Abstract

Awake video-assisted thoracic surgery (VATS) has been increasingly employed in a variety of procedures involving pleura, lungs, and mediastinum. Adequate anesthesia and analgesia obtained from thoracic epidural anesthetic (TEA) allow VATS to be performed in awake patients. The potential general anesthesia-related adverse effects, such as intubation-related trauma, pneumonia, ventilator-associated lung injury, effects of neuromuscular blocking agents, and postoperative nausea and vomiting, can thus be avoided. Moreover, TEA holds the benefits of reducing pulmonary and cardiac morbidities and mortalities after noncardiac surgery. Patients who undergo awake VATS may also benefit from the efficient contraction of the dependent hemidiaphragm and preserved hypoxic pulmonary vasoconstriction during surgically-induced pneumothorax. Preliminary results from early case series have indicated certain benefits, including greater patient satisfaction, less nursing care, less sore throat, earlier resumption of oral intake, lower rate of morbidity, reduced perioperative pain, reduced cost, and shorter hospital stay. However, anesthesia for awake VATS presents a particular challenge to anesthesiologists and requires extra vigilance. Potential hazards include paradoxical respiration and mediastinum shift after surgery induced pneumothorax, which may cause progressive hypoxia, hypercapnia and hypotension. Anesthesiologists should be acquainted with the procedure to be performed, be knowledgeable on the physiological changes, be aware of the potential problems, and have good judgment on suitable timing for conversion of regional anesthesia to intubation general anesthesia in enforced circumstance.

Keywords

anesthesia, epidural; hypercapnia; hypoxemia; pulmonary ventilation: one-lung; thoracic surgery, video-assisted;

1. Introduction

The first series of patients receiving thoracoscopy was reported in 1921 by the Swedish physician Jacobaeus.¹ With the improvements in minimally invasive surgical approaches over the last two decades, video-assisted thoracoscopic surgery (VATS) has become a major practice for diagnostic and therapeutic purposes in thoracic surgery. VATS offers well-depicted advantages with regard to reduction of morbidity, improvement of pulmonary function, reduction of pain, shortening the length of hospital stay, and reducing cosmetic concerns.2, 3, 4 To facilitate the thoracic procedures under optimal visualization, a well-collapsed lung on the operative side must be achieved in most circumstances. VATS can be performed under local, regional, or general anesthesia depending on the type and duration of the procedure, the cardiopulmonary status of the patient, and the patient’s tolerance and coordination.5, 6, 7, 8, 9 In most cases, general anesthesia is required for separation of lungs using a double-lumen endobronchial tube (DLT) or bronchial blocker. However, general anesthesia-related adverse effects, such as intubation-related trauma, increased risk of pneumonia, ventilator-associated lung injury, impaired cardiac performance, effects of neuromuscular blocking agents, and postoperative nausea and vomiting, have prompted some surgeons to prefer awake VATS under regional anesthesia.10, 11, 12, 13, 14

Awake VATS under regional anesthesia has been increasingly employed in a variety of procedures involving pleura, lungs, and mediastinum.11, 12, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27 Anesthesia for these procedures is mainly achieved by thoracic epidural anesthesia (TEA) with or without additional sedation and/or local infiltration of local anesthetic. The surgical outcomes of these early series have been encouraging. However, the anesthetic management can be one of the most challenging issues for anesthesiologists. A comprehensive knowledge of related techniques from anesthesiologist's point of view has not been well addressed. As successful awake VATS largely relies on appropriate anesthetic management, it is imperative for anesthesiologists to become well acquainted with these techniques. Here we review the current literature with the aim of providing information for anesthesiologists who will participate in the care of patients undergoing awake VATS.

2. Possible physiological changes during awake thoracoscopic surgery

Thoracic surgery causes considerable physiological changes that require special anesthetic consideration, especially during awake, nonintubated, thoracoscopic procedures. The physiological derangements are mainly attributed to lateral decubitus position, surgery-induced pneumothorax, collapse of the operative lung, and influence of the chosen anesthetic techniques.

