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Reoperative Cardiac Surgery
Chapter 23
Reoperative Cardiac Surgery Amanda J. Rhee, MD • Joanna Chikwe, MD
Key Points 1. Reoperative cardiac surgery presents greater risk than first-time surgery because patients are usually older, have more comorbidity, and have more advanced cardiovascular disease. Also, resternotomy can be hazardous due to adhesions of cardiac structures to the sternum. Bypass conduits may not be available owing to prior use, and the frequency of valve replacement versus valve repair is higher. 2. A thorough history, clinical evaluation, and review of imaging must be performed— with particular thought to weighing the risk of surgery against the possibility of medical management with multidisciplinary expertise—before making the decision to proceed. 3. Preinduction anesthestic preparations include placement of defibrillator pads, pacemaker or defibrillator adjustments, and placement of invasive monitoring in the setting of the possibility of peripheral cannulation strategies and alternative cardiopulmonary bypass techniques such as cooling before sternotomy. 4. Emergency reexploration is a high-risk situation in which expedited surgical intervention is required, usually in the setting of bleeding with pericardial tamponade. Transfusion should be anticipated, hemodynamics supported, and heparin ready to administer in anticipation of possible cardiopulmonary bypass.
In contemporary practice, 3% to 4% of coronary artery bypass graft (CABG) operations and approximately 10% of valve surgery procedures are reoperations. Reoperative cardiac surgery carries an incremental risk of mortality and major morbidity compared with first-time or primary cardiac surgery because patients are usually older, with additional comorbidity and more advanced cardiac disease, and because of specific technical challenges presented by prior cardiac surgery. The surgical approach to incision and cannulation in coronary and valve surgery reoperations often differs significantly from the approach used in primary cases, and adverse intraoperative events that require immediate changes to the planned strategy are common and often predictable. Preoperative assessment and planning with the surgical team is therefore particularly important because optimal patient care may require the modification of several aspects of standardized cardiac anesthetic approaches. The incidence of emergency reexploration ranges from 1% to 5% after cardiac surgery, and the primary challenges relate to effectively managing major cardiopulmonary instability and ensuring safe and efficient surgery, either in the operating room or outside the operating room setting. 584
Indications for Reoperative Cardiac Surgery The indications for reoperative cardiac surgery are based on the same principles as for primary cardiac surgery. However, the incremental hazard of resternotomy, the lack of bypass conduits, the greater age and comorbidity of this patient group, and the likelihood of valve replacement rather than repair are additional considerations. Consequently, the threshold for recommending surgery rather than medical or transcatheter approaches is higher for reoperative patients. Most patients with symptomatic coronary artery or graft stenoses after CABG surgery are most effectively treated by percutaneous coronary intervention (PCI). Very symptomatic patients with significant lesions to a left anterior descending graft are generally considered to gain symptomatic and prognostic benefit from reoperative coronary artery surgery. The main indications for reoperative valve surgery include prosthetic valve dysfunction (for which the results of transcatheter valve-in-valve implantation are still preliminary) and endocarditis, which is a contraindication to transcatheter valve replacement. Paravalvular leaks are increasingly addressed by percutaneous placement of occluder devices. Late reoperation for isolated severe tricuspid regurgitation is associated with particularly high mortality and major morbidity because of the high prevalence of preoperative moderate-to-severe right ventricular dysfunction, pulmonary arterial hypertension, and multiorgan dysfunction in this population.
Reoperative Cardiac Surgery
REOPERATIVE CARDIAC SURGERY
Preoperative Assessment History Patients undergoing reoperative cardiac surgery are generally older, have more comorbidity, and more advanced cardiovascular disease than patients undergoing first-time surgery. The decision to operate usually depends on correlating a precise account of the nature, timing, and severity of symptoms with the findings from diagnostic studies and balancing the benefits of intervention against the incremental risk of mortality and morbidity posed by reoperation. Additionally, the medical history should establish details of all prior cardiovascular procedures, including date and type of PCI; any previous cardiac surgery, including incisions; history of difficult intubation or adverse reaction to anesthesia, respiratory failure, or tracheostomy; coagulopathy and blood transfusions; and postoperative sepsis and organ dysfunction. Although the balance of risks generally favors continuing antiplatelet medication until surgery in non-reoperative patients, this may not be the case in patients scheduled for reoperative surgery, who will be at greater risk of postoperative coagulopathy and bleeding. It may be appropriate to admit patients preoperatively to discontinue oral anticoagulation and transition to a shorter-acting regimen, such as a heparin infusion. Clinical Examination One of the most important risk factors for poor outcomes is frailty. Although this is not well defined, and consequently is not included in most risk models, it is a relatively easy, albeit subjective, judgment often made by looking at a patient. Physical examination of all patients referred for cardiac surgery includes a careful inspection of the entire chest and abdomen. Patients may omit to mention distant cardiac and thoracic surgery procedures, and these may become evident only from incisions, which can be inframammary, posterior thoracotomy, or axillary. All incisions, including conduit harvest sites, 585
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pacemaker or defibrillator insertion sites, and potential sites of peripheral cannulation for cardiopulmonary bypass (CPB) in upper and lower extremities, should be assessed for signs of distant or recent infection, poor healing, and vascular complications such as stenosis or aneurysm formation. Evaluation of the airway includes inspection of the suprasternal notch and trachea for evidence of prior tracheostomy. Imaging With the exception of young adult patients without risk factors for acquired or congenital coronary artery disease, all patients should have recent cardiac catheterization, including coronary angiography, to assess the patency and anatomy of native vessels and any CABG. In young patients, computed tomographic (CT) coronary angiography usually provides sufficient information about coronary anatomy. Coronary angiograms should be reviewed to determine whether grafts are close or even adherent to the sternum. Noncontrast computed tomography provides helpful visualization of calcification and aneurysmal segments along the entire arterial tree from aortic root to femoral vessels that may dictate choice of cannulation site. The presence of large amounts of prosthetic material indicates potentially severe adhesions. Intravenous contrast may be employed in CT angiography to demonstrate the course of bypass grafts more clearly; contrast is required to assess patency, and it provides detailed information on the presence of peripheral vascular disease, which is particularly relevant if peripheral arterial cannulation is planned or the patient is likely to need an intraaortic balloon pump. Echocardiography is necessary to quantify right and left ventricular function, the presence of pulmonary hypertension, and the nature and grade of any valvular dysfunction. Transesophageal echocardiography (TEE) is particularly valuable in the detailed assessment of prosthetic valve endocarditis and failed valve repair or if transthoracic echocardiographic windows are poor.
