Anesthetic Considerations

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CHAPTER 3 Anesthetic Considerations

Karen S. Sibert, Robert A. Frantz

Introduction

Anesthesia for minimally invasive thoracic surgery involves many of the same techniques that anesthesiologists use for open thoracic procedures. Successful anesthetic management includes several components:

♦ Facility with placement and adjustment of right- and left-sided double-lumen endotracheal tubes (DLTs)

♦ Knowledge of tracheobronchial anatomy and skill with fiberoptic bronchoscopy

♦ Expertise with thoracic epidural analgesia

♦ Anesthesiologists dedicated to providing anesthesia for thoracic cases

Patient Preparation and Monitoring

♦ Most patients are moderate to high anesthesia risks (i.e., American Society of Anesthesiologists [ASA] physical status class 3), and abnormal pulmonary function test results are expected.

♦ If the patient is on bronchodilator therapy, provide treatment in the preoperative area.

♦ Discuss postoperative pain management, including the possibility of epidural analgesia.

♦ Reassuringly prepare the patient to anticipate that breathing will be uncomfortable on waking due to the effect of chest tubes and lung reexpansion.

♦ Patients who have had neoadjuvant radiation therapy or chemotherapy must be identified in advance and kept on the lowest acceptable FIO₂ because they are more susceptible to hyperoxic lung injury.

♦ A single, reliable, 18-gauge intravenous catheter is adequate for many minimally invasive cases.

♦ Radial artery catheters are placed for most cases unless the patient is especially healthy or the anticipated procedure is brief.

♦ Central venous access is required less frequently unless intravenous access is limited or substantial blood loss is anticipated; central lines are routinely placed for pneumonectomy, esophagectomy, and lung volume reduction surgery.

Double-Lumen Endotracheal Tube Placement

Applications

♦ DLTs are required for most thoracic cases: wedge resection, lobectomy, pneumonectomy, lung reduction, pleurodesis, decortication, and esophagectomy.

♦ They are not required for mediastinoscopy, sympathectomy, or pericardial window (i.e., subxyphoid approach).

♦ We exclusively use DLTs for any procedure requiring lung separation. Bronchial blockers do not allow adequate deflation or suctioning of the operated lung.

♦ Routine use of a video laryngoscope permits full visualization of the DLT tip as it passes between the vocal cords.

Routine Intubation

We developed a 5-step process for passage of the DLT into the larynx, most often with the use of a Mac 4 video laryngoscope.

1. Insert the Mac blade into the right side of the mouth, and use the flange to sweep the tongue over to the left.

2. Advance the tip of the blade into the vallecula, and elevate the blade to reveal the vocal cords. In some patients, the view improves with the tip of the blade beneath the epiglottis.

3. Bend or curve the DLT at an angle of 30 to 45 degrees about 6 to 8 cm from the tip, and insert it from the right side of the mouth so that the tip approaches the vocal cords.

4. Depending on the relationship of the bronchial tip and the surrounding structures, one of two approaches is necessary:

a. If the alignment is suitable (with or without the stylet in place), pass the DLT beyond the vocal cords into the mid-trachea.

b. If the tip of the bronchial lumen impinges on the anterior or lateral laryngeal structures (i.e., anterior commissure) or the arytenoid cartilages, gently redirect or rotate the tube to guide the tip past the obstacles. It may be helpful to retract the stylet.

5. Because the DLT is often anteriorly directed at this stage, the leading edge may catch on the tracheal rings, preventing advancement of the tube. Additional gentle rotation and pressure may be necessary to “screw” the DLT into the mid-trachea, and it may be necessary to pass a fiberoptic bronchoscope through the bronchial lumen to help guide the DLT tip through the tracheal rings and into the appropriate bronchus.

Difficult Intubation

♦ Use of a DLT exchange catheter facilitates placement of a DLT in patients with an anterior larynx, limited aperture, or other difficult airway situations (Figure 3-1). The exchange catheter may be guided into the trachea using direct video laryngoscopy or advanced through a previously placed single-lumen endotracheal tube. The DLT is then passed over the catheter into the trachea. Care must be taken to pass the exchange catheter tip gently just past the vocal cords to avoid tracheal injury.

♦ Another safe approach to the difficult airway is to insert a fiberoptic bronchoscope into the trachea and pass the DLT directly over it. Maneuvers including jaw thrust, tongue retraction, and simultaneous laryngoscopy facilitate passage of the tube through the laryngeal inlet.

