Journal of Cardiothoracic and Vascular Anesthesia
Volume 23, Issue 6 , Pages 761-765, December 2009

The Role of the Anesthesiologist in Thoracic Surgery: We Can Make A Difference!

Department of Anesthesiology, University of Pittsburgh Medical Center, Pittsburgh, PA

Article Outline

 

IN THE CURRENT health care environment, anesthesiologists are acutely aware of the need to contain the costs of the care that they provide; to maximize resource utilization; and, at the same time, to continue to strive for ways to enhance and improve patient safety and outcomes. The peer-reviewed literature describes several studies that address these issues and how anesthesiologists can potentially impact successful patient outcomes. One area in particular that shows how anesthesiologists can positively impact patient outcome is perioperative pain management.

In this issue of the Journal of Cardiothoracic and Vascular Anesthesia, Dr Jacek Cywinski and colleagues from the Cleveland Clinic Foundation present a retrospective observational cohort investigation of 2,068 patients who underwent open thoracotomy for lung resection with the primary objective to identify variables associated with prolonged postoperative endotracheal intubation. The authors identified the following nonmodifiable predictors associated with prolonged perioperative intubation: (1) poor preoperative pulmonary function as defined by a low forced expiratory volume in 1 second, (2) intraoperative red blood cell transfusion, (3) elevated preoperative serum creatinine level, and (4) extensive pulmonary resection. On the other hand, the modifiable predictor, the use of thoracic epidural analgesia, was associated with a higher success rate for early extubation and potentially avoids inherent complications of prolonged mechanical ventilation (eg, ventilator-associated respiratory infections and lung injury). Additionally, prolonged mechanical ventilation can be associated with increased hospital costs in the form of intensive care unit expenses and prolonged overall hospital stays. The authors conclude that although there are pre-existing factors affecting patient outcomes that are nonmodifiable, the preoperative identification of these patients at risk for delayed extubation may allow anesthesiologists to anticipate and affect perioperative interventions (eg, the use of thoracic epidural analgesia or an alternative modality for perioperative pain management), thereby decreasing the duration or eliminating the need for postoperative mechanical ventilation and improving overall patient outcome and allowing for a more efficient allocation of resources.

The suboptimal treatment of perioperative pain is widely recognized among medical practitioners, and the pain associated with a surgical procedure remains a significant concern for patients.1 Thoracic surgery, in particular, can elicit intense postoperative pain and if inadequately treated may lead to the development of chronic pain syndromes.2, 3, 4 The trend toward lower morbidity and mortality rates in thoracic surgery has paralleled the improvement in postoperative analgesic techniques, and evidence supports the concept that at least a part of the reported improvement can be attributed to more effective management of postoperative pain.5, 6, 7, 8

The posterolateral thoracotomy incision is reported to be among the most intense pain experienced.2, 3, 9 Chest wall nociception, whether generated by surgery or traumatic injury, is conducted via the intercostal nerves to the dorsal horn in the spinal cord, the autonomic nervous system, and the vagus nerve. Skin incision, dissection of the skeletal muscle, rib and intercostal space retraction, and dissection of the parietal pleura is mediated via the intercostal nerves to the dorsal horn in the spinal cord.10 Stimuli generated by dissection of the visceral pleura are primarily conducted via the autonomic nervous system; however, the vagus nerve conducts noxious stimuli caused by retraction of the lung. Noxious stimuli originating from manipulation of the diaphragm, the mediastinum, and pericardial pleura are relayed via the phrenic nerve.11 Stretching of the brachial plexus and distraction of the shoulder are postulated to be mediated by the sympathetic nervous system.12

Each of these pain pathways produces a characteristic perception of pain. Pain mediated via the intercostal nerves is primarily sharp in nature. Intercostal nerves may be targeted with analgesics and/or local anesthetics individually or in multiples in the epidural or paravertebral space. The advantage of the multiple and central neuraxial analgesic techniques is that the posterior ramus of the intercostal nerve is also blocked. This is very important for patients undergoing a posterolateral thoracotomy incision and of lesser importance for patients undergoing thoracoscopy.

