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Chapter: Clinical Anesthesiology: Anesthetic Management: Anesthesia for Thoracic Surgery

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Anesthesia for Lung Resection: Anesthetic Considerations

The majority of patients undergoing pulmonary resections have underlying lung disease.

ANESTHETIC CONSIDERATIONS

1. Preoperative Management

The majority of patients undergoing pulmonary resections have underlying lung disease. It should be emphasized that smoking is a risk factor for both chronic obstructive pulmonary disease and coronary artery disease; both disorders commonly coexist in patients presenting for thoracotomy.Echocardiography is useful for assessing baseline cardiac function and may suggest evidence of cor pulmonale (right ventricular enlargement or hyper-trophy) in patients with poor exercise tolerance. Stress echocardiography (exercise or dobutamine) may be useful in diagnosing coronary artery disease in patients with suggestive signs and symptoms.

Patients with tumors should be evaluated for complications related to local extension of the tumor and paraneoplastic syndromes (above). Preoperative chest radiographs and CT or MR images should be reviewed. Tracheal or bronchial deviation can make tracheal intubation and proper positioning of bronchial tubes much more difficult. Moreover, airway compression can lead to difficulty in venti-lating the patient following induction of anesthesia. Pulmonary consolidation, atelectasis, and large pleu-ral effusions predispose to hypoxemia. The location of any bullous cysts or abscesses should be noted.

Patients undergoing thoracic procedures are at increased risk of postoperative pulmonary and car-diac complications. Perioperative arrhythmias, par-ticularly supraventricular tachycardias, are thought to result from surgical manipulations or distention of the right atrium following reduction of the pul-monary vascular bed. The incidence of arrhythmias increases with age and the amount of pulmonary resection.

2. Intraoperative Management

Preparation

As with anesthesia for cardiac surgery, optimal prep-aration may help to prevent potentially catastrophic problems. The frequent presence of poor pulmonary reserve, anatomic abnormalities, or compromise of the airways, and the need for one-lung ventila-tion predispose these patients to the rapid onset of hypoxemia. A well thought-out plan to deal with potential difficulties is necessary. Moreover, in addi-tion to items for basic airway management, special-ized and properly functioning equipment—such as multiple sizes of single- and double-lumen tubes, a flexible (pediatric) fiberoptic bronchoscope, a small-diameter “tube exchanger” of adequate length to accommodate a double lumen tube, a continuous positive airway pressure (CPAP) delivery system, and an anesthesia circuit adapter for administering bronchodilators—should be immediately available.

Patients undergoing open-lung resections (seg-mentectomy, lobectomy, pneumonectomy) often receive postoperative thoracic epidural analgesia, unless there is a contraindication. However, patients are increasingly being treated with numerous anti-platelet and anticoagulant medications, which may preclude epidural catheter placement.

Venous Access

At least one large-bore (14- or 16-gauge) intrave-nous line is mandatory for all open thoracic surgi-cal procedures. Central venous access (preferably on the side of the thoracotomy to avoid the risk of pneumothorax on the side that will be ventilated intraoperatively), a blood warmer, and a rapid infu-sion device are also desirable if extensive blood loss is anticipated.

Monitoring

Direct monitoring of arterial pressure is indicated for resections of large tumors (particularly those with mediastinal or chest wall extension), and any procedure performed in patients who have limited pulmonary reserve or significant cardiovascular disease. Central venous access with monitoring of central venous pressure (CVP) is desirable for pneumonectomies and resections of large tumors. Less invasive measures of cardiac output through use of pulse contour analysis and transpulmo-nary thermodilution provide better estimates of cardiac function and volume responsiveness. Pulmonary artery catheters are very rarely used. Measurement of pulmonary artery pressures may also not be accurate due to intrin-sic and extrinsic PEEP, lateral decubitus, and open chest. In patients with significant coronary artery disease or pulmonary hypertension, intraoperative monitoring can be enhanced by the use of trans-esophageal echocardiography.

Induction of Anesthesia

After adequate preoxygenation, an intravenous anesthetic is used for induction of most patients. The selection of an induction agent should be based on the patient’s preoperative status. Direct laryngoscopy should generally be performed only after adequate depth of anesthesia has been achieved to prevent reflex bronchospasm and to obtund the cardiovascular pressor response. This may be accomplished by incremental doses of the induction agent, an opioid, or deepening the anesthesia with a volatile inhalation agent (the latter is particularly useful in patients with reactive airways).

Tracheal intubation with a single-lumen tracheal tube (or with a laryngeal mask airway [LMA]) may be necessary, if the surgeon performs diagnostic bron-choscopy (below) prior to surgery. Once the bron-choscopy is completed, the single-lumen tracheal tube (or LMA) can be replaced with a double-lumen bronchial tube (above). Controlled positive-pressure ventilation helps prevent atelectasis, paradoxical breathing, and mediastinal shift; it also allows control of the operative field to facilitate the surgery.