Figure 3-1 Insertion of a soft-tipped exchange catheter into the trachea facilitates passage of a double-lumen endotracheal tube in a patient with a difficult airway.

Achieving Optimal DLT Placement

♦ Correct placement of a DLT can be achieved in one of two accepted ways:

• Insert the DLT into the trachea, and use fiberoptic bronchoscopy (FOB) to direct the tube down the appropriate mainstem bronchus.

• Insert the DLT to an estimated appropriate depth in the mainstem bronchus during the initial laryngoscopy (our usual practice), and use FOB to confirm placement and adjust the tube position as necessary.

Choice of Right versus Left DLT

In many institutions, left DLTs are used for all thoracic cases because of the perceived difficulty in situating right-sided tubes properly to ventilate the right upper lobe (RUL). We disagree; we routinely use right DLTs for most left lung cases, and left DLTs for all right lung cases. There are multiple advantages to this approach:

♦ There is no risk of inadvertently stapling the cuff of a left DLT during left lobectomy or pneumonectomy.

♦ A complete view of the carina and the mainstem bronchus of the operated lung is obtained during bronchoscopy.

♦ Bronchoscopy through the tracheal lumen to check the distal cuff position does not interrupt ventilation of the nonoperated lung.

♦ If the tracheal (proximal) cuff is damaged by the patient’s teeth during insertion, lung isolation is still accomplished by the intact distal cuff.

♦ If a left DLT is used for left lung surgery, it is possible for pressure on the operated lung to occlude the tracheal lumen, which is ventilating the right lung, or to push the bronchial cuff back into the trachea.

♦ Right DLTs are easy to insert because the path to the right mainstem bronchus is more direct. A contralateral tube is imperative when a sleeve resection is performed (e.g., if a left-sided tube is used when the left mainstem bronchus is open during a bronchial sleeve), the tube interferes with suturing and the patient is not ventilated well.

Troubleshooting after Initial Insertion

♦ In 5% to 10% of cases, a left DLT goes down the right mainstem bronchus, despite the usual leftward rotation, as it is advanced. Withdraw the tube into the trachea, and advance it into the left bronchus under direct FOB vision.

♦ When the patient is turned lateral and flexed, the DLT usually retracts cephalad at least a centimeter and may need to be advanced to avoid herniation of the distal cuff over the carina. This is especially likely in edentulous patients. It is always easier to pull a DLT back than to advance it after it has become warm and flexible.

♦ Always repeat fiberoptic bronchoscopy after lateral positioning to confirm proper tube placement.

♦ Hypoxemia is usually a sign of an improperly placed tube; we rarely find it necessary to use continuous positive airway pressure (CPAP) for the operated lung or positive end-expiratory pressure (PEEP) greater than 5 cm to the nonoperated lung. During lobectomy, the oxygen saturation always improves after clamping of the arterial blood supply to the lobe.

♦ With a right DLT, if the distance to the takeoff of the RUL bronchus is very short, the distal cuff may herniate over the carina. In this event, connect the FOB to suction, and pass it down the left mainstem bronchus to deflate the left lung.

♦ After the patient is positioned laterally, the alignment of the RUL orifice on a right DLT may be altered. It may be difficult to regain perfect alignment, but the SaO₂ often is not adversely affected.

Fiberoptic Bronchoscopy and Tracheobronchial Anatomy

♦ Trachea and main carina (Figure 3-2)

The main carina normally has a sharp bifurcation.

The membranous trachea is posterior and has a flat appearance.

The anterior trachea is arc-shaped and has visible rings.

♦ Right mainstem bronchus and secondary carina (Figure 3-3)

On the right is the orifice of the RUL.

On the left is the origin of the right bronchus intermedius.

♦ RUL bronchus and segmental bronchi (Figure 3-4)

Unique trifurcation includes apical, anterior, and posterior segments.

♦ Right bronchus intermedius and bifurcation into the right middle lobe (RML) and right lower lobe (RLL) (Figure 3-5)

RML has a slightly smaller lumen and two bronchial segments.

RLL has a larger lumen with one superior and four basal segments.

♦ Left mainstem bronchus, carina, and bifurcation into the left upper lobe (LUL) and left lower lobe (LLL) (Figure 3-6)

The LUL and LLL are approximately equal in size.

♦ Left lower lobe (Figure 3-7)

One superior segment and three (usually) or four basal segments

♦ Left upper lobe (Figure 3-8)

Upper division has three segments.