2.1. Effects of positioning

Most of the thoracoscopic surgical procedures are performed in the lateral decubitus position, which provides optimal access to the structures in the thorax. In addition, patient in the lateral position has significantly better oxygenation than patient in the supine position during one-lung ventilation (OLV).²⁸ However, impaired chest movement and limited expansion of the dependent lung in this position can cause compromised respiratory efforts. These derangements become more salient after induction of general anesthesia, neuromuscular blockade, and initiation of mechanical ventilation, as paralysis of both hemidiaphragms allow the abdominal contents to rise up against the thorax and impede positive-pressure ventilation of the dependent lung. Therefore, in lateral decubitus position, ventilation favors the nondependent lung with better compliance and favors the perfusion of the dependent lung as a result of gravity. The resulting ventilation/perfusion mismatch increases the risk of hypoxemia. Nevertheless, the match of ventilation/perfusion is preserved in awake patients with spontaneous ventilation due to more efficient contraction of the dependent hemidiaphragm. Consequently, patients undergoing awake VATS may benefit from the efficient contraction of the dependent hemidiaphragm.

2.2. Surgically-induced pneumothorax

In the normal respiration cycle, adequate ventilation is accomplished by creating negative intrathoracic pressure during inspiration and positive pressure during expiration. Once either hemithorax is opened, the negative pressure to keep the affected lung to expand is lost and subsequently the lung collapses. Although a collapsed lung is required for optimal visualization and surgical manipulation in VATS, respiratory derangement may occur during an awake state due to two major physiologic changes. First, spontaneous ventilation in patients with surgery-induced pneumothorax results in paradoxical respiration. On expiration, gas flow may, in part, enter the lung in the open hemithorax from the lung in the closed hemithorax. On inspiration, the reversal phenomenon occurs. Second, mediastinal structures swing to-and-fro between the dependent and nondependent hemithoraces during the respiratory cycle, which may cause hemodynamic instability and decrease the dependent lung to offer efficient tidal volume. Therefore, there are risks of developing hypoxemia and hypercapnia from paradoxical respiration and hypotension from mediastinal shift during awake VATS.

2.3. OLV

Adequate collapse of the operative lung to facilitate surgery is required in most thoracic procedures, especially during thoracoscopy. It can be achieved by separating the lungs with a DLT or bronchial blocker. In nonintubated patient with spontaneous ventilation, the operative lung undergoes collapse with inefficient paradoxical respiration after surgically induced pneumothorax. In either circumstance, the collapsed lung continues to be perfused without being ventilated, which may create a large right-to-left intrapulmonary shunt. The widened alveolar-to-arterial oxygen gradient can increase the risk of intraoperative hypoxemia.

Hypoxic pulmonary vasoconstriction (HPV) is an intrinsic physiologic mechanism to prevent right-to-left shunt. Through an adaptive vasomotor response to alveolar hypoxia, the pulmonary arteries constrict and the blood flow is redirected to the alveoli rich in higher oxygen contents. HPV is generally considered to be protective during OLV; however, different anesthetic regimens during thoracic surgery have different effects on HPV and so the incidence of hypoxemia.²⁹ Volatile anesthetics have been reported to inhibit HPV and may promote hypoxemia during OLV.27, 28 In contrast, intravenous anesthetics, such as propofol, and thoracic epidural anesthetics, which cause sympathetic blockade have little or no direct effect on HPV.29, 30, 31, 32, 33 Accordingly, awake VATS performed under TEA with or without supplemental sedative infusion may preserve HPV and thus the risk of hypoxemia is reduced.

3. Indications for awake thoracoscopic surgery

Awake VATS was initially purposed for diagnostic means and management of simple pleural procedures.⁶ Subsequently, numerous case series and randomized controlled studies have reported the feasibility and safety of awake VATS in treating spontaneous pneumothorax,16, 17, 18, 34, 35 bullous emphysema,²⁵ resection of pulmonary nodules,11, 15, 19, 20, 21 lung volume reduction surgery,22, 23 decortication for empyemic thoracis,²⁴ biopsy for anterior mediastinal masses,²⁶ and even very complex procedures, such as lobectomy for lung cancer.¹² Awake VATS also has been reported to successfully treat critical patients with pericardial or pleural effusion36, 37 and bullous emphysema for bullectomy,³⁸ complicated by acute respiratory failure. Yen et al also reported a high-risk case of polymyositis with a huge pulmonary bulla undergoing awake mini-thoracotomy for surgical unroofing of the bulla under TEA.³⁹ Although solid evidence of success are lacking, the preliminary results have encouraged the expansion of the indications for awake VATS.