Positioning

Following induction, intubation, and confirma-tion of correct tracheal or bronchial tube position, additional venous access and monitoring may be obtained before the patient is positioned for surgery. Most lung resections are performed with the patient in the lateral decubitus position. Proper positioning avoids injuries and facilitates surgical exposure. The lower arm is flexed and the upper arm is extended in front of the head, pulling the scapula away from the operative field (Figure 25–11). Pillows are placed between the arms and legs, and an axillary (chest) roll may be positioned just beneath the dependent axilla to reduce pressure on the inferior shoulder (it is assumed that this helps to protect the brachial plexus); care is taken to avoid pressure on the eyes and the dependent ear.


Maintenance of Anesthesia

All current anesthetic techniques have been success-fully used for thoracic surgery, but the combination of a potent halogenated agent (isoflurane, sevoflu-rane, or desflurane) and an opioid is preferred by most clinicians. Advantages of the halogenated agents include: (1) potent dose-related bronchodila-tion; (2) depression of airway reflexes; (3) the ability to use a high inspired oxygen concentration (Fio 2), if necessary; (4) the ability to make relatively rapid adjustments in anesthetic depth; and (5) minimal effects on hypoxic pulmonary vasoconstriction . Halogenated agents generally have minimal effects on HPV in doses <1 minimum alveolar con-centration (MAC). Advantages of an opioid include:generally  minimal  hemodynamic  effects;depression of airway reflexes; and (3) residual 3  postoperative analgesia. If epidural opioids are  used  postoperatively,  intravenous  opioids should be limited during surgery to prevent excessive postoperative respiratory depression. Maintenance of neuromuscular blockade with a nondepolarizing neuromuscular blocker (NMB) during surgery facilitates rib spreading as well as anesthetic management. Intravenous fluids should generally be restricted in patients undergoing pul-monary resections. Excessive fluid administration in thoracic surgical patients has been associated with acute lung injury in the postoperative period. No fluid replacement for estimated “third space” losses should be administered during lung resection. Excessive fluid administration in the lateral decubi-tus position may promote a “lower lung syndrome” (ie, gravity-dependent transudation of fluid into the dependent lung). The latter increases intrapulmo-nary shunting and promotes hypoxemia, particularly during one-lung ventilation. Moreover, the collapsed lung may be prone to acute lung injury due to surgi-cal retraction during the procedure and possible ischemia–reperfusion injury. During lung resec-tions, the bronchus (or remaining lung tissue) is usu-ally divided with an automated stapling device. The bronchial stump is then tested for an air leak under water by transiently sustaining 30 cm of positive pressure to the airway. Prior to completion of chest closure, all remaining lung segments should be fully expanded manually under direct vision. Controlled mechanical ventilation is then resumed and contin-ued until chest tubes are connected to suction.

Management of One-Lung Ventilation

Although still an intraoperative problem, hypox-emia has become less frequent due to better lung isolation methods, ventilation techniques, and the use of anesthetic agents with less detrimental effects on hypoxic pulmonary vasoconstriction. Attention has currently shifted toward avoidance of acute lung injury (ALI). Fortunately, ALI occurs infrequently, with an incidence of 2.5 % of all lung resections combined, and an incidence of 7.9% after pneumo-nectomy. However, when it occurs, ALI is associ-ated with a risk of mortality or major morbidity of about 40%.

Based on current data, it seems that protective lung ventilation strategies may minimize the risk of acute lung injury after lung resection. This ventila-tory strategy includes the use of lower tidal volumes (6–8 mL/kg), routine use of PEEP (5–10 cm H2O), lower Fio2 (50% to 80%), lower ventilatory pres-sures (plateau pressure 25 cm H2O; peak airway pressure 35 cm H2O) through the use of pressure-controlled ventilation and permissive hypercapnia. The use of lower tidal volumes may lead to lung derecruitment, atelectasis, and hypoxemia. Lung derecruitment may be avoided by application of external PEEP and frequent recruitment maneuvers. Although PEEP may prevent alveolar collapse and development of atelectasis, it may cause a decrease in Pao2 due to diversion of blood flow away from the dependent, ventilated lung and an increase in total shunt. Thus, PEEP must be customized to the underlying disease of each patient, and a new appli-cation of PEEP will almost never be the appropriate way to treat hypoxemia that occurs immediately after the onset of one-lung ventilation. Patients with obstructive pathology may develop intrinsic PEEP. In these patients, the application of external PEEP may lead to unpredictable levels of total PEEP. Although the management of one-lung ventilation has long included the use of 100% oxygen, evidence of oxygen toxicity has accumulated both experimen-tally and clinically. Although there is no convincing evidence that outcomes are worsened with the use of 100% oxygen, some clinicians recommend titrating Fio2 to maintain the oxygen saturation above 90%, especially in patients who have undergone adjuvant therapy and are at risk of developing ALI. Although there is no unequivocal evidence that one mode of ventilation may be more beneficial than the other, pressure-controlled ventilation may diminish the risk of barotrauma by limiting peak and plateau air-way pressures, and the flow pattern results in a more homogenous distribution of the tidal volume and improved dead space ventilation.

