scores as the baseline. The patients’ characteristics and types of operations were compared with the 
2 or Wilcoxon’s rank sum tests as appropriate. A P value of 
0.05 denoted statistical significance. All analysis was performed using SAS Version 8 for Windows (SAS, Cary, NC).
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Results |
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Adequate dermatomal block was achieved with thoracic epidural analgesia in all the 44 patients recruited. Thirty-four of these patients (78%) experienced ipsilateral shoulder pain. Of the patients who had shoulder pain, four were excluded from further study, as three of them had inadvertently received ketorolac 10 mg IV and one patient had been given tramadol 100 mg IM. Of the remaining 30 patients, 15 were randomized to receive suprascapular nerve block with 0.5% bupivacaine (Group B) and 15 received 0.9% saline (Group S). Table 1 illustrates the patients’ characteristics, which were similar statistically. The total amount of epidural solution used and the types of operation were also similar in both groups. There was no significant difference between the pain scores in the two groups as displayed in Figure 1 and Table 2, except at the 4-h assessment, when the VAS and VRS were significantly lower in Group S.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The frequent incidence (78%) of postthoracotomy shoulder pain in this study is similar to that reported in previous studies that involved patients who had undergone major pulmonary resection (1,3). The majority (91%) of our patients had undergone lobectomy or pneumonectomy. The high initial mean VAS of over 7 confirms the severity of this pain, and, together with its frequent incidence, indicates the scale of the problem.
To ensure that shoulder pain could be distinguished from the pain of the surgical incision, the epidural infusion was titrated to produce adequate dermatomal analgesia. Patients and assessors had no difficulty in identifying the presence of shoulder pain. In addition, there was no difficulty in locating the suprascapular nerve using the nerve stimulator. Our study used the posterior approach to the suprascapular nerve. Dangoisse et al. (11) validated this technique by using magnetic resonance imaging scans, which showed the injected solution filling the supraspinous fossa and reaching the branches that go laterally to innervate the shoulder joint. The volume of 0.5% bupivacaine used was sufficient to produce a loss of supraspinatus muscle twitching and hence suprascapular nerve blockade. Previous studies on the use of suprascapular nerve block for shoulder pain (5) have shown that as little as 3–8 mL of 0.25%–0.5% bupivacaine ± methylprednisolone 80 mg have produced effective analgesia for frozen shoulder and rheumatoid arthritis. It seems probable that the volume and technique used achieved reliable suprascapular block in our bupivacaine group.
It is clear from the VAS and VRS pain measurements that supraclavicular nerve block is ineffective in the management of postthoracotomy shoulder pain. The significantly lower pain scores in the saline group at the fourth hour are difficult to explain. We considered the possibility of a mechanism similar to the classic gate-control theory as the cause, but this would not explain such an isolated finding. Therefore, the most likely explanation is a chance statistical finding.
The lack of effect of supraclavicular nerve block implies that pain from distraction of the shoulder capsule is unlikely to be a major component of postthoracotomy shoulder pain. This is in keeping with the available evidence that strongly suggests that this pain is most likely referred from the diaphragm and pericardium (3) and conducted by the phrenic nerve. This being the case, our study has implications for the two major models, which suggest peripheral mechanisms for referred pain. Mackenzie (10) and Ruch (12) both proposed peripheral pathways of referred pain that rely on somatic afferent input to the spinal cord at a similar level to incoming visceral signals. These theories are illustrated in Figure 2.
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Ruch (12) proposed the convergence-projection theory in which visceral and somatic afferent neurones converge onto common spinal neurones. Ascending spinal pathways are then misconstrued as originating from the somatic structure. Mackenzie’s convergence-facilitation theory suggests that visceral afferent activity does not produce pain itself, but instead that this activity produces an irritable focus within the spinal cord. Then other, even minor, somatic inputs at the same segmental level give rise to an abnormal and referred pain. Using this theory after thoracotomy, any small stimulus from the shoulder that is transmitted down the somatic afferent suprascapular nerve to the spinal cord will become amplified and distorted in the cervical dorsal horn by visceral pain coming from the diaphragm via the phrenic nerve. These exaggerated signals are then transmitted to the brain where they are perceived as a severe pain arising in the ipsilateral shoulder. Both of these theories would seem unlikely on the basis of our study, as the somatic afferent activity would have been abolished in the bupivacaine group.
In conclusion, despite being a safe and reliable technique, suprascapular nerve block using 0.5% bupivacaine does not treat ipsilateral shoulder pain occurring after thoracotomy in patients with effective thoracic epidural analgesia. This pain is unlikely to originate in the shoulder joint and if, as seems most likely, the pain is referred from the diaphragm, the suprascapular nerve is not involved in the pain pathway.
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Acknowledgments |
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The authors gratefully acknowledge the assistance of Anthony D. Grayson, BSc, who performed the statistical analyses.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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- Burgess FW, Anderson DM, Colonna D, et al. Ipsilateral shoulder pain following thoracic surgery. Anesthesiology 1993; 78: 365–8.[Web of Science][Medline]
- Ng KP, Chow YF. Brachial plexus block for ipsilateral shoulder pain after thoracotomy. Anaesth Intensive Care 1997; 25: 74–6.[Medline]
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Scawn NDA, Pennefather SH, Soorae A, et al. Ipsilateral shoulder pain following thoracotomy with epidural analgesia: the influence of phrenic nerve infiltration with lidocaine. Anesth Analg 2001; 93: 260–4.
[Abstract/Free Full Text] -
Urmey WF, McDonald M. Hemidiaphragmatic paresis during interscalene brachial plexus block: effects on pulmonary function and chest wall mechanics. Anesth Analg 1992; 74: 352–7.
[Abstract/Free Full Text] - Wassef MR. Suprascapular nerve block: a new approach for the management of frozen shoulder. Anaesthesia 1992; 47: 120–4.[Web of Science][Medline]
- Meyer-Witting M, Foster JMG. Suprascapular nerve block in the management of cancer pain. Anaesthesia 1992; 47: 626.
- Risdall JE, Sharwood-Smith GH. Suprascapular nerve block: New indication and a safer technique. Anaesthesia 1992; 47: 626.
- Mark JB, Brodsky JB. Ipsilateral shoulder pain following thoracic operations. Anesthesiology 1993; 79: 192.
- Holt M. Ipsilateral shoulder pain following thoracic operations. Anesthesiology 1993; 79: 192.
- Mackenzie J. Symptoms and their interpretation. London: Shaw, 1909.
- Dangoisse MJ, Wilson DJ, Glynn CJ. MRI and clinical study of an easy and safe technique of suprascapular nerve blockade. Acta Anaesthesiol Belg 1994; 45: 49–54.[Medline]
- Ruch TC. Visceral sensation and referred pain. In: Fulton JF, ed. Howell’s textbook of physiology. 15th ed. Philadelphia: WB Saunders, 1946: 385–401.
This article has been cited by other articles:
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  A. Ng and J. Swanevelder Pain relief after thoracotomy: is epidural analgesia the optimal technique? Br. J. Anaesth., February 1, 2007; 98(2): 159 - 162. [Full Text] [PDF]
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S. H. Pennefather, M. E. Akrofi, J. B. Kendall, G. N. Russell, and N. D. A. Scawn Double-blind comparison of intrapleural saline and 0.25% bupivacaine for ipsilateral shoulder pain after thoracotomy in patients receiving thoracic epidural analgesia Br. J. Anaesth., February 1, 2005; 94(2): 234 - 238. [Abstract] [Full Text] [PDF]
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