The patient population for awake VATS tends to be either very healthy patients undergoing minor procedures or high-risk patients in whom the avoidance of morbidity of conventional thoracotomy and the need for intubated general anesthesia could be reduced. As a general rule, the procedures should not be too long and the patients should be carefully selected. Close cooperation of patient is a prerequisite for awake VATS. Furthermore, procedures requiring lung isolation to protect the contralateral lung from contamination, such as by massive bleeding, pus, alveolar proteinosis or bronchopleural fistula, should be an absolute contraindication for awake VATS.

4. TEA for awake thoracoscopic surgery

Regional anesthesia for awake VATS consists of intercostal nerve block, paravertebral block, thoracic epidural block, peripheral field block, and/or ipsilateral stellate ganglion block (block of coughing reflex). In most circumstances, TEA can be sufficient enough to serve solo for VATS.

4.1. Benefits of TEA

The risks and benefits of TEA have recently been extensively reviewed by Freise and Van Aken.⁴⁰ TEA has been demonstrated to improve left ventricular function in coronary artery disease, unstable angina pectoris, and myocardial infarction.41, 42, 43, 44 It was also reported to improve diastolic function in patients with coronary artery disease.⁴⁵ Meta-analyses showed that TEA may decrease cardiac morbidity and mortality after noncardiac surgery.46, 47 Although high thoracic epidural block may reduce vital capacity and forced expiratory volume in 1 second as a result of direct motor block of intercostals muscles,48, 49 a meta-analysis showed reduction of pulmonary complications after epidural analgesia, probably due to earlier mobilization, reduced opioid consumption, and adequate pain relief for coughing.⁵⁰ Moreover, epidural anesthesia may accelerate recovery of intestinal function,51, 52 decrease systemic stress response to surgery,⁵³ and potentially reduce tumor recurrence rate and improve survival in certain cancer surgery.⁵⁴

4.2. Risks of TEA

While the use of TEA has numerous benefits in awake VATS, there is concern about its risks. The complications of TEA can be mildly annoying or catastrophic. High TEA involving segments T1 to T5 may have minimal vasodilatory effect and may cause significant but small reduction in heart rate.55, 56 Hypotension and bradycardia after TEA can be forestalled and corrected respectively with intravenous fluids and vasopressors. Inadvertent subdural and subarachnoid injections, which may cause profound hypotension, apnea, and unconsciousness, require airway support, rapid infusion of intravenous fluids, and administration of vasopressors to restore and maintain hemodynamic stability. Severe neurological complications such as permanent paraplegia after epidural anesthesia is extremely rare; the incidence as estimated is around 0.02%.57, 58, 59, 60 The causes are diverse, and include epidural hematoma, epidural abscess, direct cord trauma, spinal infarction, and neurotoxicity by accidental subarachnoid injection or chemical contamination.⁶¹ Performing TEA with exceptional caution, close observation after the procedure, and prompt management of adverse effects are imperative to forestall or attenuate the undesired sequelae.

4.3. Outcome in awake VATS

Based on the preliminary data from various randomized studies, the principal beneficial effects of TEA for awake VATS, as opposed to intubated general anesthesia for conventional thoracotomy, of greater patient satisfaction and thrift of nursing care,¹¹ less sore throat, earlier oral intake,¹² lower rate of morbidity,¹² reduced perioperative pain,¹⁷ economization of cost,¹⁷ and shorter in-hospital stay.11, 12, 17, 23 The anesthesia duration, length of surgery, and blood loss are comparable or seemingly better in awake VATS.12, 13, 18, 24 Moreover, the perioperative surgical stress response could be attenuated in awake VATS as a result of reduced postoperative stress hormones and lymphocyte counts.62, 63

5. Perioperative concerns of awake thoracoscopic surgery

Anesthesia for awake VATS requires extra vigilance to ensure the success of the surgery and the safety of the patient. The anesthesiologists should be acquainted with the procedure to be performed, aware of the potential problems, and ready for converting TEA to general anesthesia with intubation if circumstances compel.