At the end of the procedure, the operative lung is inflated gradually to a peak inspiratory pressure of less than 30 cm H2O to prevent disruption of the staple line. During reinflation of the operative lung, it may be helpful to clamp the lumen serving the dependent lung to limit overdistension.

Periodic arterial blood gas analysis is helpful to ensure adequate ventilation. End-tidal CO2 mea-surement may not be reliable due to increased dead-space and an unpredictable gradient between the arterial and end-tidal CO 2 partial pressure.

Management of Hypoxia

Hypoxemia during one-lung anesthesia requires one or more of the following interventions:

Adequate position of the bronchial tube (or bronchial blocker) must be confirmed, as its position relative to the carina can change as a result of surgical manipulations or traction; repeat fiberoptic bronchoscopy through the tracheal lumen can quickly detect this problem. Both lumens of the tube should also be suctioned to exclude excessive secretions or obstruction as a factor.

Increase Fio2 to 1.0

Recruitment maneuvers on the dependent, ventilated lung may eliminate atelectasis and improve shunt.

Optimize PEEP to the dependent, nonoperative lung.

Ensure adequate cardiac output and adequate oxygen carrying capacity.

CPAP or blow-by oxygen to the operative lung will decrease shunting and improve oxygenation. However, inflation of the operative lung during VATS will make identification and visualization of the lung structures difficult for the surgeon; therefore, such maneuvers should be applied carefully and cautiously.

Two-lung ventilation should be instituted for severe hypoxemia. If possible, pulmonary artery clamp can also be placed during pneumonectomy to eliminate shunt.

In patients with chronic obstructive lung disease, one should always be suspicious of pneumothorax on the dependent, ventilated side as a cause of severe hypoxemia. This complication requires immediate detection and treatment by aborting the surgical procedure, reexpanding the operative lung, and immediately inserting a chest tube in the contralateral chest.

Alternatives to One-Lung Ventilation

Ventilation can be stopped for short periods if 100%oxygen is insufflated at a rate greater than oxygen consumption (apneic oxygenation) into an unob-structed tracheal tube. Adequate oxygenation canoften be maintained for prolonged periods, but pro-gressive respiratory acidosis limits the use of this technique to 10–20 min in most patients. Arterial Pco2 rises 6 mm Hg in the first minute, followed by a rise of 3–4 mm Hg during each subsequent minute.

High-frequency positive-pressure ventilation and high-frequency jet ventilation have been used during thoracic procedures as alternatives to one-lung ventilation. A standard tracheal tube may be used with either technique. Small tidal volumes (<2 mL/kg) allow decreased lung excursion, which may facilitate the surgery but still allow ventilation ofboth lungs. Unfortunately, mediastinal “bounce”— a to-and-fro movement—often interferes with the surgery.

3. Postoperative Management

General Care

Most patients are extubated shortly after surgery to decrease the risk of pulmonary barotrauma (par-ticularly “blowout” [rupture] of the bronchial suture line). Patients with marginal pulmonary reserve should remain intubated until standard extubation criteria are met; if a double-lumen tube was used for one-lung ventilation, it should be replaced with a regular single-lumen tube at the end of surgery. A catheter guide (“tube exchanger”) should be used if the original laryngoscopy was difficult (above).

Patients are observed in the postanesthesia care unit, and, in most instances, at least overnight or longer in an intensive care unit or intermediate care unit. Postoperative hypoxemia and respiratory aci-dosis are common. These effects are largely caused by atelectasis and “shallow breathing (‘splinting’)” due to incisional pain. Gravity-dependent transuda-tion of fluid into the intraoperative dependent lung may also be contributory. Reexpansion edema of the collapsed nondependent lung can also occur.

Postoperative hemorrhage complicates about 3% of thoracotomies and may be associatedwith up to 20% mortality. Signs of hemorrhage include increased chest tube drainage (>200 mL/h), hypotension, tachycardia, and a falling hematocrit. Postoperative supraventricular tachyarrhythmias are common and usually require immediate treat-ment. Routine postoperative care should include maintenance of a semiupright (>30°) position, supplemental oxygen (40% to 50%), incentive spi-rometry, electrocardiographic and hemodynamic monitoring, a postoperative chest radiograph (to confirm proper position of all thoracostomy tube drains and central lines and to confirm expansion of both lung fields), and adequate pain relief.