Before Induction Days Before Induction IV
Reoperative patients require the same laboratory tests as patients undergoing first-time surgery. The presence of renal or hepatic dysfunction at baseline means that particular attention must be paid to maintenance of adequate systemic flows, perfusion pressure, and venous drainage on CPB. Patients with preoperative anemia and thrombocytopenia, particularly if they have low body surface areas, are more likely to require blood products than if they were undergoing first-time surgery. In reoperative patients, the hemostatic benefits of stopping antiplatelet drugs (particularly dual antiplatelet therapy) before surgery outweigh the risks of acute coronary ischemia. In patients with or at high risk of acute coronary syndromes, short-acting antiplatelet drugs can be used as a bridge to surgery. Intravenous heparin should be stopped 4 to 6 hours before the planned surgery time and eptifibatide (Integrilin) infusions at least 12 to 24 hours beforehand. Withholding long-acting vasodilators, particularly angiotensin-converting enzyme inhibitors, for 48 hours before surgery may reduce the risk of postoperative vasoplegia. Immediately Before Induction Adhesive external defibrillator pads must be attached to the patient before induction. The external defibrillator pads are retained throughout the case for several reasons: internal paddles usually cannot be used because of dense adhesions; electrocautery of adhesions close to myocardium may directly induce ventricular fibrillation; and 586
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damage to patent bypass grafts during mediastinal dissection can cause severe myocardial ischemia leading to ventricular fibrillation. A significant proportion of reoperative patients have cardiovascular implantable electronic devices that should be checked preoperatively by an individual familiar with the device to ascertain its functionality and to devise a plan for intraoperative management. The defibrillator function mode of an implantable cardioverterdefibrillator should be disabled for the duration of surgery. Otherwise, defibrillation shocks (which can precipitate asystole or ventricular fibrillation) may be triggered by electrocautery. The devices should be interrogated again and appropriate defibrillator and pacing settings restored postoperatively, before the removal of temporary epicardial pacing wires. The external defibrillator pads should remain in place for the entire period that the permanent devices are disabled. In reoperative cases in which CPB times may be prolonged, with associated vasoplegia or low cardiac output states, arterial pressure tracings from distal arteries are often damped and may be unreliable. The presence of two arterial catheters is particularly valuable in reoperative patients. The plan should be discussed with the surgical team because cannulation and the operative strategy will dictate the available location and utility of these catheters.
Anesthesia Balanced and high-dose narcotic techniques can be used in the reoperative setting. Particular attention must be paid to patients who are at high risk of cardiovascular collapse during induction, such as those with unprotected critical left main (or left main equivalent) coronary artery stenosis, severe aortic stenosis, or cardiac tamponade. Emergency sternotomy, internal cardiac massage, and institution of central CPB are usually not possible because of adhesions that prevent safe, rapid access to the mediastinum. Therefore, in selected reoperative patients thought to be at particularly high risk of cardiovascular decompensation during induction of anesthesia, it may be appropriate to place arterial and central lines in the awake patient and then perform preparation and draping for sternotomy and/or rapid femoral cannulation with the surgeon scrubbed before anesthesia is induced.
Before Incision
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The strategy and order of sternotomy, heparinization, cannulation, and institution of bypass may be very different in a reoperation because the safest sequence of these steps is dictated by the risk posed by resternotomy (Table 23.1). Cross-matched blood should be checked and made immediately available before incision. The CPB circuit should be fully primed, and the bypass lines should be brought up to the field before sternotomy, during which time the perfusionist, attending anesthesiologist, and circulating nurse must be present.
Incision The sternal skin incision is usually made in the standard fashion, and then the sternal wires are untwisted, cut, and either bent to the sides or removed entirely. This can theoretically result in laceration of vascular structures in close proximity underneath, including the right ventricle. Some surgeons elect routinely to perform an initial dissection under the sternum using thoracoscopic guidance. In cases in which an aneurysmal aorta is thought to be densely adherent to the posterior sternal table, a small transverse incision may be made in the second or third left intercostal space to allow the aorta to be dissected free before median sternotomy. 587
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Table 23.1 Risk Stratification of Low-, Medium-, High-, and Very-High-Risk Sternotomies, With a Summary of Operative Strategy Tailored to Address Risks Preoperative Assessment of Risk
Intraoperative Strategy
Increasing risk of major injury
• Resternotomy, dissection of adhesions, standard aortocaval cannulation; initiate bypass; proceed with residual adhesiolysis and cardiac surgical procedure • Optional: expose peripheral cannulation sites before stenotomy • As above • Optional: peripheral arterial cannulation, with 5000 units of heparin given and arterial line flushed intermittently by perfusion; resternotomy and division of adhesions as above • If major vascular injury occurs, venous cannulation can be performed peripherally, and centrally and after full heparinization cardiopulmonary bypass (CPB) is commenced • Peripheral and arterial cannulation with full heparinization before resternotomy • Optional: institute CPB, stop ventilation, and drain venous return into pump reservoir to decompress right side of heart
Low-risk resternotomy: • Prior cardiac surgery without patent coronary bypass grafts • Aorta and mediastinal structures a safe distance from the sternum Moderate-risk resternotomy: • Patent coronary bypass grafts that lie >1 cm from the sternum, including patent left internal mammary artery (IMA) to left anterior descending coronary artery routed lateral to the sternum
High-risk resternotomy: • Patent left IMA graft crossing midline close to sternum, right ventricle adherent to sternum, normal aorta in close proximity to sternum • Third- or fourth-time resternotomy Very-high-risk resternotomy: • Patent left IMA graft crossing midline adherent to sternum and large area of myocardium at risk, aortic tube graft or aneurysm adherent to sternum
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• Peripheral and arterial cannulation with full heparinization, institution of CPB, cooling before resternotomy • Optional: circulatory arrest under moderate hypothermia during sternotomy
Adapted from Akujuo A, Fischer GW, Chikwe J. Current concepts in reoperative cardiac surgery. Semin Cardiothorac Vasc Anesth. 2009;13:206–214.
