Pain control for thoracotomy

Transcription

1 Richard Hughes MB ChB, FRCA Fang Gao FRCA MPhil Key points Thoracotomy is one of the most painful surgical procedures. The aim of pain control is to achieve a patient able to move freely and cough effectively with a low pain score (dynamic analgesia). The segmental effects of thoracic epidural local anaesthetic and opioid combinations produce reliable dynamic analgesia after thoracotomy. Only dynamic analgesia has been shown consistently to decrease post-thoracotomy respiratory complications. A balanced technique using oral analgesia alongside neuraxial techniques and multidisciplinary input provides the best overall pain relief. Richard Hughes MB ChB, FRCA Research Fellow in Anaesthesia Birmingham Heartlands Hospital Birmingham B5 9SS Fang Gao FRCA MPhil Consultant Anaesthetist Department of Anaesthesia and Intensive Care Medicine Birmingham Heartlands Hospital Bordesley Green East Birmingham B5 9SS Tel: Fax: fang.smith@heartsol.wmids.nhs.uk (for correspondence) Thoracotomy is widely recognized as being one of the most painful surgical procedures. Acute post-thoracotomy pain is aggravated by the constant movement of breathing. However, vigorous physiotherapy and incentive spirometry are encouraged to prevent atelectasis and secretion retention. Pain relief is, therefore, essential to facilitate coughing and deep breathing and to promote early mobilization. Many factors can affect the analgesic outcome after thoracotomy, including surgical technique, choice of analgesic modality, postoperative level of care, ongoing input from acute pain and physiotherapy services and patient factors, such as psychological preparation. Moreover, thoracotomy has been thought to be associated with a high incidence of chronic neurogenic pain, which might be reduced by good acute postoperative analgesia. Types of thoracic incision Access to the thoracic cavity can be achieved in many ways depending on the operative site, procedure and surgeon s preference. The advent of thoracoscopic surgery has enabled many procedures to be performed without full open thoracotomy. Several different thoracotomy incisions are used in current practice. Posterolateral thoracotomy is the most popular approach providing good access to lung, oesophagus, mediastinal structures, descending aorta and diaphragm. Anterolateral and axillary thoracotomies are usually used for specific lung resections and a thoraco-abdominal incision for oesophageal, aortic and upper abdominal surgery. In addition, Clamshell thoracotomy is used for bilateral procedures such as lung transplant and resection of bilateral pulmonary metastases. The limited (muscle-sparing) thoracotomy is a more conservative approach that has been developed in the interests of reducing chest wall trauma. In this technique, the muscles are divided along their fibres and retracted rather than cut. Studies comparing this with posterolateral thoracotomy have demonstrated a reduction in acute postoperative pain and pain related morbidity. Although the majority of procedures do not require a full standard posterolateral thoracotomy incision, the smaller incision of muscle-sparing thoracotomy does result in reduced access. Primarily used for cardiac surgery, a median sternotomy is also suitable for anterior mediastinal surgery. With little overlying muscle and a relatively static role in breathing, this is far less painful than any of the thoracotomy approaches. Anatomy and pathophysiology of pain in thoracic surgery Nociceptive transmission is via C and Ad fibres and can be considered in three discrete routes. Intercostal nerves carry impulses from the skin and intercostal muscles. Stimuli from lung and mediastinum are carried by the vagus nerve. The visceral pleura is relatively insensitive, except to stretch. Parietal pleura, which is highly sensitive to noxious stimuli, receives innervation from intercostal and phrenic nerves. In addition, latissimus dorsi and serratus anterior are supplied by the thoracodorsal and long thoracic nerves, respectively. These arise from roots C5 C7 via the brachial plexus. Thoracotomy for lung resection usually involves a skin incision at the 5th intercostal space, a variable degree of muscle cutting and either excision or division of a rib. Oesophageal surgery requires a lower incision, usually around the 7th intercostal space. A posterolateral thoracotomy incision usually traverses around six dermatomal levels, starting at the 3rd thoracic dermatome posteriorly extending to the 7th or 8th thoracic dermatome anteriorly. Chest wall muscles involved are latissimus dorsi, serratus anterior, pectoralis major and the intercostal muscles. Forceful retraction of the wound is needed to achieve reasonable access and this frequently causes pressure on the intercostal nerves and may cause acute intercostal neuritis. Other sites damaged by retraction are the anterior and posterior intercostal articulations. Continuing Education in Anaesthesia, Critical Care & Pain Volume 5 Number ª The Board of Management and Trustees of the British Journal of Anaesthesia [2005]. All rights reserved. For Permissions, please journals.permissions@oupjournals.org doi /bjaceaccp/mki014