Lingula has two segments, usually immediately visible.

♦ Optimally placed right DLT

View through bronchial lumen: RUL takeoff is visible through the aperture in the DLT at the end of the white line (Figure 3-9).

View through tracheal lumen: blue rim of the distal cuff is visible at right of carina (Figure 3-10).

♦ Optimally placed left DLT

View through bronchial lumen: left mainstem carina and the LUL and LLL bronchi are visible (Figure 3-11).

View through tracheal lumen: blue rim of the distal cuff is visible at left of carina (Figure 3-12).

Figure 3-2 View of the main carina shows the arc-shaped rings of the anterior trachea above and the posterior membranous trachea below.

Figure 3-3 The right mainstem bronchus has the orifice of the right upper lobe to the right and the origin of the bronchus intermedius to the left.

Figure 3-4 The right upper lobe bronchus is characteristically trifurcated into three segments.

Figure 3-5 In the right bronchus intermedius, the right middle lobe orifice is smaller, and the right lower lobe orifice typically has a flat septum separating the superior segment from the basal segments.

Figure 3-6 In the left mainstem bronchus, the left upper lobe and left lower lobe bronchi are approximately equal in size.

Figure 3-7 The left lower lobe bronchus has one superior segment and three (sometimes four) basal segments.

Figure 3-8 In the left upper lobe bronchus, the upper division has three segments, and the lingula has two segments.

Figure 3-9 View through the bronchial lumen of an optimally placed right double-lumen endotracheal tube shows the takeoff of the right upper lobe orifice through the aperture at the end of the white line.

Figure 3-10 View through the tracheal lumen of an optimally placed right double-lumen endotracheal tube shows the rim of the distal cuff to the right of the carina.

Figure 3-11 View through the bronchial lumen of an optimally placed left double-lumen endotracheal tube shows the left upper lobe and left lower lobe bronchi.

Figure 3-12 View through the tracheal lumen of an optimally placed left double-lumen endotracheal tube shows the rim of the distal cuff to the left of the carina.

Induction, Maintenance, and Emergence from Anesthesia

♦ All medication choices are geared toward prompt emergence from anesthesia and extubation in the operating room whenever possible.

♦ Reduce FIO₂ in any patient who has received neoadjuvant chemotherapy or radiation therapy to reduce the risk of hyperoxic lung injury; oxygen saturation of 86% to 90% is acceptable during one-lung ventilation.

♦ Minimize intravenous fluid administration to reduce the risk of postexpansion pulmonary edema.

Induction

♦ Avoid benzodiazepines in geriatric patients or any patient with borderline respiratory function.

♦ Propofol is well tolerated by most patients, although we often use reduced doses; etomidate is appropriate for patients with compromised cardiac function or hypovolemia.

♦ Keep narcotic doses low to avoid postoperative respiratory depression; 100 to 150 mcg of fentanyl is sufficient for many cases.

♦ Intubation is usually accomplished with nondepolarizing muscle relaxants; rocuronium has the advantages of rapid onset and minimal histamine release.

Maintenance

♦ Clamp the tracheal lumen of the DLT well before surgical entry to the thorax to allow the lung time to deflate; confirm tube placement with FOB after lateral positioning, and suction the operated lung as necessary.

♦ Dexamethasone (8 to 10 mg IV) helps to reduce vocal cord edema, diminish airway reactivity, and prevent postoperative nausea.

♦ Desflurane is a useful inhaled agent because it can be rapidly titrated on and off, and it acts as an effective bronchodilator. Desflurane reduces hypoxic pulmonary vasoconstriction but not to a clinically significant degree.

♦ Propofol infusion may be helpful, especially for rigid bronchoscopy in which an air leak may limit the use of inhaled agents.

♦ Maintain normothermia with fluid warming (especially if transfusion is necessary) and use of a forced-air warming blanket for the lower body.

Intraoperative Issues and Caveats

♦ Short-lived fluctuations in blood pressure are common because of variations in the level of surgical stimulus, mechanical pressure on the heart or great vessels, and relatively dry fluid status.

♦ Pharmacologic support of low blood pressure is better than giving large quantities of crystalloid. Hypertension can be managed acutely with small doses of propofol or esmolol; use longer-acting antihypertensive agents only with caution until surgery ends.

♦ Intraoperative arrhythmias are often secondary to instrumentation and resolve when manipulation is stopped.