The anterior sternal table is divided with an oscillating saw. Under an optional period of apnea, the posterior table is then divided along its entire length with either the oscillating saw or a heavy blunt-tipped scissors. This part of the sternotomy poses the most risk to underlying structures. Injury to these structures is particularly problematic because hemorrhage and hemodynamic instability may prevent completion of the sternotomy—in which case the surgeon will have insufficient surgical access to address the injury effectively. To minimize the risk of this scenario, surgeons commonly try to decompress the mediastinal structures by asking the anesthesiologist to hold ventilation and, in the case of patients who have been cannulated and heparinized, 588
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asking the perfusionist to exsanguinate the patient into the pump temporarily. On rare occasions, the safest option is to commence CPB using peripheral cannulation, cool the patient, and arrest the circulation before skin incision and sternotomy (see Table 23.1). Electrocautery is used to dissect the heart away from the left sternal edge and then the right sternal edge. Excessive retraction of the sternum before this dissection is fully completed can result in right ventricular rupture. Other possible complications during this initial dissection are ventricular arrhythmias, including fibrillation as a result of electrocautery in proximity to the myocardium and injury to a patent left internal mammary artery (IMA) graft resulting in myocardial ischemia and a high likelihood of ventricular dysfunction and/or ventricular fibrillation. Subsequent mediastinal dissection is targeted at obtaining access to central cannulation and aortic cross-clamp sites, specifically the aorta and the right atrium. A “no touch” technique is used for bypass grafts to avoid distal embolization and myocardial ischemia. The most common injuries during this phase of dissection are to the right atrium, which is frequently thin walled and densely adherent at sites of prior cannulation and atriotomy. Such injuries can usually be addressed with primary suture closure, but occasionally institution of CPB is mandated to effect a repair. For patients undergoing a mitral, a tricuspid, or (occasionally) an aortic valve procedure, a right thoracotomy may be less hazardous than a median sternotomy. This technique is used to reduce the risk of injury to structures lying adjacent to the sternum. The disadvantage with a right thoracotomy approach is that access to the lateral border of the heart, the ascending aorta, and the aortic valve is limited.
Cannulation Arterial and/or venous cannulation for CPB can be peripheral, central, or a combination of both. The choice depends on the risks posed by sternal reentry and the presence of peripheral arterial disease, as well as the presence of multiple sites of previous surgery on the aorta and right atrium, which may limit the room available for central cannulation. For example, the presence of multiple patent graft anastomoses to the aorta may favor peripheral arterial cannulation. For patients who are at high risk of catastrophic injury to mediastinal structures, arterial (and in certain cases venous) cannulation may be carried out peripherally before sternotomy. The choice of cannulas should take into account the patient’s body surface area: if the venous cannula is too small, the perfusionist will be unable to drain the venous return adequately, and if the arterial cannula is too small, the perfusionist will be unable to provide adequate arterial flow without excessive line pressures. Should the peripheral vessels be too small to permit adequately sized cannulas, it is usually possible to add additional cannulas centrally subsequently, if needed, to improve the adequacy of systemic perfusion. The right or left axillary artery and vein may be exposed by a 5-cm incision in the deltopectoral groove. Use of the axillary artery for arterial cannulation offers less risk of limb ischemia and cerebrovascular events than use of the femoral artery, which is less well collateralized and provides retrograde arterial flow. The most common complication of axillary artery cannulation involves trauma to the branches of the brachial plexus that are intimately involved with the artery. Injury to the artery itself, causing ischemia, dissection, and hyperperfusion, is also possible. The risks of ischemia and dissection are minimized by cannulating a T-graft sewn to the axillary artery rather than cannulating the artery directly. Institution of CPB via the T-graft may be associated with hyperperfusion of the ipsilateral arm. If arterial cannulation alone is carried out peripherally, it is unnecessary to fully heparinize the patient initially. A single dose of 5000 units of heparin will be sufficient to keep the line free of thrombus 589
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IV
if the perfusionist flushes the cannula intermittently before institution of CPB. Full heparinization to an activated coagulation time greater than 480 seconds is usually required before venous cannulation, use of pump (cardiotomy) suction, or institution of CPB, although policies may vary from institution to institution. The main indication for peripheral venous cannulation (which mandates full heparinization) before sternotomy is the surgeon’s decision to institute CPB before sternotomy. The axillary vein is sometimes used, but the larger femoral vein, which has a straighter course to the right atrium, provides the most reliable access and venous drainage. A major complication of femoral venous and arterial cannulation, which may not manifest until later in the case, is retroperitoneal hemorrhage caused by perforation of the femoral or iliac vessel or retrograde dissection of the aorta. A significant retroperitoneal bleed or dissection on CPB is characterized by low flows, low systemic pressures, poor venous drainage owing to loss of circulating volume and, eventually, abdominal distension from accumulating hematoma and venous stasis.
Cardiopulmonary Bypass The patient can be placed on CPB before resternotomy, if indicated. Safe institution of CPB should be confirmed by the anesthesiologist, perfusionist, and surgeon. This is even more important if the patient has been placed on bypass emergently because cannula choice and placement may not be optimal. If proximity of right-sided heart structures to the sternum is a concern (particularly the right ventricle in patients with severe pulmonary hypertension), some surgeons take the precaution of temporarily draining the circulating volume into the venous reservoir of the CPB circuit before sternotomy. This has the theoretical advantage of decompressing the right side of the heart, which may reduce the risk of injury from the sternal saw. After the sternotomy is completed, the remainder of the mediastinal dissection can be carried out with the patient on or off CPB, depending on the challenges presented by adhesions and pathology. Although starting CPB early increases bypass time, it likely reduces the risk of injury to important structures and does not appear to increase morbidity, mortality, or postoperative bleeding. The main reason this is not done routinely is that the patient is fully heparinized while lysis of adhesions is carried out, potentially leading to increased transfusion requirements during the procedure; red cell salvaging may minimize transfusions.
Myocardial Protection Whereas the approach to myocardial protection for reoperative cardiac surgery follows the same basic principles as for first-time surgery (ie, decompression of the heart, usually in cold diastolic arrest to minimize myocardial oxygen demand), there are several additional factors that commonly impact the myocardial protection strategy. Patients undergoing reoperative cardiac surgery typically have worse myocardial function and more advanced coronary and valvular heart disease than patients having first-time surgery. In most reoperations, technical challenges increase the cross-clamp time significantly. If one or more patent IMA grafts are present, they will perfuse the coronary circulation with systemic blood flow after the aorta is cross-clamped. The subsequent washing out of cardioplegic solution from the myocardium with systemic blood, which is usually warmer and normokalemic, will cause the heart to resume electrical activity. If this is not addressed, the areas of myocardium not perfused by the IMA may become ischemic. If there is any more than mild aortic insufficiency, fibrillatory arrest will result in ventricular distension unless the left ventricle is vented, 590
Coagulation Management
Reoperative Cardiac Surgery
and retrograde blood flow from the aorta can make mitral valve surgery very challenging in this scenario. Retrograde cardioplegia is a useful adjunct, but correct placement of a coronary sinus catheter is more challenging in reoperative patients because manual palpation is usually prevented by diaphragmatic adhesions. Consequently, the surgeon is more reliant on TEE to assess coronary sinus placement, and it is crucial to monitor the coronary sinus pressure continuously during cardioplegia to confirm an appropriate pressure response. Additionally, if the aorta is open, the surgeon should see cardioplegia effluent from the left and right main coronary ostia.
Because of the large surface area of dissection (particularly in a fully heparinized patient) and prolonged CPB time, coagulopathy is common in reoperative patients. Point-of-care testing, including platelet function assays and thrombelastography, and transfusion algorithms are useful to guide therapy toward restoration of hemostasis and minimizing transfusion requirements.