2 Table 1 Factors contributing to post-thoracotomy acute pain Skin and muscle trauma Posterior costovertebral ligament damage Costochondral dislocation Acute intercostals neuritis Chest drains pleural irritation Shoulder pain Anxiety Up to three chest drains may be inserted after thoracotomy. These are usually sited in the 8th or 9th intercostal space. This is frequently outside the area covered by epidural or paravertebral block and may be what troubles patients most. The prolonged lateral decubitus position with upper arm supported on a gully may be associated with postoperative generalized muscular pain. Shoulder pain is a common complaint after thoracotomy although the aetiology is less clear. Furthermore, patients may well be extremely anxious after major thoracic surgery, exacerbating the perception of postoperative pain. These factors are summarized in Table 1. Impact of analgesia on outcome Good pain relief is an obvious humanitarian issue. Also, the consequences of poor analgesia can be costly in terms of human life and in the cost to the health care provider. Shallow breathing and impaired coughing resulting from postoperative pain are a major cause of atelectasis and retention of secretions, both of which can lead to hypoxaemia, hypercapnia and respiratory failure, especially in patients with pre-existing lung disease. In addition to these specific adverse pulmonary effects, acute pain causes increased sympathetic tone accompanied by increased myocardial oxygen demand, increased afterload, myocardial dysfunction and arrhythmias. Poor analgesia may also result in a delay in mobilizing patients, resulting in an increased incidence of deep venous thrombosis and pulmonary embolism. It has been demonstrated that poor analgesia is associated with increased ICU admissions, and longer stays in ICU and hospital overall. 1 The choice of analgesic technique The decision as to which technique to use for a particular patient is usually a matter of the anaesthetist s preference and what services are available. When no contraindication to central neuraxial or regional analgesia exists, this is commonly accepted as the best approach. 1 3 When this is impossible, whether attributable to local or systemic infection, refusal by the patient or anatomical difficulties, parenteral opioid infusion is the technique of choice. Whatever the method chosen, the patient should have adequate preoperative counselling, including a full explanation of the proposed technique so that the patient knows what to expect. This can reduce the psychological component of pain. Many patients have a stoical attitude towards analgesia, and either do not like taking tablets or do not wish to bother the medical and nursing staff. Inevitably, differences between patients result in a varied response to the same analgesic techniques. In order to deliver good quality analgesia, a reliable method of feedback from patients is needed so that analgesia can be optimized. Assessment of pain relief in patients after thoracotomy should take into account dynamic analgesia, 4 with pain scores reflecting functional ability to cough and breath deeply. Various methods of scoring pain are available but numerical rating scores have been shown to be the most accurate and reproducible. The importance of good analgesia should be impressed upon all patients. Whilst a realistic view must be maintained, patients should be encouraged to seek attention if pain prevents deep breathing or coughing or disrupts sleep. This has the effect of empowering the patient and will improve overall analgesia and compliance with postoperative physiotherapy. A frequent problem in delivering good analgesia is ensuring that the analgesic plan is actually carried out. Appropriate regimens or drugs may be prescribed, but unless there is adequate communication between anaesthetists, surgeons and nurses, these may fail to reach the patient at the right time. Appropriate anti-emetic therapy and avoidance of potent emetic stimuli can reduce the likelihood of vomiting, a painful event in the postoperative period. Analgesic approaches There are a selection of analgesic techniques which have been refined to give good pain relief with minimal side-effects. There are systemic methods which includes infusion and patient-controlled analgesia (PCA) or regional techniques that mainly rely on epidural, intrathecal or paravertebral blocks. Other techniques range from intercostal nerve block to cryoprobe neurolysis. Parenteral opioid infusions Reasonable analgesia can be achieved with i.v. opioid infusions: however, their side-effects (respiratory depression and inhibition of the cough reflex) are undesirable after thoracotomy. For this reason, an i.v. infusion of opioid is not the technique of choice, although it may need to be used if other methods are contraindicated. PCA is often not effective immediately after thoracotomy as patients are often too drowsy to use the demand button properly. It can be used as part of a balanced technique once the patient is sufficiently alert, as long as opioids are not being administered concurrently via the intrathecal or epidural routes. Where parenteral opioids are used, whether by infusion or PCA, adequate loading doses must be given to achieve therapeutic plasma concentrations. PCA devices must also be set to provide a sufficient bolus. Epidural analgesia Epidural analgesia is considered by many to be the gold standard. 