♦ Diltiazem (20 mg IV) may be given slowly to reduce the incidence of postoperative atrial fibrillation in patients undergoing lobectomy or pneumonectomy, particularly if the pericardium is entered.

♦ Avoid overdosing with muscle relaxants; thoracic patients may be at risk for prolonged muscle relaxant effects due to Eaton-Lambert syndrome, myasthenia gravis, steroid-induced myopathy, or chronic debilitation.

Ventilation Parameters

♦ During one-lung ventilation, reduce the tidal volume (VT) to 5–6 mL/kg.

♦ Monitor to ensure a peak airway pressure (PAP) of less than 35 cm H₂O and a plateau pressure of less than 25 cm H₂O.

♦ Apply PEEP up to 5 cm H₂O except for patients with chronic obstructive pulmonary disease (COPD).

♦ Adjust the respiratory rate to maintain a normal PaCO₂.

Emergence

♦ Reinflate the operative lung gradually; manual ventilation is the best means of controlling airway pressure.

♦ Consider allowing the patient to resume spontaneous ventilation during closure of the subcutaneous tissue and skin.

♦ The use of pressure support with or without synchronized intermittent mandatory ventilation (SIMV) facilitates spontaneous ventilation and lung reinflation.

♦ Ensure that muscle relaxation is completely reversed!

♦ Extubate patients awake in the semi-sitting position if they are obese or were difficult to intubate.

♦ Consider deep extubation in the lateral position for selected patients (e.g., normal weight, easy airway); this has the advantage of reducing cough, bronchospasm, hypertension, and tachycardia.

♦ Add ketorolac (30 mg IV) near the end of the case for patients with normal renal function and coagulation parameters.

♦ Lidocaine (50 to 100 mg IV) may help the patient tolerate the endotracheal tube until extubation.

♦ Many patients benefit from bronchodilator therapy immediately on arrival to the postanesthesia care unit (PACU).

Procedure-Specific Pearls and Pitfalls

Mediastinoscopy

♦ Significant blood loss rarely occurs but can be massive and can require median sternotomy for control.

♦ Place the pulse oximeter sensor and arterial catheter (if used) on the patient’s right. If the mediastinoscope occludes the brachiocephalic artery, diminished blood flow to the right arm can be recognized promptly and the surgeon alerted so that the duration of reduced flow to the right carotid artery can be minimized.

Thymectomy for Myasthenia Gravis

♦ Avoid muscle relaxants if possible.

♦ Adequate intubating conditions may be achieved with a combination of propofol and deep anesthesia with inhaled agents (i.e., desflurane or sevoflurane).

Bilateral Thoracic Sympathectomy

♦ Bilateral thoracic sympathectomy is frequently performed on healthy patients for hyperhidrosis.

♦ A single-lumen tube suffices, and respiration is suspended during the key portions of surgical exposure while CO₂ is insufflated to decompress the lung.

♦ Monitor bilateral upper extremity temperatures for confirmation of sympathectomy.

Esophagectomy

♦ Depending on the site of the lesion, the patient may require right video-assisted thoracic surgery (VATS) or right thoracotomy in addition to laparotomy.

♦ The left side of the neck must be left free if a cervical anastomosis is planned.

♦ Hypotension is common during mediastinal dissection of the esophagus and may require pharmacologic support; some surgeons request dopamine infusion routinely.

♦ Maintain normal temperature and acid-base status; these patients require generous hydration.

♦ Prolonged hypotension or hypovolemia may contribute to ischemia of the esophageal anastomosis.

Pleurodesis and Decortication

♦ Pleurodesis and decortication are often undertaken in very ill patients with metastatic cancer, chronic pleural effusion, empyema, or hemothorax.

♦ Anticipate substantial intraoperative blood loss during decortication, especially if the pleural peel is old.

♦ These patients are at high risk for postoperative mechanical ventilation due to their underlying disease processes.

Bilateral Lung Volume Reduction Surgery

♦ Lung volume reduction surgery is recommended only for patients with severe, refractory COPD.

♦ Bronchodilator and steroid therapy should be optimized preoperatively.

♦ Instruct the patient in the use of pursed-lip breathing after surgery to augment pulmonary function by supplying auto-PEEP.

♦ A thoracic epidural catheter should be placed before surgery unless there is a contraindication (see “Postoperative Analgesia”).

♦ Gentle induction works best, with reduced propofol dosing, a nondepolarizing muscle relaxant, and an inhaled agent for bronchodilation.