Intraoperative Emergency Scenarios Intraoperative adverse events occur in 3% to 10% of reoperative cardiac procedures, with a quarter occurring before or during sternotomy and most of the remainder occurring during mediastinal dissection before institution of CPB. Potentially lifethreatening injuries related to sternotomy include trauma to patent bypass grafts (which are the most frequently injured structures) and injury to the aorta. Additionally, injuries to the right atrium, right ventricle, and innominate vein are common and challenging to address, especially in patients with right-sided heart failure. Rapid volume replacement via large peripheral or central venous catheters or via the arterial cannula may be required. Major injury to arterial structures is immediately lifethreatening, either from hemorrhage or from myocardial ischemia, and usually mandates immediate heparinization, cannulation, and institution of CPB. In the event of major hemodynamic instability that is likely to necessitate CPB (including major bleeding), the anesthesiologist should administer a dose of heparin sufficient to institute CPB (300–400 units/kg or an in vitro titration dose calculated to exceed 2.5–3.0 units/mL of blood). Assuming no access to central cannulation sites, extrathoracic sites should be cannulated emergently and CPB initiated. When the patient is fully heparinized and an arterial cannula is in place, “suction bypass” may be initiated to allow for partial temporary CPB. In this scenario, all venous return to the CPB circuit comes from cardiotomy suction (“coronary suckers”) placed into the mediastinum and/or lacerated cardiac structures until venous cannulation can be established. The patient should still be ventilated because the left side of the heart is likely to be ejecting blood returning from the pulmonary veins. The period of cardiotomy suction bypass should be as short as possible; extensive hemolysis results from the turbulent flow and mixture with air in the cardiotomy tubing. If there is a major injury to the aorta, institution of CPB alone will not be sufficient to control the problem. The primary goal is to obtain some degree of control of the bleeding by direct compression or occlusion sufficient to allow effective CPB for several minutes. Restoration of aortic continuity often requires institution of systemic hypothermia so that the aorta may be assessed and repaired during a period of moderate hypothermic circulatory arrest. If a patent CABG is inadvertently lacerated or transected, it is possible to reduce the risk of resultant myocardial ischemia and ventricular fibrillation by inserting an 591
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intracoronary shunt to restore flow across the injured portion. It is frequently necessary to rapidly institute CPB, however. This is clearly the case if significant ST-segment elevation, bradycardia, or ventricular fibrillation is associated with arterial bleeding in this setting. The primary aim initially is decompression of the left ventricle and restoration of adequate systemic circulation. The eventual goal is restoration of coronary perfusion by repair of the injury or replacement of the graft.
EMERGENCY REEXPLORATION Indications Emergency reexploration is needed in approximately 1% to 3% of patients in the first few hours to days after cardiac surgery. Emergency resternotomy is indicated for definitive management of cardiac tamponade and acute massive mediastinal hemorrhage. Emergency resternotomy permits internal cardiac massage (which has been shown to increase the cardiac index to 1.3 L/min per m2 from 0.6 L/min per m2 in the closed chest), placement of epicardial pacing wires, relief of tension pneumothorax, internal defibrillation, and management of excess mediastinal bleeding. Consequently, the other main indication for emergency reexploration is cardiac arrest that does not respond satisfactorily to a few minutes of cardiopulmonary resuscitation and is likely to have a cause that can be addressed by emergency resternotomy. After cardiac surgery, 20% to 50% of cardiac arrests result in emergency sternotomy. With the exception of catastrophic surgical bleeding or acute cardiac tamponade, the timing of intervention for excess mediastinal bleeding is almost always subject to some debate. When the surgical team has specific concerns about surgical bleeding sites, the threshold for surgical reexploration may be low. It may be much higher in the setting of significant coagulopathy, particularly if an extended effort was made to secure hemostasis in the operating room. In general, indications that the patient may require reexploration for bleeding include (1) greater than 400 mL bleeding in 1 hour; (2) greater than 200 mL/hour for more than 2 hours; (3) greater than 2 L of blood loss in 24 hours; (4) increasing rate of bleeding, particularly in the absence of coagulopathy; and (5) bleeding associated with hypotension, low cardiac output, or tamponade.
General Considerations Anesthetic and surgical considerations in patients undergoing emergency reexploration differ from those in patients undergoing reoperative cardiac surgery, including surgical revision of bypass grafts or other cardiac procedures in the early postoperative setting. In the setting of emergency reexploration, patients are characteristically hemodynamically unstable and often undergoing cardiopulmonary resuscitation with external cardiac massage. The trigger for emergency resternotomy may have been preceded by several hours of a low cardiac output state, with profound metabolic disturbances. In the case of persistent hemorrhage, the patient may be coagulopathic and may have already received massive transfusions. Emergency reexploration often takes place in the intensive care unit if the patient is too unstable to be transferred to the operating room. Advanced preparation in the form of practice drills and team protocol development is important to help overcome the disadvantages of reduced access to operating room personnel, equipment, and space that can be major obstacles to the safe and effective resuscitation of these patients. Additionally, the longer the time between the index cardiac surgery procedure and cardiac arrest, the less likely it is that the cause of cardiac arrest can be effectively addressed by emergency resternotomy. 592
Akujuo A, Fischer GW, Chikwe J. Current concepts in reoperative cardiac surgery. Semin Cardiothorac Vasc Anesth. 2009;13:206–214. Braunwald E, Antman EM, Beasley JW. ACC/AHA guideline update for the management of patients with unstable angina and non–ST-segment elevation myocardial infarction—2002: summary article. Circulation. 2002;106:1893–1900. Breglio A, Anyanwu A, Itagaki S, et al. Does prior coronary bypass surgery present a unique risk for reoperative valve surgery? Ann Thorac Surg. 2013;95:1603–1608. Chikwe J, Adams DH. Frailty: the missing element in predicting operative mortality. Semin Thorac Cardiovasc Surg. 2010;22:109–110. Crooke GA, Schwartz CF, Ribakove GH, et al. Retrograde arterial perfusion, not incision location, significantly increases the risk of stroke in reoperative mitral valve procedures. Ann Thorac Surg. 2010;89:723–729. Dunning J, Fabbri A, Kolh PH, et al. Guideline for resuscitation in cardiac arrest after cardiac surgery. Eur J Cardiothorac Surg. 2009;36:3–28. Etz CD, Plestis KA, Kari FA, et al. Axillary cannulation significantly improves survival and neurologic outcome after atherosclerotic aneurysm repair of the aortic root and ascending aorta. Ann Thorac Surg. 2008;86:441–446, discussion 446–447. Ferraris VA, Saha SP, Oestreich JH, et al. 2012 Update to The Society of Thoracic Surgeons guideline on use of antiplatelet drugs in patients having cardiac and noncardiac operations. Ann Thorac Surg. 2012;94:1761–1781. Ghanta RK, Kaneko T, Gammie JS, et al. Evolving trends of reoperative coronary artery bypass grafting: an analysis of The Society of Thoracic Surgeons Adult Cardiac Surgery Database. J Thorac Cardiovasc Surg. 2013;145:364–372. Roselli EE, Pettersson GB, Blackstone EH, et al. Adverse events during reoperative cardiac surgery: frequency, characterization, and rescue. J Thorac Cardiovasc Surg. 2008;135:316–323. Shore-Lesserson L, Manspeizer HE, DePario M, et al. Thromboelastography-guided transfusion algorithm reduces transfusions in complex cardiac surgery. Anesth Analg. 1999;88:312–319. The Society of Thoracic Surgeons Task Force on Resuscitation After Cardiac Surgery. The Society of Thoracic Surgeons expert consensus for the resuscitation of patients who arrest after cardiac surgery. Ann Thorac Surg. 2017;103:1005–1020. Thourani VH, Suri RM, Gunter R, et al. Contemporary real-world outcomes of surgical aortic valve replacement in 141,905 low-risk, intermediate-risk and high-risk patients. Ann Thorac Surg. 2015;99:55–61. Yusuf S, Zhao F, Mehta SR, et al. Effects of clopidogrel in addition to aspirin in patients with acute coronary syndromes without ST-segment elevation. N Engl J Med. 2001;345:494–502.