1 3 Usually, the catheter is sited at a level corresponding Continuing Education in Anaesthesia, Critical Care & Pain Volume 5 Number

3 approximately with the midpoint of the dermatomal distribution of the skin incision. Although lumbar catheters have also been used with modified infusion mixtures, thoracic epidural analgesia is superior to lumbar epidural analgesia because of the synergy between local anaesthetics and opioids in producing neuraxial analgesia. 1 Studies suggest that epidural local anaesthetics increase segmental bioavailability of opioids in the cerebrospinal fluid and increase the binding of opioids to m receptors and the blocking of the release of substance P in the substantia gelatinosa of the dorsal horn of the spinal cord. 5 Utilizing only the thoracic segmental effects of local anaesthetic and opioid combinations is the only way to minimize motor and sympathetic blockade, maintain conscious level and cough reflex and reliably produce increased analgesia with movement and increased respiratory function after thoracotomy. There are numerous regimens in different combinations and concentrations available and fentanyl or diamorphine combined with levobupivacaine are probably the most popular regimens used in the UK. The epidural mixture can be administered either as a continuous infusion, by patientcontrolled epidural analgesia (PCEA) or a combination of the two. PCEA allows easy supplemental boluses before mobilizing or physiotherapy. However, there are significant drawbacks. Firstly, there is a failure rate of up to 15%, even in experienced hands. Placement of a thoracic epidural catheter may be technically difficult because of caudal angulation of the spinous processes and spinal cord damage is theoretically more likely than with lumbar placement. Postoperative care needs appropriately trained personnel, and inadequate blocks can be time-consuming to remedy. Furthermore, the consequential bilateral sympathetic blockade frequently causes hypotension, especially in this group of patients who are managed in a relatively hypovolaemic state for reasons of pulmonary function. This may require the infusion to be stopped. Motor blockade of intercostal muscles may reduce the effectiveness of coughing, especially in patients who already have a low FEV 1. The technique is contraindicated in the presence of local or systemic sepsis, for example in patients undergoing open drainage and decortication of an active empyema. Intrathecal opioids The terms intrathecal and subarachnoid are synonymous. Preservative-free opioids introduced into the lumbar subarachnoid space will produce analgesia extending cranially to varying extents depending on the volume, strength, baricity of solution and choice of opioid. The pharmacokinetic profile of different intrathecal opioids is largely dependent on their physical characteristics. Highly lipid soluble drugs such as fentanyl and diamorphine tend to penetrate the spinal cord easily and consequently act rapidly with restricted cranial spread. While this is ideal for lower limb or lower abdominal surgery, it is not suitable for thoracic procedures. Morphine, possessing lower lipid solubility, tends to spread within the cerebrospinal fluid to the thoracic region more readily before penetrating the spinal cord to its site of action, the substantia gelatinosa of the dorsal horn. This characteristic makes it the intrathecal opioid of choice for use in thoracotomy. The technique of lumbar puncture is familiar to most anaesthetists and is relatively quick and simple to perform compared with siting a thoracic epidural needle. Doses are usually determined by the weight and age. A range of 5 20 mgkg 1 of morphine has been reported in the literature. The regimens used at the authors thoracic centre are mgkg 1 for patients up to 70 yr of age but mgkg 1 for patients more than 70 yr old. Total dose may be the biggest factor affecting spread and magnitude of effect, but increasing the total volume and performing barbotage (inducing turbulence by repeated aspiration and re-injection of CSF) can increase cranial spread. However, barbotage has been implicated in causing nerve damage during the aspiration phase; it is less commonly used nowadays. Single intrathecal injections of morphine have been successfully used pre- or intraoperatively to provide h of postoperative pain relief. 