Postoperative Analgesia

The importance of adequate pain management in the thoracic surgical patient cannot be overstated. Inadequate pain control in these high-risk patientswill result in splinting; poor respiratory effort; and the inability to cough and clear secretions, with an end result of airway closure, atelectasis, shunting, and hypoxemia. Irrespective of the modality used, there must be a comprehensive plan for pain management.

A balance between comfort and respiratory depression in patients with marginal lung function is difficult to achieve with parenteral opioids alone. Patients who have undergone thoracotomy clearly benefit from the use of other techniques (described below) that may reduce the need for parenteral opi-oids. If parenteral opioids are used alone, they are best administered via a patient-controlled analgesia device.

In the absence of an epidural catheter, intercos-tal or paravertebral nerve blocks with long-acting local anesthetics may facilitate extubation, but have a limited duration of action, so alternative means of pain management must be employed. Alternatively, a cryoanalgesia probe may be used intraoperatively to freeze the intercostal nerves (cryoneurolysis) and produce long-lasting anesthesia; unfortunately, max-imum analgesia may not be achieved until 24–48 hr after the cryoanalgesia procedure. Nerve regen-eration is reported to occur approximately 1 month after the cryoneurolysis. Infusion of local anesthetic through a catheter placed in the surgical wound dur-ing closure will markedly reduce the requirement for parenteral opioids and improve the overall quality of analgesia relative to parenteral opioids alone.

Epidural analgesia is the current optimal method for acute pain control following thoracic surgical procedures. It provides excellent pain relief, continuous therapy, and avoidance of the side effects associated with administration of systemic opioids. On the other hand, epidural techniques require attention from the acute pain team for the duration of the infusion and subject the patient to the long list of epidural-related side effects and complica-tions. However, there is still much debate over the level of placement of the epidural catheter (tho-racic versus lumbar), type of medication adminis-tered (opioid and/or local anesthetic), and timing of medication administration (before surgical inci-sion vs before end of surgery). Most practitioners use a combination of opioid (fentanyl, morphine, hydromorphone) and local anesthetic (bupivacaine or ropivacaine), with the epidural catheter placed at a thoracic level.

Postoperative Complications

Postoperative complications following thoracotomy are relatively common, but fortunately most are minor and resolve uneventfully. Blood clots and thick secretions may obstruct the airways and result in atelectasis; suctioning may be necessary. Atelectasis is suggested by tracheal deviation and shifting of the mediastinum to the operative side fol-lowing segmental or lobar resections. Therapeutic bronchoscopy should be considered for persistent atelectasis, particularly when associated with thick secretions. Air leaks from the operative hemitho-rax are common following segmental and lobar resections. Most air leaks stop after a few days.Bronchopleural fistulae present as a sudden large air leak from the chest tube that may beassociated with an increasing pneumothorax and partial lung collapse. When they occur within the first 24–72 hr, they are usually the result of inade-quate surgical closure of the bronchial stump. Delayed presentation is usually due to necrosis of the suture line associated with inadequate blood flow or infection.Some complications are rare, but deserve spe-cial consideration because they can be life-threaten-ing and require immediate exploratory thoracotomy. Postoperative bleeding was discussed above. Torsion of a lobe or segment can occur as the remaining lung on the operative side expands to occupy the hemithorax. The torsion usually occludes the pul-monary vein to that part of the lung, causing venous outflow obstruction. Hemoptysis and infarction can rapidly follow. The diagnosis is suggested by an enlarging homogeneous density on the chest radio-graph and a closed lobar orifice on bronchoscopy.

Acute herniation of the heart into the opera-tive hemithorax can occur through the pericardial defect that may remain following a pneumonectomy. A large pressure differential between the two hemithoraces is thought to trigger this catastrophic event. Cardiac herniation into the right hemithorax results in sudden severe hypoten-sion with an elevated CVP because of torsion of the central veins. Cardiac herniation into the lefthemithorax following left pneumonectomy results in sudden compression of the myocardium, result-ing in hypotension, ischemia, and infarction. A chest radiograph shows a shift of the cardiac shadow into the operative hemithorax.

Extensive mediastinal dissections can injure the phrenic, vagus, and left recurrent laryngeal nerves. Postoperative phrenic nerve palsy presents as eleva-tion of the ipsilateral hemidiaphragm together with difficulty in weaning the patient from the ventilator. Large chest wall resections may include part of the diaphragm, causing a similar problem, in addition to a flail chest. Paraplegia rarely follows thoracot-omy for lung resection. There are reports of cellulose gauze and other debris migrating from the thoracic gutter into the spinal canal, resulting in spinal cord compression. If an epidural catheter has been placed, any loss of motor function or unexplained back pain should immediately trigger imaging to rule out epi-dural hematoma.

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