♦ Highly compliant lungs with bleb formation reach excessive tidal volumes easily; avoid aggressive mask ventilation during induction.

♦ Maintain pressure-controlled ventilation with initial peak inspiratory pressure (PIP) settings of 12 to 14 cm H₂O (preferred). PIP greater than 20 cm is rarely necessary.

♦ Allow higher than normal Pco₂ (i.e., permissive hypercapnia) with slower inspiratory and expiratory cycling of the ventilator to reduce the risk of barotrauma and air trapping. Oxygenation is seldom a problem.

♦ Lung deflation often requires FOB-directed suctioning.

♦ Reinflation of the first lung should be accomplished by manual ventilation with pressures of less than 20 cm, gradually increasing each breath until the lung is expanded. Although the surgeon may request higher pressure to test the suture line, it is important to avoid causing another bleb to rupture.

♦ Assess suture line leaks by using a volume meter attached to the anesthesia circuit. At a reasonable PIP, measure the difference between inspiratory and expiratory volumes. Too great a difference implies that the suture line must be inspected for a leak. Some air leak is to be expected; the amount varies according to the patient’s lung volumes.

♦ As operation begins on the second side, the ventilated lung is the previously reduced lung. Compliance is often decreased, and a lower tidal volume must be tolerated to avoid excessive PIP.

♦ Check for excessive air leak on the second side as described previously.

♦ Extubate the patient in a semi-sitting position when awake and following commands; encourage the use of pursed-lip breathing.

♦ Order bronchodilator treatment to be started immediately on arrival to the PACU.

Postoperative Analgesia

Analgesia for Routine Thoracoscopic Cases

♦ In our institution, less than 5% of thoracoscopic cases convert to open thoracotomy, and we do not place epidural catheters for routine single-lung VATS procedures.

♦ The surgeons infiltrate the skin with local anesthesia before incision and often perform thoracic intercostal nerve blocks from T2 to T11 before wound closure.

♦ Ketorolac is a useful adjunct.

♦ The PACU nursing staff plays a vital role in titrating narcotic analgesia. Too little can cause the patient to splint and refuse to cough due to pain; too much can easily result in carbon dioxide retention. Small incremental doses work best, such as hydromorphone (0.2 to 0.5 mg IV) or fentanyl (25 to 50 mcg IV).

Thoracic Epidural Analgesia

♦ We place epidural catheters preoperatively in patients undergoing open thoracotomy, pneumonectomy, lung volume reduction surgery, bilateral VATS, and rib or chest wall resection.

♦ About 5% of video-assisted lobectomies are scheduled as possible open thoracotomies due to previous neoadjuvant radiation therapy or chemotherapy, Pancoast tumor, chest wall involvement, or the need for sleeve resection; these patients receive epidural catheters.

♦ Epidural placement before induction of general anesthesia produces improved analgesia because the epidural can be activated before the conclusion of surgery.

♦ The epidural catheter is usually inserted at the mid-thoracic level. Placement at a more cephalad level does not block pain from the chest tube insertion sites.

♦ In the event of unanticipated conversion of VATS to open thoracotomy, some anesthesiologists place an epidural catheter before emergence from anesthesia, with minimal or reversed neuromuscular blockade. Others prefer to awaken the patient and insert the epidural in the PACU.

♦ Anesthesiologists disagree about whether it is ever justifiable to insert a thoracic epidural catheter in an unconscious adult patient who cannot report pain or paresthesia.

♦ We make limited use of the epidural catheter during surgery except to give a test dose of local anesthetic and a loading dose of 2.5 to 4 mg of preservative-free morphine. A fully activated epidural increases the risk of intraoperative hypotension.

♦ Because fluid administration is kept to a minimum for most thoracic patients, especially those undergoing pneumonectomy, blood pressure may need support with a low-dose infusion of phenylephrine for the first 24 hours.

♦ Near the conclusion of surgery, we administer epidural fentanyl (50 to 100 mcg) with 0.25% bupivacaine or 1% lidocaine with 1:200,000 epinephrine (4 to 6 mL). A continuous infusion is started after the patient arrives in the PACU, usually consisting of fentanyl (5 to 10 mcg/mL) and bupivacaine (0.05% to 0.0625%) at 3 to 6 mL/hr.

♦ Communication with PACU staff and the pain management service is essential for continuity of care during the postoperative period.

Related

Atlas of Minimally Invasive Thoracic Surgery (Vats)