Pain that results from dissection of the mediastinal and diaphragmatic pleura is primarily conducted via the vagus and phrenic nerve, respectively. The characteristic pain produced is that of nonincisional, deep-seated, ill-defined, nonlocalized discomfort. Patients may also complain of shoulder pain that is caused by diaphragmatic irritation. Chest drains produce both incisional and nonincisional pain profiles. An understanding of these multiple afferent pathways involved in the etiology of post-thoracotomy pain leads to an appreciation of why no single analgesic technique is completely satisfactory and why post-thoracotomy analgesia should be multimodal.

The impact of thoracotomy pain on postoperative pulmonary function is significant and can impair a patient's ability to generate an effective cough to clear the airways of secretions. This may lead to further deterioration of a patient's pulmonary function and increase the length of hospital stay and health care cost as well as cause an increase in patient morbidity and mortality. Other contributing factors to postoperative pulmonary impairment after thoracic surgery include a loss of functional lung units, atelectasis, a loss of function of incised or retracted intercostal muscles, rib dislocation, exacerbation of pre-existing lung disease, and diaphragmatic dysfunction.13, 14 Impairment of pulmonary function during thoracic surgery begins with the induction of general anesthesia. General anesthesia causes a reduction in functional residual capacity (FRC) of approximately 20%.13, 14 This condition is exacerbated by positioning of the patient in the lateral decubitus position. Mechanical ventilator pressures to preserve functional residual capacity, high inspired oxygen concentrations, and alternating single- with double-lung ventilation exert consequences on the pulmonary vasculature and right ventricular function. The surgical manipulation and resection of the lungs combined with the physiologic alterations of general anesthesia reduce lung compliance through increased interstitial and intra-alveolar water. These negative effects coupled with the pain and trauma of incision and disruption of the intercostal muscles along with diaphragmatic splinting can explain why patients develop a restrictive ventilation pattern with dysfunctional respiratory activity.13 As the functional residual capacity diminishes, ventilation-perfusion mismatching resulting from atelectasis and the accumulation of lung water leads to hypoxemia and predisposes the patient to the development of other infective processes. Carbon dioxide retention results from ineffective gas exchange, a process that may be exacerbated by the overzealous administration of opioids to treat pain.

Thoracotomy also stimulates the stress response, which adversely affects circulating catecholamine levels, glucose homeostasis, nitrogen balance, coagulation, and sodium balance.15, 16 The stress response leads to increased levels of adrenocorticotropic hormone, cortisol, catecholamines, interleukins, decreased insulin release, and fibrinolysis. These hormonal changes increase myocardial oxygen consumption as well as the risk of myocardial ischemia and infarction; may cause hypertension, the development of coagulopathy, and a decrease in regional blood flow; and increase the risk for infection, depression, and insomnia. Therefore, one of the goals for effective postoperative pain management is to suppress the development of the acute postoperative stress syndrome. In this regard, opioids have been shown to be ineffective in preventing the changes associated with stress even when used as a patient-controlled analgesia technique. Adverse side effects from opioids including pruritus, nausea and vomiting, respiratory depression, urinary retention, constipation, and immunosuppression represent serious limitations to their use. The modern approach to postoperative pain management is based on the use of a multimodal regimen including both pharmacologic and nonpharmacologic techniques. In addition to being multimodal, the approach to acute pain management is also multidisciplinary, being focused not only on the patient's pain but also on his/her entire recovery. This is a team approach including the surgeon; the anesthesiologist; nurses; respiratory therapists; and, most importantly, the patient. In this regard, preoperative education of the patient is essential and includes (1) informing the patient of his/her options, (2) setting realistic expectations (eg, the minimization of postoperative pain but not its complete elimination), (3) reassuring the patient that there is an acute pain specialist available to respond to the patient at all times, and (4) educating the patient as to the critical importance of his/her own motivation, involvement, and effort in his/her recovery.17, 18, 19, 20