Reoperative Cardiac Surgery
SUGGESTED READINGS
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Reoperative Cardiac Surgery Amanda J. Rhee, MD • Joanna Chikwe, MD
Key Points 1. Reoperative cardiac surgery presents greater risk than first-time surgery because patients are usually older, have more comorbidity, and have more advanced cardiovascular disease. Also, resternotomy can be hazardous due to adhesions of cardiac structures to the sternum. Bypass conduits may not be available owing to prior use, and the frequency of valve replacement versus valve repair is higher. 2. A thorough history, clinical evaluation, and review of imaging must be performed— with particular thought to weighing the risk of surgery against the possibility of medical management with multidisciplinary expertise—before making the decision to proceed. 3. Preinduction anesthestic preparations include placement of defibrillator pads, pacemaker or defibrillator adjustments, and placement of invasive monitoring in the setting of the possibility of peripheral cannulation strategies and alternative cardiopulmonary bypass techniques such as cooling before sternotomy. 4. Emergency reexploration is a high-risk situation in which expedited surgical intervention is required, usually in the setting of bleeding with pericardial tamponade. Transfusion should be anticipated, hemodynamics supported, and heparin ready to administer in anticipation of possible cardiopulmonary bypass.
In contemporary practice, 3% to 4% of coronary artery bypass graft (CABG) operations and approximately 10% of valve surgery procedures are reoperations. Reoperative cardiac surgery carries an incremental risk of mortality and major morbidity compared with first-time or primary cardiac surgery because patients are usually older, with additional comorbidity and more advanced cardiac disease, and because of specific technical challenges presented by prior cardiac surgery. The surgical approach to incision and cannulation in coronary and valve surgery reoperations often differs significantly from the approach used in primary cases, and adverse intraoperative events that require immediate changes to the planned strategy are common and often predictable. Preoperative assessment and planning with the surgical team is therefore particularly important because optimal patient care may require the modification of several aspects of standardized cardiac anesthetic approaches. The incidence of emergency reexploration ranges from 1% to 5% after cardiac surgery, and the primary challenges relate to effectively managing major cardiopulmonary instability and ensuring safe and efficient surgery, either in the operating room or outside the operating room setting. 584
Indications for Reoperative Cardiac Surgery The indications for reoperative cardiac surgery are based on the same principles as for primary cardiac surgery. However, the incremental hazard of resternotomy, the lack of bypass conduits, the greater age and comorbidity of this patient group, and the likelihood of valve replacement rather than repair are additional considerations. Consequently, the threshold for recommending surgery rather than medical or transcatheter approaches is higher for reoperative patients. Most patients with symptomatic coronary artery or graft stenoses after CABG surgery are most effectively treated by percutaneous coronary intervention (PCI). Very symptomatic patients with significant lesions to a left anterior descending graft are generally considered to gain symptomatic and prognostic benefit from reoperative coronary artery surgery. The main indications for reoperative valve surgery include prosthetic valve dysfunction (for which the results of transcatheter valve-in-valve implantation are still preliminary) and endocarditis, which is a contraindication to transcatheter valve replacement. Paravalvular leaks are increasingly addressed by percutaneous placement of occluder devices. Late reoperation for isolated severe tricuspid regurgitation is associated with particularly high mortality and major morbidity because of the high prevalence of preoperative moderate-to-severe right ventricular dysfunction, pulmonary arterial hypertension, and multiorgan dysfunction in this population.
Reoperative Cardiac Surgery
REOPERATIVE CARDIAC SURGERY
Preoperative Assessment History Patients undergoing reoperative cardiac surgery are generally older, have more comorbidity, and more advanced cardiovascular disease than patients undergoing first-time surgery. The decision to operate usually depends on correlating a precise account of the nature, timing, and severity of symptoms with the findings from diagnostic studies and balancing the benefits of intervention against the incremental risk of mortality and morbidity posed by reoperation. Additionally, the medical history should establish details of all prior cardiovascular procedures, including date and type of PCI; any previous cardiac surgery, including incisions; history of difficult intubation or adverse reaction to anesthesia, respiratory failure, or tracheostomy; coagulopathy and blood transfusions; and postoperative sepsis and organ dysfunction. Although the balance of risks generally favors continuing antiplatelet medication until surgery in non-reoperative patients, this may not be the case in patients scheduled for reoperative surgery, who will be at greater risk of postoperative coagulopathy and bleeding. It may be appropriate to admit patients preoperatively to discontinue oral anticoagulation and transition to a shorter-acting regimen, such as a heparin infusion. Clinical Examination One of the most important risk factors for poor outcomes is frailty. Although this is not well defined, and consequently is not included in most risk models, it is a relatively easy, albeit subjective, judgment often made by looking at a patient. Physical examination of all patients referred for cardiac surgery includes a careful inspection of the entire chest and abdomen. Patients may omit to mention distant cardiac and thoracic surgery procedures, and these may become evident only from incisions, which can be inframammary, posterior thoracotomy, or axillary. All incisions, including conduit harvest sites, 585
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pacemaker or defibrillator insertion sites, and potential sites of peripheral cannulation for cardiopulmonary bypass (CPB) in upper and lower extremities, should be assessed for signs of distant or recent infection, poor healing, and vascular complications such as stenosis or aneurysm formation. Evaluation of the airway includes inspection of the suprasternal notch and trachea for evidence of prior tracheostomy. Imaging With the exception of young adult patients without risk factors for acquired or congenital coronary artery disease, all patients should have recent cardiac catheterization, including coronary angiography, to assess the patency and anatomy of native vessels and any CABG. In young patients, computed tomographic (CT) coronary angiography usually provides sufficient information about coronary anatomy. Coronary angiograms should be reviewed to determine whether grafts are close or even adherent to the sternum. Noncontrast computed tomography provides helpful visualization of calcification and aneurysmal segments along the entire arterial tree from aortic root to femoral vessels that may dictate choice of cannulation site. The presence of large amounts of prosthetic material indicates potentially severe adhesions. Intravenous contrast may be employed in CT angiography to demonstrate the course of bypass grafts more clearly; contrast is required to assess patency, and it provides detailed information on the presence of peripheral vascular disease, which is particularly relevant if peripheral arterial cannulation is planned or the patient is likely to need an intraaortic balloon pump. Echocardiography is necessary to quantify right and left ventricular function, the presence of pulmonary hypertension, and the nature and grade of any valvular dysfunction. Transesophageal echocardiography (TEE) is particularly valuable in the detailed assessment of prosthetic valve endocarditis and failed valve repair or if transthoracic echocardiographic windows are poor.