6 However, they need to be followed with some other form of analgesia. There is a significant delay between administration of intrathecal morphine and the onset of analgesia (usually 1 2 h). Thus, additional short-acting intraoperative analgesia (such as a remifentanil infusion or fentanyl boluses) must be given until a clinical effect of the morphine is seen, for example haemodynamic stability and/or reduction of requirement for inhalational anaesthetic agents. Postoperatively, pain relief in the recovery ward can be very variable; visual analogue scale (VAS) score for pain during coughing can vary from no pain to severe pain. Boluses of i.v. morphine and/or combined with intercostal nerve blocks are common rescue methods of pain relief in the recovery ward or high dependence unit (HDU) for severe pain. The technique avoids the need for an infusion catheter connected to an infusion pump and this makes nursing care easier and improves the mobility of the patient. However, a single-shot intrathecal technique allows neither top-ups if analgesia is inadequate nor an infusion for continuous pain relief for days. Planning is needed to ensure adequate analgesia is in place when the effect of the intrathecal opiate wears off (usually on the first postoperative morning). This is best dealt with by parenteral opioids (such as PCA) on a background of simple analgesics such as paracetamol and (if not contraindicated) nonsteroid anti-inflammatory drugs (NSAIDs). 7 The most significant adverse effect of intrathecal morphine is the development of delayed sedation and respiratory depression caused by excessive rostral spread. The incidence of delayed severe respiratory depression requiring re-intubation and ventilation has been estimated as 1 2%. However, the incidence of less severe respiratory depression (Pa CO2 > 7 kpa or ventilatory frequency <6 bpm) without requiring intubation has been reported as up to 25%. This delayed respiratory depression is of slow-onset and associated with progressive somnolence. After intrathecal morphine, all patients must be closely monitored in a clinical area where ventilatory frequency and degree of sedation can be 58 Continuing Education in Anaesthesia, Critical Care & Pain Volume 5 Number

4 monitored every min for at least 24 h in order to detect and treat this potentially dangerous complication. Urinary retention, pruritus, and nausea and vomiting are side-effects of both epidural and intrathecal techniques. As with any technique involving dural puncture, headache is also a risk. Paravertebral blocks Paravertebral blockade has undergone a resurgence recently and, as part of a balanced technique, offers one of the best options for post-thoracotomy analgesia. The paravertebral space is a wedge shaped area immediately lateral to the intervertebral foramen. It communicates above and below with adjacent paravertebral spaces. Communication with the epidural space has also been described in some cadaveric dye studies. The intercostal nerve passes through the space without a fascial sheath, where it can be reliably blocked with local anaesthetic. At this point the nerves lie outside the parietal pleura and the term extrapleural blockade has been used synonymously with paravertebral blockade. Paravertebral block can be a single-shot technique or may be given as an infusion via a catheter placed with a Tuohy needle. This can either be inserted using loss of resistance as in placing an epidural catheter or under direct vision by the surgeon at thoracotomy. In the case of the latter, posterior parietal pleura can be stripped away by blunt dissection to allow the catheter to sit in a preformed pocket. Plain local anaesthetic solutions (e.g. bupivacaine %) or equivalent are generally used at a rate of ml h 1. Many of the disadvantages of epidural analgesia come from its bilateral effect. The unilateral nature of a thoracotomy means that bilateral analgesia should be unnecessary. Advantages of paravertebral blockade lie mainly in the fact that the concomitant sympathetic and motor blocks are unilateral and that opioids are not needed in the mixture. This results in less hypotension, better preserved respiratory function and less stress response compared with the thoracic epidural technique with local anaesthetic alone. 