Minimally invasive approaches to thoracic surgery that use video-assisted thoracoscopic techniques (VATSs) are considered to elicit less pain than the conventional posterolateral thoracotomy,21 but less pain does not mean that these patients do not experience any pain. Therefore, even in patients undergoing VATS, effective postoperative pain management is essential, especially when the expectation of many patients is to be completely free of pain when having minimally invasive surgery. Patients of the contemporary era are empowered with knowledge from a variety of sources including the Internet, consumer organizations, and patient organizations. In order to make informed and contributory decisions, it is necessary that patients be informed about the risk of morbidity from inadequately treated perioperative pain versus that caused by the inherent risks of the analgesic regimens. Likewise, patients have the expectation to opt out of a specific therapy should it fail to meet their expectations or if the therapy's complications are deemed worse than the discomfort.

Thoracic epidural analgesia (TEA) only recently made its debut as a mode of pain management for patients undergoing thoracic surgery. In 1957, Crawford et al22 reported a series of 2,172 operations that were conducted with “peridural anesthesia.” They described early postoperative improvements in patients receiving this analgesia compared with those who received only general anesthesia. It was not until the 1970s that TEA became widely used for postoperative analgesia in thoracic surgery; however, it was initially used only for high-risk patients.23, 24

TEA became the gold standard for postthoracotomy analgesia with the introduction of neuraxial opioids. A classic study by Bromage et al25 showed the advantages of epidural opioids for postoperative analgesia in comparison with local anesthetics alone for thoracotomy and upper abdominal surgery. The use of continuous infusion techniques and the development of ambulatory and patient-controlled analgesia systems enabled TEA to become accepted as a safe and beneficial way to manage perioperative pain.26, 27 A review published by Cook and Riley28 determined that by 1997 80% of all institutions that performed greater than 100 thoracotomies annually used midthoracic epidural techniques and opioid/local anesthetic combinations as standard practice to provide perioperative analgesia.

TEA is a safe way to provide excellent analgesia,29 and it offers several advantages over other analgesic techniques. Experimental evidence shows that TEA is superior in terms of its effects on perioperative pulmonary function, reduction of the neurohumeral stress response to anesthesia and surgery, myocardial function, oxygen delivery, reduction of myocardial irritability, restoration of gastrointestinal function, and postoperative patient mobility.30, 31, 32, 33, 34 It has been shown that the benefits of epidural analgesia are greatest when TEA is used in high-risk patients,35 including reduced intensive care unit stay, quicker recovery, and overall hospital cost savings.

As with other regional anesthetic techniques, TEA may have undesirable technique- and agent-related side effects. The overall incidence of complications related to technique is approximately 3%. These complications include technical failure, inadvertent dural puncture, postoperative radicular pain, transient peripheral nerve lesions, and inadvertent epidural venous puncture. Spinal cord damage as a result of needle trauma or epidural hematoma formation occurs rarely with an incidence estimated at 0.07%.

The technical failure rate for TEA has been reported to be less than 10% on average and can be further reduced with experience, use of fluoroscopy and radiocontrast for catheter placement, the use of a reliable sensory level with local anesthetic administration, and the catheter being secured properly to reduce the incidence of catheter dislodgement.29 Most of the adverse effects seen with TEA are related to the analgesic agents, primarily local anesthetics and opioids. Common adverse effects related to local anesthetics include motor blockade (muscle weakness) and sympathetic blockade (hypotension secondary to peripheral vasodilatation). Bradycardia may occur as a result of blockade of the cardiac sympathetic accelerator fibers (T1-T6), particularly when catheters are placed in the high thoracic region. Hemodynamic changes may be minimized through the use of continuous infusions of local anesthetics rather than intermittent bolusing techniques as well as using lower concentrations of local anesthetics combined with an opioid.

All clinically available opioids have been used for TEA.29, 36 Adverse effects of neuraxial opioids result from systemic absorption and are also related to the opioid's lipophilicity or hydrophilicity. Common systemic side effects include sedation, nausea, vomiting, inhibition of gastrointestinal motility, pruritus, and respiratory depression. When used in combination with a local anesthetic, the opioid requirement is often minimized.