Before Induction Days Before Induction IV
Reoperative patients require the same laboratory tests as patients undergoing first-time surgery. The presence of renal or hepatic dysfunction at baseline means that particular attention must be paid to maintenance of adequate systemic flows, perfusion pressure, and venous drainage on CPB. Patients with preoperative anemia and thrombocytopenia, particularly if they have low body surface areas, are more likely to require blood products than if they were undergoing first-time surgery. In reoperative patients, the hemostatic benefits of stopping antiplatelet drugs (particularly dual antiplatelet therapy) before surgery outweigh the risks of acute coronary ischemia. In patients with or at high risk of acute coronary syndromes, short-acting antiplatelet drugs can be used as a bridge to surgery. Intravenous heparin should be stopped 4 to 6 hours before the planned surgery time and eptifibatide (Integrilin) infusions at least 12 to 24 hours beforehand. Withholding long-acting vasodilators, particularly angiotensin-converting enzyme inhibitors, for 48 hours before surgery may reduce the risk of postoperative vasoplegia. Immediately Before Induction Adhesive external defibrillator pads must be attached to the patient before induction. The external defibrillator pads are retained throughout the case for several reasons: internal paddles usually cannot be used because of dense adhesions; electrocautery of adhesions close to myocardium may directly induce ventricular fibrillation; and 586
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damage to patent bypass grafts during mediastinal dissection can cause severe myocardial ischemia leading to ventricular fibrillation. A significant proportion of reoperative patients have cardiovascular implantable electronic devices that should be checked preoperatively by an individual familiar with the device to ascertain its functionality and to devise a plan for intraoperative management. The defibrillator function mode of an implantable cardioverterdefibrillator should be disabled for the duration of surgery. Otherwise, defibrillation shocks (which can precipitate asystole or ventricular fibrillation) may be triggered by electrocautery. The devices should be interrogated again and appropriate defibrillator and pacing settings restored postoperatively, before the removal of temporary epicardial pacing wires. The external defibrillator pads should remain in place for the entire period that the permanent devices are disabled. In reoperative cases in which CPB times may be prolonged, with associated vasoplegia or low cardiac output states, arterial pressure tracings from distal arteries are often damped and may be unreliable. The presence of two arterial catheters is particularly valuable in reoperative patients. The plan should be discussed with the surgical team because cannulation and the operative strategy will dictate the available location and utility of these catheters.
Anesthesia Balanced and high-dose narcotic techniques can be used in the reoperative setting. Particular attention must be paid to patients who are at high risk of cardiovascular collapse during induction, such as those with unprotected critical left main (or left main equivalent) coronary artery stenosis, severe aortic stenosis, or cardiac tamponade. Emergency sternotomy, internal cardiac massage, and institution of central CPB are usually not possible because of adhesions that prevent safe, rapid access to the mediastinum. Therefore, in selected reoperative patients thought to be at particularly high risk of cardiovascular decompensation during induction of anesthesia, it may be appropriate to place arterial and central lines in the awake patient and then perform preparation and draping for sternotomy and/or rapid femoral cannulation with the surgeon scrubbed before anesthesia is induced.
Before Incision
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The strategy and order of sternotomy, heparinization, cannulation, and institution of bypass may be very different in a reoperation because the safest sequence of these steps is dictated by the risk posed by resternotomy (Table 23.1). Cross-matched blood should be checked and made immediately available before incision. The CPB circuit should be fully primed, and the bypass lines should be brought up to the field before sternotomy, during which time the perfusionist, attending anesthesiologist, and circulating nurse must be present.
Incision The sternal skin incision is usually made in the standard fashion, and then the sternal wires are untwisted, cut, and either bent to the sides or removed entirely. This can theoretically result in laceration of vascular structures in close proximity underneath, including the right ventricle. Some surgeons elect routinely to perform an initial dissection under the sternum using thoracoscopic guidance. In cases in which an aneurysmal aorta is thought to be densely adherent to the posterior sternal table, a small transverse incision may be made in the second or third left intercostal space to allow the aorta to be dissected free before median sternotomy. 587
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Table 23.1 Risk Stratification of Low-, Medium-, High-, and Very-High-Risk Sternotomies, With a Summary of Operative Strategy Tailored to Address Risks Preoperative Assessment of Risk
Intraoperative Strategy
Increasing risk of major injury
• Resternotomy, dissection of adhesions, standard aortocaval cannulation; initiate bypass; proceed with residual adhesiolysis and cardiac surgical procedure • Optional: expose peripheral cannulation sites before stenotomy • As above • Optional: peripheral arterial cannulation, with 5000 units of heparin given and arterial line flushed intermittently by perfusion; resternotomy and division of adhesions as above • If major vascular injury occurs, venous cannulation can be performed peripherally, and centrally and after full heparinization cardiopulmonary bypass (CPB) is commenced • Peripheral and arterial cannulation with full heparinization before resternotomy • Optional: institute CPB, stop ventilation, and drain venous return into pump reservoir to decompress right side of heart
Low-risk resternotomy: • Prior cardiac surgery without patent coronary bypass grafts • Aorta and mediastinal structures a safe distance from the sternum Moderate-risk resternotomy: • Patent coronary bypass grafts that lie >1 cm from the sternum, including patent left internal mammary artery (IMA) to left anterior descending coronary artery routed lateral to the sternum
High-risk resternotomy: • Patent left IMA graft crossing midline close to sternum, right ventricle adherent to sternum, normal aorta in close proximity to sternum • Third- or fourth-time resternotomy Very-high-risk resternotomy: • Patent left IMA graft crossing midline adherent to sternum and large area of myocardium at risk, aortic tube graft or aneurysm adherent to sternum
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• Peripheral and arterial cannulation with full heparinization, institution of CPB, cooling before resternotomy • Optional: circulatory arrest under moderate hypothermia during sternotomy
Adapted from Akujuo A, Fischer GW, Chikwe J. Current concepts in reoperative cardiac surgery. Semin Cardiothorac Vasc Anesth. 2009;13:206–214.