8 Consequently, additional analgesics such as NSAIDs may be given to appropriate patients and parenteral opioids in the form of PCA may be used to supplement analgesia. Neurological damage and CSF tap are still potential complications, although theoretically less likely than with the thoracic epidural route. Surgically placed catheters may give more reliable results. Despite these potential advantages, the technique has not gained great popularity which may be related to lack of evidence of its advantages over a combination of local anaesthetic with opioids given by a thoracic epidural technique. Intercostal nerve blocks Unilateral intercostal blocks are quick and simple to perform. Single injections for two or three intercostal spaces above and below the incision have the advantage of localized analgesia without the risks of sympathetic nerve blockade. Used alone, however, this technique is short-acting. Multiple intercostal Posierior division Recurrent branch Transversus thoracis catheters can be sited but are generally too time-consuming and complicated to be useful in everyday practice. The intercostal nerve gives off a posterior division shortly after it emerges from the intervertebral foramen (Fig. 1). One of the limitations of intercostal nerve blockade is that it is usually performed anterior to this point (especially above the 6th rib because of the presence of the scapula), resulting in inadequate posterior analgesia. 9 Large volumes of local anaesthetic are needed if multiple injections are performed and it is easy to exceed the toxic dose inadvertently. Inter-pleural analgesia This technique is also known as intrapleural analgesia. Local anaesthetic (e.g. bupivacaine %) may be injected between visceral and parietal pleura either as a single bolus or as an infusion via an indwelling catheter. The procedure can be performed either by the anaesthetist when the chest is closed or by the surgeon when the chest is open. The technique has been found to have some benefit but local anaesthetic tends to pool in dependent areas and is also lost through chest drains, limiting effectiveness. Cryoprobe neurolysis Rami communicantes Sym pathetic ganglion Internal mam. art. Anterior culaneous I n t e r c o s Fig. 1 Anatomy of an intercostal nerve. Lateal cuntaneous The technique of destroying individual intercostal nerves by intraoperative application of a low temperature probe has been used to provide analgesia. The results may last for 3 months until the nerves grow back by axonal regeneration. However, in common with intercostal nerve block, this suffers from the problem of missing the posterior division, which supplies the posterior ligaments, muscles and skin. Furthermore, significant long-term morbidity such as neuralgia and paraesthesia are commonly seen, and this technique is rarely used today. t a l e x I n t e r c o Intercostal nerve Pleura t e r n u s s t a l i n t e r n u s Continuing Education in Anaesthesia, Critical Care & Pain Volume 5 Number

5 Balanced analgesic technique Wherever possible, use should be made of synergistic, multimodal analgesia. While regional and neuraxial methods (such as epidural with local anaesthetic alone or combined with opioids) have obvious advantages, some afferent routes will not be blocked by the techniques described above (for example diaphragmatic irritation via the phrenic nerve). If additional systemic analgesics can be administered, global analgesia will be improved. Regular paracetamol, parenteral or oral opioids and, where appropriate, NSAIDs are good choices and will also assist when stepping down from regional and neuraxial techniques. However, the risk of renal impairment caused by use of NSAIDs in potentially dehydrated thoracic patients should be born in mind. References 1. Slinger PD. Thoracic anaesthesia. In: International Anaesthesia Research Society 2004 Review Course Lectures, Tampa, FL, 2004; P Watson A, Allen PR. Influence of thoracic epidural analgesia on outcome after resection for esophageal cancer. Surgery 1994; 115: Licker M, de Perrot M, Hohn L, et al. Perioperative mortality and major cardio-pulmonary complications after lung surgery for non-small cell carcinoma. Eur J Cardiothoracic Surg 1999; 15: Concha M, Dagnino J, Cariaga M, Aguilera J, Aparicio R, Guerrero M. Analgesia after thoracotomy: epidural fentanyl/bupivacaine compared with intercostal nerve block plus intravenous morphine. J Cardiothorac Vasc Anesth 2004; 18: Hansdottir V, Woestenborghs R, Nordberg G. The pharmacokinetics of continuous epidural sufentanil and bupivacaine infusion after thoracotomy. Anesth Analg 1996; 83: Liu N, Kuhlman G, Dalibon N, Moutafis M, Levron JC, Fischler M. A randomized, double-blinded comparison of intrathecal morphine, sufentanil and their combination versus IV morphine patientcontrolled analgesia for postthoracotomy pain. Anesth Analg 2001; 92: McCrory C, Diviney D, Moriarty J, Luke D, Fitzgerald D. Comparison between repeat bolus intrathecal morphine and an epidurally delivered bupivacaine and fentanyl combination in the management of postthoracotomy pain with or without cyclooxygenase inhibition. J Cardiothorac Vasc Anesth 2002; 16: Richardson J, Sabanathan S, Jones J. A prospective, randomized comparison of preoperative and continuous balanced epidural or paravertebral bupivacaine on post-thoracotomy pain, pulmonary function and stress responses. Br J Aanesth 1999; 83: Debreceni G, Molnar Z, Szelig L, Molnar TF. Continuous epidural or intercostal analgesia following thoracotomy: a prospective randomized double-blind clinical trial. Acta Anaesthesiol Scand 2003; 47: See multiple choice questions Continuing Education in Anaesthesia, Critical Care & Pain Volume 5 Number