5.1. Anesthetic procedures

Patients presenting for awake VATS should undergo routine preoperative assessment. When selecting the procedure or for high-risk patients, a more comprehensive survey of cardiovascular and pulmonary statuses is required. Standard perioperative monitoring items should include electrocardiogram, peripheral oxygen saturation, noninvasive blood pressure, and end-tidal carbon dioxide. Oxygen saturation detected by pulse oximeter is particularly useful in monitoring the trends of oxygenation and early disclosure of hypoxemia; however, pulse oximetry cannot play the part of arterial blood gas analysis for detecting acid-base imbalance and oxygenation disturbances.⁶⁴ End-tidal carbon dioxide to monitor spontaneous ventilation in awake patients can be achieved by insertion of a detector into either nostril.¹² The need for invasive monitoring, such as direct arterial pressure and central venous pressure, should be individualized based on the patient's general condition and the type of procedure.

Awake VATS is frequently performed under TEA. With or without premedication, the epidural needle is usually inserted between the T4 and T6 interspaces to achieve somatosensory and motor block at the T1 to T9 level, depending on the type of procedure.11, 12, 20 TEA is maintained by a continuous infusion of local anesthetics with or without opioids being added.11, 12 A warm-cold discrimination test is commonly used to demarcate the levels of blockade. Field block with local anesthetic infiltration or intercostal nerve block can be used as an adjunctive technique to TEA before incision. A procedure involving the apex or pleura may need supplemental intravenous agents due to possible incomplete block. Pain from failed or incomplete analgesia may cause cardiopulmonary compromise and requires immediate conversion to general anesthesia. Instead of using TEA, paravertebral block has been reported to be an alternative sole anesthetic technique for awake VATS.³⁷ However, more clinical experience is required to determine its role on awake VATS.

Whether or not to sedate the patients during awake VATS depends on anesthesiologist's experience and should be individualized from patient to patient depending on the procedure. Sedation may reduce anxiety and discomfort during awake VATS. However, it may also increase the risks of hypercapnia and hypoxemia. In this setting, it is ideal to have the patient sufficiently sedated but remaining cooperative and complying with the instructions of ventilation control. Moreover, it is necessary to maintain the patency of the airway, monitor the spontaneous ventilation, supply oxygen by nasal prongs or mask to maintain oxygen saturation above 90%.12, 20 Sedation by intravenous propofol using a target-controlled infusion and incremental fentanyl injection has been reported to be able to maintain a mildly sedated status with unmolested communication and cooperation in low-risk patients.¹² However, another major group preferred a light sedation with no more than 1 or 2 mL midazolam, particularly in patients with severe emphysema.²⁴ Thus, the patients are able to cough and make deep inspiration to facilitate lung expansion at the end of the procedure.

5.2. Intraoperative management

Lung collapse develops gradually after open pneumothorax created by trocar insertion so that awake VATS can be performed.⁷ However, lung movement as a result of spontaneous paradoxical respiration can be an obstacle to surgical maneuvers. Lung movement during breathing has been reported to be significant especially when the respiratory rate is more than 20 breaths/minute, which might be decreased by increasing sedation with permissive hypercapnia.¹² Continuous infusion of remifentanil has been reported to slow the respiratory rate without sedative effect in a critical patient undergoing awake thoracoscopic bullectomy.³⁸ Insufflation of carbon dioxide to improve visualization in intubated VATS is not recommended in awake VATS, because this technique may cause hemodynamic instability as a result of mediastinum compression and further deteriorate hypercapnia.⁹ Nevertheless, lung collapse has been generally reported to be satisfactory without the needs of additional management in most awake patients with spontaneous ventilation.7, 27, 65

Predominance of vagal tone after sympathetic block by TEA might potentially increase bronchial tone and reactivity.⁷ Although there was one study that showed that blockade of pulmonary sympathetic innervation seemed to bear no relevance to airway resistance,⁶⁶ mechanical irritation induced coughing reflex is frequently a problem during awake VATS. Coughing reflex or reflexive bronchoconstriction can be suppressed with intravenous lidocaine at the plasma concentrations of 1 to 2 μg/mL67, 68; however, continuous intraoperative lidocaine infusion may raise the concern of toxic threshold of 5 μg/mL.65, 66 Inhalation of aerosolized 2% lidocaine in a high oxygen flow for about 30 minutes before surgery might reduce the coughing reflex in response to surgical manipulation.³⁶ Ipsilateral stellate ganglion block with 10 mL of 0.25% bupivacaine has also been reported to achieve cough control in patients with overactive coughing reflex.¹³ In addition, Chen et al found that intrathoracic vagal block with 2 mL of 0.25% bupivacaine performed somewhere adjacent to the ipsilateral vagus nerve could effectively abolish coughing reflex without affecting heart rate, breathing rate, and blood pressure.¹²

Intraoperative hypotension has been reported to be a transient problem during awake VATS.²⁴ Hypotension can be caused by epidural local anesthetics or mediastinum shift, especially in high-risk patients with reduced cardiopulmonary reserve. Judicious fluid replacement, administration of vasopressors or inotropics and avoiding excessive mediastinum compression during lung manipulation may reverse this undesirable adverse effect.