The use of a combination of local anesthetics and opioids for TEA is standard practice. Local anesthetic/opioids may be delivered via a continuous infusion alone or in combination with patient-controlled epidural analgesia. The combination of local anesthetics with opioids seems to exert a synergistic analgesic effect that is thought to be caused in part by the facilitation of the transfer of the opioid into the cerebrospinal fluid by the local anesthetic as well as the increase in the affinity of the opioid receptor for the opioid, which is caused by the local anesthetics. These mechanisms are independent of the dose of the local anesthetic.37 This makes it possible to use low doses of local anesthetics in combination with opioids in order to minimize the sympathetic block side effects (hypotension) that can be a drawback to TEA.

Paravertebral nerve blocks are multiple-level intercostal nerve blocks that have replaced the direct and multiple applications of local anesthetics to intercostal nerves, cryotherapy, and interpleural local anesthetics.38 Paravertebral nerve blocks may be performed either by multiple injections or by inserting a catheter into the paravertebral space for use with a continuous infusion of local anesthetic.39, 40 The levels of analgesia and restoration of pulmonary function seen with TEA can also be achieved with a paravertebral nerve block when a multimodal analgesic regimen including the use of intravenous opioids and nonsteroidal anti-inflammatory agents is added. Outcome studies of the effect of paravertebral nerve blocks on morbidity and mortality rates after thoracic surgery have yet to be determined. It is widely accepted that the use of multimodal analgesia in conjunction with a paravertebral nerve block is an excellent alternative to TEA. Paravertebral catheters may be inserted either percutaneously or under direct vision during thoracotomy. This technique is particularly useful for patients in whom placement of TEA is difficult or contraindicated.

A paravertebral nerve block is a concept that dates back to 1906 and is attributed to Sellheim. In 1912, the technique was first used by Kappis, and Laewen dubbed it “paravertebral conduction” anesthesia.41 It was used during the early 20th century to treat conditions ranging from angina pectoris to abdominal surgery.42 After World War II, the paravertebral nerve block continued to be practiced in veterinary medicine and all but disappeared in human medicine. It was not until an article in 1979 was published by Eason and Wyatt43 that the technique was resurrected. They suggested that with a different approach to percutaneous access, paravertebral nerve blockade lent itself both to the detection of the loss of resistance and easier catheter insertion and that it was suitable for treating post-thoracotomy pain.42 Sabanathan et al44 described a direct open technique for the placement of paravertebral catheters.

Paravertebral nerve blockade offers several advantages, particularly when a catheter is used to provide a continuous infusion of local anesthetic. Once a physician becomes facile with the technique, it may be implemented rapidly and can be effective at blunting the noxious stimuli resulting from the initiation of surgical skin incision and rib retraction. Paravertebral nerve catheters can be used as an adjuvant to general anesthesia for patients undergoing major thoracic surgery via thoracotomy or VATS to provide either unilateral or bilateral analgesia. They may be inserted either percutaneously or with an open technique, allowing the surgeon to directly visualize the position of the catheter. The technique has very few adverse effects that are primarily minor and easily corrected.

Adverse effects of the paravertebral nerve block are generally minor and are easily corrected. These effects may be technique related (eg, technique failure) and agent related. There is a 3.8% incidence of vascular puncture, skin hematoma, and pain at the site of injection. Percutaneous placement of paravertebral nerve blocks and catheters is not advised in circumstances in which intercostal vessels may be enlarged (eg, coarctation of the aorta or thoracic aortic aneurysms) and predispose the patient to major vascular injury. The incidence of pleural puncture with associated pneumothorax or lung parenchyma penetration has a reported incidence of 1.1% and 0.5%, respectively, and there is an 8-fold increase in risk when a bilateral block is attempted.45, 46 The failure rate has been reported to be as high as 6% to 10% even in the most experienced of hands.47 This complication may be reduced by using techniques such as ultrasonography, a nerve stimulator, and direct catheter insertion during surgery. Lastly, hypotension resulting from sympathetic blockade has an incidence of 4%.47

There has been concern expressed regarding the potential for continuous infusions of local anesthetics to cause toxicity because of the vascularity of the thoracic paravertebral space. The proximity of the neuraxis should always make the physician aware of the risk for the occurrence of a total spinal block should the dura be punctured during the procedure.