The anterior sternal table is divided with an oscillating saw. Under an optional period of apnea, the posterior table is then divided along its entire length with either the oscillating saw or a heavy blunt-tipped scissors. This part of the sternotomy poses the most risk to underlying structures. Injury to these structures is particularly problematic because hemorrhage and hemodynamic instability may prevent completion of the sternotomy—in which case the surgeon will have insufficient surgical access to address the injury effectively. To minimize the risk of this scenario, surgeons commonly try to decompress the mediastinal structures by asking the anesthesiologist to hold ventilation and, in the case of patients who have been cannulated and heparinized, 588
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asking the perfusionist to exsanguinate the patient into the pump temporarily. On rare occasions, the safest option is to commence CPB using peripheral cannulation, cool the patient, and arrest the circulation before skin incision and sternotomy (see Table 23.1). Electrocautery is used to dissect the heart away from the left sternal edge and then the right sternal edge. Excessive retraction of the sternum before this dissection is fully completed can result in right ventricular rupture. Other possible complications during this initial dissection are ventricular arrhythmias, including fibrillation as a result of electrocautery in proximity to the myocardium and injury to a patent left internal mammary artery (IMA) graft resulting in myocardial ischemia and a high likelihood of ventricular dysfunction and/or ventricular fibrillation. Subsequent mediastinal dissection is targeted at obtaining access to central cannulation and aortic cross-clamp sites, specifically the aorta and the right atrium. A “no touch” technique is used for bypass grafts to avoid distal embolization and myocardial ischemia. The most common injuries during this phase of dissection are to the right atrium, which is frequently thin walled and densely adherent at sites of prior cannulation and atriotomy. Such injuries can usually be addressed with primary suture closure, but occasionally institution of CPB is mandated to effect a repair. For patients undergoing a mitral, a tricuspid, or (occasionally) an aortic valve procedure, a right thoracotomy may be less hazardous than a median sternotomy. This technique is used to reduce the risk of injury to structures lying adjacent to the sternum. The disadvantage with a right thoracotomy approach is that access to the lateral border of the heart, the ascending aorta, and the aortic valve is limited.
Cannulation Arterial and/or venous cannulation for CPB can be peripheral, central, or a combination of both. The choice depends on the risks posed by sternal reentry and the presence of peripheral arterial disease, as well as the presence of multiple sites of previous surgery on the aorta and right atrium, which may limit the room available for central cannulation. For example, the presence of multiple patent graft anastomoses to the aorta may favor peripheral arterial cannulation. For patients who are at high risk of catastrophic injury to mediastinal structures, arterial (and in certain cases venous) cannulation may be carried out peripherally before sternotomy. The choice of cannulas should take into account the patient’s body surface area: if the venous cannula is too small, the perfusionist will be unable to drain the venous return adequately, and if the arterial cannula is too small, the perfusionist will be unable to provide adequate arterial flow without excessive line pressures. Should the peripheral vessels be too small to permit adequately sized cannulas, it is usually possible to add additional cannulas centrally subsequently, if needed, to improve the adequacy of systemic perfusion. The right or left axillary artery and vein may be exposed by a 5-cm incision in the deltopectoral groove. Use of the axillary artery for arterial cannulation offers less risk of limb ischemia and cerebrovascular events than use of the femoral artery, which is less well collateralized and provides retrograde arterial flow. The most common complication of axillary artery cannulation involves trauma to the branches of the brachial plexus that are intimately involved with the artery. Injury to the artery itself, causing ischemia, dissection, and hyperperfusion, is also possible. The risks of ischemia and dissection are minimized by cannulating a T-graft sewn to the axillary artery rather than cannulating the artery directly. Institution of CPB via the T-graft may be associated with hyperperfusion of the ipsilateral arm. If arterial cannulation alone is carried out peripherally, it is unnecessary to fully heparinize the patient initially. A single dose of 5000 units of heparin will be sufficient to keep the line free of thrombus 589
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if the perfusionist flushes the cannula intermittently before institution of CPB. Full heparinization to an activated coagulation time greater than 480 seconds is usually required before venous cannulation, use of pump (cardiotomy) suction, or institution of CPB, although policies may vary from institution to institution. The main indication for peripheral venous cannulation (which mandates full heparinization) before sternotomy is the surgeon’s decision to institute CPB before sternotomy. The axillary vein is sometimes used, but the larger femoral vein, which has a straighter course to the right atrium, provides the most reliable access and venous drainage. A major complication of femoral venous and arterial cannulation, which may not manifest until later in the case, is retroperitoneal hemorrhage caused by perforation of the femoral or iliac vessel or retrograde dissection of the aorta. A significant retroperitoneal bleed or dissection on CPB is characterized by low flows, low systemic pressures, poor venous drainage owing to loss of circulating volume and, eventually, abdominal distension from accumulating hematoma and venous stasis.
Cardiopulmonary Bypass The patient can be placed on CPB before resternotomy, if indicated. Safe institution of CPB should be confirmed by the anesthesiologist, perfusionist, and surgeon. This is even more important if the patient has been placed on bypass emergently because cannula choice and placement may not be optimal. If proximity of right-sided heart structures to the sternum is a concern (particularly the right ventricle in patients with severe pulmonary hypertension), some surgeons take the precaution of temporarily draining the circulating volume into the venous reservoir of the CPB circuit before sternotomy. This has the theoretical advantage of decompressing the right side of the heart, which may reduce the risk of injury from the sternal saw. After the sternotomy is completed, the remainder of the mediastinal dissection can be carried out with the patient on or off CPB, depending on the challenges presented by adhesions and pathology. Although starting CPB early increases bypass time, it likely reduces the risk of injury to important structures and does not appear to increase morbidity, mortality, or postoperative bleeding. The main reason this is not done routinely is that the patient is fully heparinized while lysis of adhesions is carried out, potentially leading to increased transfusion requirements during the procedure; red cell salvaging may minimize transfusions.