Hypoxemia and hypercapnia may develop during awake VATS due to increased intrapulmonary shunt and paradoxical respiration. Ensuring the patency of a patient's airway is of paramount importance, particularly in one being sedated. Thus, hypoxemia can be prevented with simple administration of oxygen through a Venturi mask in most circumstances.⁷ However, hypercapnia may deteriorate due to sustained hypoventilation of the operative lung and rebreathing of the residue gas from the contralateral lung. In addition, hypoventilation may be, to some extent, due to blocking of the intercostal muscles by TEA and, probably on rare occasions, the diaphragmatic excursion is hampered as a consequence of the effect of high TEA on the phrenic nerve (C3–C5). Permissive hypercapnia implicates an increase in the partial pressure of carbon dioxide to exceed the normal range as a result of hypoventilation. It can result in respiratory acidosis, pulmonary vasoconstriction, activation of sympathetic nervous system and increased intracranial pressure, but in general, the patients undergoing awake VATS find these conditions tolerable. It has been suggested that permissive hypercapnia is safe and may improve hemodynamics and the ventilation/perfusion match due to the release of catecholamines and increased parenchymal compliance.7, 69 Nevertheless, the awake patient can be coached to regulate the ventilation slowly and deeply in case of the onset of hypercapnia.⁶⁵ Occasionally, assisted positive pressure ventilation via a mask is needed in patients with shortness of breath or extremely suppressed spontaneous ventilation. Persistent application of positive pressure ventilation may hamper the surgical field by the partially inflated lung. In this circumstance, conversion to general anesthesia may then be considered.

The incidences of conversion to general anesthesia ranged from 0% to 10%, based on the preliminary data from case series and randomized studies.12, 13, 17, 19, 21, 22, 23, 24, 25 The commonest reason for conversion to general anesthesia was dense pleural adhesions.11, 21, 22 Chen et al reported in their study that three patients (10%) undergoing lobectomy without intubation required conversion of TEA to intubated general anesthesia because of persistent hypoxemia, poor epidural anesthesia and bleeding requiring extensive thoracotomy.¹² The higher conversion rate in lobectomy might be due to the complexity of the procedure. In this circumstance, intubation of a single lumen endobronchial tube with placement of a blocker may serve the purpose. Intubation should be performed after adequate oxygenation and might be performed under fiberoptic guidance, without changing the patient’s position.¹²

At the end of awake VATS, a chest tube is inserted during wound closure. The chest tube is connected to an underwater sealed bottle so that the surgically induced pneumothorax can be terminated. In a fully awake patient, he (she) is asked to breathe deeply and cough to reexpand the collapsed lung.12, 27 Moreover, positive pressure ventilation delivered via a mask is applied to facilitate lung expansion as needed. If the lung expansion is not adequate in follow-up chest x-ray, negative pressure suction to promote lung expansion may be considered.

5.3. Postoperative management

Although major complications after awake VATS have not been documented to date, there are still needs for postoperative pulmonary therapy. Aggressive chest physiotherapy, administration of bronchodilators, early mobilization, and use of incentive spirometry can be helpful to improve postoperative lung function.

While the pain after awake VATS is reduced,¹⁷ postoperative analgesia can be achieved by either on-demand or patient-control analgesia using nonsteroidal anti-inflammatory drugs or opioids in most circumstances. In case of more painful procedures, thoracic epidural analgesia via an indwelled catheter should be considered.11, 12 The combination of nonsteroidal anti-inflammatory drugs and paravertebral block has also been reported to have excellent pain relief for VATS.⁷⁰ However, thoracic epidural analgesia holds the benefits of improving pulmonary function and promoting better postoperative outcomes.⁷¹

6. Conclusion

Awake VATS presents a particular challenge to anesthesiologists and requires extra vigilance. Current preliminary data support the feasibility and safety of awake VATS under regional anesthesia, especially by TEA. Nevertheless, large scale studies are needed before the overall risks and benefits can be concluded.