As previously stated, only local anesthetics are suitable for injection or infusion into the paravertebral space. A variety of local anesthetics with varying concentrations are used. Most commonly, 0.25% or 0.5% bupivacaine or 0.2% ropivacaine is used. The advantage of ropivacaine over bupivacaine is that the potential to cause cardiotoxicity is much less. For catheter techniques, an infusion of the local anesthetic is provided at a rate of 0.5 to 1.0 mL per segment to be blocked or at a rate of 0.1 mL/kg/h for the majority of adult patients. This dose should be decreased in smaller adults, the elderly, or the chronically ill.48, 49

It is the present authors' practice at the University of Pittsburgh to use either thoracic epidural anesthesia/analgesia or paravertebral analgesia for all open thoracic surgical procedures, including lung transplantation and minimally invasive direct coronary artery bypasses, unless there is a clear contraindication. The present authors have found that the benefit to risk ratio strongly favors the benefit and the superior analgesia obtained, compared with those patients who only receive either intermittent intravenous opioid analgesia or patient-controlled opioid analgesia alone, does indeed facilitate earlier extubation and reduces overall hospital stay. The patient outcome is very similar to that described by Cywinski et al when a neuraxial anesthetic technique is used during open thoracic surgical procedures.

Immense changes and progress in pain management have occurred during the past 20 years. Patient outcomes in thoracic surgery that have been considered to be a direct function of pain include postoperative mobility; duration of hospital stay; atelectasis, pneumonia, and respiratory failure; and the development of chronic pain syndromes. Of these factors, the respiratory components are regarded as most critical and reflect the morbidity and potential for mortality.50

Postoperative epidural analgesia is currently the only pain-management technique that has achieved a level 1 evidence base for decreasing the incidence of adverse pulmonary outcomes after thoracic surgery. The use of epidural local anesthetic/opioid combined therapy shows a superior analgesic effect over either agent used alone along and provides a lower incidence of adverse effects. Nonsteroidal anti-inflammatory drugs may be used alone for the treatment of minor incisional pain; however, they are only useful for treating severe pain as a component of a multimodal analgesic regimen.

There is currently a strong push at the level of the federal government for health care reform, and much discussion exists regarding how physicians should be reimbursed for services provided. Some have suggested that a reimbursement system should be configured to reflect the use of best practices derived from evidence-based outcomes data. The study by Cywinski et al, despite the retrospective nature, suggests that there are patient parameters that are both modifiable and nonmodifiable with regard to open thoracic surgical procedures. From the data presented, it would appear that anesthesiologists could directly exert a positive effect on patient outcome by facilitating early extubation with the use of thoracic epidural anesthesia/analgesia and potentially avoiding the inherent complications of prolonged mechanical ventilation. The preoperative recognition of the nonmodifiable predictors for prolonged intubation and mechanical ventilation may be valuable for identifying those patients at risk earlier in their hospitalization and allowing for a more efficient and effective allocation of postoperative resources.

Anesthesiologists have long been advocates for the development of practices and techniques that provide superior patient care and enhance patient safety. Although patients do not always recognize these efforts, anesthesiologists have made great strides to raise patient awareness of the critical role that anesthesiologists play in making modern medicine possible. Anesthesiologists must continue to be advocates for the specialty and for patients by providing the best perioperative care there is to offer. This can be achieved by continuing to investigate modifiable and nonmodifiable parameters of risk that impact patient outcome.

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PII: S1053-0770(09)00329-2

doi:10.1053/j.jvca.2009.08.009

Journal of Cardiothoracic and Vascular Anesthesia
Volume 23, Issue 6 , Pages 761-765, December 2009

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