Myocardial Protection Whereas the approach to myocardial protection for reoperative cardiac surgery follows the same basic principles as for first-time surgery (ie, decompression of the heart, usually in cold diastolic arrest to minimize myocardial oxygen demand), there are several additional factors that commonly impact the myocardial protection strategy. Patients undergoing reoperative cardiac surgery typically have worse myocardial function and more advanced coronary and valvular heart disease than patients having first-time surgery. In most reoperations, technical challenges increase the cross-clamp time significantly. If one or more patent IMA grafts are present, they will perfuse the coronary circulation with systemic blood flow after the aorta is cross-clamped. The subsequent washing out of cardioplegic solution from the myocardium with systemic blood, which is usually warmer and normokalemic, will cause the heart to resume electrical activity. If this is not addressed, the areas of myocardium not perfused by the IMA may become ischemic. If there is any more than mild aortic insufficiency, fibrillatory arrest will result in ventricular distension unless the left ventricle is vented, 590
Coagulation Management
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and retrograde blood flow from the aorta can make mitral valve surgery very challenging in this scenario. Retrograde cardioplegia is a useful adjunct, but correct placement of a coronary sinus catheter is more challenging in reoperative patients because manual palpation is usually prevented by diaphragmatic adhesions. Consequently, the surgeon is more reliant on TEE to assess coronary sinus placement, and it is crucial to monitor the coronary sinus pressure continuously during cardioplegia to confirm an appropriate pressure response. Additionally, if the aorta is open, the surgeon should see cardioplegia effluent from the left and right main coronary ostia.
Because of the large surface area of dissection (particularly in a fully heparinized patient) and prolonged CPB time, coagulopathy is common in reoperative patients. Point-of-care testing, including platelet function assays and thrombelastography, and transfusion algorithms are useful to guide therapy toward restoration of hemostasis and minimizing transfusion requirements.
Intraoperative Emergency Scenarios Intraoperative adverse events occur in 3% to 10% of reoperative cardiac procedures, with a quarter occurring before or during sternotomy and most of the remainder occurring during mediastinal dissection before institution of CPB. Potentially lifethreatening injuries related to sternotomy include trauma to patent bypass grafts (which are the most frequently injured structures) and injury to the aorta. Additionally, injuries to the right atrium, right ventricle, and innominate vein are common and challenging to address, especially in patients with right-sided heart failure. Rapid volume replacement via large peripheral or central venous catheters or via the arterial cannula may be required. Major injury to arterial structures is immediately lifethreatening, either from hemorrhage or from myocardial ischemia, and usually mandates immediate heparinization, cannulation, and institution of CPB. In the event of major hemodynamic instability that is likely to necessitate CPB (including major bleeding), the anesthesiologist should administer a dose of heparin sufficient to institute CPB (300–400 units/kg or an in vitro titration dose calculated to exceed 2.5–3.0 units/mL of blood). Assuming no access to central cannulation sites, extrathoracic sites should be cannulated emergently and CPB initiated. When the patient is fully heparinized and an arterial cannula is in place, “suction bypass” may be initiated to allow for partial temporary CPB. In this scenario, all venous return to the CPB circuit comes from cardiotomy suction (“coronary suckers”) placed into the mediastinum and/or lacerated cardiac structures until venous cannulation can be established. The patient should still be ventilated because the left side of the heart is likely to be ejecting blood returning from the pulmonary veins. The period of cardiotomy suction bypass should be as short as possible; extensive hemolysis results from the turbulent flow and mixture with air in the cardiotomy tubing. If there is a major injury to the aorta, institution of CPB alone will not be sufficient to control the problem. The primary goal is to obtain some degree of control of the bleeding by direct compression or occlusion sufficient to allow effective CPB for several minutes. Restoration of aortic continuity often requires institution of systemic hypothermia so that the aorta may be assessed and repaired during a period of moderate hypothermic circulatory arrest. If a patent CABG is inadvertently lacerated or transected, it is possible to reduce the risk of resultant myocardial ischemia and ventricular fibrillation by inserting an 591
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intracoronary shunt to restore flow across the injured portion. It is frequently necessary to rapidly institute CPB, however. This is clearly the case if significant ST-segment elevation, bradycardia, or ventricular fibrillation is associated with arterial bleeding in this setting. The primary aim initially is decompression of the left ventricle and restoration of adequate systemic circulation. The eventual goal is restoration of coronary perfusion by repair of the injury or replacement of the graft.
EMERGENCY REEXPLORATION Indications Emergency reexploration is needed in approximately 1% to 3% of patients in the first few hours to days after cardiac surgery. Emergency resternotomy is indicated for definitive management of cardiac tamponade and acute massive mediastinal hemorrhage. Emergency resternotomy permits internal cardiac massage (which has been shown to increase the cardiac index to 1.3 L/min per m2 from 0.6 L/min per m2 in the closed chest), placement of epicardial pacing wires, relief of tension pneumothorax, internal defibrillation, and management of excess mediastinal bleeding. Consequently, the other main indication for emergency reexploration is cardiac arrest that does not respond satisfactorily to a few minutes of cardiopulmonary resuscitation and is likely to have a cause that can be addressed by emergency resternotomy. After cardiac surgery, 20% to 50% of cardiac arrests result in emergency sternotomy. With the exception of catastrophic surgical bleeding or acute cardiac tamponade, the timing of intervention for excess mediastinal bleeding is almost always subject to some debate. When the surgical team has specific concerns about surgical bleeding sites, the threshold for surgical reexploration may be low. It may be much higher in the setting of significant coagulopathy, particularly if an extended effort was made to secure hemostasis in the operating room. In general, indications that the patient may require reexploration for bleeding include (1) greater than 400 mL bleeding in 1 hour; (2) greater than 200 mL/hour for more than 2 hours; (3) greater than 2 L of blood loss in 24 hours; (4) increasing rate of bleeding, particularly in the absence of coagulopathy; and (5) bleeding associated with hypotension, low cardiac output, or tamponade.
General Considerations Anesthetic and surgical considerations in patients undergoing emergency reexploration differ from those in patients undergoing reoperative cardiac surgery, including surgical revision of bypass grafts or other cardiac procedures in the early postoperative setting. In the setting of emergency reexploration, patients are characteristically hemodynamically unstable and often undergoing cardiopulmonary resuscitation with external cardiac massage. The trigger for emergency resternotomy may have been preceded by several hours of a low cardiac output state, with profound metabolic disturbances. In the case of persistent hemorrhage, the patient may be coagulopathic and may have already received massive transfusions. Emergency reexploration often takes place in the intensive care unit if the patient is too unstable to be transferred to the operating room. Advanced preparation in the form of practice drills and team protocol development is important to help overcome the disadvantages of reduced access to operating room personnel, equipment, and space that can be major obstacles to the safe and effective resuscitation of these patients. Additionally, the longer the time between the index cardiac surgery procedure and cardiac arrest, the less likely it is that the cause of cardiac arrest can be effectively addressed by emergency resternotomy. 592
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